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Getting Reeds And Knowing Chamber Sizes


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Hello,

 

Please, please excuse my ignorance. I've tried to do a bit of searching on the site for this info, but couldn't quite find what I was looking for. Also, despite taking apart a number of types of accordions and concertinas, and am in the beginning stages of building an accordion, I don't really know the proper terms for the various bits, so please excuse that too.

 

Here's my main question: unless you are exactly copying an instrument in your possession, using matching reeds, how do you know what the sizes of the reed chambers (for lack of the proper term) are? Length, depth and width... My educated guess is that these dimensions are determined by the reeds themselves. So if you're buying reeds to build an accordion, do the makers of the reeds provide dimensions?

 

Thanks!

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Yeah, chamber dimensions is something you've got to figure out. The size of the reeds and the expected amplitude of their swing will do a lot to set the minimum size. As a general rule, you'll want them to be pretty small... otherwise you'll end up with a bulky instrument. You might find that reed chamber dimensions have some effect on sound quality, but I couldn't really tell you what effect, except maybe to say that many later instruments have extra walls to make the chambers smaller, presumably for better tone.

 

I guess the other factor to take into account is how close you can get your action levers. That seems less likely to be the governing factor, though.

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Here's my main question: unless you are exactly copying an instrument in your possession, using matching reeds, how do you know what the sizes of the reed chambers (for lack of the proper term) are? Length, depth and width... My educated guess is that these dimensions are determined by the reeds themselves. So if you're buying reeds to build an accordion, do the makers of the reeds provide dimensions?

 

What I seem to recall from prior discussions is that chamber dimensions (including shape?) can affect tone quality, volume, and speed of response, but that there's no formula. It's far more "art" than "science".

 

If I were trying to make a new instrument (currently no more than a dream), even though not making an exact copy, I would still start by approximately copying the dimensions of an existing instrument, then attempting various "adjustments" to see what effects they have.

 

For what it's worth, there are a few cases among the vintage Wheatstones where an instrument of a normal range has its reeds fit into a body of a size much different from the usual. E.g., there are at least a couple of "treble" Englishes in "piccolo" (octave higher, and much smaller) bodies, and I know of at least one "bass-baritone" in a body the same size as my "baritone-treble" (a fourth higher), while other instruments have been noted in larger than "normal" bodies. So it would appear that the workable chamber size can vary a great deal, though the detailed consequences of the differences haven't been well documented, as far as I know.

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Interesting, thanks gentlemen. My initial experiments with building a concertina, a very ugly proof of concept contraption, was to dismantle an old broken down accordion, using its reeds fitted to chambers exactly matching those of the accordion. Since the chambers in the accordion seemed to be different for every reed in the accordion, and not just in length, I maybe assumed incorrectly that chamber size was absolutely critical to the reeds working at all. It's good to hear that there can be some variation.

 

Is there a usual place for folks building their own to buy reeds? Maybe a model of accordion reeds that work adequately as concertina substitutes?

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Reeds will work without any chamber at all. So the variation is absolutely infinite in that direction.

Other people may have recommendations for which accordion reeds work best, but as long as you're using accordion reeds, Every Good Bunch Does Fine.

 

I've never heard anyone bother to debate exit-hole shape. Round is typical, but square should work fine. Round may get you a quicker attack or different tones by letting the airflow hit the middle of the reed just so, but square will still play music.

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I am also in the process of building (still designing actually because of lack of time...) my first concertina, and what I can tell from my experiments and observations, the reed chamber sizes on an accordion vary in size mostly because of reed speaking speed. Because of different reed position (reedblocks vs reedpan), you'll have completely different physics of sound propagation and pressure buildup inside the chamber. I've built a test chamber with variable dimension and air hole placement and my observations are, that when placing reeds in concertina fasion any chamber not smaller than reedplate will work - smaller chamber are faster, larger chambers have deeper sound. Of course if you're trying to make a virtuoso instrument, or were working with concertina reeds, precise dimensions matter... Otherwise you just have to have enough room for valves and reed swing - which can be quite significant, especially with weighted reeds. What matter most to sound [with given reed type, in this case accordion reeds] is reed placement style (concertina vs accordion), then air hole placement relative to the reed, then how rigid the connection between reed and instrument is, then amount of obstacles and bounces between and then materials you build your concertina from (there is a large debate if materials do matter (you can find it on this forum), especially different kinds of woods and should it be a tonewood or not - or is it just a surface finish that affect sound; in my experiments material did matter, but only plywood and mdf gave awfull results. Someone even tried 3d printing a reedpan...).

