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Why Have "sound-posts" In Concertinas?


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#1 chris vonderborch

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Posted 03 November 2003 - 04:05 PM

I have often wondered...are the two (usually) small dowells that connect the concertina face-plate to the action-board really necessary? I have not included them in my home-built instruments...both English and Anglo. Yet I often wonder!!! The venerable makers of old never did something for nothing.

So my question is: Are the posts simply there to strengthen the face-plate?? Or could they have an acoustic action. By this, I do not imply that they act like the sound-post of a violin. However, could they be there to somehow acoustically connect the action board (that plate with the air-holes) with the face-plate? Maybe they are designed to give some support to the action-board and the more central portions of the underlying reed-pan itself, which are well-supported around their edges.

#2 dbowers

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Posted 03 November 2003 - 09:00 PM

I believe they're only present on metal-ended instruments. My wooden Lachenal doesn't have them; the metal-ended one does.

#3 David Barnert

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Posted 04 November 2003 - 02:22 AM

I always assumed it was to keep the face plate from becoming deformed (caving in) if the screw that runs through the dowel (and holds the action board to the face plate) is too tight. It provides a clear endpoint when to stop tightening the screw.

#4 JimLucas

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Posted 04 November 2003 - 03:27 AM

I have often wondered...are the two (usually) small dowells that connect the concertina face-plate to the action-board really necessary?

I believe they're only present on metal-ended instruments. My wooden Lachenal doesn't have them; the metal-ended one does.

I've never seen a concertina with metal or wooden ends that didn't at least have marks indicating that it originally had posts. It's my understanding that they all *should* have them, though I suppose some of the earliest ones might not, i.e., that they were added at some point in the evolution of the instrument.

I always assumed it was to keep the face plate from becoming deformed (caving in) if the screw that runs through the dowel (and holds the action board to the face plate) is too tight.

To provide support against caving in, yes, but not only from tightening the screws. I've seen ends caved in from external pressure. And at least one with the opposite problem, where the original long screw holding a thumbstrap was replaced by one that didn't extend down to the finger board, and the tension from pulling the bellows tore the end apart.

Or could they have an acoustic action.

Unlikely, since they'r often capped by gaskets of carboard or some similar material, which should interfere with any acoustic coupling.

#5 wes williams

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Posted 05 November 2003 - 08:23 AM

Its probably worth reading Bob Gaskin's experiments on baffles at www.maccann-duet.com - he found that the 'sound posts' did seem to have some effect.

best wishes ..wes

#6 goran rahm

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Posted 05 November 2003 - 10:30 AM

With Englishes there use to be two or three posts. With Anglos and Duets I have occasionally found one but never given it much thought.
Anyway:
If two, one at the thumbstrap and one at the fingerplate, basically present to admit
fixation of the thumbstrap and fingerplate without load on the endplate.
If a third is present in the upper part of the keyboard region it probably firstly is to
stabilize the endplate mechanically...to protect it from deformation. I haven't bothered about history of it but on Whatstones I believe present on most instruments I have seen from 1860s up to 1890s or so, maybe some later too.

They certainly may do good ( as protection)particularly on flat ended instruments.

For acoustics...? I would say yes regarding particularly flat metal ends ('dead' flat, not with bent down edges) since those may suffer from distorsion and noise due to vibrations of the metal ends. This can also be cured however by creating a certain domelike tension of the enplate by having the just two present posts a little higher than the exact natural distance between end and action board.

NO further acoustic advantage expected...

Goran Rahm

#7 d.elliott

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Posted 05 November 2003 - 06:27 PM

the 'sound posts' are actually spacers, often with card packers to set the distance between the action box cover and the pad board/ action plate assembly. Their purpose, in conjunction with the special long screws, (particularly on English system machines) is to the transmit the bellows operation and support loads from the thumb straps and finger slides through the delicate fretted cover into the guts of the instrument, without applying undue forces into the action box cover.

As Jim said, they all have at least two such spacers or pillars. Their other purpose is simply to hold the cover a set distance from the action board so that it does not collapse inwards.

I would judge that any accoustic value would be less than minimal

Dave

#8 duckln

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Posted 05 November 2003 - 07:38 PM

I would judge that any accoustic
value would be less than minimal

Dave

The center 'holes' in the reed pans are, IMO, maximized. This may be
so that the sound from the sound boards, trapped in the bellows can emit through the holes
through the both fretted ends. This is somewhat like a megaphone, and with
with top of the line domed ends, the sound is enhanced and dispersed.
The spacers needed for end center support also act as to make the ends
more rigid to allow the sound board to vibrate against it. So I don't
think that posts transmit sound out, but act to keep the sound in.

