AMCA
Standard 300-05
Reverberant Room Method for
Sound Testing of Fans
AIR MOVEMENT AND CONTROL
ASSOCIATION INTERNATIONAL, INC.
The International Authority on Air System Components
AMCA Standard 300 - 05
Reverberant Room Method for
Sound Testing of Fans
AIR MOVEMENT AND CONTROL ASSOCIATION INTERNATIONAL
30 WEST UNIVERSITY DRIVE
ARLINGTON HEIGHTS, IL 60004-1893 U.S.A.
PHONE: (847) 394-0150
fax: (847) 253-0088
web: WWW.AMCA.ORG
© 2005 by Air Movement and Control Association International, Inc.
All rights reserved. Reproduction or translation of any part of this work beyond that permitted by Sections
107 and 108 of the 1976 United States Copyright Act without the permission of the copyright owner is
unlawful. Requests for permission or further information should be addressed to the Executive Director,
Air Movement and Control Association International, Inc.
ii
Forward/Authority
AMCA Standard 300-05 was adopted by the membership of the Air Movement
and Control Association International, Inc. on 30 July 2005. The effective date of
this standard is 01 November 2005.
Tung Nguyen (Chair)
Emerson Ventilation Products
Dr. John Cermak
Acme Engineering & Manufacturing Corporation
Joseph Langford
American Coolair Corp.
David Wolbrink
Broan-Nutone LLC
Jeff Hill
Cleanpak International
Dr. W.T.W. Cory
Flakt Woods Ltd.
Iain Kinghorn (Alt.)
Flakt Woods, Ltd.
Pete Neitzel
Greenheck Fan Corporation
Max Clarke (Alt.)
Greenheck Fan Corporation
Thomas Gustafson
Hartzell Fan, Inc.
Ralph Sussey
Howden Buffalo, Inc.
Dr. John Murphy
JOGRAM, Inc.
Tan Tin Tin
Kruger Ventilation Industries Pte. Ltd.
Ralph Sexton
Matthews & Yates
Boyd Kunze
The New York Blower Company
Scott Hausmann
The Trane Co.
Scott Williamson
Twin City Fan Companies, Ltd.
Disclaimer
AMCA International uses its best efforts to produce standards for the benefit of the
industry and the public in light of available information and accepted industry practices. However, AMCA does not guarantee, certify or assure the safety or performance of any products, components or systems tested, designed, installed or operated in accordance with AMCA standards or that any tests conducted under its
standards will be non-hazardous or free from risk.
Objections
Air Movement and Control Association International, Inc. will consider and decide
all written complaints regarding its standards, certification programs, or interpretations thereof. For information on procedures for submitting and handling complaints, write to:
AIR MOVEMENT AND CONTROL ASSOCIATION INTERNATIONAL
30 WEST UNIVERSITY DRIVE
ARLINGTON HEIGHTS, IL 60004-1893 USA
iii
Foreward
This standard was originally developed in response to the need for a reliable and
accurate method of determining the sound power levels of fan equipment. The
original document was written by the AMCA P158NB Sound Test Code
Committee. Where possible, it was based on ASHRAE Standard 36-62, and combined state-of-the-art with practical considerations. It was first published as a
Recommended Practice in February 1962, and adopted as a Standard Test Code
in October 1963. The sound power reference level now used in this standard was
changed in January 1965, from 10-13 watts to 10-12 watts. The third edition
(January 1967) AMCA 300-67 Test Code for Sound Rating included minor revisions. In 1974, minor editorial changes were made, and size-speed conversions
were transferred to AMCA 301 Methods for Calculating Fan Sound Ratings From
Laboratory Test Data. The 1985 edition continued the original philosophy of combining the theoretical and the practical. The 1996 edition was improved by
increasing the accuracy of Reference Sound Source values through improvements in calibration requirements and procedure, and where appropriate, calling
for units of measure in SI (I-P) sequence. Where there have been successful
improvements in state-of-the-art, full advantage has been taken. This latest edition refines the duct end correction factors to values whose source can be traced
to its origin.
Introduction
This standard establishes a method of determining the sound power levels of a
fan. The method is reproducible in all laboratories that are qualified to the requirements of this standard.
The method employs standard sound measurement instrumentation, applied to
rooms that are restricted to certain acoustic properties. The test setups are
designed generally to represent the physical orientation of a fan as installed, following ANSI/AMCA 210 Laboratory Methods of Testing Fans for Aerodynamic
Performance Rating. Sound is defined as radiant mechanical energy that is transmitted by pressure waves in air; it is the objective cause of hearing. Sound pressure level is described mathematically as a logarithmic quantity derived from
sound pressure. The unit of sound pressure level is the decibel, referenced to a
base of 20 micropascals, or 20 microbar. The sound pressure level at any given
point in space depends on the distance between the source and the receiver,
reflection if in an enclosed room, proximity of the source to other sound sources,
etc.
Sound in a room is the result of one or more active sound power sources within
that room. Sound power is the total sound energy radiated per unit time. Sound
power level is described mathematically as a logarithmic quantity derived from the
sound power. The unit of sound power level is the decibel referenced to 1 picowatt (1.0E-12 watt). Sound power levels determined through use of this standard
are useful for comparison between fans and in acoustical design.
Since sound power is independent of acoustic environment, two or more fans proposed for a specific aerodynamic performance condition may be evaluated by
comparison to determine whether one is more suitable for an application than
another. Moreover, fan sound power levels establish an accurate base for estimating the acoustical outcome of the fan installation in terms of sound pressure
levels. A successful estimate of sound pressure levels requires extensive information on the fan and the environment in which it is to be located.
It is often advantageous for the fan equipment user to employ acoustical consultation to ensure that all factors that affect the final sound pressure levels are considered. Additional information on the complexity of this situation may be found in
other documents available elsewhere.
iv
Contents
Page
1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
2. Normative references . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
3. Definitions / units of measure / symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
3.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .1
3.2 Symbols . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
4. Instruments / methods of measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
4.1 Sound level meter . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
4.2 Microphone system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
4.3 Frequency analyzer and weighting system . . . . . . . . . . . . . . . . . . . . . . .3
4.4 Data recording equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
4.5 Reference sound source (RSS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3
4.6 Test method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
4.7 Accuracy of results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
5. Equipment / setups . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
5.1 Reverberant room . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
5.2 Setup categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
5.3 Aerodynamic performance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .5
5.4 Mounting methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
5.5 Duct length . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
5.6 Microphone travel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
5.7 Calibration of system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6
5.8 Equations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
6. Observations and conduct of test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
6.1 Observations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10
6.2 Information to be recorded . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
7. Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .11
7.1 Background correction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
7.2 Sound power level (Lw) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
8. Results and report . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
8.1 Test subject . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12
8.2 Laboratory and instruments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
8.3 Acoustical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13
Annex A (normative) Room qualification: full and one-third octave . . . . . . . . . .15
A.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
A.2 Instruments and quipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
A.3 Test procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
v
A.4 Computation procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15
A.5 Qualification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16
Annex B (informative) Room qualification: pure tones / narrow-band . . . . . . .17
B.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
B.2 Instruments and equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
B.3 Test procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .17
B.4 Computation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
B.5 Qualification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18
Annex C (informative) Uncertainties analysis . . . . . . . . . . . . . . . . . . . . . . . . . . .21
C.1 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
C.2 Uncertainties . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
C.3 Room response . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21
C.4 Fan operating points . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
C.5 Instrument error . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23
C.6 Reference sound source (RSS) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
C.7 Estimated standard deviation for determination of sound power levels 24
C.8 Duct end reflection corrections . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .24
C.9 Octave band vs. One-third octave band . . . . . . . . . . . . . . . . . . . . . . . .25
C.10 Accuracy of the 63 hz octave band . . . . . . . . . . . . . . . . . . . . . . . . . . . .26
Annex D (informative) Alternative procedure for reference sound source calibration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
D.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
D.2 Equipment and facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
D.3 Qualification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
D.4 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27
D.5 RSS sound power levels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28
Annex E (normative) Duct end reflection correction . . . . . . . . . . . . . . . . . . . . . .29
E.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
E.2 End reflection curves . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .29
Annex F (informative) Filter-weighted measurements . . . . . . . . . . . . . . . . . . . .34
Annex G (informative) Radiation of sound by fan casing . . . . . . . . . . . . . . . . . .35
G.1 General . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
G.2 Instruments and equipment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
G.3 Setup and test . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
G.4 Observations and calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35
Annex H (informative) Total fan sound testing with attached ducts . . . . . . . . . .36
Annex J (informative) References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38
vi
AMCA 300-05
AMCA INTERNATIONAL INC.
REVERBERANT ROOM
METHOD
FOR SOUND TESTING
OF FANS
1. Scope
This standard applies to fans of all types and
sizes.
This standard is limited to the
determination of airborne sound emission for the
specified setups. Vibration is not measured, nor
is the sensitivity of airborne sound emission to
vibration effects determined.
The size of a fan that can be tested in
accordance with this standard is limited only by
the practical aspects of the test setups.
Dimensional limitations, test subject dimensions,
and air performance will control the test room
size and power and mounting requirements for
the test subject.
The test setup requirements in this standard
establish the laboratory conditions necessary for
a successful test. Rarely will it be possible to
meet these requirements in a field situation.
This standard is not intended for field
measurements.
2. Normative references
The following standards contain provisions that,
through specific reference in this text, constitute
provisions of this American National Standard.
At the time of publication the editions indicated
were valid. All standards are subject to revision,
and parties to agreements based on this
American National Standard are encouraged to
investigate the possibility of applying the most
recent editions of the standards listed below.
