Mystery of misbehaving F3 note.

[Łukasz Martynowicz]

4 hours ago, ttonon said:

Lukasz, from my calculations, I see no possible resonance interference with the tongue vibration.  This applies to both Helmholtz and quarter-wave tube resonance.  

 

I thus cannot make a suggestion here, only I'm still not clear on what the basic problem is.  Are you saying that all the F3 reeds you put into the "bad" cavity show the same problem?  Also, that when you put those same reeds into a different cavity but with the same dimensions of the "bad" cavity, there is no problem?  

 

Best regards,

Tom

Exactly. Bad cavities are on the LH side of the instrument and good ones are on the RH, reeds are identical and it does not matter which one I mount where. The .wav file above is with endplates mounted, but this problem is present without the endplates as well. Endplates emphasise it further.
 

Some parameter of reedpan is causing this but not simply inner vs outer chamber placement, as both initial chambers are outer ones. I suspect it is either amount of solid wood block left in the reedpan, differences in reedpan’s wood parameters between sides or the exact layout of surrounding voids, because I can get significant improvement in spectrum shape during tests by using tack to mount the reed to the reedpan instead of rigid screw connection and thus decoupling it mechanically. 
 

But using tack is not a valid permanent solution so I’ve settled with increasing chamber depth to bring missing partial back as a way to rebelance this instrument. It is not ideal, as I loose some higher partials this way, but it sounds way smoother now.

 

Perhaps it is now easier for you to understand why I said, that reeds seem to not care too much for our simplistic mathematical models  

Edited September 13, 2021 by Łukasz Martynowicz

[Jake Middleton-Metcalfe]

I could not find the original thread regarding the problem - the one about pitch stability. But I did recently have a problem with a low F3 note - it sort of gurgled when I changed bellows direction at low pressure. The problem was actually the valve it was sort of curled but not curling up it was curling down. The solution was to replace it with a flat valve. 

 

 

[Jake Middleton-Metcalfe]

It sounds as if you are having a really tough time with this problem. I have been in similar situations in the past with one of those "what on earth is causing that buzzing" sort of problems. And as you are - you go through it methodically trying to find the source of the problem. It can be quite frustrating.

 

Apart from my suggestion above sadly I cant really offer much help but I will say this: every time I have been in this sort of situation with a mysterious sound problem with unknown cause - and I have been in that situation many times, the solution in the end was always something really really basic and stupid, such as: "oh the buzzing was not actually caused by the reed or the chamber its because the makers mark plate was not actually screwed down properly and was vibrating in sympathy with the reed, lets tighten that bolt, ah job done"

 

In many cases of this sort I spent rather a long time (three whole days in the case of the loose bolt) over-complicating things with scientific reasoning, beware of this.

[Theo]

2 hours ago, Jake Middleton-Metcalfe said:

In many cases of this sort I spent rather a long time (three whole days in the case of the loose bolt) over-complicating things with scientific reasoning, beware of this.

 

Been there, done that, got the teeshirt!

[Jake Middleton-Metcalfe]

3 hours ago, Theo said:

 

Been there, done that, got the teeshirt!

 

It can be frustrating! 

 

I hope you are able to come to a conclusion about it Lucasz, these things can be very tricky.

 

I once spent a couple of hours trying to work out a problem with a draw reed that would stop suddenly at high pressures - aha I think, it must be set too low to the frame. No - actually the pad had come into two parts and when you drew the bellows out firmly the bottom half would get sucked out and cover the hole. Well that was an unusual cause of that problem. For ages I tried doing things to the reed thinking that was the problem but it was not at all. 

 

Best of luck!