Topic by Jake Johnson

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  • Jake Johnson
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Topic: Longitudinal motion in the news

There's a PianoWorld discussion going on that touches, more than usually, on several of the subjects that have often come up here--longitudinal vibrations and the quadratic effect, the effect of different wire lengths, inharmonicity, etc. Apparently, longitudinal waves are hot right now, although there is some debate about their contribution. One argument is that they can to some extent be tuned to fall into concord with the lateral vibrations: [EDIT: I originally wrote, for "quadratic effect," the "Q-factor," for someone on PR forum has used the term "Q factor," when meaning, I think, the quadratic effect.]

http://www.pianoworld.com/forum/ubbthre...%20mo.html

A brief thread that also brings up the James F. Ellis book on longitudinal waves:

http://www.pianoworld.com/forum/ubbthre...%20mo.html

Last edited by Jake Johnson (12-02-2013 17:01)

Reply by tractor_music

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Re: Longitudinal motion in the news

Thanks for the pointer, I found the 5 lectures interesting.
25 years later...  I wonder how much more is understood - and of that how much is applied.

Reply by jcfelice88keys

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Re: Longitudinal motion in the news

Hello Jake,

Although I am in no way an expert on longitudinal waves in a vibrating piano string, I am aware that changing the weight (mass) of the hammers may disrupt the resonance pattern of longitudinal waves. 

Here's why: 
If we agree that the "speed" of the traversing longitudinal "ripple" is over ten times the speed of the transverse vibration, one must caution against a heavier hammer still remaining in physical contact with the string when the longitudinal "ripple" reflects back along the string.  Restated, some damping may occur by the hammer itself, if the latter has too much mass and has not physically rebounded from the string by the time the first few ripples return.

Cheers,

Joe

P.S.  I have encountered the bad effects of longitudinal waves in lower end (cheaper) pianos whose dual copper-wound strings are about to give way to three steel strings (trichords).  This usually occurs in the half octave range around C3, in the octave below middle C.  When I tune those offending strings, such that their fundamental pitches are aligned with the rest of the piano, one hears a horribly high pitched ringing sound (the actual longitudinal waves being reinforced) in these strings.  If I detune the string to rid it of excessive longitudinal waves, the note is out of tune.

Corrective action consists of two options:  1) live with the ringing sounds, or 2) detune the entire diapason of the piano such that the so-called detuned ringing notes no longer ring.  This involves lowering the pitch to A439 or A438.  Most of the time I live with the ringing.

Cheers,

Joe

Reply by Jake Johnson

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Re: Longitudinal motion in the news

There is also a 3 page thread about the Quadratic effect (understood as longitudinal motion):

http://www.pianoworld.com/forum/ubbthre...391/1.html



And another thread about the possibility of tuning the longitudinal motion:

http://www.pianoworld.com/forum/ubbthre...ost1950692

Reply by Jake Johnson

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Re: Longitudinal motion in the news

jcfelice88keys wrote:

Hello Jake,

Although I am in no way an expert on longitudinal waves in a vibrating piano string, I am aware that changing the weight (mass) of the hammers may disrupt the resonance pattern of longitudinal waves. 

Here's why: 
If we agree that the "speed" of the traversing longitudinal "ripple" is over ten times the speed of the transverse vibration, one must caution against a heavier hammer still remaining in physical contact with the string when the longitudinal "ripple" reflects back along the string.  Restated, some damping may occur by the hammer itself, if the latter has too much mass and has not physically rebounded from the string by the time the first few ripples return.

Cheers,

Joe

P.S.  I have encountered the bad effects of longitudinal waves in lower end (cheaper) pianos whose dual copper-wound strings are about to give way to three steel strings (trichords).  This usually occurs in the half octave range around C3, in the octave below middle C.  When I tune those offending strings, such that their fundamental pitches are aligned with the rest of the piano, one hears a horribly high pitched ringing sound (the actual longitudinal waves being reinforced) in these strings.  If I detune the string to rid it of excessive longitudinal waves, the note is out of tune.

Corrective action consists of two options:  1) live with the ringing sounds, or 2) detune the entire diapason of the piano such that the so-called detuned ringing notes no longer ring.  This involves lowering the pitch to A439 or A438.  Most of the time I live with the ringing.

Cheers,

Joe

I wish we could experiment with the hammer mass in our favorite modelled piano. And I miss the Quadratic effect. Which was, perhaps, hammer mass in disguise?