BTW, after some quick sums, I reckon that the Oulton Park drive by sensors are approx 2m from the track; inverse square law says that power drops in proportion to the square of the increase in distance - so going from 0.5 to 2m is 4x the distance, so power level will be 1/16th. 1/16th is almost exactly -12dB:
1/16 = 0.0625
10 log10(0.0625) = -12.04 ... let's call it -12.
So if the static test is 104dBA at 0.5m then -12dB gives you 92dBA at 2m.
Of course actually the meter could be nearer or further away but then the result adjusted by subtracting or adding some dB offset to compensate - physics is physics after all
And that is what I think Donnie are doing - I think their 98dBA limit is meant to be equivalent to a 98dBA static test - i.e. it's the equivalent of 98dBA at 0.5m. The actual mic distance from the track will be more than 0.5m, but they'll just add back the right number of dB to compensate for that (and maybe they use multiple mics in each location to account for the car taking different lines and different exhaust positioning).
The problem with working out whether or not you'll pass it is that it's very hard to measure with the engine under load (without a rolling road). If you had a friend with a sound meter you could attempt a full throttle fly by on a quiet road and try to line it up so you're near full RPM as you pass them (might take a few calibration runs to get your eye in
). The meter would need to be on fast averaging and probably have some peak hold mode to capture the loudest point. Then if you position yourself 2m from the line that the exhaust will take and then make sure your peak is less than 98-12 = 86dBA. Make sure the sound meter is on dBA (A is normalised to account for human perception of noise; without an A weighting you'll over read).
Of course no need for the complex experiment if you fail the static 98dBA test
sorry that’s flippant, you are knowledgable & articulate as always.
