Sound waves(The behavior of soundboards)

[John Delacour]

At 2:00 PM -0600 12/23/01, Ron Nossaman wrote:
>  >In my post with the topic "Rocking Bridges", to which at the time of
>>writing you have not yet responded,
>
>Nor is there any reason for me to. With you maintaining that a string
>deflected by a finger will move the bridge but one deflected by a hammer
>strike won't, I see no point in continuing.

Then you will have the leisure to watch your theories discussed in 
your absence.  I relinquish this thread with a selection of 
quotations which indicate to me that my summing up of your position, 
which you refuse to confirm, is correct.  It seems to me  a fair 
summing up.

I will now proceed to the Rocking Bridge question under a thread with 
that subject line.

JD



At 7:09 PM -0800 12/3/01, Delwin D Fandrich wrote:
>As I said, it moves the bridge. Primarily in a vertical mode (assuming a
>grand piano), but there is some fore-and-aft rocking as well. How much
>depends on the design of the bridge and location on the scale. More in the
>bass than in the treble.
>
>The bridge movement moves the soundboard causing it to vibrate much like the
>diaphragm vibrates in the loudspeaker.


At 5:42 PM +1100 12/19/01, Overs Pianos wrote:
>In a situation where the down bearing angle is in the back length 
>only, 'bridge rocking' (yes it will be minute also JD) will be 
>necessary for the minute dynamic variation in speaking length 
>tension to result in a commensurate variation in the down bearing 
>vector force.
>I read your well conceived response earlier today Ron soon after you 
>posted it. I too have described the motion of the string and its 
>resultant dynamic forces on the bridge in exactly the manner in 
>which you describe it. I understand what you're saying and agree 
>with you.


At 1:48 PM -0600 12/22/01, Ron Nossaman wrote:
>All sorts of compression waves and molecular level stress disturbances can
>be immediately moving through every part of the bridge from the first
>movement of the string, but they're clearly not what moves the bridge. The
>strings move the bridge, the bridge moves the soundboard.

At 5:42 PM -0600 12/16/01, Ron Nossaman wrote:
>Then I fail utterly to see how the soundboard can move without the bridge
>moving

At 8:00 AM -0600 12/18/01, Ron Nossaman wrote [ridiculing JD's position]:
>Meanwhile, the unchallenged fact that the bridge does move has 
>little or nothing to do with sound production, but it's definitely 
>not the string movement that is moving the bridge.

At 4:47 PM -0600 12/18/01, Ron Nossaman wrote:
JD:
>>Under these conditions the bridge cannot be moved by the strings, 
>>since a body only moves in reaction to a force and in these 
>>circumstances there is a zero force acting on the bridge.
RN:
>It doesn't matter if it's possible or not. Regardless of whether the
>strings are moving in the same or opposite directions, there will be cyclic
>changes in string tension as the vibrating strings pass from their far
>limit of excursion, through a relatively straight line neutral, to the
>other far limit and back. The tension swings will necessarily pull the
>bridge forward and back, and the bearing load changes will push it up and
>down. The bridge will move, and the soundboard will follow.

At 5:05 PM -0600 12/18/01, Ron Nossaman wrote:
>I'm to judge what happens in the bridge before the soundboard moves? Isn't
>that basically the problem with this discussion? This isn't even 
>conceptually possible, much less arguable. What you need is 
>instrumentation.

At 8:29 PM -0600 12/18/01, Ron Nossaman wrote:
>I don't know why the difference in sound. I also don't know why, if the
>energy goes directly through the bridge without moving it, and into the
>soundboard which then moves, why touching the fork to the exposed edge of
>the soundboard won't produce the same tone as pressing it against the top
>surface.

At 10:35 PM -0600 12/19/01, Ron Nossaman wrote:
>When these compression waves supposedly travel down through the bridge to
>the soundboard, moving the board before the bridge moves, how does this
>manage to happen with the board attached to the bridge at exactly the spot
>that these waves are supposed to move the board?

At 8:09 AM -0600 12/21/01, Ron Nossaman wrote:
>I have never denied the existence of compression waves
>in strings and soundboards. What I have said, and still say, is that they
>are not the principal driver of the system.

At 6:06 PM -0600 12/21/01, Ron Nossaman wrote:
>You see, the strings moving the bridge is my own theory, dreamed up 
>by me, based on sound mechanical and physics principles, so it isn't 
>likely to be on a university web site anywhere. Oddly enough though, 
>two piano designers, builders, and fellow rebuilders who have 
>against all apparent odds actually given it some thought, seem to 
>hold similar views.