Impedance problem

[David Love]

I didn't weigh it but it was a very small one that I use for making
loops for string knots.  On second thought it seems like not enough mass
to have an influence on impedance so soundboard resonance makes sense.
What is it that causes that to happen and how is it generally avoided in
design?

David Love
davidlovepianos@comcast.net 

-----Original Message-----
From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On
Behalf Of Ron Nossaman
Sent: Friday, January 21, 2005 1:15 PM
To: Pianotech
Subject: Re: Impedance problem


>I ran into an interesting phenomenon today.  Rebuilt Steinway A c1915.
>New soundboard.  Reasonably poor job but that's not the issue.  Note E5
>was extremely loud compared to its neighbor F5.  Switched hammers and
E5
>was still very much louder.  So a clamped a set of vice grips onto the
>rear bridge pins at E5.  Sure enough, the addition of some mass caused
>the loudness to diminish and the sustain to be slightly enhanced.  The
>customer thought so too.  I was surprised that the addition of mass
>would produce an effect so localized without having an appreciable
>effect on F5.  Was I hearing things?  Well clearly I wasn't, but what
>was going on underneath or in the panel that there would be such an
>effect right at that point.  Thinking about it later it occurred to me
>that rib position under the bridge at that point might have had an
>influence.  Comments?
>
>David Love


Hi David,
The fact that F5 wasn't appreciably affected and E5 was makes me suspect
a 
soundboard resonance in tune with E5 at that point. If so, the Vise-Grip
on 
the F5 bridge pins, or anywhere in that immediate vicinity, would have a

similar effect. The resonant frequency of the driven should be well
below 
that of the driver. What size (weight) Vise-Grip?

Ron N

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