FFA
Consultants in Acoustics
and Noise Control Ltd.
October 30, 2014
District of Elkford
816 Michel Road
Elkford, BC, V0B 1H0
Dear Ms. Garity Stanley:
Re: Elkford Community Centre
Acoustical Treatment Assessment
File: 114-2604-01
The district of Elkford requested an acoustical assessment of the Elkford Community Centre due to
concerns about the acoustics of the Community Hall and the Play School spaces and various
mechanical equipment noise concerns. The following letter outlines the findings of our acoustical
treatment assessment of the Elkford Community Centre Community Hall and Play School. The
mechanical equipment noise concerns will be addressed in a separate letter.
Background & Scope
Our understanding is that the Community Hall is intended to be multi-purpose space that can be
used for large gatherings and events such as weddings, dances, town hall meetings and various
other group events. The current concerns regarding the acoustic environment in the Community
Hall expressed by the District of Elkford have included high activity noise levels during gatherings,
difficulty understanding speech and a very reverberant acoustic environment in the space.
The Play School is currently being used as a preschool classroom for young children approximately
aged 2 to 6. The current concerns regarding the Play School include high activity noise levels and
difficultly understanding speech when classes are occurring.
From this we understand that the main acoustical concern for both spaces is to provide sufficient
acoustical treatment to control reverberation to provide good speech intelligibility, and to allow the
spaces to function as a multipurpose space and classroom respectively.
210N, 3015 – 5th Avenue N.E., Calgary, Alberta T2A 6T8
Telephone: (403) 508-4996, Fax: (403) 508-4998 info@ffaacoustics.com
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Room Dimensions and Finishes
Community Hall
The Community Hall is approximately 28 m long by 20 m wide with the roof slopping from
approximately 7m to 4.5m high. The two exterior walls are angled relative to the interior walls
such that the room from a plan view looks to have started as a rectangle with the southeast corner
subsequently pulled away from the northwest corner angling the east and south walls. There is a
raised stage in the northeast corner of the room.
The main acoustically reflective finishes are as follows:
•
•
•
•
•
•
Painted gypsum board walls and bulkheads
Exposed cross laminated timber walls
Painted OSB Sheathing on the underside of the roof
Punched window exterior insulating glazing
Wooden Doors
Linoleum Flooring
There are no significant acoustically absorptive finishes in the space.
Play School
The Play School is approximately 15 m long by 9 m wide with the roof slopping from
approximately 8 m to 6 m high. A non-accessible loft above the washrooms located on the east
wall of the space is open to the play school and is approximately 3 m wide by 10 m long and 3 to
5 m high. The two exterior walls are angled relative to the interior walls such that the room from a
plan view looks to have started as a rectangle with the southwest corner subsequently moved north
and west angling the west and south walls.
The main acoustically reflective finishes are as follows:
•
•
•
•
•
•
•
Painted gypsum board walls and bulkheads
Exposed cross laminated timber walls
Painted OSB Sheathing on the underside of the roof
Unpainted OSB sheathing on the top of the washrooms (bottom of the loft)
Linoleum Flooring
Punched window exterior insulating glazing
Metal Doors
•
The only acoustically absorptive finish of significance in the space is commercial carpet on the
floor.
In addition to the room finishes listed above shelves, cupboards, tables, chairs and other
miscellaneous furniture are present in the space.
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Site Visit
A site visit to the Elkford Community Centre was conducted by Mr. Justin Dos Ramos on
September 16, 2014. During the site visit reverberation time measurements were conducted in the
Community Hall and Play School with a Brüel & Kjær 2270 sound level meter.
Reverberation Time
The reverberation time is an important parameter for the control of activity noise, the
understanding of speech and the enjoyment of music in a room. The RT60, commonly referred to
as the reverberation time, is the time in seconds that sound takes to decay 60 dB in level. In
practice, the reverberation time is often determined by measuring the time required for a 20 or
30 dB decay and extrapolating that decay rate to the time required for a 60 dB decay. The just
noticeable difference in RT60 times is approximately 5%.
