Impedance problem

[Ron Nossaman]

>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