As MerlinPete says it is the unique and distinctive sound that the Merlin and Griffon makes that we are discussing. I think we would all agree that many factors such as exhaust systems and overlap etc will change the overall sound but that distinctive characteristic underlying sound is still always there making the engine clearly identifiable.

Merlinpete From what I can see on the Shackleton manifold each bank combine into a single pipe. Is that correct? Would you say that the “pulses” coming from these pipes would still be basically the same as stubs added together such that Beermats theory in #45 could still work.?

all arm-waving stuff,

Me too. Agree doppler doesn’t come into it now I have refreshed my 45 year old memory. Thinking what is likely to make so much noise with so much energy? Surely if it was mechanical that wouldn’t be good. Whilst not pretending to understand Spartabus’s posts I think he has a point and it is likely to be exhaust related which presumably is also related to cam timing and firing order which is what Creakingdoor said back at #7.

My sample was the Grace Spit. Have expanded it up similar to yours and I think it looks smoother, so un-surprisingly not all Merlins are the same. I took my sample from when I judged the plane was going past the recorder rather than coming towards or going away, good luck with that! However, isn’t the thing that the engines sound different basically at all times so there must be a fundamental difference which should be identifiable and then related to an or several event frequency/ies in the engines.

I am certainly no sound expert but to go from a pure sinusoidal wave form sound to a square one like a buzzer do you not add in more what I am calling hairlines until what was a sin wave becomes more square. Can we not see from the wave forms that the Merlin is much closer to a sin wave than the Griffon.
Sure you are all heading in the right direction just need an engine guy to relate the frequencies off the graph with what’s going on in the engines.

Are we not looking at stereo. ie left and right channels, I do not understand why they would be significantly different.
Beermat could you do one for the merlin like your first post.
Is it not the hairiness of the basic waveform that produces the gruffness? I suspect this will not be so much on the Merlin.

I wonder if looking at the wave form of the sound of these two engines would show what was producing the noise. Presumably would have to be careful regards number of blades and superchargers. If a basic frequency could be pulled out then it may be relatable to a frequency of recurring events within the engine.
This site has recordings of both the Merlin and Griffon

http://www.freesound.org/people/J%C3%BCrg%20L%C3%A4chler/downloaded_sounds/

Nice to be able to compare them whilst this interesting discussion develops.

And, of course, at Farnborough 1956 a Lincoln carried out an impressive display with all four Merlins feathered!
Jim

Does a Tyne come into this somewhere?