Sound reverberation in a space is dependent on the volume of the space and the amount of
acoustical absorption in the space. The level of a reflected sound in a room is determined by the
amount of sound absorptive surfaces, the room geometry, and the frequency spectrum of the
sound. As the distance between a sound source and a receiver in a room increases, the sound at
the position of a receiver is increasingly dominated by reflected sound.
Acoustically there is a significant difference in the requirements for rooms used for music
performance, versus motion picture or multimedia viewing, versus speech applications such as
assemblies, drama or lectures or video/teleconferencing with each of these uses requiring more
sound absorption than the one previous to it in the above list. Rooms optimized for music should
be constructed from heavy materials that do not overly absorb the bass sounds and require a larger
volume than those for speech, as they must support longer reverberation times. Rooms optimized
for speech applications require shorter reverberation times to provide better speech intelligibility.
Thus there is a tradeoff when designing multi-purpose rooms. Performing arts facilities at major
centres and universities tend to have rooms specifically designed for either music or speech
applications such as drama or lectures.
Acoustical literature and commonly recognized standards provide information as to recommended
or design RT60 times for rooms based on the usage and volume of the room. Based on our
experience, the acoustic literature and the multipurpose nature of the Community Hall we would
expect that reverberation times above 2.0 seconds would be problematic, time closer to
1.6 seconds would be acceptable and times closer to 1.2 seconds would be ideal for a fully
occupied room.
The accurate transmission of acoustical information in a classroom is imperative for optimal
academic achievement. Students must be able to hear their teachers (to receive direct instruction)
and their peers (to receive indirect instruction), and teachers must be able to speak to their classes
without straining their voices. Acoustical variables that can compromise speech perception include
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the reverberation time (RT) of the room, the overall level of the background noise, the relationship
between the level of the teacher’s voice and the background noise, and the distance from the
teacher to the child. Proper classroom acoustics are particularly important for early childhood and
elementary school environments where language acquisition is happening. Consideration of these
acoustical variables is even more critical for the design of spaces for students with hearing and
listening impairments.
It has been well-established in various studies that low background noise levels, effective noise
isolation and reverberation control are critical to providing optimal speech intelligibility and an
effective learning environment in classrooms. Excessive background noise and poor acoustics can
lead to poor understanding of speech, reading deficiencies, delayed language acquisition, and
other negative consequences for student performance. As a result, standards have been developed
with recommended criteria for classroom background noise levels, classroom demising wall and
floor/ceiling assembly Sound Transmission Class (STC) ratings, floor/ceiling assembly Impact
Insulation Class (IIC) ratings, and reverberation times for classrooms.
A commonly recognized acoustical standard for educational facilities in North America is
ANSI/ASA S12.60-2010, American National Standard Acoustical Performance Criteria, Design
Requirements, and Guidelines for Schools. For core learning spaces ≤ 283 m3 (≤ 10,000 ft3), its
maximum permitted reverberation times in the 500, 1000, and 2000 Hz octave bands are
0.6 seconds.
Our understanding is that British Columbia does not have any specific requirements for school
reverberation times, however, the Alberta Infrastructure’s Design and Construction document
“Standards and Guidelines for School Facilities (August 2007)” requires that reverberation time in
unoccupied classrooms not exceed 0.6 seconds when averaged over the frequency range of 500
Hz to 2000 Hz. Note, in both of these targets there is the assumption of a classroom with typical
dimensions (i.e. classrooms with single story ceiling heights on the order of 3 m).
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Reverberation Time Calculations
We have undertaken RT60 calculations for the spaces utilizing ODEON room acoustics software
with various amounts of acoustic treatment added to the spaces. The measured and calculated
RT60 values for the spaces are presented in Table 1, Table 2, Figure 1 and Figure 2. The calculated
values are derived from ODEON room acoustics software models which are based on drawings
provided by the District of Elkford and measurement of the room made during the site visit.
