And I have a ferrite 400 on a Mirage 2000 that turns a 5.25X4 prop almost as loud as some 049 glow engines. And the plane is faster than some low wing 40 powered sport planes.

Bruell and Kjerr have an interesting booklet on sound measurements and the effects of frequency and pitch on sound perception. Problem is, it comes with a multi-thousand dollar labratory sound level meter.

The "Irritation Factor" is definitely non-linear. A higher frequency sound lower than the ambient level can be more maddening than a lower frequency sound significantly above ambient.