BASS TO TREBLE BREak

[PianoBook@aol.com]

In a message dated 96-06-17 12:36:43 EDT, you write:

>In the above topic, one should think more in terms of matching impedance.
>When:
>1. The soundboard impedance in a particular area matches the energy level
>(mass
>and amplitude) and frequency of the string motion, and:
>2. There is good energy transfer (clean, tight string to bridge contact,
>sufficient bearing, etc.)
>
>Then the system works efficiently and more volume is produced. Adding
>stiffness
>(screw to the back post) is usually the opposite of adding mass (key weights
>in
>the bridge), and so it isn't likely that both would produce the same results
>in
>one situation.  Come to think of it though, the weights should both lower
the
>resonant frequency of the system while possibly increasing the impedance.
>I'm
>not quite well versed enough in these things to know for sure. Need one of
>the
>resident engineering types to jump in here.
>
>Rescaling can also adjust the impedance match by adjusting the string energy
>level and the stiffness of the soundboard system through increased bearing
>pressure.
>
>Hope these stray thoughts are germain.
>
>Don Mannino RPT
>
>
>

Concerning the effect of adding mass to the soundboard (which I and others
wrote about on this list some time ago -- see archives), the way it was
speculated to me by the rebuilder I worked with at the time was as follows:

The impedance of the soundboard due to its mass is its "resistance" to
vibration, which causes it to have a "resonant frequency", i.e. a frequency
at which it vibrates most efficiently.  Or perhaps different areas of the
soundboard have different impedances and resonant frequencies.  If the
resonant frequency and the frequency being played are too close together, the
board vibrates too efficiently and the sound energy is dissipated too
quickly, making the note sound dead.  By attaching a mass to the soundboard,
one effectively "de-tunes" it, changing its resonant frequency so it no
longer matches the note being played.  The sound no longer dissipates so
quickly and the sustain is longer.  This is in principle something like
making each of the three strings of a unison a slightly different length, or
detuning a unison every so slightly, to increase the sustain.

Larry Fine