Table 1
Elkford Community Center Community Hall
Calculated Reverberation Times RT60 (sec)
RT60 (seconds)
Octave Band Frequency (Hz)
Scenario Description
500 125
250
500 1000 2000 4000
2000
Average
Measured Average Reverberation Time
Unoccupied
2.8
2.8
3.1
3.5
2.7
1.8
3.1
Option A
233 m2 50mm thick acoustic panels
applied directly to the underside of
the ceiling
Unoccupied
2.4
1.9
1.8
1.8
1.7
1.4
1.8
Option B
2
456 m 50mm thick acoustic panels
applied directly to the underside of
the ceiling
Unoccupied
2.2
1.5
1.5
1.5
1.4
1.2
1.5
Unoccupied
2.2
1.4
1.4
1.4
1.3
1.2
1.4
Design RT60 Speech (For Fully Occupied Room)
1.2
1.2
1.2
1.2
1.2
1.2
-
Design RT60 Music (For Fully Occupied Room)
1.8
1.4
1.2
1.2
1.2
1.2
-
456 m2 50mm thick acoustic panels
applied directly to the underside of
the ceiling
Option C
and 86 m2 50mm thick acoustic
panels applied directly to bulkhead
faces or gypsum board walls
Notes: Acoustic panels used in the calculations are fabric covered 50 mm thick fibreglass panels mounted directly on the underside
of the roof, gypsum board bulkheads, or gypsum board walls (see option description in the table) with a NRC rating of 0.95.
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Figure 1
Elkford Community Center Community Hall
Calculated Reverberation Times RT60 (sec)
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Table 2
Elkford Community Center Play School
Calculated Reverberation Times RT60 (sec)
RT60 (seconds)
Octave Band Frequency (Hz)
Scenario Description
Measured Average Reverberation Time
Option D
2
70 m 50mm thick acoustic panels
applied directly to the underside of
the ceiling
500 -2000
125
250
500 1000 2000 4000
Unoccupied
1.4
1.6
1.7
1.9
1.6
1.1
1.8
Unoccupied
1.3
1.2
1.2
1.3
1.1
0.9
1.2
Unoccupied
1.3
1.0
1.0
1.0
0.9
0.7
1.0
Unoccupied
1.2
0.8
0.8
0.8
0.8
0.6
0.8
Average
2
70 m 50mm thick acoustic panels
applied directly to the underside of
the ceiling
Option E
and 30 m2 50mm thick acoustic
panels applied directly to gypsum
board walls
2
108 m 50mm thick acoustic panels
applied directly to the underside of
the ceiling
Option F
and 43 m2 50mm thick acoustic
panels applied directly to gypsum
board walls
Alberta Infrastructure 2007 School Design Guideline Max. Classroom RT60 (For Unoccupied Room)
ANSI/ASA S12.60-2010/Part 1, Max. RT60 for Core Learning Spaces ≤ 283 m3
(≤ 10,000 ft3), For Unoccupied Room
0.6
0.6
0.6
0.6
0.6
Notes: Acoustic panels used in the calculations are fabric covered 50 mm thick fibreglass panels mounted directly on the underside
of the roof, or gypsum board walls (see option description in the table) with a NRC rating of 0.95.
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Figure 2
Elkford Community Center Community Hall
Calculated Reverberation Times RT60 (sec)
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Discussion of Results and Acoustical Treatments
The changes in the RT60 values with various acoustical treatments can be seen in the previous
Tables and Figures. It is desirable to install acoustical treatment such that the design RT60 values
are met however it is usually not practically achievable in all octave bands.
Increasing the amount of acoustical absorption and evenly distributing it throughout the space is
effective at reducing reverberation in a space. Concentrating all of the acoustically absorptive
treatment on the ceiling is not as effective as evenly distributing it on the walls and floor as well.
However, compromises are typically made with acoustic treatment placement in public spaces and
classrooms as it is usually not practical to install acoustic treatment on the lower surfaces of the
walls because of the potential for damage to treatments. Additionally our understanding is that the
district of Elkford wants to avoid placing acoustical treatments on surfaces with exposed wood
finishes.
A healthy young person is able to hear frequencies ranging from about 20 Hz to 20000 Hz. This
range decreases with age, especially at the upper frequency limit. Music occupies the entire
bandwidth of human hearing. The human ear is most sensitive to sound energy in the frequency
range produced by the human voice (approximately 100 Hz to 10000 Hz) with maximum
sensitivity at approximately 4000 Hz due to resonance in the ear canal. The main useful voice
frequencies are contained within the 100 Hz to 3400 Hz range with much of the speech energy in
the lower frequencies and much of the speech information in the higher frequencies. Thus for
speech intelligibility considerations in a room the 125 Hz to 4000 Hz octave bands are most
important.
