| LABS
Impressive Glenn, although I would rather see the vertical axis run from 0 -3. The non linearities :-) are exaggerated by that scale.
There has been some to-ing and fro-ing about LABS etc. It probably appears confusing and contradictory at this point.
So IMHO
That LAB you use is clearly confident down to the 63Hz band. It is probably very large and certifed. Not many are certified down to this frequency band. Historically, Building Acoustics tests were to 125Hz only. Lately they are being extended downwards, to include even 31Hz in one extreme case (HVAC Noise) Older and smaller LABS, go to 125 only and are therefore not at all suitable for our purposes.
When performing tests in these LABS, RT is measured over a time and spatial average.
i.e. a number of sweeps with the microphone, or multiple microphones, at different locations. The measuring mic(s) are sometimes on a rotating boom, to further randomise the spacial average. Ultimately when the average is calculated, the result will of course be very similar each time. Statistics ensure that. However any individual sweep, even with a fixed mic, seems to give a dfferent number each time. This has been observed by myself and other Slutz here, in LABS and in site test situations. It also happens when evaluating acoustics of a room for sound purposes.
Claro?
DD
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