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How Hard/far To Push On Reeds


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I'm trying to fix a slow reed on my brass reeded English concertina.

(It's the a flat on the right; on the push)

 

I'm pretty sure that the problem is that the gap between the reed and

the frame is too small. I've done one round of opening the concertina up and pushing on the reed with toothpick.

I was pretty gentle, pushing the tip of the reed maybe one millimeter out from the reed frame;

at the end of the process I didn't see a clear change in how the reed sat.

Obviously, this hasn't fixed the problem.

 

To my untrained eye, there isn't really any gap at all; this would concern me except that

the a flat reed wasn't obviously different from the adjacent a natural.

 

How far/hard should I push on a reed to try to modify the size of the gap?

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It is one of things hard to describe because the answer is something like, push it just hard enough and no more.

 

I find you need something substantial to push with, a toothpick will never do it (mind you I've never seen your toothpicks). I hold the reed firmly shut, trapping the first third from the root with a finger, and then push upwards about a third from the tip with a small screwdriver or similar. It is vitally important the implement does not slip sideways and go between the reed and frame. As to how hard to push; you need to push the reed past the new position you want it to adopt; it will spring back and then you can see if it is far enough. Do it in small increments, push slightly further, if that did not work go slightly further again etc. The first few times I tried it I took forever. When I am dealing with reeds other than my own I still take a long time because I am learning the steel, feeling its thickness, looking for what is called the "plastic" point where it will deform and not come back. Brass will deform much easier than steel so take it very slow. Get some magnification so you can see whether there was a change. Position the reed assembly between you and a dim light so you can see how high the reed is. Look at the reeds near it and see how much lift they have as a first position to put it in.

 

HTH

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I assume, Dave M, that you have checked that the slowness in response of this reed is not caused by another issue, such as a valve sticking, or binding against the chamber wall behind said reed, or a valve that is just too thick or heavy?

 

IMHO, always worth checking a valve before adjusting the reed response....

 

 

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Reeds with too little gap up to the point where there is none, usually respond at low pressures, but may be balky to start if pressure is applied too quickly and produce a delay before finally coming to life. If they are too low, they may not start at all. Since you don't see a gap, ( mind you, very small reeds above C6 may not show one. The amount usually increases with the length of the reed ) we can probably rule out too much gap, which will also produce a slow reed. As Malcolm says, the flap valve may be the issue, especially since you don't see any difference between two reeds a semitone apart. ( rule of thumb, moderated by reed stiffness, gap about thickness of reed tip is a good starting place. (Often less), though light reeds or wide ones may have more, since they are more easily closed by air pressure.). A flap valve for the adjacent reed, if curled up or otherwise not wanting to lay flat will also slow response, since the reed in question doesn't receive full air pressure until that valve closes. Malcolm's remark about a stiff valve on the backside of the reed is the opposite problem, since it is hard to lift to allow enough air through. This usually makes the reed sound dull when it plays as compared to reeds with valves of more appropriate weight. Sometimes the leather gets hard and causes this, or sometimes someone has replaced a valve with something less than ideal.

Dana

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Thanks for the input guys, I still haven't opened it back up yet but I'll take the additional info into consideration when I do.

 

The problem is with A-flat 4, the A flat just under the thumbstrap on the rhs.

If I hold the button down and reverse the bellows, I do not notice a significant lag, its only when I go from a different button to that one

(on the push). The lag might be worse at higher volumes, but it is hard for me to tell. Sometimes I think it is user error, that I'm not

depressing the key completely/rapidly, but most of the time it really seems like the reed is just not speaking with the button depressed.

I first noticed it on an upward run f4 a-flat d e-flat, which I adapted to by using the g#; but now I'm running into the same problem with a downward c5,b-flat,a-flat,g run.

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  • 3 weeks later...

Finally got the gumption to make another go at it. I followed Chris's advice on where/how to push (I did use a thick toothpick with the end cut to make it blunt), the tip was a few (maybe 5) millimeters above the reed frame. At the end I could just make out a sliver of light between the reed and its frame (before doing this I couldn't see any kind of gap). Now the note plays much more responsively. Thanks for the tips.

Edited by DaveM
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On the subject of Elastic/Plastic Deformation In Metals:


The reed when vibrating in play, will be 'operating' within its Elastic Deformation range, ie the forces on it are not great enough to result in permanent deformation, so when play stops the reed resumes its original form. To permanently deform the reed one must apply sufficient force in order to stress the metal through its 'elasticity range'. One must be very careful to determine where any particular reed's elastic limit is, as small increments of force can have noticably larger increments in permanent deformation once the elastic limit has been reached!


A blunt wooden probe is preferable to a screw driver blade as a means to apply the force, as it is less likely to scratch or damage the the reed/shoe if it slips. To get the feel of where the reed's elastic limit is, apply light pressure to move the reed tip (by say 2mm, less for the very small reeds), then release it. Inspect to assess if any permanent deformation has occurred. This can be done simply by holding up to the light, to see if the gap is bigger (or smaller). If you want to be more scientific you could use feeler gauges to measure the gap, or increase/decrease in gap. If there is no difference, then you need to try again with a tiny bit more pressure. So if you pushed the reed tip 2mm first time, now push it a bit further (say 2.5mm). Release when you judge you have just exceeded the force you used the last time, again check the gap... Continue this process until you have achieved a noticeable, measurable change in the reed.


At this stage it is worth putting the reed back and checking out its sound. If still no improvement you may need to make further adjustment....

Edited by banjojohn
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