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#19 Dana Johnson

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Posted 14 April 2017 - 03:35 PM

Regarding vent width, or rather aspect ratio, all other things being the same, narrow reeds are less bright compared to wide ones. (From reed organ design). Adding width to a reed increases it's spring tension, but is not likely to give added effect to the air flow enough to balance the extra pressure needed to deflect the reed. To bring the reed back to similar playing pressure, the profile needs to be adjusted to increase the flexibility. Certainly a large reed eats more air than a smaller one, and can give more volume, but as mentioned, not as much as you'd think, or already loud low reeds would hopelessly drown out higher ones, which as any duet player can tell you is enough of a problem as is.
Normally tapered reeds shift the profiling by adding extra stiffness at the root end, which has the effect of making a reed higher in pitch than it otherwise might be, allowing a larger reed where they are getting small (and quieter) fast. The scaling I have seen on tapered reeds has always been from parallel or nearly so for the lowest reeds to substantially tapered at the high end, but evenly adjusted over the range of the set.
The length to width ratio is limited by the torsion mode frequency, which is well below the fundamental for normal reeds, but increases in frequency with width, at some point running afoul of the main note. I seem to recall 8:1 as the practical minimum difference, but don't remember where I read that. Most of the time, the aspect ratio does not stay the same from low to high, but has higher reeds being proportionally wider. Guessing again to try to maximize their volume.
For low reeds, shorter than ideal requires more tip weight, which in my experience means a slower reed than a longer one of the same pitch but without extra weight. Since flat reeds of a given thickness, increase increase in length by about 1.4X per octave, low notes get big fast if you don't counteract by increasing tip weight and or reducing stiffness nearer the root end. Making this more complicated is the need to keep playing pressure relatively similar over the range of the instrument. This means you can't thin too much or you will have a weak reed, so you are left with either adding length or weight. Things like bellows area mean you generally want a reasonable sized concertina, so there is only so much room for low reeds. It is all a bunch of compromises, but if you go for smooth transitions note to note, the results of the compromises aren't so noticeable. I had a lovely old Jeffries, but it had shorter heavily weighted low reeds that were slow to respond compared to the rest of the instrument. I use a long scale set of reeds, which are much better in the lower notes, but I had to rotate my reed pans to put the low notes in the longest chambers. They wouldn't have fit in the Jeffries orientation.
If you are designing your own reed set, start by measuring reeds from really good concertinas, then you can copy or average them and try to even out any obvious large steps if there are any. Most of the experimenting got done long ago, and you won't go wrong taking advantage of the work of those who went before us.
Keep in mind that good reeds can sound bad or sluggish in a incorrectly made concertina, or one with a poor choice of wood. Tone and response is as much the result of the rest of the instrument as it is of the reeds. You can't really say one concertina sounds a certain way 'because' of some aspect of the reeds. You can only do that relative to the very same concertina with a different set of reeds.
Dana

#20 Johann

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Posted 15 April 2017 - 02:32 AM

Nice to and interesting to read your Comet Dana, i Go along with you if i am talking of totally different instruments. "Adding width to a reed increases it's spring tension, but is not likely to give added effect to the air flow enough to balance the extra pressure needed to deflect the reed. To bring the reed back to similar playing pressure, the profile needs to be adjusted to increase the flexibility." So it is in reality because the person working with the reeds compensates by changing the flexibility of the reed. But If profiling is absolute the same or from physical few point if we had a reed bar without profiting all the same thickness then the stiffness doubles if the width is doubled also the weight is doubled so the resulting pitch is the same. Sure this means it needs more power and air passing through to drive the reed to the same amount of amplitude resulting in doubling the volume but as explained before this means not that we hear it as loud as expected. My experience with very low pitched reeds  in accordions is: (I speak of reeds in the range of: 27,5 Hz to ca. 123 Hz 

  • Subkontra-Oktave: (16,4 Hz -30,9 Hz) 
  • Kontra-Oktave: (32,7 Hz -61,7 Hz)
  • Große Oktave: (65,4 Hz- 123,5 Hz)

  https://en.wikipedia...ing_Systems.png )

It makes a lot of difference in volume if the size of the reeds are changed, even the stiffness of the reed and the balancing of spring stiffens to the weight may be changed to compensate some negative aspects. But keep in mind the Frame is also of importance if we want to get more volume. Take a normal accordion bass reed and change the thickness of the frame by leaving all other thins as the have been. Then a thicker frame will result in more volume if pressure of air is increased. Dynamic range is nearly doubled by doubling the thickness of the frame. If this would not be the case i had no reason to put in big helicon reeds to get the sound we want in Austrian diatonic accordions. Still there is more to it as the reed but we talk here abut the width of the reed if it results in more effective heard Volume or not. Best regards and keep to the advice Dana has given by making a new reed set. Johann 

 

PS: "or already loud low reeds would hopelessly drown out higher ones, which as any duet player can tell you is enough of a problem as is." exactly my saying, but it is a very subjective question what one wants. I make accordions with normal bass reeds or even smaller ones if asked for it and with Helicon reeds. One Musician would argue this way and an other the other way round.