The calculations were completed using 50 mm thick fabric wrapped fibreglass panels with a Noise
Reduction Coefficient (NRC) of 0.95. The NRC value is a measure of the amount of sound
absorbed by a surface. A NRC of 1.00 indicates that 100% of the sound striking the surface is
absorbed. A NRC of 0.50 indicates that 50% of the sound striking the surface is absorbed.
Alternative acoustic treatments can be substituted for the 50 mm thick fibreglass panels used in the
calculations as long as the NRC rating and the octave band absorption coefficients of the
alternative are comparable to the fibreglass panel. Possible alternative treatments are discussed in
the Acoustical Treatments section of this letter. For the calculations all wall and bulkhead
treatments were placed at least 2.7 m above the floor in the Community Hall and 2.2 m above the
floor in the Play School to reduce the risks of accidental or intentional damage.
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Community Hall
As can be seen in Table 1 and Figure 1, the measured reverberation times are up to 3.5 seconds in
the 1000 Hz frequency band critical for speech intelligibility. The calculations indicate that
(Option A) adding 233 m2 of acoustic panels to the underside of the ceiling would reduce the
reverberation times below 1.9 seconds in all the octave bands except the 125 Hz octave band.
The calculations indicate that adding more treatment to the ceiling (Option B – 456 m2 of
treatment) would further reduce the reverberation times to 1.5 seconds and below (except in the
125 Hz octave band). Adding an additional 86 m2 of panels to the bulkheads or upper gypsum
board wall areas (Option C) could further reduce the reverberation times in the Community Hall to
1.4 seconds or below (except for the 125 Hz octave band). The calculations have assumed that the
ceiling treatments would carry past the bulkhead to the ceiling areas above the stage.
The calculations indicate that the reverberation times in the Community Hall would still be above
the ideal design times of 1.2 seconds for speech. The recommended RT60 values are for a fully
occupied space. Measurements undertaken with the room fully occupied would result in lower
RT60 times than those reported in Table 1 and Figure 1 as people are acoustically absorptive and
would provide a significant amount of absorption in a large function situation. However, given that
functions are of varying size and room occupancy will vary, it is beneficial to reduce the variance
in reverberant noise control between occupancy levels so that the control of reverberation, speech
intelligibility, and proper functioning of a sound system are not dependent on the number of
people in the room.
The calculated reverberation times with treatment options B or C would be between the acceptable
to ideal range 1.2 - 1.6 seconds (except for the 125 Hz octave band), even when the room is
unoccupied or used for small functions. When fully occupied, the resulting times would likely be
very close to the design time of 1.2 second.
The calculations indicate that in all the treatment options the reverberation times in the 125 Hz
octave band are greater than in higher frequency bands. In general a lack of low frequency
absorption (increased reverberation times in the lower frequency bands) can result in a space that is
more “boomy” and at higher levels low frequency reverberation can mask speech, reducing
intelligibility. Proper design and adjustment of a sound system can compensate for this somewhat
by tightly focusing the sound coverage on the occupied areas and limiting the amount of low
frequency sound energy emitted by the system. Additionally, proportionally higher low frequency
reverberation times are beneficial for music performances.
We do not anticipate a significant issue with the low frequency reverberation times with any of the
proposed options. However, mounting the treatment with at least a 50 to 100 mm thick airspace
behind the panels would help to lower the reverberation times in the 125 Hz octave band without
requiring additional areas of treatments.
Based on the calculations and our understanding of the usage we would recommend that at least
the amounts of acoustic treatments in Option B be installed in the Community Hall. It would likely
also be beneficial if the treatment amount in Option B can be divided between the ceiling and the
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bulkhead faces/upper gypsum board walls instead of exclusively on the underside of the ceiling
(for example 370 m2 of panels on the ceiling and 86 m2 on the bulkheads or upper walls). If the
Community Hall is regularly used for small gatherings (less than 20%) of capacity then Option C
would be desirable as it provides more acoustical absorption in low occupancy situations.