ANSI/AMCA 210-99 / ANSI/ASHRAE 51-1999
Laboratory Methods of Testing Fans for
Aerodynamic
Performance
Rating,
Air
Movement
and
Control
Association
International, Inc., 30 W. University Drive,
Arlington Heights, IL 60004-1893 U.S.A, 1999
ANSI S1.4-1983; S1.4A-1985 Specification for
Sound Level Meters, Acoustical Society of
America, 120 Wall St., 32nd Floor, New York, NY
10005-3993 U.S.A., 1985 (AMCA #2315-83-AO)
ANSI S1.11-2004 Specification for Octave Band
and Fractional Octave Band Analog and Digital
Filters, Acoustical Society of America, 120 Wall
St., 32nd Floor, New York, NY 10005-3993
U.S.A., 1986 (AMCA #1727-86-AO)
ANSI S1.40-1984 Standard Specification for
Acoustical Calibrators, Acoustical Society of
America, 120 Wall St., 32nd Floor, New York, NY
10005-3993 U.S.A., 1984 (AMCA #1895-84-AO)
ANSI S12.5-1990 Requirements for the
Performance and Calibration of Reference
Sound Sources, Acoustical Society of America,
120 Wall St., 32nd Floor, New York, NY 100053993 U.S.A., 1990 (AMCA #1863-90-AO)
ANSI S12.12-1992 Engineering Method for the
Determination of Sound Power Levels of Noise
Sources Using Sound Intensity, Acoustical
Society of America, 120 Wall St., 32nd Floor,
New York, NY 10005-3993 U.S.A., 1992 (AMCA
#1850-92-AO)
ANSI/IEEE/ASTM SI 10-1997 Standard for Use
of the International System of Units (SI): The
Modern Metric System, Institute of Electrical and
Electronic Engineers, 345 east 47th Street, New
York, NY 10017 U.S.A., 1997 (AMCA #2924-97AO)
3. Definitions / units of measure /
symbols
3.1 Definitions
3.1.1 Blade Passage Frequency (BPF): The
frequency of fan impeller blades passing a
single fixed object, per the following formula:
BPF = (number of blades)(fan rotational
speed, rev/min) / 60, in Hz.
3.1.2
Chamber:
An enclosure used to
regulate airflow and absorb sound; it may also
conform to air test chamber conditions given in
ANSI/AMCA 210.
3.1.3
Decibel (dB):
A dimensionless unit of
AMCA 300-05
level in logarithmic terms for expressing the ratio
of a power, or power-like, quantity to a similar
reference quantity. (See 3.1.13 and 3.1.14)
3.1.10 Octave Band:
The interval between
any two frequencies having a ratio of two. Fan
sound power levels are reported in eight
standardized octave bands shown in Table 1.
Fan sound power levels may also be reported in
one-third octave bands, also shown in Table 1.
3.1.4 Ducted Fan:
A fan having a duct
connected to either its inlet, its outlet, or to both.
3.1.5 End Reflection: A phenomenon that
occurs whenever sound is transmitted across an
abrupt change in area, such as at the end of a
duct in a room. When end reflection occurs
some of the sound entering the room is reflected
back into the duct and does not escape into the
room.
3.1.11 Reverberant Room:
An enclosure
meeting the requirements of Annex A, or Annex
A and Annex B.
3.1.12 Shall and Should: The word shall is to
be understood as mandatory; the word should
as advisory.
3.1.6 Frequency: The number of times in
one second that a periodic function repeats
itself.
3.1.13 Sound Power Level:
The value,
expressed in decibels (dB), of ten times the
logarithm (base 10) of the ratio of the sound
power W to the reference sound power Wref,
according to:
3.1.7 Informative: A term that indicates that
the referenced material is provided as advice to
the reader but does not constitute a mandatory
requirement.
LW, in dB = 10 log10 ( W / Wref )
3.1.8 Non-ducted Fan: A fan without a duct
connected to either its inlet or outlet.
(3-1)
3.1.14 Sound Pressure Level:
The value,
expressed in decibels (dB), of twenty times the
logarithm (base 10) of the ratio of the sound
pressure p to the reference sound pressure pref,
according to:
3.1.9 Normative: A term that indicates that
the referenced material, if applied, constitutes a
mandatory requirement.
Table 1 - Standardized octave and one-third octave bands [5]
Octave Bands
Band no.
1
2
3
4
5
6
7
8
ANSI Band no.
18
21
24
27
30
33
36
39
Center frequency f, Hz
63
125
250
500
1000
2000
4000
8000
One-Third Octave Bands
Band 2
Band 1
Band 3
Band 4
ANSI Band no.
17
18
19
20
21
22
23
24
25
26
27
28
Center freq. f, Hz
50
63
80
100
125
160
200
250
315
400
500
630
Band 5
Band 6
Band 7
Band 8
ANSI Band no.
29
30
31
32
33
34
35
36
37
38
39
40
Center freq. f, Hz
800
1000
1250
1600
2000
2500
3150
4000
5000
6300
8000
10000
2
AMCA 300-05
Lp, in dB = 20 log10 ( p / pref )
(3-2)
3.1.15 Wavelength:
The distance between
two points having the same phase in two
consecutive cycles of a periodic wave, along a
line in the direction of propagation [5].
Wavelength (O) is determined by frequency and
the speed of sound in the air through which the
wave propagates:
O=c/f
(3-3)
4.3 Frequency analyzer and weighting
system
An octave band or one-third octave band filter
set is required and shall meet the Order 3 Type
3-D requirements of ANSI S1.11.
An Aweighting network shall meet the requirements
of ANSI S1.4 and S1.4A. Other weighting
networks may be used to improve the accuracy,
as outlined in Annex F.
where:
4.4 Data recording equipment
f = frequency, Hz
c = 343 m/s @ 20°C (1125 ft/s @ 68°F)
This standard does not attempt to set limitations
on data recording equipment. Considerations
include long-term stability, ease of use, and the
method of averaging the sound pressure signal.
Modern integrating-type analyzers that comply
with IEC 804 are recommended because they
produce Lp values eliminating any need for
visual averaging. Graphic level recorders can
be used to make permanent records and ease
the problem of making visual averages from
sound level meter indications.
The value for c is acceptable for use in this
standard within the limits of ± 5°C (9°F) for
standard air.
3.1.16 Standard Air: Air having a density of
3
3
1.2 kg/m (0.075 lbm/ft ). Standard air has a
ratio of specific heats of 1.4 and a viscosity of
1.8185E-03 Pa•s (1.222E-05 lbm/ft-s). Air at
20°C (68°F), 50% relative humidity, and 101.325
kPa (14.696 lbm/in.2, 29.92 in. Hg) barometric
pressure has these properties, approximately).
3.2 Symbols
(See Table 2.)
4. Instruments / methods of
measurement
4.1 Sound level meter
The sound level meter shall meet the
requirements of ANSI S1.4 and S1.4A. The
sound level meter should be capable of
accepting a microphone extension cable.
4.2 Microphone system
The microphone system (transducer and any
associated components and cable) shall meet
the requirements for use in a Type 1 precision
sound level meter according to ANSI S1.4 and
S1.4A. A microphone with a nominal diameter
of 13 mm (0.5 in.) is recommended.
4.5 Reference sound source (RSS)
The reference sound source should comply with
the requirements of ANSI S12.5.
4.5.1 The RSS shall be a small, modified, directdriven centrifugal fan having maximum overall
dimensions of 610 mm (2 ft) or less.
4.5.2
The RSS shall produce steady broadband sound over at least the frequency range
from 50 Hz to 10,000 Hz. It shall comply in all
respects with the performance requirements of
ANSI S12.5.
4.5.3 The RSS shall be equipped with vibration
isolators that minimize transmitted vibration.
The degree of isolation should be 20 dB or
more. If metal springs are used as vibration
isolators, rubber pads shall be used between the
isolator and the structure of the reverberant
room.
4.5.4
To ensure compliance with the stability
requirements of ANSI S12.5, all operating parts
of the RSS shall be rigidly and permanently
3
AMCA 300-05
Table 2 - Symbols
SYMBOL
DESCRIPTION
Amin
c
D
Eo
Ei
EW
f
J1
k
K1
Lp
Lpc
Lpb
Minimum distance to reverberant field
Speed of sound
Duct diameter
End reflection factor, at duct outlet
End reflection factor, at duct inlet
End reflection factor, adjustment to sound power level
Frequency
Bessel function of the first kind, first order
Wave number
Modified Bessel function of the second kind, first order
Sound pressure level, re 20 ȝPa (20 ȝbar)
Corrected fan sound pressure level
Sound pressure level of room background, measured over the
normal microphone path
Sound pressure level of fan + room background, measured over
the normal microphone path
Sound pressure level of the RSS, corrected
Sound pressure level of RSS + room background, measured
over the normal microphone path
Sound power level re 1 picowatt (1.0E-12 W)
Sound power level; transmitted to inlet duct from fan
Sound power level measured at the open inlet and outlet of the
fan
Sound power level measured at the open inlet of the fan
Sound power level measured at the open outlet of the fan
Sound power level transmitted to the outlet duct from fan
Sound power level of RSS
Sound pressure
Sound pressure reference level, 20 ȝPa
Fan static pressure
Fan total pressure
Ratio (of Duct area / Orifice area)
Reflection coefficient
Standard deviation
Sound power (in watts)
Reference sound power (1 picowatt)
Mechanical impedence
Ratio of transmitted to reflected sound
Ratio of specific heats
Wavelength
Angular frequency
Lpm
Lpq
Lpqm
LW
LWi
LWm
LWmi
LWmo
LWo
LWr
p
pref
Ps
Pt
r
R
s
W
Wref
ZM
D
J
O
Z
4
UNIT OF MEASURE
SI
I-P
m
m/s
m
dB
dB
dB
Hz
ft
ft/s
ft
dB
dB
dB
Hz
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
dB
Pa
bar
Pa
bar
Pa
in. wg
Pa
in. wg
dimensionless
dimensionless
dB
dB
W
W
W
W
N˜s/m
dimensionless
dimensionless
m
ft
rad/s
rad/s
AMCA 300-05
attached. No rubber or wearing parts shall be
permitted (except lubricated bearings) and
protection against corrosion shall be provided.
