NEW ACOUSTIC STANDARD AS/NZS 2107 PROMPTS OTHER CHANGES
December 1 2016
The new Standard AS/NZS 2107: 2016, Acoustics - Recommended Design Sound Levels and Reverberation Times for Building Interiors, replaces the old version AS/NZS 2107: 2000 of the same name.
As well as a bit of a technical update, the new Standard provides a more extensive range of reverberation time recommendations for a more modern list of building spaces and uses.
The issue with the new AS/NZS 2107 is that it now uses Reverberation Time (R) (also can be RT or T60) to measure the reverberation performance of a space, which is an accurate measure for those working with calculations. However this may be confusing for those of us who are not used to acoustic calculations. Most will be familiar with Noise Reduction Coefficient (NRC) which has been the traditional simple measure of reverberation performance of a space.
NRC targets, along with manufacturer's NRC product performance, give non-specialist designers an easy, if not completely accurate, solution to reverberation control for non-critical spaces (eg. not a concert hall etc). However internationally NRC is going out of favour due to lack of precision. We are yet to see which of the many contenders (European or American) will be successful in eventually replacing it. As far as we can tell there is no easy direct relationship between R and NRC.
Although AS/NZS 2107 is referenced in a few Masterspec sections, the way it is referenced means there is very little amendment required. However we have taken the opportunity to update our guidance notes on NRC recommendations, in particular on schools, with the latest information from the Ministry of Educations document Design Quality Learning Spaces - Acoustics (v2.0, Sept 2016). A word of warning about the Ministries document - in some instances it refers to Reverberation Time (RT) and in others it refers to NRC, so we recommend you study the document closely.
Reverberation control can be a tricky and complex subject, if in doubt think about consulting an expert and certainly with complex critical spaces, like auditoriums and performance spaces, expert design is usually essential.
NRC - noise reduction coefficient
- NRC measures average absorption of sound for a material or surface, range is between 0 and 1.0, 1.0 being the theoretical most absorbent (can go slightly higher under some conditions), useful for simple reverberation control.
- NRC is an old American measure but is close to the newer European measure Practical Sound Absorption Coefficient (αp) which also uses 0 to 1
R - Reverberation Time (also can be RT or T60)
- Reverberation time of an enclosure, for a sound of given frequency, from the time sound stops to the reverberation decay of the sound energy level by one millionth (equivalent to 60 decibels). Useful for more accurate and complex reverberation control.
MoE - Design Quality Learning Spaces - Acoustics (v2.0 Sept 2016)
Theatre Design - Acoustic Tips and Considerations