Reverberation Control

Acoustics
Reverberation Control

A major cause of discomfort in buildings is excessive reverberant noise caused by hard reflective surfaces such as painted plasterboard, concrete, ceramic, wood flooring, plastics and glass.

Excessive reverberation raises back ground noise levels and affects speech intelligibility, privacy, the speech development of children and second language speakers, the old and those with hearing difficulties.

Without adequate absorption sound will reflect from surfaces causing long reverberation times (RT 1.0 to 4.0 seconds + ) and because reflected noise travels a longer pathway compared to direct sound it has a time delay and overlaps and masks direct sound creating a confusion for the listener. To compensate people often raise their voices to be heard which rapidly increases the back ground noise levels.

This effect is particularly noticeable in rooms > 300 m³ or with hard ceilings, wall and floor finishes. For good communication the signal to noise ratio must be at least 6 dB over back ground noise levels. Reverberation is easily controlled by use of good quality sound absorbing finishes. Absorbers are classified according to ISO 116 54 and fall into 5 class groups Rated A to E. Class A absorbers are highest and provide more absorption per sq.m than other finishes which often means less is required. Most of the Asona composite soft fibre panels are Class A. Similar to ASTM C423 NRC 0.85 to 1.00 range.

Reverberation is easily controlled by use of good quality sound absorbing finishes. Absorbers are classified according to ISO 116 54 and fall into 5 class groups Rated A to E.

Class A absorbers are highest and provide more absorption per sq.m than other finishes which often means less is required. Most of the Asona composite soft fibre panels are Class A. Similar to ASTM C423 NRC 0.85 to 1.00 range

Care should be taken in selection and placement of acoustical treatment to achieve the desired performance objectives taking note of absorption from 125 Hz to 4000 Hz. Also many budget acoustical products lack the performance to effectively reduce reverberation and it is a mistake to rely on carpet or soft furnishings to try and compensate for poor acoustical performance of walls/ceilings.
New Zealand building designers are encouraged to refer to NZS2107 standard recommendations for reverberation and back ground noise levels in their documentation and employ the services of an acoustical consultant and quality acoustical ceiling and wall finishes to manage the interior acoustic environment.   

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