Play School
From Table 2 and Figure 2 it can be seen that the measured reverberation times are up to
1.9 seconds in the play school. The calculations indicate that (Option D) adding 70 m2 of acoustic
panels to the underside of the ceiling would reduce the reverberation times to 1.3 seconds or
below in the modelled octave bands. The calculations further indicate that adding treatment to the
gypsum board walls (Option E – 70 m2 of treatment on the ceiling and 30 m2 on the gypsum board
walls) would further reduce the reverberation times to 1.0 seconds and below (except in the
125 Hz octave band). Adding an additional 38 m2 of panels to the ceiling and 13 m2 to the walls
(Option F – 108 m2 of treatment on the ceiling and 43 m2 on the walls) could further reduce the
reverberation times in the Play School to 0.8 seconds or below (except for the 125 Hz octave
band)
The calculations indicate that the reverberation times in the Play School would still be above the
design times of 0.6 seconds. However, the volume of the playschool is much larger than a normal
size classroom and can most likely support a marginally higher reverberation time without
significantly increasing reverberant noise levels or degrading speech intelligibility. In addition, due
to the district of Elkford’s desire to not cover exposed wood wall areas and avoiding lower wall
areas because of damage to the acoustic treatments, reducing the times significantly below those in
Option F is likely not practical.
The calculations indicate that in the treatment options E and F the reverberation times in the
125 Hz octave band are greater than in higher frequency bands. In general a lack of low frequency
absorption (increased reverberation times in the lower frequency bands) can result in a space that is
more “boomy” and at higher levels low frequency reverberation can mask speech, reducing
intelligibility. However the way we understand the room is used, we do not anticipate a significant
issue with the low frequency reverberation times with any of the proposed options. The energy in
children’s voices is higher in frequency and the room will not typically be excited with low
frequency noise. Mounting the treatment with at least a 50 to 100 mm thick airspace behind the
panels would help to lower the reverberation times in the 125 Hz octave band without requiring
additional areas of treatments.
Based on the calculations and our understanding of the usage we would recommend Option C be
implemented in the Play School. However, if due to cost constraints the amount of treatment in
Option C is not feasible then we would expect that Option B would provide a significant reduction
in reverberation time, significantly improve the acoustics for teaching and student comprehension
in the Play School and reduce the reverberant buildup of noise in the space even though the design
values are not met.
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Acoustical Treatments
Acoustical Ceiling Treatments
In order for the acoustical ceiling treatments to be most effective they should be evenly distributed
across the ceiling and not obstructed by large areas of non-acoustically transparent materials.
The location of any ceiling treatments with respect to the sprinklers must meet the applicable NFPA
fire code requirements and should not interfere with the coverage pattern of the sprinklers.
The calculations were completed using 50 mm thick fabric wrapped fibreglass panels with a NRC
of 0.95 mounted directly to the underside of the ceiling. As mentioned previously mounting the
panels with a 50 to 100mm airspace behind the panels can improve the low frequency
performance of the panel and would reduce the increase in the 125 Hz octave band reverberation
times seen in the calculations.
The following alternative ceiling treatments should provide comparable levels of acoustic treatment
to the 50 mm thick fabric wrapped fibreglass panels mounted directly to the underside of the
ceiling.
•
Suspended T-Bar Fibreglass Ceiling Tiles (NRC rating of 0.90)
Suspended fibreglass ceiling tiles mounted at least 100 mm below the ceiling provide very
good acoustic absorption. If the tiles are spaced off of the ceiling in the 200 mm-400 mm
range they also provide significantly more absorption in the lower frequency bands. Larger
suspended ceiling fibreglass panels such as the Armstrong CAPZ have similar performance
to smaller tiles but may be more aesthetically appealing.
•
50 mm Thick Fibreglass Duct Liner (NRC rating of 0.90 to 0.95)
Flexible fibreglass duct liner mounted directly to the underside of the ceiling is a very cost
effective method of providing acoustical absorption to a large room with an exposed
ceiling. Duct liners are typically black faced and are available in various thicknesses. Some
manufacturers print their company and/or product name on the duct liner face. If a flat
black look is desired and the supplied duct liner has lettering on it that will be visible from
the floor, the lettering can be lightly painted over to hide it without affecting the sound
absorption. If a white ceiling is desired black duct liner may not be an appropriate choice
as painting the duct liner white would require so much paint that the acoustical absorption
would be significantly reduced. Lighter colored duct liner products may be more suitable
but we understand that these may not be readily available.
