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Dave Leggett

A Strange Hybrid Instrument

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Some years ago, I constructed a rather unusual instrument combining some features familiar to concertina players, but using small organ pipes rather than free-reeds as sound generators. I suppose you could call this a portative organ. It suffers from the limitations of such, in that one hand must be occupied in pumping bellows, allowing one hand only to pick out the melody and/or chords on the keyboard.

Possibly, a unique feature of this instrument is that the 'bellows' is an air-pump, devised on the same principle as a Japanese smith's type bellows, that using flap-valves, produces a useful draught of air in both travel directions of the piston.

The 24 pipes are all of the stopped sort; made from copper and brass tubing (4.5 - 21mm i.d. approx.). The stoppers (tompions) are turned from hardwood to just slide snugly into the pipes using melted beeswax to seal them and fix them in place once tuned. A ratio of about 8:1 stopped pipe length/width seems to give the optimum sound quality, though ratios somewhat higher or lower were found acceptable. This enables a compass of about 2 octaves up from the 'D' above 'middle C'. This pipe has a stopped-length of about 260mm (10")  (- a stopped pipe sounds an octave below an open one of the same length).

The keys are like concertina buttons and arranged in a pattern based on that of the McCann duet concertina. The action inside is made exactly like that of a concertina too, with brass rivetted levers and circular pallets covering the pipe ports. The big difference is that the 'tray' carrying the action has got to be airtight!

The pump-bellows cylinder is made from standard builder's 6" PVC drainage pipe.

I hope that the attached photos do all the explaining you might need! I used  the McCann layout because I could limp-along in that system at one time (I can't now!).

The system needs more development work, especially wrt bellows efficiency and air-leaks, in order to make playing easier.

Devise a treadle bellows or mechanical blower and control more pipes with both hands and it's an instrument with different potential. Now I'm being silly.

Its sitting on my shelf waiting for some enthusiastic caller to take -up the challenge!

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Perhaps you could incorporate a bellows from a set of Irish pipes? I'd love to see this creature in action...

 

 

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I love this instrument.

 

Many years ago, before I took up the concertina, I endeavored to build a small pipe organ, and in the process made about 20-30 pipes.  Eventually, the project was abandoned, but not because of it's doability.  Now the smaller pipes have been made into Christmas ornaments and the larger ones may someday become bases for lamps.

 

But with this said, I have often wondered if this was possible, but usually push it out of mind as a  silly "pipe-dream".

 

I would really like to hear this play, if possible.

 

Great innovation.  congratulations!!

 

Edited by Noel Ways

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I agree with Saguar-squeezer.  You are onto something. I don't think this portative organ project should be given up but rather developed. 

Edited by Noel Ways
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Very interesting.  How do you seal from air leakage around the keys?

It seems this is an instrument that will sound only on the push of the bellows.  Does that restrict any of the music that you play with it?

I'd love to hear a sound file.  Thanks.

 

Regards,

Tom

www.bluesbox.biz

Edited by ttonon

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Very interesting.  How do you seal from air leakage around the keys?

It seems this is an instrument that will sound only on the push of the bellows.  Does that restrict any of the music that you play with it?

I'd love to hear a sound file.  Thanks.

 

Regards,

Tom

www.bluesbox.biz

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Hello Folks and thanks for your interest and enthusiasm!

The very essence of this piston-bellows, Tom, is that it delivers air to the pipes in both travels of the piston. Find a video of a traditional Japanese swordsmith at work, if you want to know where the idea came from: I expect there are a few of these on you-tube!

The gap around the buttons is only sealed by a gasket of shammy-leather pierced with close-fitting button-sized holes - it does need improvement!

Regarding 'sound files', I'm sorry but I wouldn't know where to start and anyhow, I lost the facility to finger a McCann keyboard years ago!

This is the third or fourth prototype of this kind of instrument that I've made and it really does need another person to develop to full potential. I've retired as an amateur instrument maker and would willingly pass this project to someone else freely, but this individual would need to call on me sometime in person to discuss over a glass of wine or a coffee!

Best wishes,    Dave

 

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Inasmuch as you can use only one hand to play the notes, with the other pulling and pushing the piston, and the note is the same in both directions, the layout really has to be like one end of a duet system. The alternative is two ends and bagpipe bellows as suggested by Halifax.

