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Author Topic: Bellows x-section area  (Read 919 times)

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MatlockBather

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Re: Bellows x-section area
« Reply #20 on: March 06, 2017, 12:34:48 PM »

I think it depends more on the cubic capacity than from the area, however, highly dependent on the quality of reeds.

Not in simple hydraulics theory it doesn't. 


Which is true for an incompressible fluid...which air isn't. For air there is a non linear relationship between volume change and air pressure change but that too relies on the container being rigid. We are pressurising air in a leaky, floppy cardboard box so I think it all gets rather complex to actually apply engineering physics to these things. The simplest way to maybe test the volume theory thou' would be to play with bellows expanded as far as you comfortably can and then with them as closed as you can. Does it make a difference to the way the reeds speak and the way you need to play the box?
I wonder if the cross section area correlation has come about because you tend to play all boxes with the bellows extended the same amount (as this is driven by your physiology) and in so doing a bigger CSA will contain a bigger volume of air and a smaller CSA will have less volume? That would suggest you could tailor the feel of the box by altering the width that you played it.

Si

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Garry Probert

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Re: Bellows x-section area
« Reply #21 on: March 06, 2017, 12:43:21 PM »

Hi guys/gals I have no expertise in air pressure,in relation to size and volume
my liliput requires a different style of playing (wider movement)although is effectively a scaled down version of my club II
Is this because of the smaller bellows area ,in relation the the ambient air pressure
somewhere in my old fuddled brain this air
and miniaturisation thing rings a bell,can't for the life of me remember what it was ................. 
 
 
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Andrius

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Re: Bellows x-section area
« Reply #22 on: March 06, 2017, 05:06:15 PM »

I think it depends more on the cubic capacity than from the area, however, highly dependent on the quality of reeds.

Not in simple hydraulics theory it doesn't. 

Better reeds it means smaller distance between reed and frame, so less pressure to get sound.
It's really very important.
Only one way to test something is to use the same reed blocks with different size bellows
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Chris Ryall

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Re: Bellows x-section area
« Reply #23 on: March 06, 2017, 05:54:53 PM »

Agree, ditto MatlockBather's compressibility stuff (which I'd called the 'dynamics'). In theory it's temperature might even change too, but let's not get to adiabatic about things! All of which affects magnify 'per Newton of force' when the x-section area  gets less ::) so in my view circular logic.

The issues 'at reed level' are the pressure gradient, and to some affect the rate that that pressure changes.  Arguably the density of the air might have effects too, but we've discussed such things in some depth here in the past, and consensus was that the reed wasn't too bothered about that.

That's to argue that a reed "doesn't know" what volume its bellows are?  ::)
« Last Edit: March 06, 2017, 06:06:06 PM by Chris Ryall »
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Bob Ellis

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Re: Bellows x-section area
« Reply #24 on: March 07, 2017, 09:46:31 AM »

I've sent a PM too  ;)

Thanks to Steve for his PM, but I don't seem to have received yours, Chris.
« Last Edit: March 07, 2017, 02:01:57 PM by Bob Ellis »
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Chris Ryall

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Re: Bellows x-section area
« Reply #25 on: March 07, 2017, 10:00:49 AM »

.
    ;)
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Dazbo

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Re: Bellows x-section area
« Reply #26 on: March 07, 2017, 01:19:40 PM »

I think I agree with Squeezy that bellows area can give a good indication of how you, as an individual, find the playability of a box.  It might not be down to air pressures, hydraulic theory (simple or otherwise) and reed settings.

The larger the CSA of the bellows it follows the bass end will be bigger and heavier just to cope with the larger bellows size.  The larger the bass end the more gubbins manufacturers tend to put in it.  If you play with lots of cross rowing this isn't too much of a problem but if you want lots of bellows waggling and thumpy music the heavier bass has a lot more inertia to overcome.  So you use more energy for the same effect.  With the larger CSA then the treble end buttons are further apart adding larger stretches and less comfort.

Going the other way then having a smaller CSA you can run into air problems for the way you play, fingers too close together, less stability from the lighter weight of the smaller box etc.

So, I can understand why if you have a box that fits you and your needs like a glove it will be quite likely that other boxes with a similar CSA will fit you quite well too.

What would be interesting is to compare your boxes to different playing styles.  If you play with lots of cross rowing on one box and thumpy box waggling on another do you find they have signigicantly different CSAs?

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Ciao Bellow

Darren

Bob Ellis

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Re: Bellows x-section area
« Reply #27 on: March 07, 2017, 02:06:52 PM »

The point about the weight of the bass end is a valid one. I certainly notice the difference between the light 2-voice-8-bass bass end of my Gabbanelli Compact and the heavier 3-voice-12-bass bass end of my Clement Guais.
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Dazbo

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Re: Bellows x-section area
« Reply #28 on: March 07, 2017, 02:33:59 PM »

That's very interesting, thanks!

This suggests that it might be possible to tweak the feel and responsiveness of an existing box by changing the number of bellows folds or bellows fold depth.

Sadly but no. It depends on the reeds and reed valves quality only. Another important factor - corresponding acoustic camera size in reed blocks.

Bellows size can not change feel and responsiveness, only can prevent "out of air" problem.
No "out of air" problem with both accordions, but Hohner with 16 folds is more responsive like Petersburg accordion with 23 folds.

Sounds like you've never played a box with very stiff bellows then ;) I had a Dino BP II and the bellows were so stiff it was like using a bullworker rather than a musical instrument and they never loosened whilst I had it.   There must be a stage where new bellows have lost there stiffness and move easily and being worn out and leaky and that's where you want your bellows to be.  The bellows CSA and number of folds must be a factor in this - the larger the CSA and the more foldes the more work is needed to overcome the stiffness
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Ciao Bellow

Darren

Psuggmog Volbenz

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Re: Bellows x-section area
« Reply #29 on: March 08, 2017, 08:20:53 AM »

No one has yet mentioned mass or inertia. A larger bellows with more mass would be more resitive to change of motion than a smaller, less massive one; assuming that all other variables were equal. It might be informative to modify a bellows frame or end board with a port to which one could attach a manometer and quantify internal pressure variations.
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911377brian

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Re: Bellows x-section area
« Reply #30 on: March 08, 2017, 10:55:45 AM »

So true Psuggmog, my Herfeld 6 stopper has wrist straps on both ends, in fact it has two on the bass side, that should tell you something. Bellows dimensions are 14.1/2" x 9" with 12 folds. Not that difficult to play and not a lot of bellows movement required but not a box to play at speed..
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