5. Equipment/setups
4.5.5
The RSS calibration shall consist of a
determination of the sound power level radiated
by the RSS (including vibration isolators) when it
is in operation on a reflecting plane with
radiation into a free field above that plane. The
calibration shall be in accordance with ANSI
S12.5 or as provided in Annex D. The maximum
time interval since calibration shall not exceed
that specified by the manufacturer or three
years, whichever is shorter.
An enclosure meeting the requirements of
Annex A is mandatory for the purposes of this
standard.
An enclosure meeting the
requirements of Annex B is recommended for
broad-band sound testing and is mandatory for
the purpose of investigating pure tones and
narrow bands.
4.6 Test method
The test method is based on a Reference Sound
Source (RSS) substitution for the determination
of sound power. The reference document for
this method is ANSI S12.51.
Application of the test method requires that the
test subject fan be set in position in a test room
that is qualified according to the requirements of
Section 5.1.
Once the test room has been qualified, sound
pressure levels are recorded with the RSS
operating. The fan is then operated, without the
RSS in operation, at various performance points
of interest for the given test speed and the
sound pressure levels are recorded. Since the
sound power levels of the RSS are known, the
substitution method is used to determine the
sound power levels of the fan for each operating
point.
Current ANSI and ASA documents on sound
testing, facilities and equipment are useful
references. See Annex J.
5.1 Reverberant room
5.2 Setup categories
A number of specific fan test setups are allowed.
They are determined by the airflow direction
and the particular mounting arrangement of the
test subject. The test setups fall into two
general categories.
The first category is for a free-standing unit that
would be placed entirely in the test room (see
Figure 1). Results of this arrangement yield total
sound power LW of the test subject, non-ducted.
For the total sound power of a ducted test
subject located entirely in the test room, see
Annex H.
The second category includes those fans that
would be tested on a chamber or two-room
system where only the inlet or outlet terminate in
the test room (see Figures 2 and 3). These
arrangements result in the determination of inlet
(LWi) or outlet (LWo) sound power. Section 5.6
discuses the limitations that must be imposed
on the test room for determining the position of
the test subject and the location of the
microphone. The choice of test setup for a
specific test will depend on the way the fan is
expected to be applied in the field.
5.3 Aerodynamic performance
4.7 Accuracy of results
Accuracy of test results is addressed in Annex C
and depends upon several variables, including
the room qualification and the type of test setup
utilized.
Where an aerodynamic performance test is
necessary to determine the point of operation of
a test subject, the test shall be performed in
accordance with ANSI/AMCA 210 or other fan
aerodynamic performance test standard having
a demonstrated accuracy equivalent to
ANSI/AMCA 210.
5
AMCA 300-05
Where:
5.4 Mounting methods
The method of mounting a test subject, or
connecting it to a non-integral driver, or
connecting it to an airflow test facility is not
specified. Any conventional method may be
used including vibration isolation devices and
short flexible connectors. Other than these,
sound and vibration absorptive material may not
be incorporated in the test subject unless it is a
standard part of the fan. Ducts shall be of metal
or other rigid, dense non-absorptive material
and have no exposed sound absorption material
on the interior or exterior surfaces.
The driving motor and drive, when not an
integral part of the test subject, may be damped
or enclosed in any manner that does not expose
sound absorption material to the test room.
When a driving motor and drive are an integral
part of the test subject, they may not be treated
in any manner, and normal belt tensions,
bearings, and lubricants shall be used. When a
fan and its drive are both in the reverberant
room, the test results may contain sound
contributions from flanking paths as well as
mechanical and/or electrical sound from the
drive system.
5.5 Duct length
On a chamber or two-room setup, the length of
duct shall be consistent with acceptable practice
per ANSI/AMCA 210 necessary to accurately
establish the point of rating.
The length of duct shown in Figures 2 and 3 is
consistent with the procedures of ANSI/AMCA
210. Care must be exercised to ensure that no
duct resonances exist in close proximity to
specific frequencies of interest such as the
Blade Pass Frequency.
5.6 Microphone traverse and room
requirements
When using the substitution method, the
minimum distance between the sound source
and the nearest microphone position may be
calculated from:
Amin
6
C210
LWr Lpq / 20
(5-1)
Amin = the minimum distance between the
sound source and the microphone,
m(ft),
C2 = 0.61 (if using SI units), (2.0 if using
IP units), and
(LWr-Lpq) = is the maximum value for
Octave Bands 2 to 7.
If the test room and test setup have been
qualified in accordance with Annex A, the
continuous microphone traverse used for the
qualification shall also be used for the sound
pressure measurements.
If a microphone traverse is used, it shall meet
the following requirements:
a) no point on the traverse shall be any
closer than Amin from the sound source;
b) no point on the traverse shall be any
closer than 1.0 m (3.333 ft) to any
surface of the test room;
c) no point on the traverse shall, at any
time, be closer than 0.5 m (1.67 ft) to any
surface of a rotating diffuser;
d) the microphone traverse should not lie in
any plane within 10° of a room surface;
e) the microphone shall swing or move on a
normal path of an arc or straight line with
a minimum distance of 3 m (10 ft)
between the extreme points of travel;
f) the maximum air velocity over the
microphone shall be 1 m/s (200 fpm);
g) room volume is not specified but the
room must be large enough in volume
such that the volume of the test fan and
associated ductwork does not exceed
1% of the room volume;
h) neither the RSS nor fan shall be within
300 mm (1 ft) of any room centerline.
AMCA 300-05
5.7 Calibration of system
Before each sound power determination, the
following calibration checks shall be performed.
A calibration check shall be made of the entire
measurement system at one or more
frequencies within the frequency range of
interest. An acoustical calibrator conforming to
ANSI S1.40 and with an accuracy of ± 0.5 dB
shall be used for this purpose. In conformance
with ANSI S1.40, the calibrator shall be checked
at least once every year to verify that its output
has not changed. In addition, an electrical
calibration of the instrumentation over the entire
frequency range of interest shall be performed
periodically, at intervals of not more than one
year.
The microphone and its associated cable shall
be chosen so that their sensitivity does not
change by more than 0.2 dB over the
temperature range encountered during the
measurement. If the microphone is moved, care
shall be exercised to avoid introducing
acoustical or electrical noise (for example, from
gears, flexing cables, or sliding contacts) that
could interfere with measurement.
The frequency response of the instrument
system shall be flat over the frequency range of
interest within the tolerances given in Table 3,
and applied as outlined in ANSI S12.51.
Table 3 - Tolerances for the instrument
system
One-third Octave Band
Center Frequency (Hz)
40-80
100-4000
5000-8000
10000
12500
Tolerance
(dB)
±1.5
±1.0
±1.5
±2.0
±3.0
SOUND POWER CALCULATIONS
Installation Type
LW Equation
A: Free Inlet
Free Outlet
LWm=Lpc+(LWr-Lpq)
This test procedure and the above calculations are based on the following assumptions:
1.
Directivity from the fan is averaged by the reverberant room and the microphone location is
such that it is sensing total averaged sound pressure levels.
2.
No resonances are present on either the fan structure, supporting devices, or driving devices
that provide any significant pure tones that may add to the fan recorded sound pressure
levels.
Section 5, Figure 1 - Fan total sound testing
7
AMCA 300-05
1 to 3D
*May require acoustical treatment.
SOUND POWER CALCULATIONS
Installation Type
A or B: Free Inlet
C or D: Ducted Inlet
LW Equations
LWmi=Lpc+(LWr-Lpq)
LWi=Lpc+(LWr-Lpq)+Ei
This test procedure and the above calculations are based on the following assumptions:
Acoustical energy in an outlet duct which terminates in a second room or chamber does not
contribute to fan test sound pressure levels. This requires adequate transmission loss between
adjourning rooms and the addition of absorptive material within a chamber to absorb this energy.
1.
Adequate absorption takes place at the discharge of a duct in a second room or chamber so
that any energy passing down that duct is adequately attenuated.
2.
Directivity from the fan is averaged by the reverberant room and the microphone location is
such that it is recording total averaged sound pressure levels.
3.
Duct construction is such that the transmission loss through the duct wall is large enough to
eliminate any addition to measured room sound pressure levels.
4.
No resonances are present on either the fan structure, supporting devices, or driving devices
that provide any significant pure tones that may add to the recorded fan sound pressure
levels.
5.
Inlet orifices to control the operating point are not permitted, unless integral to the fan.
Section 5, Figure 2 - Fan inlet sound testing
8
AMCA 300-05
2 to 3D
*May require acoustical treatment.
SOUND POWER CALCULATIONS
Installation Type
A or C: Free Outlet
B or D: Ducted Outlet
LW Equations
LWmo=Lpc+(LWr-Lpq)
LWo=Lpc+(LWr-Lpq)+Eo
This test procedure and the above calculations are based on the following assumptions:
1.
2.
3.
4.
5.
6.
Acoustical energy in an inlet duct that terminated in a second room or chamber does not
contribute to fan test sound pressure levels. This requires adequate transmission loss
between adjoining rooms and the addition of absorptive material within a chamber to absorb
this energy.
Adequate absorption takes place at the inlet of a duct in a second room or chamber so that
any energy passing down that duct is adequately attenuated.
Directivity from the fan is averaged by the reverberant room and the microphone location is
such that it is recording total averaged sound pressure levels.
Duct construction is such that the transmission loss through the duct wall is large enough to
eliminate any addition to measured room sound pressure levels.
