This subject (engine sounds) is certainly material for a doctoral thesis - just my way of saying that the "sound quality" of an engine IS affected by a great many many factors which cannot be adequately explained by just a short post. What is fundamentally underlying the original posters note here is that ALL of the engines noted at the stated RPM's DO have the same firing frequency (# of explosions per second for a 4 cycle engine {two cyles are another matter} which is determined by dividing rotational speed by 60 and multiplying that value by the # of cylinders divided by two).The engines sure sound differently,however. As an example of firing frequency, the one cylinder engine would be 8000/60x1/2 = 66 2/3 HZ (or cycles/seconds); the 5 cyl firing is 1600/60 x 5/2 = 66 2/3; the 8 cylinder firing frequency is also 66 2/3 HZ (1000/60 x 8/4 = 66 2/3). What IS different is the rotational frequency - even that (which we would call 1 st order speed) has a great influence on sound quality. There is also a great difference in the sound quality between engines with the same firing frequency but different bank angles (e.g. a 60 degree vs a 90 degree V-6) as the spacing between firing pulses is NOT uniform on a 90 degree V-6 like the "balanced" firing configuration on the 60 deg V-6. Other factors also such as primary and secondary forces & moments (couples) are involved here also. I would add a clarification to Bob M's statement in that the tone of an engine (it's fundamental firing frequency) WOULD be somewhat the same for ALL of these noted engines running at the RPM's stated. You can, however, have a very different sound quality - see my comments above for a 60 vs 90 degree V-6. Sound quality will be significantly different when comparing a flat opposed 4 cylinder engine verses an in-line one - they can have the same firing frequency at the same RPM but the in-line 4 may have a two plane crank or crank pin offset which significantly affect sound quality. Another example would be to compare the Harley V-twin verses a twin cylinider opposed BMW - same firing frequency but markedly different sound quality; one is even firing and the other NOT. Ever hear an International Titan and compare that to a two cylinder John Deere - both are two cylinder configurations with the same fundamental firing frequency but that's about it. There's NO mistaking one for the other.
Nuff said. Just be happy when you can guess the # of cylinders correctly when you listen to the sound of an engine and appreciate/marvel at them ALL, two or four cycle, gas or diesel, etc.
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