 

I can't see how to avoid the need to seal around the buttons. Whereas a conventional concertina has the reeds and pads between the bellows and the end that is open to the atmosphere, with this instrument the pipes pretty well have to be open to the atmosphere, so the other side of the pads, connected to the cylinder via the flap-valves, does need to be sealed. That would still be the same with the double-ended bagpipe bellows version.

 

How is it achieved with a conventional pipe organ (large as in a church or portative)?

Edited by Richard Mellish
Re-thinking the air flow system. OK, I think I've grasped it now. Both ends of cylinder sealed. One one stroke air flows from one end directly to the action chamber, on the other stroke it flows from other end via the pipe.

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Thanks for comments, Halifax and Richard.

I think that an ordinary pipe, rather than a reeded one (as in bagpipes of various kinds) needs far more air than a small underarm bellows could provide. Also using two hands and  armpit power might make you feel a little like a one-man-band?

You seem now to have grasped the principle of the double-acting bellows. Yes, valves and a L-R air duct transfer air from the LHS of the cylinder to the 'wind chest' & pallets when the piston is pulled to the left.

I guess that on a full-sized organ, where large bellows probably supply twice as much air as the pipes could ever use, that a relatively small spillage of air from the 'action' in the wind-chest is a mere drop in the ocean.

Yes, the sealing round the buttons to prevent serious air spillage is a problem that has to be admitted, but I can think of one or more ways round it. It  is thinking round such problems that make the project interesting is it not?

Best wishes,    Dave

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Talking about reeded pipes, I think there's probably some mileage in exploring the Chinese SHENG in this context.  A very ancient invention, examples of this free-reeded 'piped mouthorgan' instrument when first brought to Europe in the 17/18th century apparently inspired the first harmonica, concertina and accordion inventions!

SHENG reeds somehow manage to sound either on the 'suck' or the 'blow' - clever stuff - but I've never been close enough to one in order to see how. Obviously there's major untapped potential here!

Information on 'the net' is rather sparse, but there's quite an informative 'you tube' video with a Chinese chap discussing the anatomy etc of the instrument. The entry is under the 'Philharmonia Orchestra' title. It's definitely time for some enterprising and enquiring person to take up this baton (that person can't be me)!

Happy Inventing!        Dave

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There is a paper on free reed acoustics here https://doi.org/10.1063/1.3563819  with both cutaway drawings and photos of eastern style free reeds.  

 

Interestingly eastern style free reeds seem to always be attached to a resonator.  Very noteworthy for this instrument, the resonant frequency was higher than suggested by the reed or the resonator alone.

 

I do believe in that video he said that it sounds better one direction than the other.  Before I found that, I was contemplating buying some cheap accordion reeds to see if I could modify them to be bidirectional and see what they would sound like.  Though I still wonder if the preference for direction is based solely on the resonator, and if you could get a good sound without one...

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Reeds are directional because the reed tongue needs to be raised into the airstream slightly when at rest in order to create a starting sequence. I have wondered recently whether a reed shaped like a gentle sine wave, and thus having part below the tightest part of the slot and also part above, might be induced to start both ways. There would be an efficiency penalty and a slightly different tone and the geometry of the reed slot might need adjustment.

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Hello 'fatman' and Chris,

The reference to the free reed acoustics paper (and the references that come with that) are informative on far-eastern free-reed instruments, but still lack detailed reed constructional information.

That they do 'sound both ways' is beyond dispute, the development work all having been done a few thousand years back! They do seem to have rather large gaps between the reed and frame, which perhaps comes about from both being cut integral from the same blank of material. This may contribute to the explanation of why they work?

Rich soil for someone of an enquiring mind to till (to paraphrase Tom!).

Happy researches.

Dave

 

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The subject of a bidirectional reed has come up here a couple of times recently with a "consensus" that it's either not doable or not worth doing.  However, there have apparently been attempts and at least one patent issued.  I think it's a worthwhile pursuit.  One approach that sticks in my head is to bevel the inside edges of the reed shoe affording free air access in either direction.  Perhaps it's been tried.  I'd be interested in any attempts.

