Article On Cavity Resonance Now Available

[ttonon]

Greetings,

 

The design of reed cavities in concertinas is a topic of considerable interest here, and we we visit it often on this board. An article I wrote for PICA on reed cavity design and resonance is now available for free download at: http://www.concertina.org/pica/index.htm (Vol. 2, 2005). The article discusses many aspects of this subject, both qualitatively and quantitatively, presenting sample calculations and, I think, interesting conclusions. Enjoy.

 

Best regards,

Tom

www.bluesbox.biz

[Henrik Müller]

Greetings,

 

The design of reed cavities in concertinas is a topic of considerable interest here, and we we visit it often on this board. An article I wrote for PICA on reed cavity design and resonance is now available for free download at: http://www.concertina.org/pica/index.htm (Vol. 2, 2005). The article discusses many aspects of this subject, both qualitatively and quantitatively, presenting sample calculations and, I think, interesting conclusions. Enjoy.

 

Best regards,

Tom

www.bluesbox.biz

 

Hello, Tom -

 

I've read your article - now I am digesting it... may take a little longer than reading it, but I think it is on its way to help me to understand the surprisingly bad sound from the top notes on my homemade concertina. A quick and very un-scientific check on the real-time spectrum confirms that.

 

Hasta la vista - I'll be back (with spectrums)

 

 

/Henrik

[Dana Johnson]

Henrick,

Before you reach any conclusions, you may want to check with others who have made concertinas with similar reeds and chamber sizes. From what I've seen of the Morse instruments and heard of the others out there, the upper end is usually the nicest part of the instrument. (for sound if not for ease of playability which relates to other factors.) Their cavity sizes are pretty much determined by the reed plate sizes. (depth is a variable ), so yours shouldn't be that far off. My smallest cavity (with 12mm pad hole is : 34mm long X 16mm wide X 6.5mm deep and they sound beautiful with concertina reeds. ( with accordion reeds, who knows... ) I've never noticed anyone having much success in tuning cavities. If anything, the aid of Tom's information is in detuning a cavity away from an unfortunate harmonic. The most striking tone variable I have found in concertina reeded instruments relating to chambers is the depth. The differences are apparent enough to have let me distinguish between depth differences of 1 mm. Is this due to the cavity volume change or the change in the flexibility of the chamber walls ( which can mimic a change in volume ). In violin air resonances, the height and thickness of the sides is an important factor in determining both the wood resonances and the air resonances of the body. I haven't a clue what is really happening with the change in depth, I do know what depth I like best.

Dana

[Henrik Müller]

Henrick,

Before you reach any conclusions, you may want to check with others who have made concertinas with similar reeds and chamber sizes. From what I've seen of the Morse instruments and heard of the others out there, the upper end is usually the nicest part of the instrument. (for sound if not for ease of playability which relates to other factors.) Their cavity sizes are pretty much determined by the reed plate sizes. (depth is a variable ), so yours shouldn't be that far off. My smallest cavity (with 12mm pad hole is : 34mm long X 16mm wide X 6.5mm deep and they sound beautiful with concertina reeds. ( with accordion reeds, who knows... ) I've never noticed anyone having much success in tuning cavities. If anything, the aid of Tom's information is in detuning a cavity away from an unfortunate harmonic. The most striking tone variable I have found in concertina reeded instruments relating to chambers is the depth. The differences are apparent enough to have let me distinguish between depth differences of 1 mm. Is this due to the cavity volume change or the change in the flexibility of the chamber walls ( which can mimic a change in volume ). In violin air resonances, the height and thickness of the sides is an important factor in determining both the wood resonances and the air resonances of the body. I haven't a clue what is really happening with the change in depth, I do know what depth I like best.

Dana

 

Hello, Dana -

 

I was surprised myself that the top notes turned out this way - I mean, they really stand out from the rest. I'll see if I can get down to recording some steady-state notes plus the spectrums. My basic instinct says the cavities are too large - they are approaching frequencies that get too close to the main (2', 3' 4' 5') overtones. The same instinct says depth - too much of it: 12 mm, in my case - from what I (think) I can see on Richard Morse's photos on the Button Box site, their's are much lower.

 

But until I make some changes, it's only speculations. I'll be back with some more meat on the bones, hopefully. Time, time...

 

/Henrik

[Richard Morse]

What you can't see in that Morse photo on this page is the depth of the chambers of the highest reeds. As Dana mentiioned, the depth of the chambers - particularly the highest ones, is quite important. We fill ours in to be less deep (sloped, actually rather than uniformly filled to be shallower).

 

-- Rich --

[Henrik Müller]

What you can't see in that Morse photo on this page is the depth of the chambers of the highest reeds. As Dana mentiioned, the depth of the chambers - particularly the highest ones, is quite important. We fill ours in to be less deep (sloped, actually rather than uniformly filled to be shallower).

 

-- Rich --

Thanks, Rich, instinct confirmed. Enough talk, I'll come back when I've done something!

 

/Henrik

[ragtimer]

Sometimes cavity resonances can make for an uneven-sounding scale in concertinas that mount accordion reeds in cell chambers at right angles to the soundboard. A few notes happen to hit the resonance of their chambers on some major harmonics, and thus give a full, flutey sound, which is nice -- but their neighboring notes still have the normal, reedy, thin sound that doesn't match.

 

On my Stagi Hayden Duet, the RH low F, Bb, and high F all get an extra "punch" from the resonance, and now that I've noticed it, these notes tend to stick out in a melodic scale passage. These all happen to be at the left end of their button rows, probably just a coincidence.

 

Don't get me wrong, I love my Stagi, but I can hope someday to own an upgrade with the reeds mounted flat to the pan, as in Rich's instruments to date. Or maybe one with the reed chambers carefully sized, individually, to their reed pitches? So every note gets the same benefits? FWIW, some large reed organs did amazing things with resonant chambers per reed, to emulate organ pipes and orchestral instruments.

--Mike K.