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#2137057 - 08/22/13 09:51 AM twangy note - what really should be done?
swampwiz Offline
500 Post Club Member

Registered: 03/07/07
Posts: 562
Loc: Louisiana, USA
I've resolved myself to get the twangy Eb (154 Hz) note on my Petrof IV grand fixed when I get it tuned in a few months. This problem is especially noticeable when hit strongly.

Now as I understand it, typically the cause is not the string itself (nor any associated brackets, etc.), but rather some strange resonance that cannot seem to get fixed (as a former vibroacoustic rocket scientist, I strongly doubt that, though!), and that the standard treatment is simply to voice down the hammer. One problem I've always had with this theory, however, is that with such a high transfer function attributable to something about the whole piano, there should be adjacent strings that show similar behavior - which in my case, they don't.

And it seems that doing that revoicing would make that string deader, changing the timbre. Of course, it could be that the twanginess is merely the high transfer function for a bunch of higher harmonics - and that by voicing it down, the input at those higher frequencies becomes much lower, so that the high transfer function ends up making those higher frequencies be at the proper level of attenuation. Somehow, it seems that the combination of the high transfer function and the deadened hammer would not properly smooth out the net transfer function, and the string will continue to sound funky compared to the others. I don't know, maybe one of the hallmarks of a quality piano is to have the funkiness of any strings be a little as possible, and that the Petrof, as barely in the 2nd tier (i.e., old the Roman numeraled line) can be expected to have this, whereas a high 1st tier brand like a Bösendorfer, etc. would not.

(For folks here that do not know what a "transfer function" is, it is basically the ratio of the energy of the resultant vibration to the energy of the input strike.)


Edited by swampwiz (08/22/13 09:53 AM)

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#2137072 - 08/22/13 10:27 AM Re: twangy note - what really should be done? [Re: swampwiz]
Withindale Offline
2000 Post Club Member

Registered: 02/09/11
Posts: 2172
Loc: Suffolk, England
My piano used to make several horrid noises in that register. The cure was aligning and mating the hammers to the strings, and seating the strings properly. No voicing.

Also my upright had a twangy note at the tenor bass break. It's been ok since the last tuning.
_________________________
Ian Russell
Schiedmayer & Soehne, 1925 Model 14, 55" upright
Ibach, 1922 49" upright (project piano)

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#2137093 - 08/22/13 11:24 AM Re: twangy note - what really should be done? [Re: Withindale]
swampwiz Offline
500 Post Club Member

Registered: 03/07/07
Posts: 562
Loc: Louisiana, USA
Originally Posted By: Withindale
My piano used to make several horrid noises in that register. The cure was aligning and mating the hammers to the strings, and seating the strings properly. No voicing.

Also my upright had a twangy note at the tenor bass break. It's been ok since the last tuning.


OK, so I should tell the technician to do this alignment & mating? It seemed that last time I had it tuned, and asked about it, he said that he could try voicing it. Perhaps I need to get another tech!

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#2137107 - 08/22/13 11:47 AM Re: twangy note - what really should be done? [Re: swampwiz]
BDB Offline
Yikes! 10000 Post Club Member

Registered: 06/07/03
Posts: 22173
Loc: Oakland
Perhaps you do. If a customer complained to me about one note standing out, I would just fix it. But it takes knowledge and experience to know how to do it quickly and well.
_________________________
Semipro Tech

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#2137112 - 08/22/13 11:53 AM Re: twangy note - what really should be done? [Re: swampwiz]
Ed Foote Offline
1000 Post Club Member

Registered: 05/03/03
Posts: 1292
Loc: Tennessee
Originally Posted By: swampwiz
I've resolved myself to get the twangy Eb (154 Hz) note on my Petrof IV grand fixed when I get it tuned in a few months. This problem is especially noticeable when hit strongly.

And it seems that doing that revoicing would make that string deader, changing the timbre. Of course, it could be that the twanginess is merely the high transfer function for a bunch of higher harmonics - and that by voicing it down, the input at those higher frequencies becomes much lower, so that the high transfer function ends up making those higher frequencies be at the proper level of attenuation. Somehow, it seems that the combination of the high transfer function and the deadened hammer would not properly smooth out the net transfer function, and the string will continue to sound funky compared to the others.
(For folks here that do not know what a "transfer function" is, it is basically the ratio of the energy of the resultant vibration to the energy of the input strike.)


Greetings,
First, do no harm. Swap the hammer and shank from next to the twang and see if it is the string or the hammer. If the string is faulty, and many bass strings are, you don't want to ruin the hammer. If another hammer produces the same twang, and the strings are mated to the hammer, it is a string problem. Change them. If the problem is still there, you have a resonance problem, and yes, there are some that defy discovery.
Regards,

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