Modal Analysis

[Greg Newell]

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Del,
         Thank you! Those answers serve to solidify a great deal of my=20
ideas about soundboards in general. I was hoping I was on the right track.=
=20
I guess I'm getting there a little bit at a time.

Best,
Greg



At 09:34 PM 5/9/2003, you wrote:

>
>----- Original Message -----
>From: "Greg Newell" <<mailto:gnewell@ameritech.net>gnewell@ameritech.net>
>To: "Pianotech" <<mailto:pianotech@ptg.org>pianotech@ptg.org>
>Sent: May 09, 2003 3:46 PM
>Subject: Re: Modal Analysis
>
>
>Del,
>          I wonder if you might help me understand this. You say, "And a
>good example of why soundboard cutoff bars can (should) be used to some
>advantage." In the views I saw on the web page there seemed to be quite a
>bit of movement in the area normally eliminated by a cutoff bar.
>
>Yes, and it is exactly out of phase with the motion of the bridge and the=
=20
>area of the soundboard surrounding the bridge.
>
>
>
>----------------------------
>If there
>is that much movement is that not contributing to what we hear rather than
>detracting from it? As I type and look back at the pictures in another
>window I'm tempted to rationalize that while one part of the board,
>specifically that part in question, is on the down part of a wave the rest
>of the board is up and visa versa. Is this what you wish to eliminate with
>the cutoff bar so that the board acts as a whole instead of in separate
>parts? It would be interesting to see what the board would do using this
>modal analysis with a cutoff bar installed.
>Yes, this is what I am trying to eliminate with the addition of a=20
>carefully placed cutoff bar. Energy is being traded back and forth and is=
=20
>essentially being wasted. Going back to my analogy of the piano soundboard=
=20
>functioning somewhat like loudspeaker driver: the soundboard functions=20
>best when it is appropriately sized for the frequency range through which=
=20
>it is expected to function. If it is too small it is great for sustain but=
=20
>will not be able to develope the desired power. If it is too large,=20
>however, both sustain and power suffer. Sustain because energy is being=20
>wasted in the excess soundboard area and power because acoustical energy=20
>is being traded back and forth between the various resonant areas and is=20
>effectively cancelled out.
>
>
>
>----------------------------
>          This brings me to another question. In all of the examples I've
>seen of pictures with cutoff bars installed, all seem to be a great deal
>smaller in size than the corresponding inner rim section they are
>replacing. I understand that they are epoxied into the existing inner rim
>and doweled as well. I further understand, I think, that the cutoff bar is
>attached to any support beams over which it passes. Do the combinations of
>these items make it unnecessary that it be of similar dimension as the
>inner rim?
>
>Yes. That and the fact that they are generally rather short. Early on we=20
>did try to make them somewhat more massive but over time have found that=20
>this is not really necessary. I don't have any formula for this, I just=20
>look at the thing and decide. If it is quite a long cutoff I'll make it=
 taller.
>
>Del
>
>---
>
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>Version: 6.0.474 / Virus Database: 272 - Release Date: 4/18/2003

Greg Newell
Greg's piano Fort=E9
mailto:gnewell@ameritech.net=20

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