S&S D Duplex

[Richard Brekne]

An interesting post in which the ability of longitudinal modes to move the
bridge are recognized, and at the same time their importance in the overall
sound of the piano is deemed of very minor significance. Reminiscient of the
middle road I tried to take in last years disscussions on the many threads
steming from the Soundboard Vibration thread, tho (and quite refreshingly so I
might add) far better described and with obviously far better grasp of the
science involved then anything written then.

Thanks for the fine contribution to our understandings Sarah. A few comments
below.

RicB


Sarah Fox wrote:

>
> Actually every contact point would be a sound reflection point, resulting
> from an abrupt impedance differential.  If we're talking about compression
> waves in the string, which it appears is the implication, the free resonant
> frequency between any two contact points would be half of the speed of sound
> through spring steel (not through air), divided by distance.  It would be
> *incredibly* high (bat frequencies and beyond, not dog frequencies), and it
> would only be tunable by moving contact points (assuming the spring constant
> is indeed constant -- or approximately so).  You suggest the sound would
> stop at the hitch pin.  It would not.  That is only another contact point.
> It would travel into the plate and beyond.  It would also have a difficult
> time coupling into the bridge, except by rocking it.
>
> Personally, the importance of longitudinal vibrations doesn't seem very
> probable to me.  It is easy enough to see how transverse vibrations are
> coupled into duplex strings from vibrations in the bridge, irrespective of
> what Mr. Steinway might have claimed to the contrary.  Why invoke mysterious
> ultrasonic longitudinal vibrations?  Just because Mr. Steinway got a patent
> doesn't mean he understood the acoustics of his invention.

Agreed. Tho the point I tried to make to Phil was perhaps the desired
longitudinals result (coincidently ) from tuning the transverse as harmonics of
the fundemental. Tho indeed it may not have nearly as much to do with
longitudinals at in the end. Mr Steinway no doubt was listening to things that
made him believe this was related to L waves. And anyone exciteing these in bass
strings should be able to hear the similarity between their sound and these
whistling noises higher up the scale. Perhaps there are seperate causes for
these yet the (mistaken ?) assumption that they also stem from longitudinal
vibration would not be dificult to understand.


> In the end, could it be that the biggest benefit of a tuned duplex scale is
> the "freeing up" of the vibrations of the strings and bridge by eliminating
> the need to mute the strings on the far side of the bridge?  After all,
> mutes of any kind work through frictional dissipation of vibrational energy.
> Isn't it reasonable to expect that muting adversely affects a note's
> sustain?  If the purpose of muting is to kill objectionable ringing in
> nonspeaking string segments at inappropriate frequencies, isn't an alternate
> solution to tune those frequencies to where they are appropriate and
> therefore not objectionable?
>

Put this way, yes... this makes perfect sense and fits very very well into the
justification for Duplex alignments.

>
> ......Eventually I learned to work *with* the resonances instead of against
> them.
> I removed almost all the muffling and filled the tube with smaller
> open-ended tubes that were tuned to a variety of other frequencies.  The
> idea was to "resonate at all (or many) frequencies."  I achieved enough
> efficiency to deliver 120 dB SPL at 1000 Hz using only a half watt of input
> power!  I was up to several watts at 15 kHz, but not nearly enough to blow
> the voice coil.  In the end, my system achieved the flatness I desired,
> along with far more efficiency than I had ever hoped for.  It was sort of a
> "Bose" solution.

Very nicely put... and quite agreeable indeed.

> Hopefully the parallels to the duplex scale are obvious
> here.  Where possible, it seems best to correct the tuning, rather than to
> kill the sound.

I am also reminded of something some few have tried to say time and time again.
That just because we dont have an adequate explaination to a thing, does not
mean we should discount it. Mr Steinways duplex has been under fire for some
time by many both on and off the list. Probably for at least a couple obvious
reasons. First it is somewhat difficult to maintain (at least for the untrained)
and secondly the explanations I have seen for it up to now have been somewhat
less then satisfactory to put it mildly. Yours on the other hand, gives new
pause to reflect and rethink. Thanks muchly !

> Peace,
> Sarah
>
>

Live long and prosper :)

--

Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html