Rocking bridges

[John Delacour]

At 1:44 PM -0600 12/24/01, Ron Nossaman wrote:

>  >> Now I ask you or Del or Ron O. or anyone to explain to me how 
>this movement
>>>  (in this case rocking movement) can be in any way instrumental in the
>  >> production of sound waves at the frequency of the vibrating string.
>
>I answered it John. The bridge moves the soundboard. The soundboard displaces
>air. The rocking is only one of the movements the bridge imparts to the
>soundboard. I've already said that plenty of times. Who cares what it provides
>to the sound?

I said I'd like to get things clear at each step of the way and 
though you say you've answered the question at this second time of 
asking, you most obviously have not.

For the moment I will willingly concede that my hypothesis that the 
bridge moves "after the soundboard" in these rocking or vertical or 
any other movement, because it has never actually been a big issue. 
The answer to this question may turn up later.
So you can no longer use this as a smokescreen.

Now please answer the question.  As though it's not clear enought 
already, the bridge may or may not rock at any given moment, 
depending on the forces on it -- another telling question that you 
have side-stepped -- but if and when it does rock, it's rocking 
motion will not bear any relation to the frequency of the string, let 
alone to all the partials of many strings encouraging it to rock in 
various unpredictable directions.

In your "answer" above you say "Who cares what it provides to the 
sound?"  Either I don't understand English or this is a complete 
U-turn and you are denying that these movements contribute to the 
transmission or transduction of the sound, which is what the whole 
thing is about.  We all started out knowing that bridges and 
soundboards can move and do move, but you claimed that these 
movements have a part in transducing the sound.  The topic of the 
last two relevant threads was, you need no reminding "Sound 
Waves....", and it began with a clear statement by Del which I 
vigorously contested.  Upon this basis the whole argument has evolved

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......
>
>...Have you ever tossed a rock in a still pond? The effect is similar.

Nothing could be clearer.  He says the vertical movement and the 
(less significant) rocking movement CAUSE THE SOUNDBOARD TO VIBRATE 
and when I rejected the notion of the bridge being in any way 
analogous to the voice-coil of a loudspeaker

And later At 9:31 AM -0800 12/19/01, Delwin D Fandrich wrote:
>The question, of course, is, how does one initially get the soundboard to
>vibrate without physically moving the bridge first?

That just about sums up your position.  Both Del and you have stated 
time and again that the movement of the bridge causes the soundboard 
to vibrate and I have persistently rejected this theory.  That 
movement of the bridge entails movement of the soundboard and vice 
versa I have never doubted.  That if I thump the bridge of an 
unstrung piano the bridge and the board will vibrate is impossible to 
deny.  But that is not what you two are saying.  You are saying that 
the movement of the bridge/ soundboard produces the piano sound that 
we hear by causing the soundboard to vibrate.

JD









JD