sound meter

[Ron Van Putte]

On Apr 26, 2004, at 12:07 PM, Earl Haury wrote:

> Generally even the sound meter calibrators are +- 0.5 dB. Makes the 
> flight zero for >94 (F3A) really a tough rule (even flying behind the 
> flight line only zero's the maneuver)! Albeit, a fail isn't official 
> until verified by a second meter - but generally both are calibrated 
> with the same device, so the calibrator offset will be present at both 
> meters. Calibrator equipment itself should be re-certified pretty 
> often (yearly), want to bet when the Nats equipment was last 
> certified?

Not me.  Want to bet when the AMA scales were last calibrated?  I bring 
my calibration weights to the Nats and subtract the offset when 
weighing (the AMA scales usually weigh 30-40 grams heavy).

> The only way to be sure is to use known accuracy equipment and target 
> a number that allows for equipment variance. The air density at the 
> time you make measurements will vary the results also, both from an 
> engine output (more/less rpm) and a sound transmission standpoint. 
> This can amount to a couple of dB, and the Muncie site is usually 
> better air density than soggy Houston - so the noise measured is 
> higher in Muncie. Again, allow for this in your noise plan.

Wind dramatically influences weight measurements (not surprising, since 
airplanes are supposed to develop lift), so we measure airplane weights 
in an enclosed area.

Ron Van Putte
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