Page 24 - Summer2019

Acoustic Comfort in Restaurants
Acoustic Metrics
Average Absorption Coefflclent
P',_::|',"T',"':|'.‘_'_" Classroom (0.25) Active soclal space (030) Hotel Ballroom
(E 5 0.10 E , (1!) 0.20-0.25 (3) 03043-35 (ll) 0.35-0.45
. . . , 9 , . ‘ _ —. . . - 7
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. __ ..v' 1 ‘ 1 _"~— ““:""' ,_ —.~
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= . . . . .
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15 =1 (a) 0.50-0.75 (a) 0.75-1.00
TaloNIdeo conlmnclng Room (0.50) “Do-Id" Rocordlns Sfudlo (0-75)
Figure 1. Examples ufvmious mums and a typical average caefitcient (a) associated with each ufthem.
speech is what is important in detennining both speech intel- The £1 for the room is
ligibility and speech privacy, both of whichwillbe important in
restaurant acoustic comfort. Each surface in the room is either 1': = Al S (2)
acoustically reflective or absorptive. Every material absorbs or
reflects sounds to some extent across the frequency range in The 1'1 in a room is a number that falls between 0 and 1. Zero
which people can hear. means a room that is completely sound reflective, and 1 is
a room that is completely sound absorbent. Most practi-
Equation 1 is used to calculate the total sound absorption in cal rooms will fall somewhere in the middle of this range,
the room. This is done by summing the surface areas of the not being either too reflective or too absorptive. Figure 1
various materials in the room multiplied by their respective gives examples of typical rooms and their corresponding 1':
absorption coefficients. The total sound absorption in the values to show where various room types may fall within
room is then divided by the total surface area in the room this range. For example, a concert hall (see Hochgraf, 2019
using Equation 2 to get the average absorption coefficient ((1) for a related article) or a music recital hall may have very
for that room. little sound-absorbing material (but instead having very
carefully angled reflective surfaces that direct sound to
The total sound absorption in a room is where it needs to go), therefore having an E1 of 0. 10 or there-
abouts. Whereas a hotel conference room or ballroom, with
A = S‘ :1‘ + S2 :12 + .. + S" an= XS| a| (1) carpeted flooring, acoustic ceiling tile, and acoustic wall
panels, may have an E1 of 035. And a specialty recording
where A is the absorption of the room (in m‘ sabins), S“ is the studio designed to be acoustically “dead,” with almost every
area of the actual surface (in m‘). and an is the absorption coef- single surface as sound absorbent as possible, may reach 1':
ficient of the actual surface. values of 0.75 or so.
12 | Anal-an-1-:.:lgy| Summu 20:9