Posted: Fri Nov 19, 2010 5:37 am
For the port ratios on sirens, simply listen to the audio to discern the 2 tones separately, then find their values in Hz. Multiply the tone by 60 to get pulses per minute, then divide by motor RPM, usually 3450 or 3600 for synchronous motors. T-Bolts are a bit different. I can always tell the 5 port choppers by listening to the dominant tone, and the harmonics of the rotor vibration. I also listen to F1 a lot, and they used to run V10 engines to around 19000 rpm, which sounds quite a bit like a thunderbolt rotor turning 9K.