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Am I Just Being A Sucker?


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I don't know, but I imagine it is formed somewhere in close proximity to a Morris dance?

 

I envisage a test rig involving a Morris dance concertina player, a concertina with a hose and non-return valve attached, a Morris Minor with four flat tyres, a stopwatch and some brown ale. The rest is mathematics.

 

Terry

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I asked because I am trying to size some pressure sensors for use in a concertina shaped midi controller.

 

However, your point about maximum pressure being generated at a Morris dance is probably correct. Ian Robb ruefully told me that he had blown out the bellows on his TT Aeola EC while playing for Morris.

 

Don.

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Hmmm, now if you taped a stout plastic bag over one end of the conca (not the one with the air button!), attached a pressure gauge into the bag, filled the conca via the air button or keys on the open side, opened some keys on the bag end and squeezed, wouldn't that tell you the pressure in the bellows, without having to drill a hole in them?

 

Or cut a board of "craftwood" (MDF) to size and bolt it to one end of the bellows. Seal it with self-adhesive door sealer if it leaks. Add a handle and a hole to measure bellows pressure through?

 

Prof. Neville Fletcher and I once measured the air pressure in Grey Larson's mouth while he was playing flute. He looked worried when I mentioned drilling a small hole in the back of his neck. We actually used some capillary tubing out the side of his mouth. We used a simple manometer to measure the pressure, but you'd need a tall one for a concertina.

 

Terry

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I have been tempted to tap a bellows into the magnehelic to find out this but I suspect maths can tell us. If you google pressure in a cylinder with a piston there are plenty of returns which are promising but the maths runs past my capabilities immediately. Perhaps there are people with the skills here?

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What's much more important than the pad pressure is, in my experience, the seal around the reedpan, and the seal between the reedpan and the actionboard. The button pressure is tested in my case with the 'kiss test' - after repadding an actionboard I hold the actionboard up to my lips and blow through each hole. Obvious leaks become easily apparent. However, I have long learnt that most apparent leaks coming from the ends are usually nothing to do with the pads (and tightening the pad pressure up is a complete waste of time and makes the instrument unplayable), but rather are related to loose fitting reedpans within endframes, and/or gaps in the seal between the actionboard and the reedpan. Get those sorted and voila!

 

My experience is somewhat counter to yours, yes what you say does matter, and yes I usually roughen up gaskets and some times replace them, I also check chamber gasket heights relative to bellows frame seal surfaces, but this is standard service stuff. The number of action box to bellows frames leakage problems I have ever had is possibly two or three over, perhaps 500 instruments. The internal cross chamber / cross reedpan leakages usually present as ghost notes and burbles etc., not instrument leakage.

 

 

Now, here's an interesting comparison. I ran the Magnahelic tester on the RH action plate of my Simpson anglo. Almost all pads came in between 1 and 2 on the scale, compared to the typical 4 on the poorly repadded Lachenal I've been looking at. Only one of the Simpson pads read a 4, while a number of the Lachenal pads read 6 and even 8. Now this becomes even more interesting when we compare playing weights. The Simpson buttons require somewhere around 60gms on average, while the Lachenal keys require between 100 and 200gms. So, not only does it leak more, but it leaks more with higher spring pressure. Hmmmm.

 

Now, this is all at the very low pressure designed to test flute pads. For realistic concertina measurements, the tester should ideally simulate typical or indeed maximum bellows pressure.

 

Terry

 

I have to wonder, given the nature and variations in mechanical design, the age of the instruments and the technology available in the mid to late 1800's when most refinement to design was done, are we not, as it were, chasing the far 'end of a f*rt'? Surely what is important is a seal to preserve air efficiency in play, and consistency in action pressure (by feel) across a specific instrument? Surely this scientific pad & Key testing is just of academic interest and between us grumpy old men; and really not for the confusion of the tyro who is accessing these pages for guidance? Geoff Crabb posted details a neat little key depression-load setting tool which is probably more than many people actually use.

 

Dave

Edited by d.elliott
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OKay, I went and did it and it took all of 20 minutes. So much for procrastination. This is the first thing I have done in a new workshop so a milestone of sorts. I used Terry's method number two, a piece of mdf screwed in place of the end and I ran an airtight tube from it to the Magnehelic gauge. This is a vacuum gauge made by Dwyer. It does not measure pressure so only worked on the draw.

