not a large error -- a HUGE error
we did in air sound tests -looking for sound which were irritating and sounds which were of the type which were simply "background noise".
some frequences or undulating sounds were horrible -attention getters
an undulating siren -as bad as it gets ( the German ambulance sound)
it is difficult to pick n choose which sounds will offend-hence the worthless sound tests presently used .
My 160 on huge cans and a 30x14 prop - really easy to tolerate - a wretched, in cowl small glow engine diving and revving upwards of 20000rpm - intolerable - to me .
Personally -I would look at 100 ft as a minimum test distance and also record frequencies .