Emulating Low Gears

ok, i think i get this.... or what your trying at. variable intake length/volume.

i read it, thinking...no, wait...its LENGTH LENGTH LENGTH! but.....

when designing a speaker box, you cant care less at the actual individual dimensions, as long as you end up with the desired VOLUME....... but im still doubtful wether this works when dealing with induction pulses in a pipe in an engine... but still, it is sort of like a bass reflex system...sooooo. im not going to stop you, it might just work... and hey, its great when that happens!

if i was you, id be scouring scrapyards and pawnshops for.... A TRUMPET! three airtight valves, three different lengths of pipe already attached...

or look up how the valves work... theyre not thaaaat hard to make...
 
HeadSmess said:
when designing a speaker box, you cant care less at the actual individual dimensions, as long as you end up with the desired VOLUME....... but im still doubtful wether this works when dealing with induction pulses in a pipe in an engine... but still, it is sort of like a bass reflex system...sooooo. im not going to stop you, it might just work...
Actually, while the volume of the speaker box is critical, the individual dimensions are also quite important.

Each dimension of an enclosure has a specific frequency associated with it. This is the frequency whose wavelength is the same as the dimension. And, you can get standing waves at that frequency, and at every multiple of it. This makes the sound at the standing wave frequency (and multiples) somewhat louder than at other frequencies. (Resonant peaks) If your enclosure has two sides the same length, the sound spikes will be worse, and it will be worse yet if the box is in the shape of a cube, because the standing wave will triple amplified. Ideally, the three sides of an enclosure should be approximately .621.62 ratio. This will reduce the resonant peaks due to standing waves to a minimum. This ratio is also known as the 'golden ratio.'

In the case of exhaust tubing for tuned pipes, both the pipe diameter and the pipe length come in to play, and they interact with each other. The smaller the pipe diameter, the slower the pressure pulse propagation through it. So, the length increase would need to be greater than you would otherwise expect if you just calculated a length based on a constant volume.) Also, as I recall, the velocity change due to tube diameter change is not linear...

The same effect (slowing due to tube diameter reduction) on a much larger scale is what causes tsunamis to build height near the shore. As the water gets shallower, the leading edge of the tsunami slows down, (it's 'tube' has gotten narrower) and the later stages of the pressure wave push into it. Since the water is incompressible (relative to air) the increased water volume in the same square footage (as seen from above) forces the level of the water up...
 
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Actually, while the volume of the speaker box is critical, the individual dimensions are also quite important.

Each dimension of an enclosure has a specific frequency associated with it. This is the frequency whose wavelength is the same as the dimension. And, you can get standing waves at that frequency, and at every multiple of it. This makes the sound at the standing wave frequency (and multiples) somewhat louder than at other frequencies. (Resonant peaks) If your enclosure has two sides the same length, the sound spikes will be worse, and it will be worse yet if the box is in the shape of a cube, because the standing wave will triple amplified. Ideally, the three sides of an enclosure should be at a .621.62 ratio. This will reduce the resonant peaks due to standing waves to a minimum.

Are you an old school car stereo guy?
 
More for home stereo - wrote a Thiele-small program for loudspeaker design in the early eighties. On a mini-computer, the size of a washing machine, no less!
 
Here's an idea: Think trombone, rather than trumpet...

Change the length of the tuned pipe, by using a U-Shaped sliding portion of the tube. Move the U away from the engine and the pipe gets longer (and is more effective at lower RPM.) Slide the U-tube towards the motor, and the RPM tuning goes up.

Ref the sketch, below. I assumed stainless bellows to seal the U-Tube, but, you could use something similar to piston rings to seal it, I suppose...

If you were REALLY good, you could come up with a centrifugal 'clutch' sort of arrangement to automatically tune the pipe to the engine RPM!
 

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Here's an idea: Think trombone, rather than trumpet...

Change the length of the tuned pipe, by using a U-Shaped sliding portion of the tube. Move the U away from the engine and the pipe gets longer (and is more effective at lower RPM.) Slide the U-tube towards the motor, and the RPM tuning goes up.

Ref the sketch, below. I assumed stainless bellows to seal the U-Tube, but, you could use something similar to piston rings to seal it, I suppose...

If you were REALLY good, you could come up with a centrifugal 'clutch' sort of arrangement to automatically tune the pipe to the engine RPM!

Nice! This is much better than the on off valve concept - immediate on the fly length adjustment! I'm going to have to go back to the drawing board. The only thing about that is it's a very long length at it's shortest length, and only gets longer...
 
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