ORIGINAL: Silent-AV8R
ORIGINAL: abel_pranger
I presume Scale Aerobatics is flown at the IAC, and the rules for that event allow 107 dBA @ 9 ft. I don't even want to know what sound levels are allowed for Pylon racers.
That is incorrect. The Scale Aerobatics rules define the limits as 96 dBA over soft surface and 98dBA over hard surfaces measured at 25 feet. There is no measurement at 9 feet and no limits set. That is what you calculated it wold be at 9 feet. But since that is not how the measurement is defined it really is not correct to say that is the limit for Scale Aerobatics.
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It is not incorrect unless my calculation is wrong. Possible, but this is Physics 101 stuff, and projections from measurements at one point to expected levels at another distance by the spherical spreading model are routinely used in the industry. You can't reasonably measure everywhere, so you interpolate/extrapolate as necessary to fill in the blanks. As I mentioned in an earlier post, it's a good idea to confirm such extrapolations on occasion to validate them. This has been done countless times, more than sufficient to validate that the mathematical model used to represent the physical process is reliable.
Abel