Acoustics

advertisement
HERRING STORER ACOUSTICS
Suite 34, 11 Preston Street, Como, W.A. 6152
P.O. Box 219, Como, W.A. 6952
(08) 9367 6200
Telephone:
(08) 9474 2579
Facsimile:
Email:
hsa@hsacoustics.com.au
Acoustics: Back to basics
Fundamentals of Acoustics
Presented by
Tim Reynolds
Fundamentals To Cover
Common Noise Sources
 Some Basic Definitions
 Basic Terminology
 Criteria
 Noise Sources and Typical Examples
 Basic Noise Controls
Noise Source
Decibel Level dB(A)
Jet Takeoff (100m)
130
Live rock band
120
Chain Saw
110
Lawn Mower
100
Diesel Truck, food blender
090
Dishwasher
080
Freeway Traffic at 15m
070
Conversation
060
Quiet Suburb
050
Library, living room
040
Quiet rural area
030
020
010
Threshold of hearing
000
Definitions
Decibel (dB) The human ear has a vast sound-sensitivity range of a thousand billion to one. The decibel
is a logarithmic unit that allows this range to be compressed into a somewhat more
comprehensible range. The decibel is ten times the logarithm of the ratio of a sound level
to a reference sound level. Decibel noise levels cannot be added arithmetically since they
are logarithmic numbers.
dB(lin)
Decibel measurement without any adjustment.
dB(A)
Decibel measurement according to the "A" weighted scale. The human ear does not
respond equally to the same sound pressure at different frequencies. The "A"
weighting has predetermined adjustments made at certain frequencies to make the
measured sound level approximate to the response of the ear.
Leq
Equivalent Continuous Sound Level. The Leq measurement integrates these
fluctuations in noise to give the equivalent continuous level containing an equal
amount of energy over the time of measurement.
LA1
Represents the A-weighted noise level which is exceeded for 1 per cent of the
measurement period.
LA10
Represents the A-weighted noise level which is exceeded for 10 per cent of
the measurement period.
LA90
Represents the A-weighted noise level which is exceeded for 90 per cent of the
measurement period. Also often used to represent background noise level.
Sound Pressure Level (SPL) The sound pressure level is the noise level of a sound measured at a point using a
standard noise level meter relative to a standard noise level (2x10-5 N/m2).
Sound Power Level (SWL)
The sound power level of a source is the sound energy emitted by the source. The
sound power level of a source cannot be measured directly, but is calculated based
on measured sound pressure levels at a known distance (10-12W).
Noise level measurements can be broken down into Octave or 1/3 Octave Bands, with the following centre frequencies.
Measurement 1 - Time History
Noise Level
LA10 Overall
LAEq Overall
LA90 Overall
64
62
60
58
54
52
50
48
46
44
42
Time (Sec)
59
57
55
53
51
49
47
45
43
41
39
37
35
33
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
40
1
SPL (dBA)
56
Measurement 2 - Time History
Noise Level
LA10 Overall
LAEq Overall
LA90 Overall
60
58
56
54
50
48
46
44
42
Time (Sec)
55
53
51
49
47
45
43
41
39
37
35
33
31
29
27
25
23
21
19
17
15
13
11
9
7
5
3
40
1
SPL (dBA)
52
CRITERIA
Environmental Noise
Environmental Protection (Noise) Regulations 1997
Internal Noise Levels
AS/NZ 2107:2000 Acoustics - Recommended design sound levels
and reverberation times for building interiors
Others
Building Code of Australia (BCA) – Part F5
GreenStar
ENVIRONNEMENTAL PROTECTION (NOISE) REGULATIONS 1997
The allowable or assigned noise level at the surrounding locales is
prescribed by the Environmental Protection (Noise) Regulations 1997.