 

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Edited by Johann, 15 April 2017 - 03:25 AM.


#21 alex_holden

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Posted 15 April 2017 - 06:26 AM

Thanks Dana, a great deal of food for thought as always. I think I will go back to the drawing board again and alter the vents to Chris's observation of making the root 0.1mm wider than the tip, regardless of the length. I've already averaged out the length and tip width over the range I'm working with.

#22 alex_holden

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Posted 15 April 2017 - 09:56 AM

I measured acouple of Jeffries sets about ten years ago and the taper in the reeds was consistent, not consistent as in a particular angle, but in that each reed vent, no matter the pitch, was 4thou (.1mm) narrower at the tip than the root. Consequently the taper angle increased as the pitch went up.


Just crunched the numbers in a spreadsheet. The Lachenal reeds I've been working from have taper angles scattered around 0.7 to 1.5 degrees in the range I'm interested in. If I instead make the taper consistently 0.1mm over the length of the vent, I end up with 0.21 degrees at the low end up to 0.36 degrees at the high end.

#23 Chris Ghent

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Posted 15 April 2017 - 10:21 PM

Alex, a couple of thoughts. First, unless you know exactly why a set of reeds do not perform well it might not be a good idea to copy any aspect of them. I am suggesting a Lachenal reed is not a good starting point unless it is one from a better Edeophone. Second, I take it these are single sided angles you quote? Mine are around twice those numbers.

I initially set out to have four angles up the range from about .5° included up to 1° at the top. Because the reed blank method involves diesets and they are stratospherically beyond my machining capacity both in equipment and mentally, I had to shell out and have them made. I have two diesets in the midrange (from memory they are .6° and .8° included) and I never did get the other two made because at the time I was broke. As a result the lower reeds are slightly more tapered than I wanted and the high reeds less so, but by tiny amounts. I would be surprised if they were more than 1.5% larger/smaller in square area than my original plan.

Over time I have experimented with relief angles in the vent and with profiles but not with the reed taper. It is worth noting substantial makers like Dana, the Dippers and Wally Carroll use parallel reeds. If these dimensions are significant then the aforenamed makers have other ways to acheive the same ends...

#24 alex_holden

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Posted 16 April 2017 - 12:43 AM

Second, I take it these are single sided angles you quote? Mine are around twice those numbers.


Those are the angles between both sides. I thought they sounded rather small. I just drew one up in CAD to double-check that I got my spreadsheet formula right.

I initially set out to have four angles up the range from about .5° included up to 1° at the top. Because the reed blank method involves diesets and they are stratospherically beyond my machining capacity both in equipment and mentally, I had to shell out and have them made. I have two diesets in the midrange (from memory they are .6° and .8° included) and I never did get the other two made because at the time I was broke. As a result the lower reeds are slightly more tapered than I wanted and the high reeds less so, but by tiny amounts. I would be surprised if they were more than 1.5% larger/smaller in square area than my original plan.


Thanks, that's useful to know. A small number of fixed angles would make the tongue manufacturing easier (my shear is adjustable, but it's a painstaking process to get the angle dialled in perfectly).

#25 Dana Johnson

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Posted 16 April 2017 - 01:28 PM

Take a normal accordion bass reed and change the thickness of the frame by leaving all other thins as the have been. Then a thicker frame will result in more volume if pressure of air is increased. Dynamic range is nearly doubled by doubling the thickness of the frame. If this would not be the case i had no reason to put in big helicon reeds to get the sound we want in Austrian diatonic accordions. Still there is more to it as the reed but we talk here abut the width of the reed if it results in more effective heard Volume or not. Best regards and keep to the advice Dana has given by making a new reed set. Johann 

Hi Johann, I really appreciate your solid base of experience, which is for the most part valid on concertinas as well as accordions. For most concertinas, frame thickness is an after thought as people tend to start with what they have seen, and for limited range instruments, you can get by with one thickness and not notice a difference. I used to use thicker material (.093 inches) for my lower reeds in a c/g Anglo but went to the thinner stock to try to reduce weight and noticed no difference. In the g/d and a/e, I do use the thicker material because the reeds are long enough to clear the bottom of the frame for a considerable part of their cycle, and as you say, would lose power otherwise. I once made a reed using about .020 inch steel sheet for the frame as an experiment, and was interested that while it "worked", its volume topped out at a very low level. My supposition since then had been that once the reed swings clear of the bottom of the confines of the window, increasing pressure has much less effect on volume. Consequently ideally, window thickness should be proportional to length. I have a set of bass accordion reeds that have cast plates that are tapered in depth so they are a full half inch thick at the tip end. Of course the reeds themselves are around three or four inches long.
I prefer slightly heavier reeds in my concertinas because I want a wide dynamic range, and light reed sets, while jumping out in response, can be nearly on or off as far as volume goes, precisely because they flex enough to clear the window at light playing pressure. On concertina reeds, the best vent angles also depends on the stiffness of the reeds. On accordions, my understanding is that little or no vent angle is used because of the extra air consumption when multiple banks of reeds are sounding.
For other prospective reed makers, I find that from one size of reed blank / window length, I can span 4 semitones and have reeds that all are equal in stiffness ( I measure this variable ) so they all respond at the same playing pressure. There may be a little more latitude, but, not without making the reeds weak, thick at the tip or too thin there to bend evenly. Low reeds, F3 on down, I only do 2-3 semitones because the window length is changing fast there. Too much tip weight makes sluggish reeds. For those making reeds, the central third (approximately) of the reed can be adjusted in thickness to vary the stiffness with little effect on pitch. While you can make reeds of a wide range of pitches at a given size, the requirements of a really good instrument, balanced in tone feel and power, limit the practical length, proportions and profile that will give good results. I have a reed set from a baritone Wheatstone English whose reeds are larger than the matching notes in a tenor treble. In order to have good active lower reeds, they had to be proportioned to that requirement. The rest of the reed set needed to be larger to keep the volume balanced. A good example of the reeds being constrained by their use.

