Page 52 - Special Issue

Acoustic Comfort in Restaurants
Figure 1. Examples of various rooms and a typical average coefficient (ᾱ) associated with each of them.
speech is what is important in determining both speech intel- ligibility and speech privacy, both of which will be important in restaurant acoustic comfort. Each surface in the room is either acoustically reflective or absorptive. Every material absorbs or reflects sounds to some extent across the frequency range in which people can hear.
Equation 1 is used to calculate the total sound absorption in the room. This is done by summing the surface areas of the various materials in the room multiplied by their respective absorption coefficients. The total sound absorption in the room is then divided by the total surface area in the room using Equation 2 to get the average absorption coefficient (ᾱ) for that room.
The ᾱ for the room is
The total sound absorption in a room is
A = S1 α1 + S2 α2 + .. + Sn αn= ∑Si αi
(1)
The ᾱ in a room is a number that falls between 0 and 1. Zero means a room that is completely sound reflective, and 1 is a room that is completely sound absorbent. Most practi- cal rooms will fall somewhere in the middle of this range, not being either too reflective or too absorptive. Figure 1 gives examples of typical rooms and their corresponding ᾱ values to show where various room types may fall within this range. For example, a concert hall (see Hochgraf, 2019 for a related article) or a music recital hall may have very little sound-absorbing material (but instead having very carefully angled reflective surfaces that direct sound to where it needs to go), therefore having an ᾱ of 0.10 or there- abouts. Whereas a hotel conference room or ballroom, with carpeted flooring, acoustic ceiling tile, and acoustic wall panels, may have an ᾱ of 0.35. And a specialty recording studio designed to be acoustically “dead,” with almost every single surface as sound absorbent as possible, may reach ᾱ values of 0.75 or so.
where A is the absorption of the room (in m2 sabins), Sn is the area of the actual surface (in m2), and αn is the absorption coef- ficient of the actual surface.
252 | Acoustics Today | Suprminmge2r0201,9Special Issue Reprinted from volume 15, issue 2
ᾱ = A/S (2)