AVS Club Gold
Join Date: Jul 1999
Location: Near an airport
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There are multiple approaches to "how much is enough". One published "Best Practices" metric is you don't want to raise the ambient noise floor in an adjacent occupied room by more than 3dB (using an NR, NC, NCB curve). That, of course, doesn't account for preference or a specific need. In general playback spaces, you'd generate full bandwidth pink noise at -20dBFS in the playback space and then measure the noise floor in adjacent spaces comparing that to your previous ambient measurement. Achieving NR20 within your playback space is not easy; but, achieving that suggested level of isolation from adjacent spaces in the structure is considerably more difficult. For in room audio quality, you do want to get to NR20 inside the room. The level of noise attenuation outside the room gets very much into what you want to achieve, what your budget will tolerate, and, in many respects, your perception of the result.
There are no "certified" construction methods. There are however lab tested construction methods and materials which can provide guidance with respect to methods and materials. Note, however, that controlled NVLAP lab test conditions are entirely different than what is achieved under field conditions. When reviewing materials/construction methods, ignore STC ratings. Search out the original lab test results showing the TL (Transmission Loss) values by frequency band. Also, do not be tempted to mix, match and add the values together between two different materials or constructs. It doesn't work that way...the properties of a given barrier are very unique to that specific barrier (construction and materials).
There is certainly a "diminishing" returns component ... the last 10% of improvement can easily be 70% to 80% of the cost.