5.3 Estimating Levels of Room Acoustic Treatments

The key to understanding the required level of room acoustic treatments is to study the relevant equation in section 5.1. To implement this equation, MACH Acoustics provide an excel spreadsheet 1 which can be acquired by email from ze@machacoustics.com. This spreadsheet can be used to find the exact required levels of room acoustic treatments. Estimating levels of room acoustics treatments such to approximate the required level of soft treatment, four factors need to be considered:

1 Required reverberation time
2 The average ceiling height
3 The floor finish
4 Added acoustic treatment (acoustic ceiling tiles, acoustic ceiling panels, acoustic wall panels...)

The tables below 3 to 5 present the amount of total absorption required, as a percentage of the floor area, to control the reverberation time based on the four factors above. The three different tables are provided for hard floor finishes, industrial carpet and an industrial carpet placed on an industrial underlay.

Example 1 - Carpeted Office, Ceiling Height of 2.8m and Required RT of 1 Second
From 4 the required levels of surface treatment are found by multiplying the floor area with the required percentage, for example

         28% * 60m2 = 0.28 * 60 = 16.8m
         16.8m2 of 100% acoustic absorption is therefore required within this 60m2 space.

Correction for Material Selection
The acoustic absorption of finishes is between 0 and 100% absorption, therefore a scaling factor is also needed for a given finish. As noted, materials are often rated between A and E, the scaled factors for these materials is therefore given below.

A = 1.25 * surface area of finish - see section 5.4
B = 1.42 * surface area of finish - see section 5.5
C = 2.00 * surface area of finish - see section 5.6

Example 1 - Continued
Perforated plasterboard with a Class C rating is proposed for the soffit finish. As such 33.6m2 of perforated plasterboard is required to achieve a reverberation time of 1 second.

More than One Finish
If more than one finish type is being proposed please see BB93, example Option C.

Example 2 BB93 Primary School Classroom
60m2 Classroom with a fl oor to ceiling height of 3.2m.

BB93’s reverberation time target is 0.6s

The floor is carpeted; hence 69% of the floor area is required to be treated.

        0.69 * 60 = 41.4m of Treatment is required

Option A - Class A ceiling tiles are proposed to be used, therefore 51.75m2 of treatment is needed. This figure is less that the floor area; hence a plasterboard border could be used.

Option B - Class B suspended rafts are proposed, the required area of the rafts is therefore 58.8m2.

Option C - Class B suspend rafts, in combination with 10m2 of Class A wall panels (10/1.25=8, 41.4-8=33, 33*1.42=46.9), therefore 46.9 m2 of suspend rafts are required.

Option D – The classroom ceiling height is dropped to 2.4m, Class B suspended rafts are proposed, the required area of the rafts is therefore 40m2.