Baseline Assigned Outdoor Noise Level
Premises Receiving Noise
Time of Day
Assigned Level (dB)
LAma
LA10
LA1
x
Noise sensitive premises
0700 - 1900 hours Monday to
Saturday (Day)
0900 - 1900 hours Sunday and Public
Holidays (Sunday / Public Holiday
Day)
1900 - 2200 hours all days (Evening)
Commercial premises
2200 hours on any day to 0700 hours
Monday to Saturday and 0900 hours
Sunday and Public Holidays (Night)
All hours
45 +
IF
55 +
IF
65 +
IF
40 +
IF
50 +
IF
65 +
IF
40 +
IF
50 +
IF
55 +
IF
35 +
IF
45 +
IF
55 +
IF
60
75
80
The influencing factor is calculated for the usage of land within two circles,
having radii of 100m and 450m from the premises of concern.
Penalties are also applied for annoying characteristics.
• Tonality
• Modulating
• Impulsiveness
Tonality
45.0
40.0
30.0
25.0
20.0
15.0
10.0
5.0
1/3rd Octave Band Centre Frequency (Hz)
Penalties
Where tonality is present
Where modulation is present
Where impulsiveness is present
+5 dB(A)
+5 dB(A)
+10 dB(A)
10 kHz
8 kHz
6.3 kHz
5 kHz
4 kHz
3.15 kHz
2.5 kHz
2 kHz
1.6 kHz
1.25 kHz
1 kHz
800 Hz
630 Hz
500 Hz
400 Hz
315 Hz
250 Hz
200 Hz
160 Hz
125 Hz
100 Hz
80 Hz
63 Hz
50 Hz
40 Hz
31.5 Hz
25 Hz
0.0
dB(A)
Noise Level (dB(A))
35.0
AS/NZ 2107:2000
AS2107 has the following recommended noise levels within an office
building:
Boardrooms and conference rooms
Corridors and Lobbies
General Office Areas
Private Offices
Reception Areas
Tea Rooms
Toilets
Satisfactory
Maximum
30 dB(A)
45 dB(A)
40 dB(A)
35 dB(A)
40 dB(A)
40 dB(A)
50 dB(A)
40 dB(A)
55 dB(A)
45 dB(A)
40 dB(A)
45 dB(A)
45 dB(A)
55 dB(A)
Other Criteria Used are Noise Ratings (NR) Curves
NR CURVES
160
140
120
NR 20
NR 30
Noise Level (dB)
100
NR 40
NR 50
NR 60
80
NR 70
NR 80
NR 90
60
NR 100
NR 110
40
NR 120
NR 130
20
0
31.5
62.5
125
250
500
1000
Octave Band Centre Frequency (Hz)
2000
4000
8000
160
140
120
NR 20
NR 30
NR 40
Noise Level (dB)
100
NR 50
NR 60
NR 70
80
NR 80
NR 90
60
NR 100
NR 110
NR 120
40
NR 130
Return Air
20
0
31.5
62.5
125
250
500
1000
Octave Band Centre Frequency (Hz)
2000
4000
8000
GREENSTAR
For Example, under Office Design there are point available for Acoustics.
Under IEQ-12 there are up to two points available where it is demonstrated that
for 95% of the project’s NLA does not exceed the ‘Satisfactory’ ambient internal
noise levels in accordance with AS/NZS 2107:2000.
One point is awarded for building services design, where within the entire base
building general office space, noise from the building services does not exceed 40
dB(A) Leq.
One point is awarded for the overall building, where within the base building
office space, the sound level does not exceed 40 dB(A) Leq (assuming open plan
offices).
Building Code Of Australia
Part F5 of the BCA 2013 'Sound Transmission and Insulation'.
Part F5 of the BCA 2013 details the requirements for sound transmission and
insulation of residential type buildings.
It is noted that Part F5 of the BCA 2013 is only applicable to the residential sections
of the development.
