Tone near plate struts

[Phillip L Ford]

On Fri, 29 Mar 2002 13:01:30  
 Ron Overs wrote:

>Indeed, and while the practice of using a ring bridge is an attempt 
>to alleviate this problem, it has the disadvantage of reducing the 
>fundamental tone from the lowest bass notes. In the past few years we 
>have been extending the low end of the long bridge to beyond the 
>lowest tenor note, to provide support on the 'lower' side of the 
>note. 

This sounds like a good idea.

>In our piano no. 003, it extends such that it terminates over 
>an auxiliary sound board rib (one which does not extend to as far as 
>the bass bridge or the inner rim on the straight side).

So, if I understand this correctly, this is a short rib that is sort of
'floating' between the rim and bass bridge and is beneath the end
of the long bridge.


>>. . . But on pianos that do not have a cut down bridge there is 
>>still a deterioration, or at least a change, of tone adjacent to the 
>>plate struts or braces. 
>>Phil F
>
>Phil, this is an interesting phenomena. We design the contact of the 
>bridge with the sound board such that it forms a uniform curve as it 
>approaches and leaves the immediate area under a plate strut (I do 
>not allow a dog-leg of bridge contact with the panel - dog leg 
>contacts are certainly a no no on my computer). However, since I am 
>not prepared to compromise the speaking lengths of the scale for any 
>reason, the top of the bridge must therefore lay back, and then 
>forward of the board contact as it goes down under a plate strut, 
>particularly with regard to the second break down. Theoretically at 
>least, we build the piano such that the percentage of breaking strain 
>is uniform. Therefore, we would expect the tuning to be relatively 
>stable also at the plate struts. However, while the stability is 
>superior to those pianos of the straight bridge under the strut 
>variety, some instability with temperature and humidity variations 
>continue to occur - as it does also at the string gauge changes. 

To what do you attribute this instability?

>Tonally, there seems to be more risk of variation if the note to not 
>spacing across the strut is wider. Since the wider the space between 
>the adjacent note centres (at the struts), the greater will be 
>requirement for the bridges to lean over as they approach the struts. 
>I believe it is important to minimise the bridge lean as much a 
>possible.

>As the bridge rocks during the cycle (and if you don't believe that 
>the bridge rocks then that's OK, but I happen to believe that it 
>does), the rear leaning section will tend to increase sound board 
>panel depression as the speaking length tension increases, while the 
>forward leaning section will tend to reduce panel compression.

I'm not sure that I understand why this is.  Can you explain further?

>This 
>may indeed cause a difference in the tonality on either side of the 
>strut.

An interesting idea.  I hadn't thought of this.

> It should cause the board impedance to be lower on the treble 
>side and higher on the bass side. 

Is this for the same reasons that you stated above about the string
load either increasing or decreasing panel compression?

>Any other thoughts on this matter? Its an interesting question Phil.
>
>Ron O.

Everything I see here seems to indicate to me that you believe that the
reason for the tonal difference is due to the bridge and board.  Is that
correct?  Do you think that the presence of the plate strut has any
effect on the tonal difference?  I had it in my mind that somehow
the plate was contributing to this (either additional local mass, or additional
local stiffness, or something else).  I haven't formulated any specific idea
of what the phenomenon is or how it works or would be described.  It was
just gut feeling (which has been wrong before).  I've been trying to think
of some experiment to attempt to prove it to myself one way or the other.  I
haven't come up with anything so far.

Phil F


See Dave Matthews Band live or win a signed guitar
http://r.lycos.com/r/bmgfly_mail_dmb/http://win.ipromotions.com/lycos_020201/splash.asp