No resonances are present on either the fan structure, supporting devices, or driving devices
that provide any significant pure tones that may add to the recorded fan sound pressure
levels.
Outlet orifices to control the operating point are not permitted, unless integral to the fan.
Section 5, Figure 3 - Fan outlet sound testing
9
AMCA 300-05
5.8 Equations
The type of fan and its test setup determine the
calculations required to determine the sound
power levels (LW, LWm, LWi, LWmi, LWo, LWmo) of
the test subject. Equations for each test setup
are included under the specific arrangement
along with any qualifying statements or
limitations. Also included are any assumptions
that were made regarding these specific setups.
End reflection factors (Ei) and (Eo), when
required, shall be calculated from Annex E Duct
End Reflection Correction, using the appropriate
duct and orifice size.
measured in the test room with the test subject
and the RSS off.
The background noise
includes all noise sources not directly
associated with fan sound.
Examples of
background noise sources are: noise due to the
motion of the microphone and noise due to any
other external source. Efforts should be made
to keep the background noise level at a
minimum. For a test, or set of determinations, at
various points of test subject operation,
background sound pressure levels need to be
observed once.
6.1.2.2 Sound pressure levels, RSS (Lpqm)
6. Observations and conduct of test
RSS sound pressure levels are those measured
in the test room with the RSS operating and the
test subject off. RSS sound pressure levels
include background sound pressure levels. For
a test, or set of determinations, at various points
of test subject operation, RSS sound pressure
levels need to be observed once.
6.1 Observations
6.1.2.3 Sound pressure levels, fan (Lpm)
6.1.1 Point of operation
Fan sound pressure levels are those measured
in the test room with the test subject operating
and the RSS off. Fan sound pressure levels
include background sound pressure levels. Fan
sound pressure levels must be observed for
each operating point.
It cannot be assumed that the inlet and outlet
sound powers are always equal. Therefore,
total sound power levels shall not be used to
derive inlet or outlet sound power levels.
Although the acoustical observations necessary
to determine sound power output are the same
for all types of fans, the non-acoustical
observations necessary to determine the
aerodynamic point of operation differ. This
standard provides different test setups for the
testing of various fan types. Regardless of the
test setup, the point of operation shall be
determined.
If the sound test setup also
conforms to one of the test setups in
ANSI/AMCA 210, then the point of rating can be
established with sufficient accuracy.
If the
sound test setup does not conform to one of the
test setups in ANSI/AMCA 210, steps must be
taken to ensure that the fan rotational speed is
known within ± 1% and the point of operation
can be established within ± 5% along a system
curve.
6.1.2 Sound pressure levels
6.1.2.1
(Lpb)
Sound pressure levels, background
Background sound pressure levels are those
10
Note: The observations above are valid only
when taken in a room that is qualified per the
procedures defined in Annex A or B.
6.1.3 Test conditions
The test conditions shall, as nearly as possible,
be the same for all sound pressure level
measurements. Operation of the microphone
traverse and any rotating vanes shall be the
same for all measurements. Observers and
operators should not be in the test room during
measurements, but if it is absolutely necessary
for them to be present, they shall be away from
the test subject and remain in the same position
during the test. Readings should be a time
weighted average over an integral number of
microphone swings. The time span used shall
be sufficient to provide a stable value and shall
be a minimum of 30 seconds for frequency
AMCA 300-05
bands ” 160 Hz, and 15 seconds for frequency
bands • 200 Hz.
6.2.3 Laboratory and instruments
A)
Laboratory name
6.2 Information to be recorded
B) Laboratory location
As applicable, the following information shall be
compiled and recorded for all observations
made in accordance with this standard.
6.2.1 Test subject
A) Description of the test subject
1)
2)
3)
4)
5)
6)
Manufacturer
Model
Nominal size
Impeller diameter, mm (in.)
Number of impeller blades
Blade angle setting (adjustable or
variable pitch fans only)
7) Number of stator vanes
2
2
8) Inlet area, m (ft )
2
9) Outlet area, m (ft2)
B) Operating conditions
1) Fan rotational speed, rev/min
2) Fan airflow rate, m3/s (ft3/min)
3) Fan static pressure or total pressure
at actual test conditions, Pa (in. wg)
4) Fan air density, kg/m3 (lbm/ft3)
C) Technician(s) conducting test
D) List of test equipment
calibration information
used,
with
E) Scope of room qualification. Data shall
indicate whether the room is qualified for
full octaves or one-third octaves, and in
the case of pure tone testing, the onethird octaves for which the qualification
applies.
6.2.4 Acoustical data
A) Background sound pressure levels Lpb
B) RSS sound pressure levels Lpqm
C) Background corrections for the RSS
D) Fan sound pressure levels Lpm
E) Background corrections for the fan
F) Un-weighted fan sound power levels
LWmi or LWmo
C) Mounting conditions
G) End reflection correction data
1) Test figure per this standard
2) Test Installation Type
3) Sketch showing the test room setup,
including the dimensional locations
of the test subject and points or path
of acoustical measurements
1) End reflection correction values Ei
or Eo
2) Duct length
3) Flush or non-flush mounting of the
duct into the test room
4) Orifice plate inside diameter, m (ft)
6.2.2 Test environment
H) Test date
A) Barometric pressure, kPa (in. Hg)
B) Ambient dry-bulb temperature, °C (°F)
7. Calculations
C) Ambient wet-bulb temperature, °C (°F)
Calculations are affected by the Installation Type
and setup. See Section 5.8 in addition to the
following.
D) Fan inlet dry-bulb temperature, °C (°F)
E) Static pressure at the fan inlet, Pa (in.
wg)
11
AMCA 300-05
7.1 Background correction
7.2 Sound power level (LW)
The observed RSS or test subject sound
pressure levels include both the sound source
and background noise.
The effect of
background noise level is termed background
correction and must be subtracted from the
observed sound pressure level. Background
correction values depend on the difference
between the observed sound pressure levels
and the background noise levels.
A sound power level is calculated using
equations given in Section 5. The equations
vary with product type and test setup. The
sound power level of a full octave band may be
calculated from one-third octave band values by
using the formula:
LW
When the difference between the observed
sound pressure levels (RSS – background) in a
frequency band is less than 6 dB, the
corresponding sound pressure level from the
source cannot be determined accurately by this
standard. For any band for which the difference
between the background and the (background +
source) sound pressure level is less than 6 dB,
Lpc shall be reported as 1.3 dB less than Lpm.
The data for each such band shall be clearly
marked as upper boundary levels.
A sound pressure level reading shall be
corrected for background noise level by
logarithmic subtraction using the following
formulae:
Test subject (fan) sound pressure level:
Lpc
§ Lpb · ·
§ §¨ Lpm ·¸
¨
¸
¨ © 10 ¹
10 ¸
10 log10 ¨ 10
10© ¹ ¸
¸
¨
¹
©
LW 2
LW 3 ·
§ LW 1
10 log10 ¨¨10 10 10 10 10 10 ¸¸
¹
©
(7-3)
Where:
LW1, LW2, and LW3 are one-third octave sound
power level values.
8. Results and report
Test results are presented as the sound power
level, in dB, in each of the eight full octave
bands for each fan test speed and point of
operation. Full octave bands are given in Table
1. The report shall also include data defined in
Sections 8.1 through 8.3. This standard does
not require that pure tone effects be isolated
from broad-band sound. However, a laboratory
equipped with suitable instrumentation is
encouraged to investigate and report pure tones
separately.
(7-1)
8.1 Test subject
A) Description of the test subject
RSS sound pressure level:
Lpq
Lpb ·
§ Lpqm
¨
10
10 log10 10
10 10 ¸
¨
¸
©
¹
(7-2)
Example: The sound pressure level of a fan in a
given frequency band is observed to be 58 dB.
The background sound pressure level in the
same band is observed to be 51 dB. The
background value is subtracted logarithmically
from the fan sound pressure level using
Equation 7-1, which results in 57 dB (rounded).
12
1)
2)
3)
4)
5)
6)
Manufacturer
Model
Nominal size
Impeller diameter, mm (in.)
Number of impeller blades
Blade angle setting (adjustable or
variable pitch fans only)
B) Operating conditions
1) Aerodynamic
performance
standard
2) Fan rotational speed, rpm
3
3
3) Fan airflow rate, m /s (ft /min)
test
AMCA 300-05
4) Fan static pressure or total pressure
at actual test conditions, Pa (in. wg)
5) Fan air density, kg/m3 (lbm/ft3)
C) Mounting conditions
1) Test Figure per this standard
2) Installation Type
nearest whole decibel
B) Test date
C) Background sound pressure level in
each reported band
D) Background correction for the RSS for
each reported band
8.2 Laboratory and instruments
A) Laboratory name
B) Laboratory location
E) RSS sound pressure level in each
reported band
F) Background correction for test subject,
in each reported band
8.3 Acoustical data
A) Un-weighted fan sound power level, in
each reported band, reported to the
G) Test subject sound pressure level, in
each reported band
13
AMCA 300-05
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14
AMCA 300-05
Annex A
(normative)
Room qualification: full and one-third octave
A.1 General
This annex covers the procedures for a broad-band qualification of a test room for full and one-third
octave bands. If pure tone qualification is required, refer to Annex B Room Qualification: Pure Tones /
Narrow Band.
A.2 Instruments and equipment
The instruments and microphone traverse shall be the same as those used during the actual testing of a
fan. The instruments shall conform to the requirements given in Sections 4.1. through 4.4, inclusive. The
microphone traverse shall conform to the requirements of Section 5.6. The test procedure given in this
annex requires the use of a Reference Sound Source (RSS) having the characteristics specified in
Section 4.5.