Basic Criteria
Walls between Apartments
Walls to corridor
Floors
Rw + Ctr not less than 50
Rw not less than 50
Rw +Ctr not less than 50
ENVIRONMENTAL NOISE
Typical Example of Exhaust Fan
Being 67 dB(A) at 3 metres
(This is Sound Power of 87 dB(A))
Neighbour at 50 metres away
Reduction for distance is 24 dB(A)
Noise level at residence is 43 dB(A)
However, with penalty of +5 dB(A) for tonality,
assessable noise level would be 48 dB(A).
Say Influencing Factor was 1 dB(A),
then assigned noise level would be :
Premises
Receiving
Noise
Noise
sensitive
premises
Assigned Level (dB)
Time of Day
LA 10
LA 1
LA max
0700 - 1900 hours Monday to Saturday
46
56
66
0900 - 1900 hours Sunday and Public Holidays
41
51
66
1900 - 2200 hours all days
41
51
56
2200 hours on any day to 0700 hours Monday
to Saturday and 0900 hours Sunday and Public
Holidays
36
46
56
Noise emissions from mechanical services are :
- Steady state
- Would operate for more than 10% of time
Assessable Noise Level,
dB(A)
48
Applicable
Assigned LA10
Noise Level
(dB)
Exceedance to
Assigned Noise
Level (dB)
0700 - 1900 hours Monday to Saturday
46
+2
0900 - 1900 hours Sunday and Public Holidays
41
+7
1900 - 2200 hours all days
2200 hours on any day to 0700 hours Monday to
Saturday and 0900 hours Sunday and Public Holidays
41
+7
36
+12
Applicable Times of Day
Possible Noise Control :
•
•
•
•
•
•
Barrier
Enclose in plantroom
Reduce speed
Located equipment further away from neighbours
Attenuators
Acoustic Louvres
Noise Reductions with Unpodded Silencers
SWL (Linear)
SWL (dB(A)
Level at residence
With 1D unpodded Silencer
With 2D unpodded Silencer
100.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
8K
4K
2K
1K
500
250
125
63
dB(A)
0.0
Noise Reductions with Acoustic Louvres
SWL (Linear)
SWL (dB(A)
Level at residence
With 300mm Acoustic Louvre
With 600mm Acoustic Louvre
100.0
90.0
80.0
70.0
60.0
50.0
40.0
30.0
20.0
10.0
8K
4K
2K
1K
500
250
125
63
dB(A)
0.0
NOISE PATHS
Also need to consider regenerated noise.
INTERNAL DESIGN TO CONTROL NOISE
Supply Air




Bends
Internal Insulation
Acoustic Type Flexible Ductwork
Add attenuators
Also consider :
 Air velocity
 Design to registers
INSERTION LOSS OF FLEXIBLE DUCT
300 Diameter, 3m length
Plain Flex
Acoustic Flex
35
30
Insertion Loss dB
25
20
15
10
5
Octave Band Centre Frequency (Hz)
8K
4K
2K
1K
500
250
125
63
0
Noise Reductions with Flexible Duct
SWL (Linear)
SWL (dB(A)
With Plain Flexible Duct
With Acoustic Flexible Duct
95.0
90.0
85.0
80.0
75.0
70.0
65.0
60.0
55.0
50.0
45.0
40.0
35.0
30.0
25.0
20.0
15.0
10.0
5.0
8K
4K
2K
1K
500
250
125
63
dB(A)
0.0
RETURN AIR
 Bends without Turning Vanes
 Return Air plenums
 Add attenuators
Noise Reductions - Bends
SWL (Linear)
SWL (dB(A)
With Turning Vanes
Without Turning Vanes
8K
4K
2K
1K
500
250
125
63
dB(A)
95.0
90.0
85.0
80.0
75.0
70.0
65.0
60.0
55.0
50.0
45.0
40.0
35.0
30.0
25.0
20.0
15.0
10.0
5.0
0.0
Breakout
Need to consider :
 From flexible connections
 Flexible ductwork
Also need to consider Regenerated Noise
From Fantech
Web Site
Download