Sound Waves Physics

[Robin Hufford]

Richard,
     I would be most interested to hear what you have to say about these
issues.
Regards, Robin Hufford

Richard Brekne wrote:

> Subject:
>         NEWTON BBS Piano Sound ---Physics
>
> Hi List:
>
> I dont have any URL's to show anyone, but I posed the
> following question to the NEWTON Physics Website, a
> government supported site that you can write physics
> questions in and get replies from bonified educated physics
> doctors and masters. Don, you mentioned that the most simple
> answer was probably the right one. Simple answers to complex
> questions always put me on guard. Ron, JD, and Robin, I have
> a few comments, questions and observations about some of the
> posts written the last couple days, but I will take them in
> a seperate post later on. Just wanted to send this off for
> your edification. Seems pretty clear to me he makes a strong
> point out of compression (sound) waves being transfered all
> over the place as well as going good for some of the effects
> of transverse waves Ron and Del talk about.  His answer
> points (to me) in the direction of both the lists present
> theories being involved in the production of sound waves
> from the instrument.
>
> RicB
>
> > > >    Question -   When the hammer strikes a string in a
> piano, the string
> > > > is set in vibration which in turn has an effect on the
> bridge attached to
> > > > the sound board. Is this affect such that the string
> physically moves the
> > > > bridge and then in turn the bridge moves the sound
> board, or is it such
> > > > that there is a transfer of energy in the form of
> internal compression
> > > > waves through the bridge and delivered to the sound
> board which sets up
> > > > the movement in the sound board which in turn moves
> the bridge? Also,
> > > > just how much air displacement is necessary in the
> form of a compression
> > > > wave to become audible ? Thank you.
>
> Nathan A. Unterman wrote:
>
> >This is a complex question. When the hammer strikes a piano
> string, both
> >transverse and longitudinal waves are induced, both the
> fundamental
> >frequency and overtones of varying intensity that depend
> upon the
> >construction of the instrument. These vibrations are
> transferred to the
> >bridge and to the rest of the piano. The transverse waves,
> where the motion
> >of the string is perpendicular to the string can also be
> transferred to the
> >piano frame directly, especially in a "grand piano" with
> its large area
> >resonator. To indicate how complicated this whole process
> is, the piano
> >transfers its sound waves to the floor upon which the
> instrument is placed,
> >so the "quality" of the sound will depend upon the
> composition of the floor.
> >A piano on a carpet produces sounds different than the same
> instrument on a
> >bare wood floor.
> >
> >The longitudinal waves have an amplitude of the order of
> millimeters, or
> >fractions thereof. The intensity of the sound is
> proportional to the square
> >of the displacement, and different ears hear sounds of
> different frequencies
> >and intensities. The commonly used scale for measuring
> sound intensity is
> >the logarithmic "decibel" scale. One decibel is taken to be
> the onset of
> >hearing by humans, but that is quite variable.
> >
> >The amplitude of an audible sound depends upon the
> sensitivity of the ear,
> >but also on the medium transmitting the sound. A classic
> example is a rail
> >road. It is possible to hear an oncoming train a much
> further distance away
> >by placing ones ear on the track, rather than listening for
> the train sound
> >traveling through air alone.
> >
> >So you see, your inquiry is really quite complicated. Sorry
> I cannot give a
> >simple answer.
> >
> >Vince Calder
>
> --
> Richard Brekne
> RPT, N.P.T.F.
> Bergen, Norway
> mailto:rbrekne@broadpark.no