 

Side note - accordion reeds are low pressure reeds and different qualities of those reeds are best heard on low pressure instruments. Concertinas are high pressure instruments, so there is no point in putting expensive reeds in your first instrument - any reed will work.

I seriously doubt, that both modern cheap china concertinas or old german-anglos were carefully designed instruments. They rather are/were a mockup of parts assembled together to fit both purpose and cost of an instrument. To be honest, you can build a concerina from MDF and an old shelve, put cheap russian accordion reeds in it and as long as the reeds have clearance and are not rusty and your craftsmanship is good enough, you'll end up with at least a decent playing instrument. Maybe not a beautifull or durable, but it will sound like a hybrid concertina. My first concertina was a cheapest old german anglo I could buy and still, when I upgraded to Elise it was a downgrade in terms of sound - not because of cheap reeds or any usually discussed problem, but because of steel/plastic combo, loose, unbushed buttons which buzzed when the air moved around them. After I've replaced them with rigid, fully bushed ones my Elise works like charm, the only problem left are lowest, weighted reeds that are so slow to speak that using them for accompaniment is demanding and tricky.

 

As Jim said, it is more "art" than "science" because of amount of interlocking factors, that even free-reed instruments builders with years of experience will often bump into results completely opposite to expectations (e.g. usage of balsa wood for reedblocks, discussed in some thread here or on melodeon.net).

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Round vs. square - several of the accordions I dismantled had square holes, so I thought that might be common. I made my ugly proof of concept beast with square holes because the accordion i salvaged the reeds from had them. Using drill bits would have been easier!

 

Lukasz, thanks for your advice. Can you talk more about what it means, in terms of building, for low vs. high pressure?

 

Are there books that would be helpful for me to read. I know just enough to know I know nothing.

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So you're just a little behind me with your knowledge :D There are probably some printed resources on accordion restoration, but most practical aspects of bulding free reed instruments are "secret of a trade"... with very limited "first hand" information. Bob Tedrows photo essay on building one of his concertinas can be found on his site - this is by far the most extensive set of informations regarding building a hybrid I found. There are numerous articles spread out on the web. Most of them aren't easy to find by google - search forums about accordions, this forum, bandoneon forums, melodeon forums etc... There were a great blog with history of "making concertina on the kitchen table" but I can't find it anymore - maybe someone here knows the person who build that instrument? Or maybe the builder himself is here?

 

As for low vs high pressure: pressure of a bellows is determined by the area of its cross section. Accordions have at least twice as big as concerinas, so when you squeze them with same force they produce lower air pressure. From what I managed to learn, more expensive accordion reeds are engineered to have better response at low pressures (can play softer and quieter) and more stable frequency across different volumes/pressures.

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So you're just a little behind me with your knowledge :D There are probably some printed resources on accordion restoration, but most practical aspects of bulding free reed instruments are "secret of a trade"... with very limited "first hand" information. Bob Tedrows photo essay on building one of his concertinas can be found on his site - this is by far the most extensive set of informations regarding building a hybrid I found. There are numerous articles spread out on the web. Most of them aren't easy to find by google - search forums about accordions, this forum, bandoneon forums, melodeon forums etc... There were a great blog with history of "making concertina on the kitchen table" but I can't find it anymore - maybe someone here knows the person who build that instrument? Or maybe the builder himself is here?

 

As for low vs high pressure: pressure of a bellows is determined by the area of its cross section. Accordions have at least twice as big as concerinas, so when you squeze them with same force they produce lower air pressure. From what I managed to learn, more expensive accordion reeds are engineered to have better response at low pressures (can play softer and quieter) and more stable frequency across different volumes/pressures.