A.3 Test procedure
Eight or more measurements shall be made of the reverberant field sound pressure levels in the room,
each with the RSS placed at a different location within the room, under the following conditions:
A.3.1 Each location for the RSS shall be selected on the floor and shall not be closer than 1 m (3 ft)
from a wall and not closer to any microphone than permitted by equation Amin (Section 5, Figure 4). The
distance between any two RSS locations shall be greater than 0.9 m (3 ft). No source location shall lie
within ± 300 mm (1 ft) of a room centerline. The RSS locations shall be in the general vicinity of the
locations intended for the test subject as seen in a plan view of the test room.
A.3.2 With the RSS at each of the eight (or more) above locations, determine the average sound
pressure levels in accordance with the procedures of Section 6.
A.3.3 The microphone traverse, sound diffuser (if any), instruments and observation times shall be
identical to those to be used for a test subject.
A.4 Computation procedure
For each frequency band for which the test room is to be qualified, the standard deviation s, in dB, shall
be computed using the formula:
1/ 2
s
nRSS
2½
­
° 1
°
ªL
Lpq º ¾
®
pq
«
»
j
¼ °
°̄ nRSS 1 j 1 ¬
¿
¦
(A.4-1)
Where:
(Lpq)j = the sound pressure level, in dB, averaged over all microphone positions, when the RSS is in the
jth location
___
Lpq = arithmetic mean of (Lpq)j values, in dB, averaged over all RSS locations
15
AMCA 300-05
nRSS = number of RSS locations, a minimum of eight
A.5 Qualification
For each frequency band, the test room qualifies for the measurement of broad-band sound if the
computed standard deviation s, in dB, does not exceed the limits given in Table A1.
Table A1 - Maximum allowable standard deviation S, (dB)
Octave
Band
Center
Frequencie
s (Hz)
63
125
250 and 500
1000 and
2000
4000 and
8000
16
One-Third
Octave Band
Center
Frequencies
(Hz)
50 to 80
100 to 160
200 to 630
800 to 2500
Maximum
Allowable
Standard
Deviation (dB)
s
3.0
1.5
1.0
0.5
3150 to 10000
1.0
AMCA 300-05
Annex B
(informative)
Room qualification: pure tones / narrow-band
B.1 General
This annex covers the procedure for the qualification of a test room to investigate pure tones. The
reference document for this procedure is ANSI S12.51. Qualification testing applies only to those onethird octave bands having mid-frequencies from 100 Hz to 2500 Hz, inclusive, as shown in Table B1.
Qualification excludes those bands having mid-frequencies below 100 Hz and is not required for those
bands having a mid-frequency greater than 2500 Hz. The qualification testing applies to a specific
location in the test room and determines which of the one-third octave bands the test room location is
qualified for. A sound test based on such qualification must state the mid-frequency of the one-third
octave band(s) qualified for the test by this procedure.
B.2 Instruments and equipment
The instruments shall be as specified in Section 4 with the following substitutions / additions.
a)
b)
The signal analyzer shall be a one-third octave band analyzer conforming to ANSI S1.11.
The sound source will consist of:
1) A loudspeaker / horn: one or more, each having a sufficiently smooth frequency response
within the range of frequencies to be qualified.
2) A frequency generator, tunable to and meeting the tolerances given for the frequencies given
in Table B1. A digital frequency synthesizer is recommended for ease of setting frequency.
3) A frequency counter accurate within ± 0.05 Hz over the pertinent frequency range.
4) A power amplifier of suitable power and having an output impedance compatible with the
loudspeaker(s) / horn(s).
5) A voltmeter capable of monitoring within ± 0.05% of the voltage across the loudspeaker(s) /
horn(s) at all test frequencies.
B.3 Test procedure
Qualification testing consists of two sections, the first being concerned with the near-field characteristics
of the loudspeaker / horn and the second with the test room itself. In both sections, measurements are
made for each of the discrete frequencies associated with the one-third octave band being qualified. The
same test equipment must be used for both sections of the qualification testing.
B.3.1 Loudspeaker / horn test
The loudspeaker / horn shall be located on the horizontal surface of a hemi-anechoic field with the open
cone facing upward. A microphone with diaphragm horizontal is located over the center of the
loudspeaker / horn 10 to 20 mm (0.375 to 0.75 in.) above the plane of the loudspeaker / horn rim. The
input voltage to the loudspeaker / horn must be sufficient to overcome background noise but must in no
case be permitted to cause physical distortion of the loudspeaker / horn components. The sound
pressure levels for the discrete frequencies of a one-third octave band are then measured. The
loudspeaker / horn is suitable only if the sound pressure levels at adjacent frequencies do not differ by
more than 1 dB. This test determines the near-field characteristics of the loudspeaker / horn and gives
calibration sound pressure levels for the loudspeaker / horn.
B.3.2 Room test
The loudspeaker / horn shall be positioned in the room at the horizontal and vertical coordinates intended
17
AMCA 300-05
for the test subject and placed so that the open cone faces away from the nearest room surface. Using
the same input voltage to the loudspeaker(s) / horn(s) as for the loudspeaker / horn test, space and time
averaged sound pressure levels Lps are measured for the discrete frequencies of the one-third octave
band.
B.4 Computation
The room test sound pressure level is then corrected to remove the effect of the loudspeaker’s / horn’s
near-field characteristic by subtracting the loudspeaker / horn test sound pressure level. The arithmetic
mean for the room sound pressure level is then calculated, and the standard deviation s of the difference
between the average sound pressure level and the arithmetic mean sound pressure level is determined
by:
1/ 2
n
2½
­
°
° 1
Lps Lps ¾
®
¦
k
°
°̄ n 1 k 1
¿
>
s
@
(B.4-1)
Where:
(Lps)k = the corrected sound pressure level, in dB, averaged over all microphone positions, of the kth
discrete frequency,
___
= the arithmetic mean of (Lps)k values averaged over all n test frequencies within the one-third
Lps
octave band,
n = the number of discrete frequencies within the one-third octave band.
B.5 Qualification
A test room is accepted as qualified for pure tone testing within a given one-third octave band if the
standard deviation s, in dB, for that band does not exceed the values given in Table B2. If a one-third
octave band does not qualify, some modification will be required to the microphone location, to the test
position, or to the room absorption [7] [8].
18
AMCA 300-05
Table B1 - Test frequencies for alternative qualification of reverberant room facility for measuring
sound power levels of noise sources containing significant discrete frequency components (from
ANSI S12.51-2002)
Center frequency of one-third octave bands, Hz
100
---90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
--1
125
-113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
1
160
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
1
200
---180
182
184
186
188
190
192
194
196
198
200
202
204
206
208
210
212
214
216
218
220
222
--2
250
-226
228
230
232
234
236
238
240
242
244
246
248
250
252
254
256
258
260
262
264
266
268
270
272
274
276
2
315
---285
288
291
294
297
300
303
306
309
312
315
318
321
324
327
330
333
336
339
342
345
348
--3
400
361
364
367
370
373
376
379
382
385
388
391
394
397
400
403
406
409
412
415
418
421
424
427
430
433
436
439
3
500
--445
450
455
460
465
470
475
480
485
490
495
500
505
510
515
520
525
530
535
540
545
550
555
--5
630
--564
570
576
582
588
594
600
606
612
618
624
630
636
642
648
654
660
666
672
678
684
690
696
702
-6
800
--712
720
728
736
744
752
760
768
776
784
792
800
808
816
824
832
840
848
856
864
872
880
888
--8
1000
---900
910
920
930
940
950
960
970
980
990
1000
1010
1020
1030
1040
1050
1060
1070
1080
1090
1100
1110
--10
1250
-1130
1140
1150
1160
1170
1180
1190
1200
1210
1220
1230
1240
1250
1260
1270
1280
1290
1300
1310
1320
1330
1340
1350
1360
1370
1380
10
1600
1470
1480
1490
1500
1510
1520
1530
1540
1550
1560
1570
1580
1590
1600
1610
1620
1630
1640
1650
1660
1670
1680
1690
1700
1710
1720
1730
10
2000
---1800
1820
1840
1860
1880
1900
1920
1940
1960
1980
2000
2020
2040
2060
2080
2100
2120
2140
2160
2180
2200
2220
--20
2500
-2260
2280
2300
2320
2340
2360
2380
2400
2420
2440
2460
2480
2500
2520
2540
2560
2580
2600
2620
2640
2660
2680
2700
2720
2740
2760
20
Tolerance of
Increment,
Hz
±0.3
±0.3
±0.3
±0.5
±0.5
±1
±1
±1.5
±2
±3
±3
±5
±5
±5
±5
Number
of
test
frequencies,
n
22
26
27
22
26
22
27
23
24
23
22
26
23
22
26
Increment,
Hz
Table B2 - Maximum allowable sample standard deviation, s
One-third Octave
Band Center
Frequencies (Hz)
100 to 160
200 to 315
400 to 630
800 to 2500
Maximum
Allowable
Standard
Deviation s (dB)
3.0
2.0
1.5
1.0
19
AMCA 300-05
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20
AMCA 300-05
Annex C
(informative)
Uncertainties analysis
C.0 General
The analysis of the uncertainty associated with measurements made in accordance with this standard
provides identification of certain critical points so as to recognize the limitations of the results.
Furthermore, it provides an approximation, in real values, of the imprecision in the recorded results.
C.1 Definitions
Precision error is an error that causes readings to take random values on either side of some mean
value.
Systematic error is an error that persists and cannot be considered as due entirely to chance.
Uncertainty is an estimated value for error, i.e., what we think an error would be if we could and did
measure it by calibration. Although uncertainty may be the result of both precision and systematic errors,
only precision errors can be treated by statistical methods.
