Environmental Technology III

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Environmental Technology III
ACOUSTICAL DESIGN ANALYSIS OF THE KENT STAGE 175
East Main Street Kent, OH 44240
Final Presentation Joshua Haney 4/15/2004
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Building Description
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Building Description
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Building Description
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Building Description
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Building Description
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Building Description
LETS ROCK!
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Building Description
Floor Plan
entry
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Building Description
Section
The Kent Stage

• Is located in historic downtown Kent, Ohio.

• Was built in the late 1920s for use as both a
  motion picture theater and a live
• performance theater.

• Was converted into a modern movie theater, at
  which time the original domed ceiling
• was covered by a suspended ceiling of
  acoustical tiles.

• Has been renovated and now serves as a
  performance venue used almost exclusively
• for the performance of folk music sponsored by
  the Kent Folk Society.

• Uses an electronic amplification and speaker
  system for musical performances.

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Environmental Condition of Investigation
As both a musician and an architecture student,
acoustics are of extreme importance to me.
Having had no formal education in the area, this
semester has served as an opportunity to learn as
much as possible about the acoustical design of
spaces particularly spaces designed for musical
performance. This project focuses on three
factors affecting sound quality perception 1)
Reverberation Time 2) Sound Path 3) Sound
Distribution
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Important Concepts
Reverberation Time
Reverberation Time is the time it takes sound to
decrease 60 dB from its original Sound Level,
once the source sound is stopped. Reverberation
Time is a function of both Volume and Total Room
Absorption. The larger the volume, the longer
the Reverberation Time, because it takes longer
for sound waves to reach surfaces such as walls
and ceiling.
Initial Time Delay Gap
The Initial Time Delay Gap (ITDG) is the time
interval between the arrival of the direct sound
and the first reflected sound of sufficient
loudness. Early Sound, important for clarity and
definition of music, refers to the direct and
reflected sound arriving within the first 80ms
after a sound is initiated.
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Geometric Evaluation
1) What is the lateral view angle? The
audience is arranged within 140 degrees of the
sound source.

• Is located in historic downtown Kent, Ohio.

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Geometric Evaluation
2) Does the space make use of sound reflectors
above the stage? No sound reflectors are
used. 3) If so, are the reflectors concave,
flat, or convex? Does not
apply. 4) Does the design include irregular wall
or ceiling surfaces to aid in sound diffusion?
None are diffusing. 5) Of what materials
is the wall construction? The walls above
the chair rail are of rayon fabric over an air
space of variable depth. The wall below the
chair rail is of rough finished plaster. 6)
What is the spaces height (H)? The
height varies from 95 202. 7) What is
the spaces width (W)? The width is
794. 8) What is the spaces length to width
ration (L/W)? L/W 1.3

• Is located in historic downtown Kent, Ohio.

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Geometric Evaluation

• What is the spaces height to width ratio (H/W)?
• H/W .25 (max.) allow lateral
• reflections to reach audience first.
• 10) What is the general shape of the floor plan?
  
• Generally rectangular.
• Is absorptive material used on the back wall to
  prevent echo?
• What kind? Or is the back wall composed of an
  irregularly
• shaped surface (i.e. convex, etc.) to provide
  diffusion?
• The back wall is flat. Above the chair rail it
  is composed of the same
• rayon fabric. Below the chair rail, it is
  covered with carpet.

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Geometric Evaluation
12) How many seats are in the seating area?
633. 13) What quantity of floor area is
provided for each seated listener? 6 SF
(2x3). 14) What materials are found on /
around the stage? The stage is surrounded only
by absorptive curtains. 15) Is the space
buffered from background noise sources (i.e.
mechanical rooms, etc.) by lobbies and/or
corridors? The main entrance to the space is
buffered nicely by the entry lobby. Stage left
is buffered by an adjacent building. Stage right
on the other hand has two exits opening
directly into an alley. The background noise
from traffic is significant. 16) What is the
Sound Level of background noise? To be
determined from recordings.

• Is located in historic downtown Kent, Ohio.

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Hypotheses
General The Kent Stage is appropriately designed
as a theater for the performance of music and
drama. Specific 1) The Kent Stage has a
Reverberation Time of 1.2 1.4 sec. This
Reverberation Time is recommended as ideal for
small theaters by M. David Egans
Architectural Acoustics. 2) The Initial Time
Delay Gap (ITDG) between the arrival of direct
sound and the first reflected sound of sufficient
loudness is less than 20 ms. Reflected sound
arriving after 20 ms is heard as an echo and can
result in poor sound clarity. 3) If a sound
of known Sound Level and Frequency is produced
at a fixed point on the stage, the Sound Level
measured at predetermined points in the seating
area equidistant from the source will be equal.