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25 mm thick Fabric Covered Acoustic Panels or 25 mm Thick Fibreglass Duct Liner
mounted 25-100 mm off of the ceiling (NRC rating of 0.85-0.90)
Using a thinner acoustic panel or fibreglass duct liner and providing an airspace of between
25 and 100 mm between the underside of the ceiling and the panel can allow a thinner
product to have a performance similar to a thicker panel. Care must be taken when
comparing pricing/bids to ensure that the mounting method of a thinner product includes
mounting with an airspace behind the product to bring the performance up to the 50 mm
thick panel performance.
Another option for the ceiling would be fabric-covered fibreglass baffles up between the joists
evenly distributed across the ceiling.
Acoustical baffles constructed from at least 50 mm thick fibreglass are also very efficient at
absorbing sound and are another alternative to suspended T-bar clouds. Typically, they are
constructed with some type of hanging frame or cloth, mesh, or perforated vinyl bag to hold the
fiberglass with attachment points for mounting to the ceiling. One construction method is to have
two 25 mm thick pieces of a prefinished fiberglass product, such as a duct liner or fiberglass ceiling
tile, mounted back to back in a frame. Another option is to use a 50 mm thick raw fiberglass with
an acoustically transparent covering applied over the fiberglass mounted in a frame. It is important
to note that in order to be acoustically effective the covering needs to be permeable to air. The
glass fibre used in the baffles should be a semi-rigid or rigid product that ranges in density from 24
to 112 kg per cubic metre (1.5 to 7 lb. per cubic foot). The more economical baffles are typically in
the 24 to 48 kg per cubic metre (1.5 to 3.0 lb. per cubic foot) density range. The cost of the baffles
will also depend on the quality of the covering selected. Thicker baffles (75 mm or 100 mm thick)
would provide better low frequency absorption and would be recommended.
Hanging the baffles vertically perpendicular to each other in a crossed pattern is also slightly more
acoustically effective than in-line, parallel to each other as sound reflections from the ceiling are
interrupted in two directions rather than just one, and horizontal or angled baffles are slightly more
acoustically effective at reducing initial sound reflections from the ceiling than vertical baffles as
more of the reflective ceiling surface is obscured from below. All of the baffles can be hung at the
same elevation or at different elevations depending on the desired visual effect. When hung
horizontally they should be suspended at least 500 mm below the underside of the ceiling in order
to allow sound to get up between the ceiling and the baffles and be absorbed by both sides of the
baffles.
Typical baffle layouts are on the order of one (1) 1200 mm x 600 mm x 50 mm vertical fibreglass
baffle per 3 - 6 sq. m of floor area. Different sizes of baffles could be used provided they are the
same thickness, provide the equivalent total baffle surface area of 1200 mm x 600 mm baffles, and
are evenly spaced. Additional calculation may be required to determine the number of baffles
required to provide reverberation times comparable to those provided in tables 1 and 2.
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Acoustical Wall Panels
So long as it is properly constructed, the effectiveness of installing acoustic treatment at reducing
reverberation is determined by the total amount installed and how evenly distributed it is. Wall
mounted acoustic panels can be very efficient at absorbing sound.
For our calculations we have 50 mm thick fabric wrapped fibreglass panels with a Noise Reduction
Coefficient (NRC) of 0.95 mounted directly to the gypsum board wall or bulkhead. As is mentioned
above, mounting the panels with a 50 to 100mm airspace behind the panels can improve the low
frequency performance of the panel.