The uncertainty in a researched value is described by specifying the measured value followed by the
uncertainty interval at the desired confidence level:
LW = m ± w at P confidence level
(C.1-1)
Where:
m = measured value
w = uncertainty
P = percent
C.2 Uncertainties
The uncertainties associated with the determination of sound power levels through measurements
performed in accordance with this standard are room response (C.3), fan operating points (C.4),
instrument error (C.5), and RSS (C.6). Uncertainties associated with duct end reflection corrections
involve the accuracy of estimating the losses from orifice plates (C.8). Other areas of interest involve the
use of octave or one-third octave bands (C.9) and the problems associated with testing in the 63 Hz band
(C.10).
C.3 Room response
A reverberant room is an appropriate place for determining the acoustical power of a source, such as a
fan, that emits a steady sound power. The reverberant room must be diffuse enough to produce a
reverberant field.
When a sound source is operated inside a reverberant room, the sound waves are reflected by the walls
and are propagated in all directions. If the paths of all the waves could be seen, we would notice a
number of repetitions, (e.g., the path followed by a wave between two parallel walls). These paths are
called normal modes. The greater the number of normal modes, the better the sound dispersion in the
room. The modes must be sufficiently numerous in any measurement band so that the microphone
traverse will serve to average the sound pressure. The number of normal modes in a given space
21
AMCA 300-05
increases with frequency. Hence, it is usually more precise to measure higher frequencies. When the
number of modes are few, it helps to measure the sound in many locations and average the results. Two
important sources of error may affect the measurements made in a reverberant room: 1) the error
introduced by measuring the sound field at a limited number of points, and 2) variations in sound power
due to the location of the sound source. Many sources radiate sound that is not entirely broad-band, but
contains significant discrete-frequency components, or pure tones. Some fans generate a pure tone at
the blade passage frequency and sometimes at harmonic frequencies.
In a reverberant room, a pure tone tends to excite certain modes that will dominate all others. This
noticeably increases the variability of the pressure field due to an insufficient dispersion of the sound field.
Due to the consequent inaccuracy of sound pressure averaging, the precision of the results is reduced.
C.3.1 Broad-band measurement in a reverberation room
Broad-band sound is uniformly distributed in frequency with relatively steady levels and with no prominent
discrete-frequency or narrow-band components. Measurement of broad-band sound may be made in a
test room qualified per Annex A.
C.3.2 Pure-tone measurement in a reverberation room
When a discrete-frequency component is present in the sound spectrum of a source, the spatial
variations in sound pressure level usually exhibit maxima separated by minima having an average
spacing of approximately 0.8 O, where O is the wavelength corresponding to the discrete frequency of
interest.
The presence of a significant discrete-frequency component in the sound produced by a source can often
be detected by a simple listening test. If such a component is audible, or detectable by narrow-band
analysis, the qualification procedure described in Annex B is recommended.
If the test room is not qualified for pure-tone measurement, the measurement uncertainty will most
probably be higher in the bands containing the blade passage frequency and its harmonics than if
measured in a qualified test room.
Discrete-frequency components may be present in the sound spectrum even when these components
are not audible. A conclusion that no discrete-frequency components are present can only be reached by
performing the test described in C.3.3.
C.3.3 Test for discrete-frequency components
The following procedure can be used to estimate the spatial standard deviation of the sound pressure
levels produced by the test subject in the test room.
Select an array of six fixed microphones (or a single microphone at six positions) spaced at least O/2
apart, where O is the wavelength of the sound corresponding to the lowest band mid-frequency of interest
and meeting all the requirements for microphone positions in Annex A. Locate the sound source at a
single position in the test room in accordance with Annex A.
Obtain the time-averaged sound pressure level Lpj at each microphone position according to the
techniques described in Annex A.
For each one-third octave band within the frequency range of interest, calculate the standard deviation s,
in dB, from the following equation:
22
AMCA 300-05
1/ 2
s
ª 1 nm
2º
Lpcj Lp j »
«
¦
«¬ nm 1 j 1
»¼
(C.3-1)
Where:
Lpcj = sound pressure level, corrected for the background sound level in accordance with the procedures
of Section 6.2.1 for the jth microphone position, dB
__
Lpj = arithmetic mean of (Lpc)j values, averaged over all microphone positions, dB
nm = number of microphone positions = 6
The magnitude of s depends upon the properties of the sound field in the test room. These properties are
influenced by the characteristics of the room as well as the characteristics of the sound source (i.e.,
directivity and spectrum of the emitted sound). In theory, a standard deviation of 5.57 dB corresponds to
a spectral component of zero bandwidth, i.e., a discrete tone.
Table C1 - Characterization of the presence of discrete-frequency or narrow-band components,
based upon the spatial variation of the sound field
Standard
Deviation, s
(dB)
s<1.5
1.5<s<3
s>3
Characterization
Assume broad-band source (use
procedures of Annex A).
Assume that a narrow-band of
noise is present. Recommend use
of the qualification procedure in
Annex B.
Assume that a discreet tone is
present. Test room must qualify
per Annex B.
C.4 Fan operating points
When the sound power levels of a fan are determined, each measurement must relate to one point of
operation of the fan. Uncertainty in identifying this point thus affects the global uncertainty of the results.
Therefore it is recommended that the procedures of ANSI/AMCA 210 or other recognized fan
aerodynamic performance test standard be used as a guideline in identifying the test subject’s operating
points. The sensitivity of the sound levels to a change in point of operation is a function of the test
subject’s performance characteristics, and this will dictate how accurately the point of operation must be
determined. A fan that exhibits a large change in sound power level as airflow is changed (at a given fan
rotational speed) is of more concern than one that shows a small change in sound power level for the
same airflow change.
C.5 Instrument error
The frequency response of the instrument system shall be flat over the frequency range of interest to
within the tolerances given in Table C2.
23
AMCA 300-05
Table C2 - Tolerances for the instrument system
Frequency
(Hz)
100 to 4000
5000 to 8000
10000
Tolerance
(dB)
±1.0
±1.5
±2
C.6 Reference sound source (RSS)
The sound power produced by the RSS shall be determined in octave and one-third octave bands within
the tolerances specified in Table C3.
Table C3 - Calibration accuracy for RSS
One-Third
Octave Band
Center
Frequency (Hz)
100 to 160
200 to 4000
5000 to 10000
Tolerance
(dB)
±1.0
±0.5
±1.0
C.7 Estimated standard deviation for determination of sound power levels
The determination of sound power levels through measurements made in accordance with this standard
will result, with very few exceptions, in standard deviations that are less than or equal to those given in
Table C4. The standard deviations in Table C4 take into account the cumulative effects of all causes of
measurement uncertainty noted in C.3 through C.6 above, except for duct end reflection corrections and
the testing in an unqualified test room of fans containing pure-tones.
Table C4 - Estimated deviation of sound power level determinations
Octave
Band
Center
Frequency
(Hz)
125
250
500 to 4000
8000
One-Third
Octave Band
Center
Frequency
(Hz)
100 to 160
200 to 315
400 to 5000
6300 to 10000
Standard
Deviation
(dB)
3.0
2.0
1.5
3.0
C.8 Duct end reflection corrections
Table C5 gives the uncertainties for duct end reflection correction E for various 0.5 kD and r values.
24
AMCA 300-05
Table C5 - Uncertainties in duct end reflection correction E
Duct
Configuration
Uncertainty in E (dB)
Range of 0.5 kD
<0.25
0.25-1 >1
Flush
1
±3
±2
±0.5
Free Space
1
±3
±2
±0.5
1-2
±3
±2
±0.5
2-5
±4
±3
±1
Note: When pure tones are present, uncertainties will be substantially greater.
r
C.9 Octave band vs. one-third octave band
According to this standard, the frequency analysis of sound may be performed either in full octave bands
or in one-third octave bands. Qualification of a reverberant test room for pure tones can only be effected
in the one-third octave bands. Full octave band analysis takes less time because fewer numerical values
are treated. However, this analysis supplies little information on the shape of a sound spectrum.
Furthermore, full octave band analysis does not allow isolation of pure tones in a spectrum; the poor
resolution of an octave band gives little information about a steeply sloping spectrum. The pure-tone
value produced by a test subject may be reduced by 1 to 2 dB without changing the octave band reading.
For certain test conditions, this standard uses a duct end reflection correction factor that is frequency
dependent. Because of this dependence, analysis in full octave bands instead of one-third octave bands
may cause an error of up to ± 2 dB.
Example:
Test Conditions: A fan having a 508 mm (20 in.) diameter inlet, no orifice plate, and low airflow.
There is a significant difference between the two methods of determining the octave band values. This
difference is a function of two things:
1) The shape of the sound spectrum determined by one-third octave band analysis, and
2) The slope of the duct end reflection attenuation curve at the point where the attenuation value is
evaluated.
The error made in using octave band analysis can overestimate or underestimate the real values.
Therefore, the use of one-third octave band analysis is recommended. Refer to Figure C1.
If full octave band analysis is performed, a precaution would be to adjust the fan rotational speed to
caused the blade passage frequency to fall in the central one-third octave band of any full octave band.
Care should also be taken to keep the blade passage frequency from falling on the border between
bands, thus avoiding the problems associated with the characteristics of filter skirts.
Table C6 - Example using full octave band analysis
1/3 Octave
Center
Frequency,
(Hz)
50
63
80
Lp
Measured
80
65
64
Combined
+E
= (Lp+E)
dB
80.2
+10.2
=90.4
25
AMCA 300-05
Table C7 - Example using one-third octave band analysis
1/3 Octave
Center
Frequency,
(Hz)
50
63
80
Lp
Measured
Combined
+E
80
65
64
+12.1
+10.2
+8.3
=92.1
=75.2
=72.3
=(Lp+E)
dB
=92.2
C.10 Accuracy of the 63 Hz octave band
At low frequencies, the sound power output of a source depends upon its position in the test room. At
low frequencies, very few modes are excited, and because of reflections from test room surfaces, the
reflected pressure at the source combines with the direct sound pressure field produced by the source.
