Spring 'touch' Pressure

[goran rahm]

Correction:

 

Rich said:I still don't understand your reply. What is the "pad opening area"

 

Goran before: .....the air passage area (the imaginary mantle surface between the pad circumference and the the circumference of the pad hole = "pad opening area" as I called it before)

 

Goran now:Sorry...the above was not entirely correct...hard to express it...

maybe rather: 'the imaginary mantle surface area between the circumference of the (pad-) hole and a projection of the (pad-) hole circumference upon the surface of the pad by the nearest point to point representations'

...sounds absolutely silly....better descriptions welcome....!?

 

'the smallest 'mantle' formed by the circumference of the pad hole and the pad surface'....???

 

Goran

[JimLucas]

'the smallest 'mantle' formed by the circumference of the pad hole and the pad surface'....???

Göran, I think the physical/mathematical idea you're trying to express is the area of the minimal surface extending between the pad and the board surface, through which the air must flow in order to get into the hole. In less technical language, that would be how much room the air has for getting under the pad and into the hole.

 

Note that this assumes the size of the hole is more than adequate for letting enough air into the reed chamber. And thus that the surface area mentioned above must be significntly smaller than the total area of the hole for there to be any noticeable restrictive effect.

 

[Edited to correct typo.]

Edited December 3, 2003 by JimLucas

[Richard Morse]

I can't see there is any difference [in our viewpoints] except in that you assume that other factors are unchanged and I left them out. The point of the discussion being that you can not normally execute your proposed relocation of the fulcrum unless either:

1) reducing pad opening area (which *may* be negative)

2) getting a longer button travel (which may be negative also or at least demand other contruction/design changes (compared to the "traditional" concept)

I HAD assumed that all other action factors had not changed because massive redesign/construction of the concertina is unreasonable. For you to say that moving the fulcrum toward the pad "would get a longer button travel to open the pad fully" while not telling us that you "left out" all other action considerations - is misleading and impractical.

 

You could have presented your argument clearly by saying that moving the fulcrum toward the pad would normally reduce the pad clearance - possibly with negative results. I fully agree with that statement.

 

The pad opening area of course is depending on the pad thickness

what does the pad thickness have to do with it?

Since You Rich seemed to presuppose that the "traditional" construction is used... you have fixed measures for the involved parts and in that case introduction of thicker pad will reduce the air passage area

Unfortunately you have "left out" considerations (point of thickness origination) which is misleading - particularly when you say "of course" which most people would take as "there is no other possibility". I see now that you are assuming that the pad get thicker TOWARD the pad pan. I originally saw this possibility and immediately disregarded it as being impractical and assumed you meant that the pad would get thicker AWAY from the pad pan - which wouldn't affect the air passage area at all.

 

There are many things that affect the pad opening area. You make it sound like the pad opening area is *governed* by the pad thickness.

[goran rahm]

Rich:You could have presented your argument clearly by saying that moving the fulcrum toward the pad would normally reduce the pad clearance - possibly with negative results. I fully agree with that statement.

 

Goran: it is obvious that I expressed myself vague and unnecessarily complicated...thus causing confusion. Seems the real question can be reduced to whether you don't experience the suggested negative results ('choking' of air passage and/or reduced amplitude and/or change in tone character) when moving the fulcrum towards the pad:

- reduced pad clearance...what are the related conditions ...?

A quick and approximate calculation seems to give that

a 16mm hole needs a 4mm pad lift if the hole will remain as the smaller area.

With 3:5 leverage a 3mm button travel gives 5mm pad lift. Moving the fulcrum to 1:1 would give a pad lift of 3mm (possibly too little) and this would give an increased pad closing force from 40 to 70 gram assuming we had the 70 grams at the button unchanged. To even out the difference of needed pad force for the tightness comparing say a 16mm hole with a 12 mm one you would have to increase the force to about the double.

 

Is the above (or similar) something you have experienced Rich? Do the calculations seem roughly adequate and is it about the same as you have practised? Do you notice any tendency of low range pads to leak and have you managed to 'treat' it?