Wall panels can be installed in horizontal or vertical bands on the walls but are more effective
when spread out evenly across the walls, such as in a checkerboard pattern. This is due to the
increased absorption resultant from the additional exposed panel edges. Panels mounted on
opposing parallel walls are most effective at reducing flutter echoes between the walls if they are
staggered across from each other (i.e. so that the areas of untreated wall surfaces directly across
from each other are minimized). Ideally there should be no large flat acoustically reflective parallel
wall surfaces left untreated directly across from each other between approximately 900 mm AFF
and 2400 mm AFF (i.e. where people are located and can create and hear flutter echoes). In
practice concerns about impact damage or interference with furniture will limit the treatment areas
to the upper walls.
Acoustic Panel Fibrous Core
The fibrous backing or core for the wall and ceiling panels should be a semi-rigid or rigid product
with a density of at least 48 to 112 kg per cubic metre (3 to 7 lb. per cubic foot). Higher densities
(in the 96 to 112 kg per cubic metre, 6 to 7 lb. per cubic foot range) provide slightly higher
absorption and better impact resistance. Mineral fibre or fibreglass insulation would be acceptable
acoustically.
Acoustic Treatment Coverings
It must be ensured that the covering on any wall or ceiling-mounted panels or baffles is sufficiently
acoustically transparent or the effectiveness of the treatment will be significantly reduced. Fabrics
that are selected for acoustical applications typically are loosely-woven panel goods that allow the
free passage of air through the fabric. An easy test of acoustical performance is to attempt to inhale
or to blow through a fabric sample. The easier the air moves through the fabric, the better suited it
will be for acoustical uses. Fabrics that have been treated with anything heavier than an
18.6 gram per square metre (0.5 once per square yard) acrylic or latex backing will generally be
unsuitable acoustically.
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Current technology allows for the printing of large scale photographs or murals on acoustically
transparent coverings for wall panels. This allows for wall panels that improve the acoustics of a
room while providing striking visual enhancement and a medium for art display or signage.
Alternatively, the panels and cloth covering can be varied in shape and color and size to allow the
treatment to be shaped into an artistic scene or fit with an architectural theme.
Acoustic wall panels with alternative treatment coverings besides fabric are also available. The
options are numerous but generally fall into one of the following types: perforated wood, slatted
wood, perforated metal and perforated gypsum board. For these types of panel coverings the open
area of the perforations or slits must be sufficient to allow the sound to reach the fibrous backing.
We generally recommend that any facing on an acoustic panel have an open area of at least 30%
to allow the sound to pass through to the acoustically absorptive medium behind the covering.
A sample of the acoustic panel and any facings or coverings should be provided by the supplier in
order to ensure that the panel is durable enough, that the facing or covering is sufficiently
acoustically transparent, and that its appearance is suitable.
The panels and baffles must be constructed from materials that meet appropriate flame spread and
smoke developed requirements as indicated in the British Columbia Building and Fire Codes.
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Summary
Reverberation time measurements were conducted in the Elkford Community Centre Community
Hall and Play School. These spaces were then acoustically modelled using ODEON room
acoustics software with various acoustical treatments added to the spaces. Based on the
calculations and our experience on similar projects, our comments and recommendations can be
summarized as follows:
•
We recommend that approximately 456 m2 of 50 mm thick fibreglass acoustic panels be
installed on the ceiling of the Community Hall (Option B). If possible it would be
beneficial to divide this amount of treatment between the underside of the ceiling and the
upper gypsum board walls or bulkheads.
•
We recommend that approximately 108 m2 of 50 mm thick fibreglass acoustic panels be
installed on the ceiling and 43 m2 of 50 mm thick fibreglass acoustic panels be installed on
the upper gypsum board walls (Option F) in the Play School.
•
Alternative acoustic treatments may be substituted for the 50 mm thick fibreglass acoustic
panels as long as NRC rating and octave band acoustical absorption coefficients are
comparable to the treatments used in the calculations.
•
All acoustical treatments must be constructed from materials that meet appropriate flame
spread and smoke developed requirements as indicated in the British Columbia Building
and Fire Codes. The placement of acoustic treatments must not interfere with the coverage
pattern of the sprinklers and meet all NFPA fire code requirements
We trust this provides you with the information you require. Once you have reviewed this
information, we would be happy to discuss our findings further. If you have any questions
concerning the above please contact me.
Sincerely,
FFA Consultants in Acoustics and Noise Control Ltd.
Matthew Faszer, EIT
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