 

it is here: http://www.concertinamatters.se/

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Nathaniel, most accordions that I’ve seen make use of an upright reed block design, as opposed to the flat design, which is incorporated in most concertinas. The flat design is used along with the upright design in American made Cajun accordions.

 

Here’s what I think provides the reasoning behind the tapered upright design, but first of all, let’s consider the dimensions of the reed itself, which is essentially the dimensions of the reed plate (the metal piece on which the reed tongues are riveted). The width of all the reed plates are the same, generally around 0.65 inches, and this is ultimately determined by the required width of the keys, which is as small as possible, but still with the ability to be conveniently manipulated, and that has been largely standardized. The length of the reed plates is influenced largely by the required pitch of the reed, and like the lengths of piano strings, the scaling relationship between pitch and tongue length has been arrived at through much trial and error. Thus, a given tongue length and corresponding plate length will provide a certain range of pitches, and there are a few different length categories that span the pitch range of the instrument.

 

The length and width of the cavities are directly dependent on the corresponding plate dimensions, with the cavity dimensions slightly smaller, in order to allow the reed to be placed as a cavity cover without leaks.

 

The depth of the cavity is a little more complicated, but to understand that we first need to understand that the reed is oriented with the free end of the tongue at the top of the upright reed block, away from the air hole. This is to save space. If the larger reeds were mounted with the free end down, their vibrating tips would strike a neighboring reed, unless the spacing between blocks is increased. Thus the taper, giving more room for the tongues to vibrate and thus minimize the distance between reed blocks. The depth of the cavity under the vibrating reed tip is made deep enough so that the vibrating tip does not bottom out. With this dimension fixed for the largest reeds, the overall width of the reed section of the instrument becomes fixed.

 

The depth of the cavity at the air hole end is determined by the size of the air hole. It’s desirable to make this hole as large as possible, in order to get as much sound out of the instrument as possible. But the air hole dimension in the direction along the length of the keyboard is largely fixed, because, as mentioned, the width of the keys has been fixed. The dimension in the perpendicular direction is also confined in order to keep the size and weight of the entire instrument down, and there are diminishing returns in making this dimension much larger than the first dimension. Apparently, size and weight are of such importance so that the resulting sound volume achieved by dimensioning the air hole according to this requirement has proven adequate. But usually, you see rectangular, nearly square holes, because as Chris points out, they have more area than a round hole with diameter determined by the minimum dimension. With the depth of the cavity now fixed at both ends, the block is simply tapered to fit.

 

The above gives a general procedure. There can be complications, and most of them arise because of spurious acoustical effects. For instance, I’ve seen some cavities for the smallest reeds stuffed with wood in a curved shape. Since the tongue vibrational amplitude of these reeds is so small, the cavity depth can be made very small at the free tip end, but there needs to be an abrupt increase in order to open the cavity up to the air hole. I’ve also seen some of these higher pitched reeds mounted with the vibrating tip end downward, near the air hole. Their vibrational amplitude is so small, there’s no danger of striking a neighboring reed. I believe these approaches are taken in order to prevent choking of the reed, which can happen when the length of the cavity operates like a quarter wave tube, preventing the reed from speaking. I can only guess, but perhaps also, one can achieve more sound volume by stuffing the cavity for these small reeds.

 

It’s thus my belief that, apart from exceptional instances, there are no dominating acoustic reasons why the tapered accordion reed block has assumed its present shape. Although I do think it’s possible that tweaking the basic design might affect the sound of the instrument, I’d be pleasantly surprised if anyone can demonstrate a pronounced effect.

 

Concerning the flat mounted design, there’s no longer a need for a taper in the cavity depth, and this is normally not done. Perhaps there’s an opportunity here for some experimentation. I think it’s generally true that real estate issues require the air hole to be mounted at one end of the cavity, rather than, say, in the middle. Which end can be an issue for the larger reeds, and I think the sound can be possibly be affected. In my experience, I currently find it best to mount the hole at the end away from the vibrating tip, but I sometimes become puzzled by it, and perhaps others can comment on that.

 

If you’re interested in reading what I’ve written on the acoustic effects of cavity design, you can go here.

 

Best regards,

Tom

www.bluesbox.biz

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