Pianotech

  • 1.  Steinway O Chladni Figure

    Posted 06-16-2019 00:52
    My latest Chladni Video. 
    https://www.youtube.com/watch?v=iiP_6aSAbm8&t=2s

    It's interesting to compare this 1919 Steinway O video with my  previous 1902 Mason and Hamlin AA video.
    https://www.youtube.com/watch?v=aFbb1mzhx5E
    enjoy!
    -chris

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    Troubles are Bubbles, and they just float away.
    chernobieffpiano.com
    grandpianoman@protonmail.com
    Knoxville, TN
    865-986-7720
    ------------------------------


  • 2.  RE: Steinway O Chladni Figure

    Registered Piano Technician
    Posted 06-16-2019 10:53
    Chris,

    Very interesting.  What do you use (and how) to generate the frequency?

    Pwg

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    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
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  • 3.  RE: Steinway O Chladni Figure

    Posted 06-16-2019 14:01
    Hi Peter,
    Just a phone app through the stereo system. I place one speaker under the piano. Easy.
    -chris

    ------------------------------
    Troubles are Bubbles, and they just float away.
    chernobieffpiano.com
    grandpianoman@protonmail.com
    Knoxville, TN
    865-986-7720
    ------------------------------



  • 4.  RE: Steinway O Chladni Figure

    Registered Piano Technician
    Posted 06-16-2019 18:35
    I'm going to try it on an M and a B here in the shop.

    Pwg

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    Peter Grey
    Stratham NH
    603-686-2395
    pianodoctor57@gmail.com
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  • 5.  RE: Steinway O Chladni Figure

    Posted 06-16-2019 19:32
    And report the results. I think just mode 1 is good enough. Watch for where the node is in the treble. If it goes into the top two sections, I believe that is a weakness and is not desirable. I have been using walnut shells(sandblasting medium from harbor freight) as it moves quite well.
    Good luck!
    -chris

    ------------------------------
    Troubles are Bubbles, and they just float away.
    chernobieffpiano.com
    grandpianoman@protonmail.com
    Knoxville, TN
    865-986-7720
    ------------------------------



  • 6.  RE: Steinway O Chladni Figure

    Posted 06-18-2019 09:19
    That’s cool, Chris - I use this method with smaller string instruments such as guitars and violins. I find it to be a very useful tool in the quiver for fine-tuning the stiffness characteristics of soundboards, as well as the box when it’s closed up. It’s also a great way to compare different instruments, and identify where different modes land frequency wise, as well as mode shapes, etc, etc.
    I’m currently restoring a small Bosendorfer (170 from 1912) and I have been looking forward to running modal analysis on it just as you describe. I typically use tea leaves, and I use a frequency generator app off of my laptop. I run this through an amp, with the speaker placed under the soundboard. I will sometimes also use a small hand held speaker which will work just as well as on smaller instruments, (mAy also work on piano on mid / treble modes?). In the d days I used a stAnd-one frequency generator for sweeping up through the f range. One word of caution is to use hearing protection, as the acoustic energy to drive a clear mode can sometimes be quite high, and deceptively so because of the pure tones and focused frequencies. I’m REALLY interested in this topic, if you haven’t guessed :-) Based on my experience with other string instruments, this almost certainly has potential to be useful for soundboard development.
    Regards, John

    Sent from my iPhone




  • 7.  RE: Steinway O Chladni Figure

    Posted 06-18-2019 12:07
    This has greater importance to the wider tuning community than has perhaps been appreciated.

    The thread about the three strings tuned together lowering the pitch was fascinating. For me it seems that inharmonicity is more likely to arise from the lengthened effect of the fundamental frequency as a result of the soundboard becoming part of the vibration than it is from longitudinal modes, or imperfect resonation due to the thickness of the string. Obviously a soundboard and bridge will vibrate with the fundamental vibration of the string but the harmonics of the string won't have such energy, so that the soundboard won't be vibrating with it and the harmonics will be confined between agraffes and bridge, whereas the fundamental node will be beyond the bridge.

