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Thoughts On A Combined Reed/action Plate Design


RAc
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There are so many problems with this design I can think of, that I don't even know where to start...

 

First of all, such design seems valid only for linear keyboards, as you cannot freely move airholes around and you have quite space-demanding design...

 

Then, your reed chambers would be HUGE, as you must effectively make them longer by a diameter of your air hole. Otherwise your pad will obstruct inner reed valve. This raises a numerous problems with reed response times and tone balance, as you will have to increase each chamber lenght by a fixed amount, thus for smaller reeds probably doubling the chamber lenght… And you create a LOT of unwanted bouncing of sound and obstruct chamber resonance properties with this "inner pad". And resulting sound will probably change substantially with button travel, as you're moving parts inside of a resonant chamber...

 

Another problem with this design is a small effective airhole: with normal setup, you need only short pad travel, because you have a cylindrical gap between airhole and pad (in open position you need a height of quater of hole diameter to have equal flow areas). With this design you obstruct a lot of this cylinder with back and side walls of a chamber. Try to imagine a smoke traveling through reed and airhole in this setup to visualise what I'm thinking about.

 

Last problem I can think of is the wobblines of this setup - in normal concertina construction, you have two guiding constraints for a button: an endplate hole and an actionboard hole. Together they make button motion almost linear. But with your design you only have endplate guide and a wobbly spring. You will have to either add an inner pole to guide a button and pad assembly or find another way to ensure perfect closing of airhole (like conical hole closure for example) and limit angular deviation from straight button travel.

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Hmmmm!!

 

Some there are that say ... "Great minds think alike ". My grandmother used to say that ... "All madmen dance to the same tune" that used to bring us down to earth!!!

 

I had some similair thought a few years ago and what I came up with was ......

 

Buttons operating valves sitting in two layers of pots with the air flow being distibuted thru tubes to the reed chambers - see diagrams for how it might look on an Anglo.

 

It depends on how small the dimensions could go before affecting air flow.

 

My thoughts at the time were inclined towards injection moulding but today of course I would think that 3D printing is the way to go.

 

 

 

 

 

 

Jake

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Good on you, Ruediger - I'm keenly watching your progress and would be happy to confer by Skype or Google Hangouts Live if you were interested.

I especially like your 'revisionist' attitude to the concertina.

 

Basically concertinas haven't been greatly revised for about 200 years. Mostly the changes seem to be enhancing the existing design without 'rethinking it boldly'. Some hours of musing could provide the world with a cheaper, more robust, more adjustable, easier-to-open-and-repair, possibly even nicer-sounding instrument than any we've yet seen.

 

By chance, this week I replaced a button by sculpting some HDPP plastic to make a one-piece item (See attached photo) It seems better in concept than the plastic-with-metal-hook version that my Stagi 56 key tenor-treble has. I've done videos, but haven't edited and published them yet. Of course, 3D printing of them is the next step. I'm just busy with house renovation at the moment.

 

Bruce (Tomo) Thomson

20 Lyndhurst St. Chelwood Village,Palmerston North, New Zealand

06 357 7773 021 1 76 9711

palmytomo@gmail.com

Skype: palmytomo

Google+ Bruce Thomson

 

 

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I can see the last point (obstructing with the innards of a resonance chamber), thanks for pointing it out! But I don't understand your first point at all; why would the reed chambers need to be huge?

 

 

This one is more true with hybrid concertinas and accordion reeds, but applies to a proper concertina reeded instrument also - you have to place your pad assembly out of the way of swinging reed and inner reed valve. Normally you can have your air hole directly above the reed (flat mounted accordion reeds have chambers rougly the lenght of a reed shoe, concertina reeds chambers can be and often are extended for acoustic reasons). In your design you have to place the button assembly "out of the way" - you cannot place your pad and spring over the reed.

 

In my opinion, both yours and Jake's designs are valid only from a pneumatical point of view. They will both produce controlled pressure and airflow to feed the reed. But both of you seem to forget, that it is the musical instrument that you're working on. Every bounce of sound matters, every cubic inch of confined space that vibrating air has to travel inside a concertina will alter the sound. Make a simple experiment: build a variable volume reed chamber (a moveable one side, like a piston), apply airflow through a reed mounted to it and listen to the sound while moving a piston. And measure response time of the reed depending on volume (cubic space not loudness :D). Then put a tube (either straight or bent like in Jakes design) on the airhole and listen how sound produced by such setup changes drastically - depending on materials used the sound would be more or less muffled and altered in timbre. In Jake's design the amount of distance that the air has to travel inside a tube will decrease the loudness significantly, and the reeds will be very slow to speak because the sheer amount of air trapped between stationary reed and button, that needs to be moved/compressed before the reed starts to speak…

 

 

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I do think, however, that your implication "seem to forget..." is a little bit unfair.