This affects the radiation impedance seen by the source, and therefore its sound power output. This is
particularly true of the 63 Hz octave band. Most standards do not discuss this band, although it is
important to fan manufacturers and users alike. Measurements in this band must be reported. However,
the measured sound pressure values, and therefore the determined sound power level values, have an
uncertainty of ± 6 dB at best.
OCTAVE
BAND
OCTAVE
BAND
OCTAVE
BAND
OVER ESTIMATION
NO ERROR
UNDER ESTIMATION
Figure C1 - Effect of summing one-third octave bands
26
AMCA 300-05
Annex D
(informative)
Alternative procedure for reference sound source calibration
D.1 General
Calibration of a Reference Sound Source (RSS) in conformance with the requirements of ANSI S12.5
requires a hemi-anechoic room qualified for measurements over the entire frequency range of interest.
Laboratories that otherwise would be able to perform the required calibration but which are not qualified
for measurements in the first octave band may use the alternative procedure of this Annex. This
alternative procedure is based on sound intensity measurements per ANSI S12.12.
D.2 Equipment and facilities
Equipment and facilities shall be as required for RSS calibration in conformance with ANSI S 12.5, with
the exception that the hemi-anechoic chamber need not be qualified below the 125Hz full octave band
(100 Hz one-third octave band). Sound intensity measuring equipment shall comply with the
requirements of ANSI S 12.12.
Additional RSS units may be sound power level calibrated by comparing the sound power levels of the
source to another unit that was calibrated in accordance with Sections D.1 through D.5. It is not
necessary that each and every reference sound source be calibrated directly in accordance with the
procedures described below. It may be possible to transfer a calibration from one unit to another by
using a simpler type of test. For example, the Substitution Method of the present standard might be used
to calibrate (secondary calibration) one reference sound source relative to another, similar, reference
sound source that has been calibrated as described below (primary calibration). In order that such a
secondary calibration does not result in an unacceptable degradation of accuracy, it normally will be
necessary to use more source locations and microphone positions than the minimum requirements of the
present standard and to exercise additional caution in carrying out the measurements.
D.3 Qualification
The RSS calibration procedure of ANSI S12.5 shall be carried out over the 50 Hz through 10,000 Hz onethird octave band frequency range and 63 Hz through 8000 Hz full octave band frequency range. If the
calibration is in conformance with ANSI S12.5 in all respects except for the qualification of the test facility
below the 100 Hz one-third octave band, the alternative calibration procedure below may be used. If the
calibration is not in complete conformance with ANSI S12.5 for any other reason, the alternative
calibration procedure is not applicable.
D.4 Procedure
The requirements of ANSI S12.5 are duplicated in the lowest three full octave (nine one-third octave)
bands, with the substitution of sound intensity level measurements, made in compliance with ANSI
S12.12, for the sound pressure level measurements required by ANSI S12.5. For all measurements,
sound intensity shall be measured in the outward radial direction. The sound power levels determined
from these measurements shall be compared with those determined from the corresponding sound
pressure level measurements. If in all frequency bands the determined sound power levels differ by no
more than the tolerances given in Table D1, the calibrated sound power levels for the RSS are reported
as specified in Section D.5. The directivity index is not calculated from the intensity measurements.
27
AMCA 300-05
Table D1 - Tolerance for measured sound power level difference
Octave Band
(Hz)
63
125-250
One-third
Octave
Band (Hz)
50-80
100-315
Tolerance
(dB)
±4.0
±1.0
D.5 RSS sound power levels
The reported RSS sound power levels and directivity index shall be as determined by the ANSI S12.5
procedure for the 100 Hz through 10,000 Hz one-third octave bands and the 125 Hz through 8,000 Hz full
octave bands. For the 50 Hz through 80 Hz one-third octave bands and the 63 Hz full octave band, the
reported RSS sound power level(s) shall be as determined from the sound intensity measurements, and
the directivity index is not to be reported. The calibration report shall be marked to indicate the levels
determined from sound intensity measurements, and shall indicate whether the calibration was performed
in full compliance with this Annex.
28
AMCA 300-05
Annex E
(normative)
Duct end reflection correction
E.1 General
Conditions at the end of a test duct will prevent some of the sound energy from being transmitted into the
test room. Therefore, the sound power measured in the room will be less than the true sound power in a
duct. Unless an anechoic termination is used, correction factors must be added to the fan sound
pressure measured in the test room in order to account for the reduction caused by end reflection.
The prediction of the duct end reflection is difficult. Theoretical solutions exist only for round ducts with
highly idealized end conditions and are based on the assumption that the frequency is low enough that
only plane waves exist (which implies that ka<S). Actual fan test setups rarely, if ever, conform to the
conditions under which the theoretical solutions are valid. Using the methods suggested in this Annex
will result in predicted values that are reasonably close to the actual values. Nonetheless, the test setup
should be selected to minimize the potential error by using components that most closely reproduce the
theoretical conditions.
For open ducts (i.e., no orifice) theoretical solutions exist for two cases: a thin-walled round duct
terminating in an infinite space [On the Radiation of Sound from an Unflanged Circular Pipe, Levine,
H., and Schwinger, J. – Physical Review, Vol. 72, No. 4, February 15, 1948] and a round duct terminating
in an infinite wall [Fundamentals of Acoustics, 3RD Edition, Kinsler, Frey, Coppens and Sanders, Wiley,
New York, 1982 , equations 9.13 and 9.14]. Most test setups incorporate terminations that use a flanged
duct terminating in a large space, which would make the solution provided by Levine & Schwinger more
appropriate, assuming no orifice is used.
For ducts with orifices, no theoretical solution exists for the case of a duct terminated in infinite space.
For the flush-mounted duct (duct terminated in an infinite wall) the effect of an orifice plate with a round,
centrally located hole can be calculated [Acoustics, Beranek, L., McGraw-Hill, New York, 1950, Section
5.2].
For most test setups, when the test is conducted using an orifice on the tested end, there is no theory to
predict the end correction values.
E.2 End reflection curves
It is strongly recommended that, whenever possible, sound test setups be chosen so that there is no
requirement to apply duct end correction. In the event that circumstances require a setup indicating the
presence of a duct end correction there are four cases to be considered. The four cases are considered
separately below.
E.2.1 Open ducts in a large space
To determine the end reflection values, it is necessary to first calculate the reflection coefficient R, which
gives the fraction of the energy reflected back into the duct. Levine and Schwinger reduced the exact
solutions to manageable forms, one for ka<1 and one for ka>1. Note: k = Z/c = 2ʌ/O, a = D/2, and
Z = 2 Sf.
The two equations are:
29
AMCA 300-05
R
4
ª ka 2 º ª
ka §
§ 1 · 19 · º
» «1
¨ log10 ¨
exp«
¸ ¸»
6 ©
© Jka ¹ 12 ¹ »
«¬ 2 »¼ «¬
¼
ª
R
Ska exp( ka)«1
«¬
3 1 º
»
32 ka 2 »
¼
Eq. E-1
for ka < 1
Eq. E-2
for ka > 1
The ratio between the transmitted sound and the reflected sound is D = 1 - ~R~2 and thus the end
correction (in dB) is E 10 log10 D . These equations shall be used to calculate E as a function of ka
(0.5kD). The resulting curve is shown for illustrative purposes in Figure E1 (r=1). Values are presented
up to ka = 4, even though the equations are strictly limited to ka < 3.832.
r=5
r=2
r=1
Figure E1 - End correction for open ducts in large space
30
AMCA 300-05
E.2.2 Open ducts terminated in a wall
For the case of a round duct terminated at a large wall, the end correction can be determined using
equations 9.13 and 9.14 from Kinsler, Frey, Coppens and Sanders with the impedence calculated
using equations 5.1, 5.2 and 5.3 from Beranek. It should be noted that there is no transition at the wallduct interface. The equations to be used to calculate E as a function of ka are given below.
J (2ka) º
SUc
K1 2ka
» j
ka »¼
2k 2
Eq. E-3
J1 W
W
W3
W5
W7
2 2 2 2 2 2
˜ ˜˜
2 2 ˜4 2 ˜4 ˜6 2 ˜4 ˜6 ˜8
Eq. E-4
K1 W
·
W7
2 §W3 W5
¨
2 2 2
˜ ˜˜¸
S© 3
3 ˜5 3 ˜5 ˜7
¹
Eq. E-5
ª
Sa2Uc «1 1
ZM
«¬
ZM Sa 2 Uc 1
R
B
A
D
1 R
E
10 log10 D
ZM Sa 2 Uc 1
2
Eq. E-6
Eq. E-7
Eq. E-8
The series for the Bessel functions J1 and K1 converge rapidly (at least for values of ka < 3.6), so the
computation of E vs. ka is straightforward. The resulting curve for illustrative purposes is shown in Figure
E2 (r=1). As before, values are shown up to ka = 4, but for ka >3.6, the value of D is defined to be 1.
E.2.3 Orificed ducts terminated in a large wall
If a round duct terminating into a large wall is fitted with an orifice plate with a centrally located round
hole, the equations in Section E.2.2 may be easily modified to predict the end reflection. Continuing with
the assumption of plane wave propagation, the end reflection may be calculated by calculating R using ka
based on the orifice radius, and calculating the transmission coefficient Į by assuming that the orifice
reduces the transmission coefficient by a factor of 1/r, where r is the ratio of duct area to orifice area. End
reflection values for r = 2 and r = 5 are shown for illustrative purposes in Figure E2.
