Impedance Problem

[David Love]

Not really on this post.  Aside from changes in tension that often occur
at the bass tenor break, the fact that these two areas of the soundboard
differ both in terms of rib placement and proximity to the rim can cause
impedance differences unrelated to resonant frequency issues.  I've
gotten into the habit of balancing these sections with the placement of
brass weights underneath the bridge where it seems necessary.  Nothing
scientific, add and listen and when it seems right, put it there more
permanently.  In this case, the small vise grips probably did not add
enough mass to change the impedance and it probably would not have had
an effect on only one of two adjacent notes (as Ron N. pointed out).
The more likely culprit in this case was resonant frequency and the vise
grips just changed things enough to disturb the natural frequency of
that section.

David Love
davidlovepianos@comcast.net 

-----Original Message-----
From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On
Behalf Of Richard Brekne
Sent: Saturday, January 22, 2005 1:16 PM
To: pianotech@ptg.org
Subject: re: Impedance Problem

Hi Dave

I assume we are still talking about the vise grips on the back bridge 
pin absorbing quite a bit of sound for that loud note... but doesnt 
effect the neighboring notes.

I'd like to know whether you tried moving the grips to each adjacent 
note and observing the behaviour of these same notes

Impedance problems per definition a related to resonant frequencies, and

their nodes and anti nodes in the soundboard. If you are right on a 
node, any input frequencies that correspond to that node frequency will 
get sucked up more or less.  On the other hand...if you are right at the

antinode for a resonant frequency and input that frequency... its going 
to be readily resonated.

This is all better described in the 5 Lectures.

Cheers
RicB

>
>I think there are two issues.  One is impedance matching (or lack of)
>between the low end of the tenor bridge and the top end of the bass
>bridge.  The other issue is resonant frequencies when there is a
>sympathetic match between a certain note and a section of the
soundboard
>that it excites.
>
>David Love
>davidlovepianos@comcast.net 
>
>  
>

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