 

 

Don't get me wrong, I was not intending to insult you or Jake in any way. In fact, I had some similiar thoughts about "pneumatically improving" concertina design when I first started designing my DIY Hayden. That was until I made this very experiment I have described earlier and realised, that sound produced by the reed is a very fragile thing and everything affects it, usually in the least desirable way. There are numerous long threads here on concertina.net about such minute changes to instrumenst as beveling airholes on chambers that are placed not on the edge of the reedpan or have additional 5mm of action board "in the way"of the sound. My "seem to forget" coment was only meant to point out, that concertina design should be s"ound-centric" and not "pneumatic-centric" and that many (otherwise great or intiguing) engeneering ideas simply do not apply to concertinas.

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the amount of distance that the air has to travel inside a tube will decrease the loudness significantly,

 

When the switch is turned on in an electrical circuit the light bulb does not have to wait for electrons to travel from the switch to the bulb for the light to come on -- fortunately, because electron drift velocity is very slow in comparison to the speed of the electric field change (which is at the speed of EM waves within the wire). Rather, electrons that are already in the filament are directly affected by the electric field gradient (voltage), and heat generated by the resistance to their movement causes the filament to glow.

 

In the same way, the response of of a reed to a pressure gradient does not depend on air physically moving through the whole pathway, which is quite slow in comparison to the speed of the pressure changes. Air molecules already at the reed site are those responsible for affecting the reed when the pressure field changes.

 

Of course you are right that changes in some aspect of the design of a musical instrument can have substantial effects on the instrument's performance. But that doesn't mean that an experienced or inventive instrument maker can't make other changes to compensate.

Edited by rlgph
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I do think, however, that your implication "seem to forget..." is a little bit unfair.

My "seem to forget" coment was only meant to point out, that concertina design should be s"ound-centric" and not "pneumatic-centric"....

 

In similar situations in discussions I try to say "neglected to mention", rather than "seem to forget". Much of the time I suspect that when someone neglects to mention a factor that I think is relevant, it's not because they aren't aware of the factor, but because it's worth bringing to the attention of less experienced readers of this very public forum.

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When the switch is turned on in an electrical circuit the light bulb does not have to wait for electrons to travel from the switch to the bulb for the light to come on -- fortunately, because electron drift velocity is very slow in comparison to the speed of the electric field change (which is at the speed of EM waves within the wire). Rather, electrons that are already in the filament are directly affected by the electric field gradient (voltage), and heat generated by the resistance to their movement causes the filament to glow.

Not entirely true. While the filament doesn't have to wait for individual electrons to travel to it from the switch, the change in the electric field gradient isn't instantaneous. It may seem so to us, but it can't be faster than the speed of "light" (electromagnetic waves) in the wire.

 

In the same way, the response of of a reed to a pressure gradient does not depend on air physically moving through the whole pathway, which is quite slow in comparison to the speed of the pressure changes. Air molecules already at the reed site are those responsible for affecting the reed when the pressure field changes.

But as with the electromagnetic wave above, the pressure change is transmitted at a finite speed... the speed of sound. This happens through collisions between molecules, even though for individual molecules to travel the full distance takes a much greater time, if it happens at all.

 

Of course you are right that changes in some aspect of the design of a musical instrument can have substantial effects on the instrument's performance. But that doesn't mean that an experienced or inventive instrument maker can't make other changes to compensate.

Nor is there any guarantee that they can... or even that if such a solution does exist, it's easy to find or construct.

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When the switch is turned on in an electrical circuit the light bulb does not have to wait for electrons to travel from the switch to the bulb for the light to come on -- fortunately, because electron drift velocity is very slow in comparison to the speed of the electric field change (which is at the speed of EM waves within the wire). Rather, electrons that are already in the filament are directly affected by the electric field gradient (voltage), and heat generated by the resistance to their movement causes the filament to glow.

 

Not entirely true. While the filament doesn't have to wait for individual electrons to travel to it from the switch, the change in the electric field gradient isn't instantaneous. It may seem so to us, but it can't be faster than the speed of "light" (electromagnetic waves) in the wire.