 

The results...

 

Gentle quiet playing - 1"WC

Mid range playing - 2.5"C

Loud playing - off the scale. What a disappointment! My gauge only goes up to 3"WC. By the speed it hit the end stop I would say it was heading for at least 4.5"WC. Sorry, not very scientific.

 

So what is "WC.

Wikipedia -Inches of water, wc, inch water column (inch WC), edit a non-SI unit for pressure. Edit It is used for measuring small pressure differences across an orifice, or in a pipeline or shaft. OK, its old fashioned but the gauge is big and clear and helped monitor starting pressure for reeds back when I was unsure of how good they needed to be.

 

Gentle quiet playing 1"WC = .036 psi

Mid range playing 2.5"WC = .09 psi

Loud playing guess 4.5"WC = 1.6 psi

 

I have to say I find these numbers disappointing. I had hoped for something like 15lbs psi. Sorry, I can't talk hectopascals. It is the one metric measure no-one in this country has ever managed to assimilate. Service stations still calibrate tyres in psi even though it is illegal. Anyway, after a little thought I calculated the area of reedpan, it is 24.5 sq" x 0.09 psi (medium pressure 2.5"WC) = 2.2lbs pressure from the hands to create the note and that might be about right. Coincidentally 2.2 lbs is a kilo.

 

But... this is a very easy concertina to play. The reeds are very efficient, not the best I have done but very good. I would say a Lachenal would need twice the effort to play at the same medium volume and would never reach the same top volume.

 

Any thoughts welcome...

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Gee, my immediate thought is the same as yours - I would have expected far higher pressures. I had quipped about needing a much taller manometer, but maybe that approach is worth a try if you have a bit more clear tubing at hand. Simply bend it into a U, peg it to a board and pour some water into it. Clamp an inch rule so that it starts at the water level. When you press or suck, the water level should rise up the rule. Note the peak level. Since we are interested in the difference between the two menisci, double the reading. That should give you the pressure in "inches of water". The calculator on your computer will allow you to convert it to any other unit, as long as you have the Unit Conversion option enabled (under View on my PC).

 

Caution - suck carefully. You probably don't need a concertina full of water!

 

Terry

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@Chris: Thanks for doing this - useful information.

 

A Concertina-shaped midi controller (a CSMC) that uses bellows and pressure sensors can choose, within reason, how much pressure to allow in the bellows. Assuming that the bellows are airtight and that the ends can be fastened without leakage then there are no pads or reeds to leak. In this case you need an escape vent to let air in when pulling and out when pushing.

 

But how big should this vent be? The short answer, for me anyway, is that it should be user configurable. Right now using a strip of electrical tape over a slit cut in a plywood dummy end, but maybe something better can be done further down the road.

 

I am wondering if it is it desirable to be as airtight as possible? If it is almost airtight then you can still pull/push with some effort but maybe it would possible to achieve finer control over volume if the leakage allowed the bellows to expand/contract with less than Herculean effort. OTOH air tight bellows let you play for a long time in one direction.

 

I don't want to hijack this thread into another midi constructors discussion - we have an existing thread for that - I was just wondering if there is a real trade off between a really, really tight concertina and manageable volume dynamics.

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Don,

 

I am still thinking about the implications of the test. The hardest thing to do when there are, as so often with concertina tests, so many variables, is to decide exactly what you have tested. I have tested this concertina with this vacuum gauge and am not yet ready to consider the results generally true. My attempt to check the result with calculations as to the square area of the concertina etc; I was hoping someone with better maths skills might chime in and validate the results or not. I might assemble the test rig again and try the end of the tube in my mouth. Not very scientific but the only other gauge I have and it might give me a physical sense of the pressure and whether those very low figures could be right. I might also for a brief moment own the only ever mouth blown concertina.

 

 

A couple of thoughts about your question...

The tighter the concertina the more attack you can get.

The less efficient the reeds are the more a leaky concertina is a problem.

 

Experience with my own midi concertina ( a converted acoustic so therefore has pads) which has a leak at the moment is that anything less than fully sealed is a pain. It does have air restrictors on the pad holes, this is why I haven't fixed the leak, not so easy to find. If the instrument is to be a reasonable playing experience facsimile for an acoustic concertina it needs to feel like there is reed resistance.