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Some time ago I set a reed down into the frame by .75mm so I could create a rounded compression point on the frame rather than using the sharp top edge. The tongue was rounded on the edge also. The intention was to remove the higher partials I theorised were produced by the sharp edges. It worked, the higher partials  were noticeably absent on the bench. In the concertina there was no appreciable difference and I surmised the structure of the concertina was filtering them out to roughly the same degree. More recently I have read of “bombate” accordion reeds which have rounded tongues for the same reason. 

 

The mirrored frame shape above and below the reed did not suggest it might start in either direction, mind you I never tried. The reed is around somewhere, I’ll set the tongue to a neutral position next time it surfaces and see if the shape lets it start both ways. Not holding my breath.

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Hi Chris,

I believe the method you chose to suppress high frequencies from the sound spectrum has theoretical backing.  As the tongue moves through its swing cycle, the pressure and aerodynamic forces on the tongue change very abruptly in both magnitude and character.  This is because the slot provides a very different environment from the free space above the slot.  In cases where the tongue passes completely through the slot, we have an additional region of free space, which is also significant.  The velocity of the tongue is zero at the extremes of motion, and it is maximum just about where it downwardly enters that slot.  Such a rapid change in forces is in mathematical terms a step function, and the representation of a step function by a Fourier series contains many higher harmonics.  So if you reduce the "suddenness" of the step function, you reduce the contribution by higher harmonics.

 

I thus believe that your approach would result in less higher harmonics.  However, I think there's a price to pay.  You see, the key feature that allows the tongue to vibrate is the "water hammer" effect that occurs by virtue of the sudden stoppage of air flow down through the slot at the moment the tongue first enters the slot.  The air "piles up" on the tongue as the air velocity rapidly drops from a high value down to the velocity of the tongue.  Without the tongue in the slot, the air velocity through the slot is several times greater than the maximum tongue velocity.  But importantly, if it wasn't for that sudden build up of (dynamic) pressure on the top surface of the tongue, in which the kinetic energy of the airflow is converted to potential (pressure) energy, the tongue could not vibrate.  So when you reduce the suddenness by which pressure forces act on the tongue, you also lessen the water hammer effect.  My guess is that such a tongue will not sound with as much volume, or energy, as with the conventional set up.  

 

In addition, I don't think your novel design will allow the tongue to vibrate with both directions of air flow.  To understand that, we need to understand how the conventional tongue starts its motion.  I explained this in a previous post, but I'll summarize it here.  Picture the quiescent tongue situated just above the slot.  With the slightest bellows pressure, air flows around the tongue and becomes turbulent under the tongue.  Characteristic of such conditions, this turbulence consists of vortices that are shed in a periodic fashion.  It's a well studied fluid mechanics problem under the heading of "bluff bodies in an air flow," and the phenomenon is sometimes described as von Karman vortex streets, and more specifically, "vortex induced vibration of a cantilever."  These vortices, much like miniature tornadoes, have reduced pressure at their interior, and the fact that they form periodically and pass on means that the tongue experiences a slight, oscillating pressure difference.  This causes the tongue to vibrate at its natural frequency, and when that vibration amplitude equals the tongue offset, the tongue blocks the slot and the total bellows pressure immediately acts on the tongue.  This is an enormous increase of pressure forcing the tongue further into the slot.  There's too much detail to explain how the steady-state vibration builds from there, and I won't try it here, but this is all we need to know in order to answer whether your tongue can be bi-directional.  

 

I think not, and the bottom line is, if the tongue can vibrate in one direction of airflow, it can't in the other.  Here's why.  If the tongue is starting in one direction, it lies at a position sufficiently removed from the slot for the changes in pressure caused by vortices to be larger than any contribution due to the bellows pressure (bellows pressure multiplied by slot cross sectional area).  With such a situation, pressure introduced from the other side of the tongue cannot reproduce the necessary starting conditions; i.e., allowing vortices to amplify tongue vibration to the point where the tongue enters the slot.  In the latter case, there is no slot for the tongue to enter, from the direction that the starting air flow wants it to go.  

 

Incidentally, we can also now understand why a tongue can't start if it's rest position lies in the slot, because then, the total bellows pressure always acts on the tongue, and any pressure fluctuations caused by shedding vortices will be much smaller than that.  As a result, the tongue could only stay in the slot, with at most a very small quivering.  

 

I agree that all that might be a little confusing, but feel free to dig up that reed and let us know if my guess is right.  I'd love to be proven wrong.

 

Best regards,

Tom

 

 

  

 

 

 

 

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