If you re-read my comment, you will see that i did not say that the change in the field was instantaneous. In fact, i said that it occurs at the speed of EM waves in the wire. So i believe my statement is true as i made it, and that similarly my statement about the time required for pressure changes is also true.

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When the switch is turned on in an electrical circuit the light bulb does not have to wait for electrons to travel from the switch to the bulb for the light to come on -- fortunately, because electron drift velocity is very slow in comparison to the speed of the electric field change (which is at the speed of EM waves within the wire). Rather, electrons that are already in the filament are directly affected by the electric field gradient (voltage), and heat generated by the resistance to their movement causes the filament to glow.

Not entirely true. While the filament doesn't have to wait for individual electrons to travel to it from the switch, the change in the electric field gradient isn't instantaneous. It may seem so to us, but it can't be faster than the speed of "light" (electromagnetic waves) in the wire.

 

In the same way, the response of of a reed to a pressure gradient does not depend on air physically moving through the whole pathway, which is quite slow in comparison to the speed of the pressure changes. Air molecules already at the reed site are those responsible for affecting the reed when the pressure field changes.

But as with the electromagnetic wave above, the pressure change is transmitted at a finite speed... the speed of sound. This happens through collisions between molecules, even though for individual molecules to travel the full distance takes a much greater time, if it happens at all.

 

Of course you are right that changes in some aspect of the design of a musical instrument can have substantial effects on the instrument's performance. But that doesn't mean that an experienced or inventive instrument maker can't make other changes to compensate.

Nor is there any guarantee that they can... or even that if such a solution does exist, it's easy to find or construct.

 

 

Jim is right, but this is even more complicated than that, because...

 

…before there is sound produced by the reed, which then travels at a speed of sound, because it is pressure gradient change, there is need for air movement at "wind speeds". When you press your bellows with air button pressed, you aren't struck by a sonic boom, just a mild wind blow. This is this "wind speed air movement" which starts reed oscilation by a transfer of momentum between air molecules and reed tongue and suction effect of the gap and then feeds reed resonance for a stable oscilation and nice concertina sound.

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Jim is right, but this is even more complicated than that, because...

 

before there is sound produced by the reed, which then travels at a speed of sound, because it is pressure gradient change, there is need for air movement at "wind speeds". When you press your bellows with air button pressed, you aren't struck by a sonic boom, just a mild wind blow. This is this "wind speed air movement" which starts reed oscilation by a transfer of momentum between air molecules and reed tongue and suction effect of the gap and then feeds reed resonance for a stable oscilation and nice concertina sound.

No. Changes in pressure fields occur at a much faster rate than wind speed. In fact, they occur at the speed of sound because sound is a (typically audible) manifestation of pressure changes. (Though sounds can have frequencies above and below audible range.) Edited by rlgph
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But the reed tongue is not propelled by a sound wave! It is the source of a sound wave, but is set in motion by an airflow at wind speeds! And this sound wave of course is propagating with the speed of sound in the air, and is moving in every direction, including against the airflow and into the bellows… This is completely different than pressure gradient between inside and outside of the bellows, resulting in wind blowing through the reed, air molecules interacting with tongue via airflow etc... You are mixing two different physical terms here. Even when oscilating at full amplitude and making sound, reed tongue movement has nothing to do with sound propagation speed… You can hear sounds as low as 10 hz - that is 10 beats per second, that is about 20 cm of reed tongue tip travel per second, not even close to 340meters per second!

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But the reed tongue is not propelled by a sound wave! It is the source of a sound wave, but is set in motion by an airflow at wind speeds! And this sound wave of course is propagating with the speed of sound in the air, and is moving in every direction, including against the airflow and into the bellows… This is completely different than pressure gradient between inside and outside of the bellows, resulting in wind blowing through the reed, air molecules interacting with tongue via airflow etc... You are mixing two different physical terms here. Even when oscilating at full amplitude and making sound, reed tongue movement has nothing to do with sound propagation speed… You can hear sounds as low as 10 hz - that is 10 beats per second, that is about 20 cm of reed tongue tip travel per second, not even close to 340meters per second!

I did not say that the reed is propelled by a sound wave! This whole discussion was generated by someone's implication that if pressure changed at one end of a tube, air had to flow through the tube before it affected whatever is at the other end of the tube. I simply said that what needed to propogate was a pressure field, and that travels at speeds much faster than air flow does.

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