Here is an actual transcript from Supreme Court in which a consultant testifies that he does not use - in fact has never used - decibel subtraction, which is the industry-recognized way to account for background noise in any kind of sound measurement.
We can, as he suggests, turn the equipment under test on and off during our measurements, but we can't "turn off" the traffic or the myriad other sources of noise, especially in a city like New York. We don't need to merely "identify" "problematic" noise sources, we need to measure them accurately and compare their sound levels with the limits of the Noise and Building codes. Decibel subtraction - far from being "contrived" - is the standard method to determine the "source only" level we need to make that comparison.
This consultant relies on "computer modeling" but does not find any use for the standard method to measure a sound in the presence of ambient noise.
[opposing consultant] — by Defendant — Direct/J. Mallin
QAnd what else did you find per your --
AIn this chart, the ambient was 50 dB and the max was
55.5 dB.
Q Now, when Mr. Fierstein was testifying earlier at this
hearing, he made reference to ambient subtraction or decibel
subtraction —- excuse me.
AYes.
QAre you familiar with that concept?
AIt’s a mathematical concept of logarithmic addition or
subtraction, so, yes, I am.
QDo you have an opinion as to the propriety of utilizing
that in situations like this to negate ambient?
AI've seen consultants use it. It's not cited in the
New York City Noise Code. I often feel it‘s personally a little
contrived. In this case, I kept the testing simple. The
mechanicals were either on or off, the door open, because that's
a real—world condition, that's what we have to achieve. So, in
this case, I don't think it was really assisting what we were
doing. Turning the units on or off, you can identify which ones
could be problematic.
QAnd have you used —— have you ever used it yourself?
ANo.
QIn any of the 150 projects —— 130 projects that you've
worked on?
AI don't use decibel subtraction for mechanical noise
identification.
QNow, based upon your retention in June of 2012, going
through August of 2013, have you reached any opinions with a
reasonable degree of professional certainty as it relates to the
efforts to abate noise in apartment 2D?
AYes. We've put —— we have done a lot. And sound
isolation always requires some finessing. You know, when it
first opens you need to do baseline testing in an apartment to
insure that it's meeting your modeling criteria. We model every
acoustic boundary, because we need some baseline to insure that
the construction is met to protect the client from GC error and
omission.
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