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Strange resonance
#2986354 05/31/20 08:34 PM
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Hi, I have been working on an 1897 or so Hazelton Brothers large ornate upright.
Everything is now beautiful except there is a strange annoying resonance when I play some bass strings, always less than an octave higher, for example playing C, the resonance is in B flat.
I'm at a loss to figure out where it is coming from. I just raised the pitch up to proper levels, from way low, breaking 2 strings but I replaced them. I tuned it myself and it is mostly good. This resonance changes with the key, always the same above the note pressed. You guys have helped me a lot on this project, thanks.

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Re: Strange resonance
Paul Roder #2986359 05/31/20 08:50 PM
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You mentioned in another post about the extreme angle of the hammers, and you filed the edges to match the originals. Check to make sure the left part of the hammer isn't hitting the right string of the next lower note just slightly.


Eric Gloo
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Certified Dampp-Chaser Installer
Richfield Springs, New York
Re: Strange resonance
Paul Roder #2986377 05/31/20 09:53 PM
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Thanks Eric! That was a great suggestion. I just checked and muted the neighboring strings just to be sure. The hammers hit only the correct strings. The filing was to stop the hammers catching on the neighbors. Something is causing a weird harmonic. Maybe it is more obvious since I tuned it? I don't remember it being this bad before I tuned it. Plus it is all the notes in that section. The harmonic adjusts with the notes.

Re: Strange resonance
Paul Roder #2986410 06/01/20 12:55 AM
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When you replace the bass strings, did you replace the backscale felt?
-chris


Chernobieff Piano Restorations
"Where Tone is Key"
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Re: Strange resonance
Paul Roder #2986476 06/01/20 06:12 AM
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I only replaced 2 very high treble strings. I did not replace any felt.

Re: Strange resonance
Paul Roder #2986481 06/01/20 06:20 AM
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Speaking of bass strings, I am thinking of taking them off and cleaning them. Is this worth it? And how do you get the wire out of the hole in the pin without damaging it? Loosening then "pry" it out with something? I watched a video where a tech cleaned them and they looked and sounded better.

Re: Strange resonance
Paul Roder #2986527 06/01/20 08:44 AM
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Originally Posted by Paul Roder
Speaking of bass strings, I am thinking of taking them off and cleaning them. Is this worth it? And how do you get the wire out of the hole in the pin without damaging it? Loosening then "pry" it out with something? I watched a video where a tech cleaned them and they looked and sounded better.
try pressing wrinkling it lightly using medical tweezers. Sometimes it helped me

Re: Strange resonance
Paul Roder #2987442 06/03/20 02:15 PM
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Hi, I believe I discovered a reason for the resonance. For these notes, it seems the shorter section of wire above the damper is still vibrating. When I put my finger on that section strings, the resonance quiets immediately. I replaced the damper felts a while ago and they are damping the primary note fairly well. In fact I press on the damper firmer into the strings and the resonance continues, however the harder I push it does reduce some. Is this just a design problem of the piano or did I do something to exacerbate it? The section exhibiting this problem crosses over between the lower 2 string notes and the upper 3 string notes above them then quiets gradually as you go higher above middle C. Is there something I can do to improve this? Dampers not flat enough or something?

Re: Strange resonance
Paul Roder #2987457 06/03/20 02:48 PM
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It could be that the old damper felts do not conform to the new strings. Filing the felt may help, but you are dealing with parts that are over 120 years old, designed for less than 20% of that age. The damper felts probably need replacing, and the damper springs, as well as a host of other things.


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Re: Strange resonance
Paul Roder #2987525 06/03/20 05:14 PM
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Hi. I already replaced all the damper felts (along with all the hammers) . I did nothing with the springs or strings in this section of the piano. I don't think it is the springs primarily because when I press the dampers a little firmer, the resonance of the string section above the damper does not dampen that much. Unless I touch that section with my finger, it immediately ends.

Last edited by Paul Roder; 06/03/20 05:15 PM.
Re: Strange resonance
Paul Roder #2987599 06/03/20 07:47 PM
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I think the end of a damper felt is resting on a node of the string, effectively causing the short part to vibrate independently (so to speak). Try lengthening or shortening the felt on the top end...try 1/4" extra (if it will fit without interfering with the hammer. If that works, trim it progressively till it starts ringing again and then you know how much extra to add.

Obviously if that doesn't work then I'm wrong and ignore what I said.

Peter Grey Piano Doctor


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Re: Strange resonance
Paul Roder #2987618 06/03/20 09:49 PM
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Thanks so much P W! I assume you mean by lengthening the felt, cut it off and glue a new felt piece higher up? I only have a few damper pieces left, precut, with the gap in the middle. After your advice, I just checked and I seem to see a correlation between the distance between the damper felt and the hammers and the effect. One other thing I just realized is I had to cut the damper in half at the worst sounding note, B one octave below middle C, because that is where the bass strings cross over so no room for the damper. (this was done in the original) It is one of the few with the gap in the middle for the center string. These split dampers in that section seem the worst, however the flat one just next seems bad too. Is there a rule when to use the split damper and the flat one? Thank you all. I am pretty sure someone would have thrown out this piano and it is a beautiful piece of history.
I can attach pictures and sound if that will help.

