S&S D Duplex

[Phillip Ford]

On Mon, 18 Nov 2002 02:37:51 -0500 Sarah Fox <sarah@gendernet.org> wrote:


> I wouldn't think that *much* of the energy is
> dissipated over time, but
> surely some is -- enough to affect sustain...  
> If vibrations
> transferred from the bridge
> are reflected back to the bridge without
> frictional attenuation, then energy
> is preserved in the system.  (If the bridge
> were rock-hard stationary, then
> energy would also be preserved.)  However, when
> vibrations are transferred
> to the duplex segment and the energy is lost,
> the bridge must do more work
> on the duplex segment to keep it in motion, and
> that work is done using
> energy from the main segments of the strings... 

But felt doesn't have to be there for energy loss (or transfer) to occur. 
Even if there was no felt some energy is being transferred to the plate by the
duplex.  Perhaps if the duplex is tuned then more energy is transferred to the
duplex which then transfers more energy to the plate which might actually
decrease sustain.

> Of course these arguments
> about vibrational reflection and energy
> conservation make certain
> assumptions about phasing relationships... and
> that's the can of worms
> underlying the entire subject of duplex tuning.

I'm not sure I really understand what you mean, but I take this to mean that
it's possible that a detuned duplex might cause less energy transfer to the
duplex than a tuned duplex.

> 
>   It's quite possible I will find some free
> time in the distant future
> and devote some time to measuring these things.
>  Unfortunately time seems to
> be my scarcest resource these days... besides
> money, that is.

Join the club.

> 
> Resonances don't sap energy.  They merely
> redirect it.

> Peace,
> Sarah
> 

OK.  Perhaps a poor choice of words.  If the energy is being 'redirected' away
from where you want it then it's 'sapping' useful energy from where you want
it.  If we assume that where we want the energy is in the speaking length,
then the question is does a tuned or untuned duplex cause more energy to
remain in the speaking length.

Phil F