Acoustics • Audio/Video • IT Infrastructure
ACOUSTIC COMMISSIONING REPORT FOR
DUKE UNIVERSITY BALDWIN AUDITORIUM
DURHAM, NC
JaffeHolden
Norwalk, CT
October 18, 2013
JH No. R11-0350
JaffeHolden.com
Headquarters: 114-A Washington Street, Norwalk, CT 06854 • 203.838.4167
Houston: 4617 Montrose Boulevard, Suite C201, Houston, TX 77006 • 713.589.7018
Duke University Baldwin Auditorium
Commissioning Report
R11-0350
10/18/2013
INTRODUCTION
The following report is intended as a users’ guide to the adjustable acoustic elements in Duke
University’s Baldwin Auditorium. These settings were developed during various commissioning
visits during the months of August and September 2013. This document is divided in two main
sections. The first contains a general overview and initial settings for the adjustable acoustics in the
Auditorium, while the second contains a summary of the acoustical measurements and associated
analysis.
ADJUSTABLE ACOUSTICS – OVERVIEW
Baldwin Auditorium is equipped with several adjustable acoustical elements that enable these
spaces to be tuned to accommodate a variety of performance types. Below are summary
descriptions of these systems:
Adjustable acoustic drapes and banners have been provided in the Auditorium. The purpose of
these banners is to add or subtract acoustical absorption in the space to achieve a reverberation
time suitable for the program being presented, as well as add or reduce Clarity and Loudness for
amplified presentations. The locations of the drapes are identified as blue and the locations of the
banners are identified in red on the following sketches:
Orchestra Level
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Balcony Level
Section
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ADJUSTABLE ACOUSTICS – COMMISSIONING SETTINGS
The following outline provides commissioning recommended settings of the adjustable acoustic
elements for various types of programs in the Auditorium. Note that all of the settings for the
acoustic drapes and banners listed here have been recorded as pre-sets in the rigging control
module and are labeled accordingly for ease of use. In addition, performer stage locations were
methodically tested throughout the tuning process to locate the acoustical “sweet spot” for the
musicians. The approximate recommended locations are displayed in the sketches below. In
general, it was found that a rather central location on stage was favorable for most ensembles
located approximately 16’ back from the stage lip. Here, the musicians benefit from useful side and
rear shell wall reflections, which help onstage hearing as well as blend the sound before radiating to
the audience. When musicians are pushed far downstage near the stage edge, they lose the
strength of these lateral reflections as well as a stage floor reflection which can help listening for
the audience in the balconies. Overall, we found that ensembles had the best sound, blend, and
balance in this central location. For programs not included, the variable acoustic elements should
be set and the performers located according to event types they most closely resemble.
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1.
Symphony/Chamber/Choral
a. Preset name: “Symphony/Chamber”
b. This setting would be used for most
large acoustic ensemble
performances including the University
Symphony Orchestra, Wind
Symphony, Chorale, and chamber
ensembles. Locating the choir ~8-10
ft from the upstage wall will keep it
within the shell enclosure, which will
help ensure good blend and balance
among the voices. The full symphony
orchestra will mostly spread out to fill
the stage.
c. Acoustic Banners and Drapes
i. All banners and drapes stored.
d. Example Choir Layout and Photo →,
Example Symphony Orchestra Layout
and Wind Symphony Photo ↓, and
Drape/Banner Configuration on the
following page
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Figure 1 Rec
e ded Ce ter i e Dista ce Betwee Upstage
Wa a d Ch ir 8 10’
Figure 2 Ch ir
Figure 3 Sy ph
y %rchestra &ay ut
Figure 4 Wi d Sy ph
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Figure 5 Re deri g f Drape*Ba
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figurati
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2.
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Symphony Rehearsal
a. Preset name: “Symph Rehearsal”
b. This setting would be appropriate for rehearsals with the same ensembles as above. The
purpose of the partially deployed banners is to simulate audience absorption in an
unoccupied Auditorium.
c. Acoustic Banners and Drapes
i. Upper side wall banners (5 & 6) deployed to 50%.
ii. All other drapes and banners stored.
d. Drape/Banner Configuration↓
Figure 6 Re deri g f Drape*Ba
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3.
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Small Ensemble
a. Preset name: “Small Ensemble”
b. Typical programs appropriate for this
setting include string quartets, piano
trios, saxophone quartets, and
woodwind quintets (performance and
rehearsal).
c. Acoustic Banners and Drapes
i. Upper side wall banners (5 & 6)
deployed to 100%
ii. All other drapes and banners
stored
d. Example String Quartet and Trio
Musician Layouts → and
Drape/Banner Configuration ↓
Figure 8 Re deri g f Drape*Ba
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er C
figurati
Figure 7 Rec
e ded Ce ter i e Dista ce Betwee Stri g
Quartet a d Stage Edge 12’
Figure 9 Rec
e ded Ce ter i e Dista ce Betwee Pia
Tri a d Stage Edge 16'
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4.