 

Rich:I see now that you are assuming that the pad get thicker TOWARD the pad pan. I originally saw this possibility and immediately disregarded it as being impractical and assumed you meant that the pad would get thicker AWAY from the pad pan - which wouldn't affect the air passage area at all.

 

Goran: Well, now we are coordinated here also..! So you see the 'fear' that a thicker pad would influence on the clearance...it does too (of course..:-)) if

the lever height remains the same. (I have met problems with this issue when I have introduced thicker pads in order to make them more silent.)

 

Rich:There are many things that affect the pad opening area. You make it sound like the pad opening area is *governed* by the pad thickness.

 

Goran: Not meant so at all..I just flicked the pad thickness in as one factor to consider among the other ones. Anyway the tolerances are small and it seems to me that often/mostly it would be difficult to 'fix' the unevenness of 'pad closing force' by relocation of the fulcrum. With a sly additional relocation of the insert point for the spring maybe something more can be gained?

Would be interesting to know in what extent this has been examined by the 'old time' makers....

in due time I will check a little more on some 'real' instruments

 

Goran Rahm

[David Levine]

In reality Goran Rahm is Rango Mahr, a deep-cover operative for al Qaida. He is wanted by Interpol and is on the most-wanted list on twenty-three planets. Be very careful here....

[Simon H]

In reality Goran Rahm is Rango Mahr, a deep-cover operative for al Qaida. He is wanted by Interpol and is on the most-wanted list on twenty-three planets. Be very careful here....

Did you really revive a six year old thread to say that?

 

I'm confused. There have been a few old threads revived lately, it would be good if the revivers would mention that the thread is old, as I go wiffling back through the responses thinking "where did alll this come from?" only to then see the date.

 

Edit: I have though spent a happy half hour reading many of the old posts from this gentleman, (subsequently banned I note). The "activity" of discourse associated with his name is quite fascinating. Very interesting to see the discussions from a few years back.

Edited February 19, 2009 by Simon H

[David Levine]

I thought this was a very interesting thread. I am changing springs on some concertinas to reduce pressure. I have one concertina that has very light springs and it is much easier to play certain ornaments on - such as a two finger triplet on one button. I'm interested in how one might be able to reduce spring pressure by bending the spring a certain amount- and then how to determine that spring pressure is equal on every button, or at least close to even.

 

Simon H, I take it you have no real interest in the thread? (I really don't know anything about Goran Rahm - if that needed to be said.)

[Hereward]

I thought this was a very interesting thread. I am changing springs on some concertinas to reduce pressure. I have one concertina that has very light springs and it is much easier to play certain ornaments on - such as a two finger triplet on one button. I'm interested in how one might be able to reduce spring pressure by bending the spring a certain amount- and then how to determine that spring pressure is equal on every button, or at least close to even.

 

Simon H, I take it you have no real interest in the thread? (I really don't know anything about Goran Rahm - if that needed to be said.)

 

I was pleaseed to see this thread and particularly Dave Prebble's opening words because I thought my instrument had too heavy keys recently when being able to compare a few others. However, in fact this was just because one of the ones I was trying had very light keys. Mine is reasonably even over the whole 48, and allowing for the fact that some will have had much more play than others and that it is 100 years old.

 

Knowledge is rarely wasted.

 

Ian

Edited February 19, 2009 by Hereward

[Simon H]

I thought this was a very interesting thread. I am changing springs on some concertinas to reduce pressure. I have one concertina that has very light springs and it is much easier to play certain ornaments on - such as a two finger triplet on one button. I'm interested in how one might be able to reduce spring pressure by bending the spring a certain amount- and then how to determine that spring pressure is equal on every button, or at least close to even.

 

Simon H, I take it you have no real interest in the thread? (I really don't know anything about Goran Rahm - if that needed to be said.)

 

Don't get me wrong - I'm interested, when I joined the forums I spent days and days searching old threads and picking up "the knowledge". My confusion was around your thread-restarting-methodology and purpose. I couldn't quite see why this thread had suddenly re-appeared with such a bizarre comment restarting it.