The curves in Figure E2 are drawn to ka = 4, even though their range of applicability may be limited to
much lower values. For the open duct (r = 1) the end reflection is clearly seen to be zero for all values of
ka > 3 since the failure to meet the plane wave criteria is not critical. For the orificed cases, the end
correction values for ka>1 are questionable due to the failure to meet the plane wave criteria, and are
0.5
very suspect for ka > (Sr) since for these values of ka the wave length is smaller than the orifice
diameter.
31
AMCA 300-05
r=5
r=2
r=1
Figure E2 - End correction for open ducts terminated in a large wall
E.2.4 Orificed ducts terminating in a large Space
Although there is no theory applicable to these cases, it is reasonable to argue on physical grounds that
the effect of the orifice must be reasonably similar to the flush-mounted case. Adopting this approach,
the curves for r = 2 and r = 5 have been added to Figure E1 by merely adding the orifice effect
determined from Figure E2. The same qualifications to the accuracy at ka > S apply here also. Values
can be found in Table E1
32
AMCA 300-05
Table E1 – End corrections for orificed ducts terminating in a large space
ka
0.14
0.15
0.16
0.17
0.18
0.19
0.20
0.25
0.30
0.35
0.40
0.45
0.50
0.55
0.60
0.65
0.70
0.75
0.80
0.85
0.90
0.95
1.0
1.1
1.2
1.3
1.4
r=2
18
17.4
16.9
16.5
16
15.6
15.2
13.5
12.2
11.1
10.2
9.4
8.8
8.2
7.7
7.3
7
6.7
6.4
6.1
5.9
5.7
5.4
4.8
4.5
4.52
4
r=5
18.6
18
17.5
17.1
16.7
16.3
15.9
14.3
13.1
12.1
11.3
10.6
10.1
9.6
9.2
8.9
8.6
8.4
8.2
8.0
7.9
7.8
7.7
7.6
7.5
7.5
7.4
ka
1.5
1.6
1.7
1.8
1.9
2.0
2.1
2.2
2.3
2.4
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
4.0
r=2
3.9
3.7
3.6
3.5
3.5
3.4
3.3
3.3
3.3
3.2
3.2
3.2
3.2
3.2
3.1
3.1
3.1
3.1
3.1
3.1
3.1
3.1
3.0
3.0
3.0
3.0
r=5
7.4
7.4
7.3
7.3
7.3
7.3
7.2
7.2
7.2
7.2
7.2
7.1
7.1
7.1
7.1
7.1
7.1
7.1
7.1
7.0
7.0
7.0
7.0
7.0
7.0
7.0
33
AMCA 300-05
Annex F
(informative)
Filter-weighted measurements
In certain sound measurement situations, the presence of high amplitude sound at frequencies ” 45 Hz
can reduce the effective dynamic range of the analyzer in the measurement frequency range of interest
for this standard (45 Hz to 11,200 Hz). While use of an analyzer with a large dynamic measurement
range can solve this problem, it may sometimes be necessary to use another approach.
Sound pressure level readings may be made with the sound level meter or signal amplifier set for a welldefined filter weighting effect in order to improve the dynamic range and measurement quality, provided
that any effect in the frequency range 45 Hz to 11,200 Hz is compensated and the equipment satisfies all
the requirements of Section 4 of this standard. The weighting filter shall be the same for all
measurements (background, RSS, and fan).
34
AMCA 300-05
Annex G
(informative)
Radiation of sound by fan casing
G.1 General
The sound radiated by a fan casing may be determined by the following method. Except as provided for
below, all the requirements of this standard apply.
G.2 Instruments and equipment
Shall be as required in Section 4.
G.3 Setup and test
The fan inlet and fan outlet shall be ducted to termination points outside the test room. Ducts and
connections should be constructed and secured such that the acoustic energy radiated through this
equipment is no more than 10% of the total energy radiated by the fan casing into the test room. The test
room sound pressure levels may be affected by sound radiating from the inlet and discharge ductwork
connected to the test subject, causing measured sound pressure levels to be somewhat higher than the
true casing radiated sound pressure levels. This effect can be minimized by using internally lined round
ductwork. No correction for duct-radiated sound power is allowed. NOTE: If there is any doubt
concerning the contribution of extraneous sound transmitted by ductwork, the importance of same can be
checked by increasing the transmission loss of the ductwork.
G.4 Observations and calculations
Sound pressure levels Lpq and Lpk shall be observed as provided for in Section 6. The sound pressure
levels Lpq and Lpk are observed and subject to the provisions for Lp in Section 6. For possible pure tones
and additional testing, the results of the test of a fan casing are subject to the same requirements as the
test of a fan.
LWk = Lpk + (LWr - Lpq ) in each frequency band
(G.4-1)
Where:
LWk = sound power radiated through the fan casing,
Lpk = fan casing sound pressure level.
35
AMCA 300-05
Annex H
(informative)
Total fan sound testing with attached ducts
It is intended that the fan sound power levels determined by this standard reflect the sound produced at a
known fan operating point. The length of test ducts used to determine sound power would, therefore, be
identical to the duct length defined an ANSI/AMCA 210. It has been determined that shorter duct lengths
are also acceptable and may be used. Care must be taken to ensure that for the actual duct lengths
used, no duct resonances exist in close proximity to specific frequencies of interest, e.g., the blade
passage frequency.
Although it is recognized that the inlet and outlet sound power levels of a fan are generally not equal, it is
necessary to make some assumptions about the relationship between these levels to apply duct end
reflection correction. The equations in Figure H1 are based upon the assumption that the inlet and outlet
sound power levels of a fan are equal.
36
AMCA 300-05
FAN
OPTIONAL
ORIFICE
FAN
B: FREE INLET
DUCTED OUTLET
FAN
C: DUCTED INLET
FREE OUTLET
D: DUCTED INLET
DUCTED OUTLET
Installation Type
LW Equations
B: Free Inlet,
Ducted Outlet
LW = Lp + (LWr – Lpq) + [3 – 10 log10 (1 + 10(Eo/10))] + Eo
C: Ducted Inlet,
Free Outlet
LW = Lp + (LWr – Lpq) + [3 – 10 log10 (1 + 10(Ei/10))] + Ei
D: Ducted Inlet,
Ducted Outlet
LW = Lp + (LWr – Lpq) + Ei + Eo + [3 – [10 log10 (10(Eo/10) + 10(Ei/10))]]
This test procedure and the above calculations are based on the following:
1. Directivity from the fan is averaged by the reverberant test room and the microphone location is such that it is
sensing total averaged sound pressure levels.
2. Duct construction is such that the transmission loss through the duct wall is large enough to eliminate any addition
to the measured sound pressure levels.
3. No resonances are present on either the fan structure, supporting devices or driving devices that provide any
significant pure tones that may add to the measured sound pressure levels.
4. The factor of 3 in the above equations is based on the assumption that fan sound power is equally distributed
between inlet and outlet.
Figure H1 - Fan total sound testing with ducts attached
37
AMCA 300-05
Annex J
(informative)
References
[1]
AMCA Standard 300-67 Test Code for Sound Rating, Air Movement and Control Association
International, Inc., Arlington Heights, IL, 1967.
[2]
AMCA Standard 301-90 Methods for Calculating Fan Sound Power Levels from Laboratory Test
Data, Air Movement and Control Association International, Inc., Arlington Heights, IL, 1990.
[3]
Harris, C.M., Editor, Handbook of Noise Control, 2nd Edition, McGraw-Hill, New York, NY, 1979
[4]
Parker, S.P., Dictionary of Scientific and Engineering Terms, 4th Edition, McGraw-Hill, New York,
NY, 1989
[5]
ANSI S1.6-1984 (R1990) Preferred Frequencies, Frequency Levels and Band Numbers for
Acoustical Measurements, Acoustical Society of America, New York, NY, 1990
(AMCA #1108-84-AO)
[6]
Sepmeyer, L.W., Computed Frequency and Angular Distribution of the Normal Modes of
Vibration in Rectangular Rooms, Journal of the Acoustical Society of America, New York, NY,
Vol. 37 – No. 3, March, 1985
(AMCA #1891-65-AO)
[7]
AMCA #1901-85-A1 List of References on Room Calibration, Air Movement and Control
Association International, Inc., Arlington Heights, IL, 1985.
[8]
Crocker, M. J., w/ Pande, L. and Sandbakken, R., Investigation of End Reflection Coefficient
Accuracy Problems with AMCA 300-67, Herrick Laboratories Report HL 81-16, Purdue
University, West Lafayette, IN, 1981.
(AMCA #1184-81-A6)
[9]
Noise Control Engineering, Vol. 7, No. 2, Noise Measurement Facilities, and ANSI S1.21-1972,
Methods for the Determination of Sound Power Levels of Small Sources in Reverberant Rooms.
[10]
ANSI S12.11-1987 (R1993) Methods for the Measurement of Noise Emitted by Small Air Moving
Devices, Acoustical Society of America, New York, NY, 1993.
[11]
Baade, P.K., 1977, Effects of acoustic loading on axial flow fan noise generation, Noise Control
Engineering, 8(1):5-15
[12]
ANSI S12.51-2002 Nationally Adopted International Standard (NAIS Standard), Acoustics –
Determination of sound power levels of noise sources using sound pressure – Precision method
for reverberation rooms, Acoustical Society of America, New York, NY, 1993.
38
AIR MOVEMENT AND CONTROL
ASSOCIATION INTERNATIONAL, INC.
30 West University Drive
Arlington Heights, IL 60004-1893 U.S.A.
Tel: (847) 394-0150
E-Mail : info@amca.org
Fax: (847) 253-0088
Web: www.amca.org
The Air Movement and control Association International, Inc. is a not-for-profit international association of the
world’s manufacturers of related air system equipment primarily, but limited to: fans, louvers, dampers, air
curtains, airflow measurement stations, acoustic attenuators, and other air system components for the industrial,
commercial and residential markets.