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Amplified/Lecture
a. Preset name: “Amplified/Lecture”
b. Typical programs appropriate for this
setting include amplified ensembles,
films, lectures, and panel discussions.
c. Acoustic Banners and Drapes
i. All drapes and banners 100%
deployed.
d. Example Big Band Musician Layout
and Photo → and Drape/Banner
Configuration ↓
Figure 11 Re deri g f Drape*Ba
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figurati
Figure 10 Rec
e ded Ce ter i e Dista ce Betwee Stage
Edge a d Fr t f Big Ba d E se b e 12 14'
Figure 12 4a55 Big Ba d Rehearsa
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5.
Percussion
a. Preset name: “Percussion”
b. Loud acoustic ensembles that require
a high degree of clarity would benefit
from this setting for both
performances and rehearsals. Typical
ensembles include the University
Djembe Ensemble and Percussion
Ensemble.
c. Acoustic Banners and Drapes
i. Lower side wall drapes (1 & 2)
stored.
ii. All other drapes 100% deployed.
d. Example Djembe Ensemble Musician
Layout and Drape/Banner
Configuration→
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Figure 13 Rec
e ded Ce ter i e Dista ce Betwee Stage
Edge a d D6e be E se b e 12 14'
Figure 14 Re deri g f Drape*Ba
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6.
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Solo Piano/Piano Vocal/Piano Violin
a. Preset name: “Piano/Vocalist”
b. Typical programs appropriate for this setting include solo piano, piano vocalist and piano
violin performances and rehearsals.
c. Acoustic Banners and Drapes
i. Upper side wall banners (5 & 6) deployed to 50%.
ii. All other drapes and banners stored (identical to Symphony Rehearsal).
d. Example Musician Layouts and Drape/Banner Configuration ↓
Figure 15 Rec
e ded Ce ter i e Dista ce Betwee Stage
Edge a d Pia *V ice 9 10'
Figure 16 Rec
e ded Ce ter i e Dista ce Betwee Stage
Edge a d S
Pia
16'
Figure 17 Rec
e ded Ce ter i e Dista ces Betwee
Stage Edge a d Vi i *Pia ( 14' t Vi i 9 16' t Pia )
Figure 18 Re deri g f Drape*Ba
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ACOUSTICAL MEASUREMENTS DATA AND ANALYSIS SUMMARY
A. Acoustical Parameters
Sound Pressure Level, Lp: A measure of the magnitude of a sound, expressed in units of
decibels (dB). Sound pressure level depends on the strength of the source, as well as
environmental effects, including distance from the source, acoustical characteristics of
nearby surface materials, and the presence of barriers. Lp roughly corresponds to the
human perception of loudness. For example, adding two sources generating the same
sound energy results in a +3 dB change in the sound pressure level, which is subjectively
equivalent to a perceptible change in level. A +10 dB change is usually perceived as twice as
loud. This report quotes a time-averaged sound level, Leq, for the ambient noise
measurements.
Reverberation Time, RT60: The length of time (in seconds) required for the sound pressure
level to decay by 60 dB. Roughly speaking, this is the time it takes for a loud sound to decay
to inaudibility after the noise source has stopped. The RT is dependent on the volume of the
room, and the size and construction (absorptive, reflective, or diffusive materials) of its
various boundary surfaces. Often, the single most absorptive “surface” in an auditorium is
the audience. Therefore, there will be a noticeable change in the RT between the occupied
and unoccupied conditions. All RT measurements quoted in this report are for the
unoccupied condition. Different RT values are appropriate for different performance types.
For example, a “dry” room with a shorter RT is necessary for speech or amplified events,
while a “live” room with a longer RT is preferred for classical music.
Noise Criteria, NC: A single-number rating to describe the ambient or background noise
level in a space. The NC rating is determined by graphing the sound pressure levels in each
octave band against a series of established noise criteria curves, and comparing them with
the tangent method. The standard NC curves use equal loudness contours to replicate the
function of the human ear, which is more sensitive to high frequency sounds than it is to
low frequency sounds.