The posts in my Aeola or Edeo, as I remember
are not cushioned. In my Lachenal, the ends are, but I think they are
primarily spacer cushions to provide ability to 'true' up or flatten
the ends. Any convexing could cause a key to stick, like my low Bb did.

Be kind
Joe

#9 duckln

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Posted 05 November 2003 - 08:08 PM

Woops! I'll have to do a major rewrite or stand down on my last post.
The role the action board plays is not covered in my postulate.

Joe

#10 goran rahm

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Posted 06 November 2003 - 10:51 AM

duckIn (Joe?):
The center 'holes' in the reed pans are, IMO, maximized. This may be
so that the sound from the sound boards, trapped in the bellows can emit through the holes
through the both fretted ends. This is somewhat like a megaphone, and with
with top of the line domed ends, the sound is enhanced and dispersed.

Goran:Sorry but this is something you got completely from imagination....
The centre holes in the reed pans are used for centering the piece when cuttting
the radial reed slots with a rotary cutter and they additionally make it easier
to remove the reed pan out of the frame....

Joe:"The spacers needed for end center support also act as to make the ends
more rigid to allow the sound board to vibrate against it. So I don't
think that posts transmit sound out, but act to keep the sound in.

Goran:Nope... There is NO "soundboard" in a concertina and not in squeezeboxes in general ..despite this 'board' actually is called so quite often...
The 'board' vibrates from sound but as far as known has no resonance qualities and whether there are any acoustical effects from its vibrations they are certainly not intentional

Joe:The posts in my Aeola or Edeo, as I remember
are not cushioned. In my Lachenal, the ends are, but I think they are
primarily spacer cushions to provide ability to 'true' up or flatten
the ends.

Goran: That is correct

Joe: Any convexing could cause a key to stick, like my low Bb did.

Goran: No, that hardly happens.If a key sticks the hole is narrow anyway ..
or the'convexing' extreme of course....

Goran Rahm

#11 duckln

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Posted 07 November 2003 - 01:43 PM

I did get carried way and that's why I followed with a 'whoops' post.
Thanks for your explanations.

I have never tuned a reed or seen a reed being bench tuned. Question:
If a reed is bench tuned, in an appropriate cavity and vacuum, is it as loud there
as when played in the concertina ?

#12 JimLucas

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Posted 07 November 2003 - 03:32 PM

If a reed is bench tuned, in an appropriate cavity and vacuum, is it as loud there as when  played in the concertina ?

Please reconsider your question.

Where is "there"? Is the sound intensity within a centimeter of the reed the same in both cases? How about "above" the action board, but still within the end of the instrument, and at an equivalent distance without the instrument? Or the intensity entirley outside the instrument?

What do you mean by "appropriate" when you say "appropriate cavity". Hardly a technical specification.

But if you try to tune the reed in a vacuum, there can be no sound at all. So no, it won't be "as loud".

Edited by JimLucas, 07 November 2003 - 03:32 PM.


#13 duckln

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Posted 08 November 2003 - 10:51 AM

'There' is at the ear of the listener and could be 1' to n'.
By vacuum I have in mind bellows, operated
to draw air through the reed, so that it can be checked.
The ideal 'there', might be 18' from the reed. The question I have
boils down to , 'does the concertina amplify the sound beyond the
cavity'?

Joe

#14 Richard Evans

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Posted 14 November 2003 - 04:26 AM

Dear Sound Post people,
The reason that the post is there is to ensure that the end is kept a constant distance from the soundboard to ensure that the mechanism does not push against the end and cause the pads to fail to seat. All that in one sentence! Many 20 key models that I have had in for repair in the past have had no posts and due to warping of the ends I have installed such posts. You will find that the correct length for the 20 key posts is 11mm. In an English concertina the posts are drilled through the middle to accept the unobtainable wood screws that hold the finger rest and the thumbstrap. If there was no support here the ends would bow in and out while playing pull notes! They are supports that is all.
Yours Concerternally,
Richard Evans

#15 Pete Dickey

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Posted 16 November 2003 - 06:03 PM

Referring to the exceptionally thin wood screws that certainly appear to be unobtainable, does anyone know just what gauge these screws are? (e.g. 1 inch number 1 's perhaps?). Perhaps armed with the appropriate size it may be possible to get hold of some or to have a batch made up which could be shared out with all who need them possibly via the forum.

Pete




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