Originally Posted by Shawk
If the fluidic resonance theory has much basis in reality, the likely noise is somewhere between 16Hz and 32Hz. This sound frequency range has a very good chance of escaping an airframe and be audible on the ground.
To whom?
It's fairly common knowledge that GOOD human hearing is in the range 50 Hz to 20,000 the upper frequency decreasing rapidly with age (and usually lower for the male gender)..
It rolls off rapidly below 50Hz to prevent damage from the energy content in low frequency sound.
Bottom string (E) on a bass guitar is around 42 Hz, and it's 2nd harmonic (84Hz) is usually
more understood by the ear than the fundamental, which itself is
more felt rather than heard.
32 Hz or less? Something by-standers commented upon, amongst the melee of other sounds from an aircraft so unusally close - nope, don't think so.
Neither do I find it credible that cavitation noise within a pump within an engine nacelle would be heard, or commented upon, whatever its frequency... over the mass of aerodynamic and other turbomachinery noise - IMHO of course!