B. Equipment
The flowing equipment was used to conduct and analyze measurements performed in the
Main Hall:
•
•
•
Larson Davis 824 Real-Time Handheld Analyzer
Larson Davis Type 2560 Transducer
17-inch diameter balloons
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C. Room Conditions
In the Auditorium, the reverberation time (RT) and background noise level (NC)
measurements were conducted in the unoccupied room with the HVAC system operating at
the normal performance setting.
D. Measurement Procedure
To measure the reverberation time, 17-inch diameter balloons were inflated close to their
burst point. The balloons were then popped with a pin generating a clean impulse in the
room. This impulse and subsequently the room’s decay were recorded with the handheld
analyzer. This procedure was repeated at each of three receiver locations in the Main Hall
as listed below:
•
•
•
Orchestra Level House Right Third Row from Stage
Orchestra Level House Left Third Row from Rear Wall
Balcony Level House Left First Row from Balcony Front
To determine the noise criteria, the ambient sound pressure level (Leq) was measured for
thirty seconds at the locations noted on the ambient noise graph in the appendix.
E. Data Analysis
The recorded data were analyzed at the Jaffe Holden office in Norwalk, CT, using
proprietary spreadsheets and software.
For each reverberation time measurement, the slope of the decay curve was determined
using the proprietary spreadsheets for each octave band. The mid-frequency average (RTmid)
was calculated from the values at 500 and 1000 Hz. These data are presented in graphical
format located in the appendices.
For each noise criteria measurement, the sound pressure level in octave bands was
calculated by logarithmically combining the third-octave band data using the following
formula:
Lp = 10 * log ( 10 Lp1 / 10 + 10 Lp2 / 10 + 10 Lp3 / 10 )
where Lp1, Lp2 and Lp3 are the sound pressure levels of the three third-octave bands that
comprise the full octave band. These data are presented in graphical format located in the
appendices.
F. Summary
The maximum RTmid of the Auditorium, unoccupied, was measured to be approximately 2.1
seconds, and the minimum RTmid was approximately 1.5 seconds. The adjustable absorptive
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banners are providing 0.6 seconds of variability in the room’s response. When the room is
fully occupied, it is anticipated that the reverberation times will be about 0.2 seconds
shorter depending on the number of audience members present.
The target NC rating for both the stage and audience seating is NC 15. Measurements taken
in August 2013 show that background noise levels were at NC 16 in orchestra level seating,
NC 17 at the center stage lip, and NC 22 at upstage left. We believe that two sources may
be contributing to these high levels. These sources are dimmer room noise breaking out of
a duct located in the upstage left drape pocket and the stage supply VAV boxes, which were
noisier than predicted.
Based on our measurements and observations, Jaffe Holden has issued recommendations
to Pfeiffer Partners to address these noise sources and reduce the overall background noise
at the stage platform. These recommendations consist of adding in-line sound attenuators
downstream of the 2 VAV boxes serving the stage platform and externally lagging the
transfer duct between the dimmer room and lower level. We had also recommended
setting the temperature threshold higher for exhaust fan (EF-3) located in the attic so it will
not kick on as frequently during hot weather. The temperature sensor should be set as low
as possible so that the heater serving the attic (FCU-1) only runs when necessary to prevent
pipes from freezing.
Measurements were taken of several different CFM settings for the main AHU’s and VAV
boxes serving the hall. Based on the results of this testing, we have provided recommended
settings for all critical recordings and performances.
Unit
Max CFM
ON/OFF
AHU-1
15,000
ON
AHU-2
N/A
ON
VAV 2-16
600
ON
VAV 2-17
600
ON
EF- 1,2,3
N/A
OFF
FCU-1 (attic)
N/A
OFF
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APPENDIX
Duke University
Baldwin Auditorium
Reverberation Time Measurements
REVERBERATION TIME
3.00
2.50
Time (seconds)
2.00
1.50
1.00
0.50
0.00
125
250
500
1000
2000
4000
8000
Octave Band Center Frequency (Hz)
Small Ensemble
Amplified/Lecture
Percussion
Piano/Vocalist or Symph Rehearsal
Symphony/Chamber
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Duke University
Baldwin Auditorium
Ambient Noise Level Measurements
NOISE CRITERIA CURVES
90
80
70
Sound Pressure Level (dB re:20microPa)
NC
60
NC 60
NC 55
50
NC 50
NC 45
40
NC 40
NC 35
30
NC 30
NC 25
20
NC 20
NC 15
10
0
31.5
63
125
250
500
1000
2000
4000
8000
Octave Band Center Frequency (Hz)
Range of Ambient Noise Levels
Upstage Left Average Background Noise Level
Center Stage Lip Average Background Noise Level
Orchestra Level Mid House Average Background Noise Level
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