Thanks, nice work, just one point, your drawing has damping on both sides of the internal section but not on the first drawing, only one side. Wouldn't this effect the sound, what would you advise.
Does the driver entry location line up with (eliminate) the 3•Fb notch or is it aimed a little higher up strategically ?
Thanks to Dave for the new drawing and Scott for the design.
I only posted about the drawing because when you (I) build things your mind's eye expects the cut pieces to look like the drawing. When they do not look like the drawing doubt arises and you work through the process of did I mess up first, then to other possibilities. A few times this has stopped me until I could work out why what I had made deviated from the drawing. Trying to avoid that spiral of doubt.
I only posted about the drawing because when you (I) build things your mind's eye expects the cut pieces to look like the drawing. When they do not look like the drawing doubt arises and you work through the process of did I mess up first, then to other possibilities. A few times this has stopped me until I could work out why what I had made deviated from the drawing. Trying to avoid that spiral of doubt.
Good Q; 'kinda sorta' wish the axial length of folded designs is always shown (at least on PPV/'bespoke' designs) based on Brian's/this (71.4 cm):
Some of these ideas seem like akward ’guesses’ based on ‘flow’ as a distance changer instead of a sinewave shape defining high or low concentrations of vibrating air particles Stuck in a pipe and it’s exit relationship to the last P/v node
This ’stuffing’, or lining, assumed to be the fix all to whatever is ‘off’ as a bandaid to the impossible ‘guesses’ we are stuck with maybe?
Yes, being parabolic (in this case) and folded, there is no harmonic pipe 'flow', but an awkward expansion rate of multiple, variable, duct harmonics, so we really should be using heat/AC duct design theory in lieu of HR's, et al, round pipes for accurate simming.
Absolutely; this is why I model the individual sections of a pipe (including bends etc.) as far as possible rather than taking it as a single element. Never 'perfect', but usually good enough for these purposes. TBH, except in extremes, for straightforward pipe designs I've found a lumped model tends to be fairly representative for Fb and the lower harmonics, with variations being on the detail level rather than anything more profound (by which point relatively minor differences in the line damping or driver production tolerance tend to have as much impact). I still try to do a more detailed assessment of the geometry when possible though, for the reasons you mention -as changes to expansion, aspect ratio etc. become progressively more dramatic, so the deviations from 'basic' conditions (ha! the underlying maths still makes my mathematically-challenged head ache 😉 ) become more obvious, especially as frequency rises.