Valves on treble reeds

[malcolmbebb]

I had noticed that some treble reeds are not fitted with valves.

 

I read that for smaller reeds, the valve restricts the airflow enough to make it more difficult for the reed to sound.

 

However, on a different box, even quite small reeds have valves (leather in this instance). But I'm not sure that they're original.

 

Is there any rule of thumb about fitting valves to treble reeds?

[Greg Jowaisas]

I had noticed that some treble reeds are not fitted with valves.

 

I read that for smaller reeds, the valve restricts the airflow enough to make it more difficult for the reed to sound.

 

However, on a different box, even quite small reeds have valves (leather in this instance). But I'm not sure that they're original.

 

Is there any rule of thumb about fitting valves to treble reeds?

 

Trial and error have been my guide. Some small reeds benefit in their response from valves; some do not. Using very thin valve leather is usually a must.

 

I suppose a general rule might be the better a reed assembly is made (close tolerances) the more likely a valve will help rather than hinder a small reed. Many Wheatstones, Linotas, Jeffries and Lachenal New Models and Edeophones seem to respond well to valves on high notes.

 

(If i have a chance I will take apart a couple of extended treble englishes and see see what has been done with the "dog and cat" notes.)

 

Greg

Edited December 6, 2010 by Greg Jowaisas

[shaunw]

When I first looked inside my first Lachenal I thought that the valves must be missing.

But now I have I looked inside at least a dozen Lachenal English concertinas, it seems

that they didn't put valves on the two highest notes on each side and that they don't need

them.

[Geoffrey Crabb]

Valves may be ommitted from the very small reeds on English and Duet concertinas to prevent the reed tongues 'choking'. Without becoming too embroiled in the technicalities of it all, not fitting a valve allows air to 'bleed' though the non-playing reed of a pair thus lowering the positive or negative pressure generated by the bellows which otherwise may overcome the resilience of the reed tongues causing them to be held in the reed slot and not vibrating.

Due to the often difference in sizes in associated pairs of reeds in Anglos, valves are generally fitted.

 

The above must not be considered definitive and as others have has expressed, some 'experimentation' is useful.

 

Happy and harmonious New Year to all

 

Geoff

[malcolmbebb]

Thanks for the replies. I think I understand the reason, there can be a lot of pressure on that little reed.

 

But I wonder, why doesn't the "unwanted" reed try to speak? I can see nothing to stop it.

[Ransom]

Thanks for the replies. I think I understand the reason, there can be a lot of pressure on that little reed.

 

But I wonder, why doesn't the "unwanted" reed try to speak? I can see nothing to stop it.

 

The reeds are set over (or under) the slot, instead of right in the middle of it. So they can only sound with air blowing them towards the slot, instead of farther away from it.

[Stephen Chambers]

But I wonder, why doesn't the "unwanted" reed try to speak? I can see nothing to stop it.

 

Except that it would need suction from that side to make it sound, not pressure.

 

As for whether to valve the high reeds or not - I'd usually follow the practice of the original maker (whatever that was), as they probably knew best with their instruments/reeds, and only experiment if I felt something needed improving...

 

You will also find certain concertina makers (notably Lachenal's) left some of the chamois leather off the top of the chamber wall, or accordion makers made holes in the reedwax/reedblock to decrease the pressure on those high reeds.

[ttonon]

 

Without becoming too embroiled in the technicalities of it all, not fitting a valve allows air to 'bleed' though the non-playing reed of a pair thus lowering the positive or negative pressure generated by the bellows which otherwise may overcome the resilience of the reed tongues causing them to be held in the reed slot and not vibrating.

 

 

You will also find certain concertina makers (notably Lachenal's) left some of the chamois leather off the top of the chamber wall, or accordion makers made holes in the reedwax/reedblock to decrease the pressure on those high reeds.

 

 

Hi Geoff and Stephen,

 

I agree that a certain kind of “bleed” or pressure relief is sometimes required to allow certain high pitched reeds to speak; however, from my own investigations, I would say that the physical mechanism is most surely an acoustical phenomenon, called resonance. The reeds are mounted on cavities, and for certain cavity geometries, resonance can occur at the frequency present in the musical tone. When the cavity is leak proof enough, its resonance can destructively interfere with the self excitation mechanism by which the reed tongue vibrates. The fact that this phenomenon occurs for high pitch reeds is because it’s only those reeds for which the wavelength of the musical tone (or some key harmonic) can become comparable to cavity dimensions. Such an occurrence is partly happenstance, requiring a match between the cavity dimensions and the fundamental (or possibly a first harmonic) wavelength. The bleed is sufficient to leak away acoustic (oscillatory) pressure within the cavity, destroy resonance, and allow the starting mechanism for self excited vibration to occur. For these higher frequencies, the cavity supports most likely either Helmholtz or quarter wave resonance. To view such a phenomenon from the point of view of steady bellows pressure does not include acoustic (unsteady) phenomenon. Concertinas are musical instruments, and the principles by which they operate must inherently be according to the principles of physical acoustics, a fairly well understood science.

 

For a more elaborate explanation of these concepts, including a survey to determine what part of the concertina musical range is susceptible to such choking behavior, and many other acoustical phenomenon involved with concertina operation, please see my article in PICA: http://www.concertina.org/pica/

 

 

Best regards,

Tom

www.bluesbox.biz

Edited January 13, 2011 by ttonon

[Theo]

Or the practical repairers take is to try the highest reeds with and without valves and see which give the performance you want. I usually find that with a typical treble English I tend to leave one or two more reeds without valves compared with the original setup, because that way they give a little more volume.