Edited by Chris Ghent
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Gee, my immediate thought is the same as yours - I would have expected far higher pressures. I had quipped about needing a much taller manometer, but maybe that approach is worth a try if you have a bit more clear tubing at hand. Simply bend it into a U, peg it to a board and pour some water into it. Clamp an inch rule so that it starts at the water level. When you press or suck, the water level should rise up the rule. Note the peak level. Since we are interested in the difference between the two menisci, double the reading. That should give you the pressure in "inches of water". The calculator on your computer will allow you to convert it to any other unit, as long as you have the Unit Conversion option enabled (under View on my PC).

 

Caution - suck carefully. You probably don't need a concertina full of water!

 

Terry

I may do this, I would need to buy tubing. Something I did not mention, when I compressed the bellows with no buttons pressed it was extremely easy to hit the end stop on the gauge, eelatively instant. I would be very surprised if the bellows could not generate a lot of pressure, it is a matter of record a concertina was used to blow up a raft in the only unsolved escape from Alcatraz.

 

The test was probably of the playing pressure needed for the reeds in this concertina.

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Right. Did the same thing as you, Chris, bolted a piece of craftwood across one side of the bellows of the Simpson anglo. Dusted off my trusty manometer. Amazingly it's had the same water in it for years and the level hasn't changed. This is highly calibrated water! Plugged the manometer into a hole through the craftwood.

 

Here's the results:

 

Squeezing or pulling just enough to sound the reed as quietly as possible - 10mm of water pressure

Playing (left hand only) - 30 to 40 mm of water pressure

Playing really loud (but still single notes) - 140mm water pressure

Not playing, but pushing or pulling pretty hard - 200mm of water pressure

 

(That's close to the limit of my manometer.)

 

Obviously we can convert those figures into any other system we need.

 

Happy to run any other tests now that I have the setup.

 

Terry

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Hard to compare the tests but I feel those numbers are not inconsistent with mine. ie. Your playing really hard 140mm, I estimated 4.5 inches (112mm) for my playing hard. It is still in the same ball park. I didn't try to play as gently as possible. Your left hand only, I could easily play at 1.5"WC. So the small numbers I came up with are not invalid because of their size.

 

I am still thinking it may be a test of the playing pressure of the reeds...

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I agree, our results are quite similar, especially given that we are dealing in vaguaries such as "really loud".

 

And yes, measurements taken with a note playing nicely should be an indicator of what pressure that reed likes. If one wanted to do some experiments in reed design, that approach might help bring some objectivity to it.

 

Would be interesting to have a digital manometer monitoring the pressure and recording to the computer as you play.

 

Terry

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I'm not sure my interests are so wide..! My Magnahelic (I have two, 3" and .5") setup was an early attempt to create a measure for starting pressure. What I found was once I saw the reeds starting at very low pressures (.1" for low reeds) and understood the parameters which made that possible I stopped referring to the gauges on a reed by reed basis.

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  • 2 weeks later...

OK, some new data. Discussion of how to build a cheap Magnahelic gauge has just come up on the musical instrument technician email list. That prompted me to test the actual operating pressure of the Magnahelic system. I was surprised when it came in as about 240mm of pressure. That's a higher pressure than I got when measuring the bellows pressure with no key opened and pressing pretty hard. So, the standard woodwind repairer's Magnahelic is actually in a good zone for testing concertina pad leakage.

 

Encouraged, I measured the leakage of all the pads in my Simpson Anglo. They all came in between 1 and 2 on the Magnahelic, with the typical around 1.4 (on the scale of 10). The RH air button came in at 8 (which is where it is calibrated for "open to atmosphere"). Argghhhh! Investigation showed the pad had collapsed sideways, with the leather more or less in the right place, the felt about 2mm offset and the card about 2mm further offset. I replaced it with a sax pad and a samper punched from the cuff of my welding gloves - back in business with a leakage around 2. (It's a big hole, compared to the note holes.)

 

Measuring leakage with the Magnahelic is very quick - you can do all the holes in an Anglo pan in less than a minute. And I find it nice to be able to put a figure on the leakage, not simply know there's a bit. But, as I said earlier, I'm a fetishist.

 

Terry

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