Violin bridges

[Ron Nossaman]

>>Actually I think that a violin bridge is more illustrative of Ron's 
>>position than your own.  If the violin top is being activated by 
>>compression waves...
>
>There's no *if* about it.  Sound is propagated in the same way 
>thoughout the cosmos.  Of Ron's 'position'  (that "bodily movements 
>of the bridge cause the soundboard to move and to produce the sound 
>of the string into the air") I will merely echo Robin in saying it is 
>"fantastic ... to think such could explain the energy transfer 
>between string and bridge/soundboard".

If I may remind you once again John, the "if" is the entire point of this
discussion.


>>   The bow is moving the string side to side. The top needs to move 
>>up and down to move the air so that we can hear the violin.  So 
>>violin makers have cleverly devised a bridge and soundpost system to 
>>convert the side to side motion of the string to up and down motion 
>>of the top.
>
>Nonsense.  The flexibility and mass of the system is concerned with 
>its acoustic impedance, just as in a piano.  It is not "up and down 
>motion" of the plate that radiates the sound any more than it is in 
>the piano.

With the speed of sound in maple across the grain at roughly
35,000"/second, adding an inch to the sound path by the inclusions would
delay a compression wave about 0.0000285 seconds, or 0.01257 of a cycle at
440cps, the wave traveling about 79.5" in one cycle at 440cps, given a tall
enough bridge. That should be pretty significant, don't you think, for
someone insisting that small effects are no effects? Particularly given
that a compression wave at a molecular level will be considerably smaller
than the physical bridge movements I've talked about. And this longer path
delays the wave from what? The frequency of the wave will still be
nominally the same at the bottom of the bridge as at the top, but the
altered mass and rigidity of the material between the string and the
soundboard will be different than in a solid bridge. That's impedance
control, as far as I'm concerned. But I'd love to hear all about how making
the sound travel farther in the bridge changes anything, most particularly
in a continuous excitation system like a violin. Wasn't that long rod
demonstration on a piano soundboard supposed to prove that those
compression waves didn't care how far they traveled and it worked anyway?
As you said, the laws of acoustics work the same everywhere. Since you
brought it up to support your claim, let's hear all about it. 



>>   The bridge is rocking about the one foot that is over the 
>>soundpost which is causing the other foot to move up and down. 
>>Apparently violin makers seem to feel that some physical movement of 
>>the top needs to take place as a result of the string movement.  I 
>>believe the cuts or incisions are not there to 'lengthen the path of 
>>the sound' (I'm not sure what the purpose of that would be anyway)
>
>Read the above URI.  What people 'seem' to do and what people 
>'believe' have no place in a serious discussion.

Exactly my thought, so let's hear all about it.


>>  but to cause the flexibility (or impedance if you like) of the 
>>bridge to be more or less the same for the four strings, since two 
>>of them are directly over the feet and the other two are over an 
>>unsupported section of the bridge.
>
>The incisions would not have that effect and the flexibility (as 
>opposed to the rockability) of the bridge is not an issue.  Acoustic 
>impedance is one thing; propagation of sound and acoustic radiation 
>are another.  The proper regulation of the former creates the 
>conditions for the efficient accomplishment of the latter.  Consider 
>the etymology and the derivation of the word 'impedance'.

And the propagation rate of sound (compression waves) is determined by
what? Resistance and density of the medium? Mass and stiffness? Impedance?
It's the same mix of physical characteristics of the media that determines
the properties of progressive or traveling waves, compression or
longitudinal waves, and stationary transverse waves. It's all vibration.


vi·bra·tion 
1.a. The act of vibrating. b. The condition of being vibrated. 

2. Physics. a. A rapid linear motion of a particle or of an elastic solid
about an equilibrium position. b. A periodic process. 

3. A single complete vibrating motion; a quiver. 

4. Slang. A distinctive emotional aura or atmosphere regarded as being
instinctively sensed or experienced. Often used in the plural. 


sound (sound) n. 
1.a. Vibrations transmitted through an elastic material or a solid, liquid,
or gas, with frequencies in the approximate range of 20 to 20,000 hertz,
capable of being detected by human organs of hearing. b. Transmitted
vibrations of any frequency. c. The sensation stimulated in the organs of
hearing by such vibrations in the air or other medium. d. Such sensations
considered as a group. 


Ron N