• Is located in historic downtown Kent, Ohio.

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Experiment Tools
Software NCH Tone Generator Spectrogram
8 Microsoft Excel Architectural Desktop
3.3 Adobe Photoshop 7.0 Hardware Boss-864
Digital Recorder Crate Pro Audio Mixer Simpson
Sound Level Meter

• Is located in historic downtown Kent, Ohio.

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Experimental Procedure
Hypothesis 1 Reverberation Time The first
hypothesis is that the Kent Stage has a
Reverberation Time of 1.2 1.4 sec. Two
different methods will be used to determine the
actual Reverberation Time
1 Measuring Reverberation Time Use NCH Tone
Generator to create sound pulses at 125, 250,
500, 1000, 2000, and 4000 Herz. Use Boss
BR-864 to record sound pulses as .wav files and
transfer files onto a CD. Play recorded
pulses at 120 dB from a fixed point at front
center stage using Crate Pro Audio Mixer with
one 50 Watt speaker. Use digital sound
recorder to record sound pulses of each Frequency
at 24 selected grid points within the
space. Export 144 recorded pulses as .wav
files. Use Spectrogram 8 software to analyze
each .wav file and export log summary as a
.text file.
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Experimental Procedure
Hypothesis 1 Reverberation Time
Import each .text file into Microsoft Excel.
Isolate the appropriate Frequency of the created
sound pulse, and graph Sound Level over Time.
Determine the Reverberation Time, the time
interval the sound takes to decrease 60 dB, of
each Frequency at each of the 24 grid
points. For each Frequency, determine the
actual Reverberation Time by averaging the times
measured at each of the 24 grid points.
Average the 500 and 1000 Herz Reverberation
Times. This is the Mid- Frequency Reverberation
Time and should be between 1.2 1.4 sec.
Average the 125 and 250 Herz Reverberation
Times. This is the Low- Frequency Reverberation
Time. Based on a Bass Ratio of 1.2, this
Reverberation Time should be between 1.4 1.7
sec. Average the 2000 and 4000 Herz
Reverberation Times. This is the High- Frequency
Reverberation Time. Based on a Treble Ratio of
0.8, this Reverberation Time should be between
1.0 1.1 sec.
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Experimental Procedure
Hypothesis 1 Reverberation Time

• Is located in historic downtown Kent, Ohio.

2 Calculating Reverberation Time Take field
measurements of the Kent Stage and produce plans,
sections, and interior elevations. Calculate
the Total Room Volume (V) of the Kent Stage.
Calculate the Surface Area (S) of each
different material. From any of several
online sources, look up the Absorption
Coefficient (a) of each material in the 125,
250, 500, 1000, 2000, and 4000 Herz Frequency
Bands. Calculate the Total Room Absorption
(a) of each Frequency by the equation a
SSa. Add appropriate additional Sabins to the
Total Room Absorption of each Frequency to
account for furnishings and occupants. The
Sabins provided by each chair and occupant can
be selected from any of several online sources.

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Experimental Procedure
Hypothesis 1 Reverberation Time

• Is located in historic downtown Kent, Ohio.

Calculate Reverberation Time of each Frequency
by the equation T .05 V/a. Average
the 500 and 1000 Herz Reverberation Times. This
is the Mid- Frequency Reverberation Time and
should be between 1.2 1.4 sec. Average the
125 and 250 Herz Reverberation Times. This is
the Low- Frequency Reverberation Time. Based on
a Bass Ratio of 1.2, this Reverberation Time
should be between 1.4 1.7 sec. Average the
2000 and 4000 Herz Reverberation Times. This is
the High- Frequency Reverberation Time. Based on
a Treble Ration of 0.8, this Reverberation Time
should be between 1.0 1.1 sec.
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Experimental Procedure

• Hypothesis 2 Sound Path
• The second hypothesis is that the Initial Time
  Delay Gap (ITDG) between the arrival of direct
  sound and the first reflected sound of sufficient
  loudness is less than 20 ms. This hypothesis can
  be tested with ray diagrams requiring a floor
  plan and a building section

Using the building section, draw the Direct
Sound Path (D) from the sound source at the edge
of the stage to ear level at every other row.
Draw the longest Reflected Sound Path (R) from
the sound source at the edge of the stage to ear
level at every other row. Recall that the angle
of incidence equals the angle of reflection at
normal to the reflecting surface. Calculate
the ITDG by the equation ITDG (R-D)(.9).  
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Experimental Procedure
Hypothesis 2 Sound Path
Using the floor plan, draw the Direct Sound
Path (D) from the sound source at the edge of
the stage to a seat at the center of the
audience, exactly half-way between the stage
edge and the back wall. Draw the Reflect
Sound Path (R) from the sound source at the edge
of the stage to the center seat. Calculate
the lateral ITDG by the equation ITDG
(R-D)(.9). Both ITDGs should be less than 20
ms. The maximum allowable deviation is 30 ms.
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Experimental Procedure