Re: Strange resonance
Paul Roder #2987967 06/04/20 06:35 PM
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Classic problem with uprights due to the fact that it is IMPOSSIBLE to put the dampers in the ideal spot simply because the hammers and dampers are on the same side of the strings so something has to give and its the dampers. The simple rule is that if a flat damper doesn't work, try a trichord. If that doesn't work, add an auxiliary over-damper. If that doesn't work, don't point it out to anyone else.

If you changed the hammers also, it is possible that you altered the strike point too, slightly, or increased the power needing to be damped.

Pwg

Last edited by P W Grey; 06/04/20 06:36 PM.

Peter W. Grey, RPT
New Hampshire Seacoast
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pianodoctor57@gmail.com
https://www.youtube.com/watch?v=PK0T7_I_nV8
Re: Strange resonance
Paul Roder #2988394 06/06/20 10:09 AM
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Originally Posted by Paul Roder
Hi, I have been working on an 1897 or so Hazelton Brothers large ornate upright.
Everything is now beautiful except there is a strange annoying resonance when I play some bass strings, always less than an octave higher, for example playing C, the resonance is in B flat.
I'm at a loss to figure out where it is coming from. I just raised the pitch up to proper levels, from way low, breaking 2 strings but I replaced them. I tuned it myself and it is mostly good. This resonance changes with the key, always the same above the note pressed. You guys have helped me a lot on this project, thanks.

BTW, B flat would be the 7th partial of C. This is highly characteristic of a damper/string node bugaboo.

Peter Grey Piano Doctor


Peter W. Grey, RPT
New Hampshire Seacoast
www.seacoastpianodoctor.com
pianodoctor57@gmail.com
https://www.youtube.com/watch?v=PK0T7_I_nV8
Re: Strange resonance
Paul Roder #2988771 06/07/20 02:09 PM
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Thanks PW. I sort of suspected there is not much I can do. I have no idea how to add an auxiliary damper, "birdcage?" I will just have to always play with damper pedal fully depressed at all times, or perhaps just remove all the dampers. Would anyone like to hear a concert? I was thinking about a damperless minute waltz. It should last about 10 minutes without the dampers smile

Re: Strange resonance
Paul Roder #2988798 06/07/20 03:46 PM
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It might be worth cutting the centre split a little deeper with a razor blade (preferable a single-edge blade, which is rigid and safer) and see if that helps it seat more effectively on the strings.

Years ago an older upright had a damping problem in the first bi-chord after the break, and I replaced the wedge damper felt with a new felt of the same size, from a pre-cut set. Nothing I could do by careful adjustment would get it to damp properly! In my box of felts I had a strip of wedge damper felt that was of slightly larger profile (not grand damper felt though) and I cut a piece of that to size and fitted it. It worked perfectly, straight away!

Auxiliary dampers are sometimes called "fly dampers" and I think it would be fiddly to make and fit one to an existing damper head. There is a picture of a set of fly dampers about two-thirds of the say down the Bechstein page of my website.

Re: Strange resonance
Paul Roder #2988821 06/07/20 04:56 PM
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Before you do anything else, take a plectrum of some sort and strum all the strings that are damped with the dampers on, that is, no pedal and no keys depressed. Localize any notes that stand out by strumming fewer and fewer strings. When you have located all that resonate longer than the others, deal with them before you attempt any modifications, starting with the lowest problem notes, because they may be the problem with higher notes. You may need to change the angles of the dampers to ensure that they are square on the string, and you need to check if they are lifting too soon pressing either the pedal or the key.


Semipro Tech
Re: Strange resonance
BDB #2988899 06/07/20 10:36 PM
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Originally Posted by BDB
. You may need to change the angles of the dampers to ensure that they are square on the string, and you need to check if they are lifting too soon pressing either the pedal or the key.
I had that problem of angles of the dampers. It was old germany upright. I changed it's angles there.

Re: Strange resonance
BDB #2989031 06/08/20 11:31 AM
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Originally Posted by BDB
Before you do anything else, take a plectrum of some sort and strum all the strings that are damped with the dampers on, that is, no pedal and no keys depressed. Localize any notes that stand out by strumming fewer and fewer strings. When you have located all that resonate longer than the others, deal with them before you attempt any modifications, starting with the lowest problem notes, because they may be the problem with higher notes. You may need to change the angles of the dampers to ensure that they are square on the string, and you need to check if they are lifting too soon pressing either the pedal or the key.



This is good advice. Also, uneven string levels can create havoc with damping and takes some finesse and careful diagnosis to correct.


Peter Grey Piano Doctor


Peter W. Grey, RPT
New Hampshire Seacoast
www.seacoastpianodoctor.com
pianodoctor57@gmail.com
https://www.youtube.com/watch?v=PK0T7_I_nV8
Re: Strange resonance
BDB #2992229 06/16/20 11:50 PM
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Thanks so much for this advice! I will try it.

Last edited by Paul Roder; 06/16/20 11:51 PM.
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