Greg, would you however consider this wild guess of mine?
The ongoing discussion re wooden ends vs. metal ends might have the wrong reference point. Metal fretwork is usually thinner, so the difference could just lie in the flatter angles in which the sound is escaping metal ends.
Might that not at least contribute to the overall effect?
Best wishes - Wolf
No acoustic engineer here. I do not have any theories about the possible effect of shape and thickness of the fret work edges.
One huge revelation came when I was lucky enough to have two very similar ebonized Wheatstone T/T Aeolas in the same place at the same time and only separated by several hundred serial #s. One was obviously louder and more aggressive in sound. The other more measured and muted. I was ready to assume the louder, brighter sounding one had "better" reeds.
I was able to switch ends (action boxes) which seemed similar in materials and construction. Suddenly the timid one took on much of the characteristics of the aggressive one. And the louder one now adopted a more tame sound with the other instrument's action box and fret work.
This dramatic change prompted me to look at the fret work of the instruments. The louder, more lively Aeola had fretwork extending to within a half inch of the edges. The more "timid" instrument had noticeably less extensive fret work leaving perhaps an inch of solid wood toward the edges. My best guess was the less extensive fret work was muting some of the sound of the quiet instrument either not letting it "escape" or perhaps absorbing some of the volume and overtones. (Perhaps a very dramatic example of the influence of fret work on sound are the "dot and comma" Aeolas. I'm lucky enough to have one at present and the sound of the closed fret work instrument is quite different.)
Dramatic but very unscientific conclusions. Nonetheless very consistent with years of observations watching and helping Wally Carroll build instruments. Wally and I had many discussions as to why concertinas sound the way they do and why, although Wally strove for and reached an amazing consistency in construction of his instruments, that there were slight variations in the overall sound of individual concertinas. I can't speak directly for Wally but I believe our conclusion was something like "the response, volume and harmonics are in the reeds and the tone color and some of the volume is due to surrounding materials."
Again, these are anecdotal observations. There is a lot going on in a concertina that produces its final sound. How snug a reed fits in its slot may be as important as what material a reed pan is made of. So many variables.
Edited by Greg Jowaisas, 22 November 2017 - 11:21 AM.