Edited by Dana Johnson, 16 April 2017 - 01:31 PM.


#26 alex_holden

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Posted 17 April 2017 - 12:50 AM

Is there an optimal relationship between the size of the vent in the reed frame, and the corresponding vent in the reed pan?

#27 Dana Johnson

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Posted 17 April 2017 - 07:24 AM

All I know is that it isn't critical. I use about 70% of the length which is on the long side. 60% is more common. Given the way reeds swing, they have to be long enough so the reed never hits the wood, but if that condition is met, it will be big enough to pass sufficient air. I have seen some concertinas that had the heel end of the port cut at a shallow angle so the size next to the reed frame was full length but the valve side was normal. This seemed like a solution in search of a problem. If the port is too short, the surface effect comes into play at higher volumes and could damp the reed somewhat. Long ports make valving a bit more difficult since the more valve you have, the more there is to create problems.

#28 alex_holden

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Posted 17 April 2017 - 02:48 PM

Thanks Dana, that's useful to know.

#29 Johann

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Posted 18 April 2017 - 11:58 AM

@Heavyweight Boxer Thanks for sharing your experiences! there is not much i would be able to add to what you did share. Is all a question of compromice and I can understnd that with your type of instruments one has definatly different limitations or gols. Best regards, Johann



#30 Alex West

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Posted 23 April 2017 - 12:11 PM

Vent width and lenght might not be critical, but I've been having trouble with a concertina in G/D where the right hand "D" row was feeling very slow to respond.  I don't think the reeds were great quality, but I got the set right, re-valved the most desperate ones (and removed valves in some cases) and they sounded OK on my tuning bench but not in the concertina.  As an experiment, I tried blocking off some of the vent to shorten the airway (matching the vent in my tuning bench) and increase the pressure a bit and it seems to be successful (crossed fingers and toes!)

 

Not scientific but it might have worked so I'll try a more permanent fix

 

Alex West



#31 Dana Johnson

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Posted 23 April 2017 - 07:15 PM

Perfectly scientific if empirically driven. Tuning benches can be misleading because of acoustic behavior that is frequency dependent. Mine for instance has a resonance around G4 and the octaves above that. This causes the reeds near that pitch to be slow, usually flat and unresponsive. If I open a adjacent port to the plenum ( usually blocked for reeds of a different size range ) the reeds spring to life and behave as they do in the instrument.
I have kept to my normal practice with my A/E, and had no problems in that pitch range on any row. Sounds a little more like a valve problem, but port length directly effects the valve, so if it works, good enough. There is also some question about the notes on the other rows in the same range. Do they work fine as is, and just the D row was squirrelly? If it is row dependent, and not pitch dependent, I'd be looking for other problems, like loose or low corner blocks. These can sap the energy from the best reeds if they are located close to the bellows frame blocks at the reed pan.
Not saying your fix didn't work, but if the valves were initially too heavy, lighter valves will give a boost without actually addressing the deeper problem. Conversely, changing the port size will change the way the valves behave. Years ago friends got in a concertina that was dull and sluggish. The blocks had been slipping and had cardboard shims stuck on them to bring the reed pan to the right height. Resetting the corner blocks and getting rid of the soft shims made it play and sound great.
Dana

Edited by Dana Johnson, 23 April 2017 - 07:16 PM.


#32 Alex West

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Posted 26 April 2017 - 03:15 AM

Dana

 

Thanks for getting me to think of other things than vent length. 

 

There's a possibility that one of the corner blocks isn't doing its job but I'm away from home at the moment and can't put a permanent fix in for that.  Ther's also a possibility that one of the valves is a little heavy so I can fix that.  By far the biggest revelation when I took a closer look was that a lot of the reed shoes, whilst apparently snug in their slots weren't propery supported along their lenght and particularly at the root.  Once I'd shimmed that out a little better on 3 or 4 of the notes, a lot of the problems disappeared

 

So I think it's been a combination of things rather than a single systemic cause.  Proper diagnosis is more than half way towards the correct solution!

 

Alex West






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