    The interaction between soundboard vibrations at different pitches, the way in which notes of the scale can interact with different harmonics of different pitched strings and - terrifying word - the temperament of the scale used for tuning will all interact in different and extremely complex ways.

    Tea leaves might seem to be a very much less intrusive indicator medium and perhaps might allow such experiments to be conducted "live" as strung looking at the system rather than the soundboard component alone. But the soundboard component alone is a root part of the system.

    Best wishes

    David P





  • 8.  RE: Steinway O Chladni Figure

    Registered Piano Technician
    Posted 06-19-2019 12:37
    David Pinnegar wrote:

    "Obviously a soundboard and bridge will vibrate with the fundamental vibration of the string but the harmonics of the string won't have such energy, so that the soundboard won't be vibrating with it and the harmonics will be confined between agraffes and bridge, whereas the fundamental node will be beyond the bridge."

    I don't understand this statement.  Are you suggesting that the string harmonics never reach the soundboard?  That doesn't make sense and is easy enough to demonstrate by simply playing one of the harmonics by itself (by touch the string at the node when it is struck).  The sound emanating from that is certainly coming from the soundboard not from the string alone and is not confined between the agraffes and bridge. 

    On the entire subject, the natural frequency of the assembly is of some interest to me as I've wondered about whether assemblies with lower natural frequencies produce a more pleasing sound than those with higher NFs, especially in the cases where severe modifications (like large cutoff bars) can change the NF more substantially and generally a higher pitched knocking sound in a piano is less pleasing than a lower pitched one, IMO.  How exactly that lowest natural frequency is related to the characteristics of the sound at "attack" is still unclear to me.    

    Still probably best to stipulate that the natural frequency of an assembly doesn't limit the frequencies at which it can vibrate.  And in the case of the harmonics, or partials, they certainly have enough energy to move the assembly on their own.  

    This very technical article might be of some interest: https://eprints.soton.ac.uk/408405/1/20160514_postprint.pdf

    As well as this classic article from Conklin: https://www.speech.kth.se/music/5_lectures/conklin/howdoes.html







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    David Love RPT
    www.davidlovepianos.com
    davidlovepianos@comcast.net
    415 407 8320
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  • 9.  RE: Steinway O Chladni Figure

    Posted 06-16-2019 21:54
    Thanks so much for doing these experiments

    Do all pianos have their f0 mode in the 40-50Hz region?  What is the effect of lower?

    Are the resonant modes expected multiples of f0?

    When strings vibrate the soundboard below the resonant frequency is the projection of the instrument's sound different?

    Best wishes

    David P

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    David Pinnegar, B.Sc., A.R.C.S.
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    +44 1342 850594





  • 10.  RE: Steinway O Chladni Figure

    Posted 06-16-2019 23:18
    Thank You David.
    I believe I am the first person to do experiments like this on multiple pianos to determine characteristics, All the other studies i have seen focused on one instrument. I'm glad that i took this approach, as i am learning some interesting things not mentioned anywhere else that has real value tp me.
    For instance, The Mason and Hamlin AA Chladni figure did not enter the top two sections in the treble. The Baldwin L in my shop also was the same as the MHAA. The Steinway O on the other hand did.  I have confirmed this with the examination of those pianos rib scales. The Steinway ribs #8 and #7 are too weak.​​  I'm sure it will be worse in a diaphramatic soundboard.

    So the chladni figure is a good tool to check for that weakness. So don't copy a Steinway rib scale, it can be improved.

    Regards to the fundamental frequency and what it should be.  The lower the better. But there are engineering limits. In every case so far, i have seen where improvements can be made. The bigger the piano the lower the frequency will be. The Steinway O was the smallest of my three tests, and thus had the highest frequency.  There will be comparisons when the new boards are installed  as well. I'm looking forward to that.
    I will be fixing ribs 8 and 7 in the new board and looking forward to that chladni figure.
    -chris




    ------------------------------
    Troubles are Bubbles, and they just float away.
    chernobieffpiano.com
    grandpianoman@protonmail.com
    Knoxville, TN
    865-986-7720
    ------------------------------