• Hypothesis 3 Sound Distribution
• The third hypothesis is that if a sound of known
  Sound Level and Frequency is produced at a fixed
  point on the stage, the Sound Level measured at
  predetermined points in the seating area will be
  equal. The method for testing this hypothesis is
  as follows

Use NCH Tone Generator to create tones at 125,
250, 500, 1000, 2000, and 4000 Herz. Use
Boss BR-864 to record tones as .wav files and
record files onto a CD. Play recorded tones at
120 dB from a fixed point at front center stage
using Crate Pro Audio Mixer with one 50 Watt
speaker. Use the Simpson Sound Level Meter to
measure the Sound Level of each Frequency at the
24 selected grid points within the space. Use
the OSHA filter. For each Frequency, graph the
distribution of sound and compare Sound Levels
at each of the 24 grid points.
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Experiment Results
Hypothesis 1 Reverberation Time
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Discuss adjustments to data.
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sample Spectrogram image
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1
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Experiment Results
Row 25
This is an example of complete readings taken at
all 24 locations using a 125 Hz frequency. Each
reading provides a corresponding reverberation
time.
The final reverberation time for the frequency is
the average of these 24 values. This procedure
is carried out for all 6 frequency bands.
Row 18
Row 9
Row 1
7
6
5
4
3
2
1
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Experiment Results
60 dB
Tr .24 sec
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Experiment Results
60 dB
Tr .26 sec
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Experiment Results
60 dB
Tr .25 sec
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Experiment Results
60 dB
Tr .14 sec
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Experiment Results
60 dB
Tr .07 sec
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Experiment Results
Tr .12 sec
60 dB
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Experiment Conclusion
Hypothesis 1 Reverberation Time
Mid-Frequency Tr .25 sec sec Low-Frequency Tr .20 sec sec High-Frequency Tr .10 sec sec The Total Room Absorption is too great.
Solve by increasing Volume OR using less
absorptive materials.
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Experiment Results
Hypothesis 1 Reverberation Time
Tr Calculations
To be completed for final report
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Experiment Results
Hypothesis 2 Sound Path
ITDG (R D)(.9)
R
R
D
166
111
73
ITDG 18 ms
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Experiment Results
170
1110
122
ITDG 15 ms
184
130
179
ITDG 12 ms
200
149
236
ITDG 10 ms
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Experiment Results
220
169
295
ITDG 8 ms
240
192
354
ITDG 7 ms
263
218
414
ITDG 6 ms
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Experiment Results
286
246
473
ITDG 5 ms
306
278
533
ITDG 4 ms
3210
371
669
ITDG 3 ms
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Experiment Results
Experiment Results
3210
417
7110
ITDG 2 ms
322
4611
7610
ITDG 2 ms
306
531
8111
ITDG 1 ms
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Experiment Results
Experiment Results
ITDG 50 ms
430
420
300
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Experiment Results
Experiment Conclusion
Hypothesis 2 Sound Path
Based on section, ITDG ITDG 20 ms. If walls are constructed of a
reflective material, echoes will result. Lateral
sound will not reach audience members before
sound reflected from the ceiling, resulting in
poor intimacy. Solve by increasing W/H ratio
to above 0.7 (currently 0.25) by increasing
height or decreasing width. Make the space
taller and narrower.
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Experiment Results
Hypothesis 3 Sound Distribution
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2
1
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Experiment Results
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Experiment Results
Average Sound Decay of Different Frequencies All
Tones created at 120 dB.
125 Herz 75 dB 250 Herz 73 dB 500 Herz 75
dB 1000 Herz 73 dB 2000 Herz 78 dB 4000 Herz 83 dB
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Experiment Conclusion
Hypothesis 3 Sound Distribution
Lowest values are in back, on stage right side,
or in front corners. Sound Level decreases with
distance. Sound Level on sides is less than in
center due to absorption by wall surfaces. Stage
right wall is more absorptive than stage left
wall. Sound Level measured at front corners lower
because of sound projection angle. 125, 250, 500,
1000 Hz are absorbed at about same rate. 2000
and 4000 Hz are absorbed less. This difference
must be attributed to the absorption coefficients
of building materials.
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Final Conclusions
Discussion
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Resources
Egan, M. David. Architectural Acoustics. New
York McGraw-Hill, 1988. Everest, F. Alton.
Master Handbook of Acoustics. New York
McGraw-Hill, 2001.
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the end.