Topic by Jake Johnson

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  • Jake Johnson
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Topic: Post about phase of lateral and transversal vibrations in guitars

Alan Carruth is a classical guitar luthier who is apparently known for his detailed examination of the physics of the guitar sound board. Interesting series of posts in a discussion of controlling the two two frequency modes on a classical guitar. Note that he is writing about the transmission of vibrations through and across the wood (with the grain and against it) not the vibrations of the strings.

http://www.classicalguitardelcamp.com/v...p?t=101819

I believe he has written more about guitar soundboards, but I have not been able to find his work quickly. Of course, he is talking about guitars, which have a different bracing pattern, so I do not know how much of this applies to a piano sound board, which may also be so thick that cross-vibrations are limited.

Last edited by Jake Johnson (27-09-2016 05:32)

Reply by jcfelice88keys

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Re: Post about phase of lateral and transversal vibrations in guitars

Jake Johnson wrote:

Alan Carruth is a classical guitar luthier who is apparently known for his detailed examination of the physics of the guitar sound board. Interesting series of posts in a discussion of controlling the two two frequency modes on a classical guitar. Note that he is writing about the transmission of vibrations through and across the wood (with the grain and against it) not the vibrations of the strings.

http://www.classicalguitardelcamp.com/v...p?t=101819

I believe he has written more about guitar soundboards, but I have not been able to find his work quickly. Of course, he is talking about guitars, which have a different bracing pattern, so I do not know how much of this applies to a piano sound board, which mayalso be so thick that cross-vibrations are limited.


In a piano's soundboard, the sound is transmitted with about 5 times more efficiency "along" (parallel to) the grains than across the grains.  This is why, the soundboards in cheaper pianos have fewer parallel grains per inch in them than do more expensive soundboards.  Steinway grands usually have 20 to 30 or more grains per inch running parallel in their soundboards, as compared to less than 10 in "house" brands of cheap pianos.

By the way, this is why the grains of spruce are aligned parallel to the bridge in a piano:  that is so that the high tones' vibrations will be carried towards the bass strings, and vice versa.

Cheers,

Joe

Reply by Jake Johnson

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Re: Post about phase of lateral and transversal vibrations in guitars

I haven't been able to find the original articles or essays, yet, but I've run across a few posts on luthier and guitar playing sites that mention his study of how the two sets of vibrations can interact--as you say, the grain of the wood is more efficient, but that means that the added impedance met by the cross-grain vibrations make them a major part of the sustain on some guitars. Which means that they can have either bad effects (phase cancellations, a sour tone) or good effects (simply an increase in sustain and a sense of an evolving timbre). Again, given the different bracing and thicker wood, I'm not sure if a piano's sound board reacts similarly. Wouldn't surprise me if the goal was to reduce the cross grain vibrations as much as possible. on a piano.

Thanks for the information about the transfer on pianos. Where did you learn about the ratio of the vibrations' transfer> (The 5-times greater speed of the vibrations along the grain of the wood?    )

Last edited by Jake Johnson (30-09-2016 06:09)

Reply by jcfelice88keys

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Re: Post about phase of lateral and transversal vibrations in guitars

Jake Johnson wrote:

Thanks for the information about the transfer on pianos. Where did you learn about the ratio of the vibrations' transfer> (The 5-times greater speed of the vibrations along the grain of the wood?    )

Hello Jake

See Larry Fine's "The Piano Book"

Joe