Sound in Feet per Second.

[Doug Richards]

Del,

Thanks a bunch for the modulus and density info.  I looked for it a whole
back and couldn't find it.  Can you tell me what type of wood these numbers
are for?  I started to do a simple finite element model of a soundboard with
a 3 string unison to look at how much the board stiffness changes the
response of the strings...  I need the modulus of both spruce and maple to
do a more accurate job, but anything you have is better than nothing.

doug richards
San Jose, CA

> -----Original Message-----
> From:	Delwin D Fandrich [SMTP:pianobuilders@olynet.com]
> Sent:	Thursday, May 28, 1998 1:22 PM
> To:	pianotech@ptg.org
> Subject:	Re: Sound in Feet per Second.
> 
	...

> THE SPEED OF SOUND (SOS) THROUGH WOOD:
> The speed of sound through wood is independent of species.
>   --  It VARIES DIRECTLY - with the square root of the modulus of
> elasticity (MOE).
>         (Transverse (radial) MOE can be 1/20 of the longitudinal value,
> hence, the
>         speed of sound across grain is 1/3 to 1/5 the longitudinal value.)
>   --  It VARIES INVERSELY - with the square root of the density of the
> material.
>   --  It VARIES WITH - grain direction, or angle.
>   --  It VARIES INVERSELY - with wood temperature and with moisture
> content (MC).
>         Both temperature and MC affect MOE.
>   --  It VARIES INVERSELY - with both frequency and with the amplitude of
> vibration.
> 
> In the piano soundboard the speed of sound in, or through, wood is only
> important because
> of its direct effect on wave velocity, hence wave impedance. It is not
> important in and of
> itself.
> 
> A piece of wood with a longitudinal modulus of elasticity (MOE) of
> 1,800,000 psi and a
> density of 30 lb/ft3 would have a speed of sound in the longitudinal
> direction of about
> 150,000 in/sec. In the transverse direction, its MOE would be about
> 100,000 psi and the
> speed of sound would be approximately 35,000 in/sec.
> 
> Regards,
> 
> Del
> 
>