Topic by Glenn NK

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  • Glenn NK
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Topic: The Self-Tuning Piano

Interesting concept.  Not easy to understand right at first unless one pays attention, and exercises "reading comprehension" ( unfortunately not always well exercised).

http://www.pianoworld.com/forum/ubbthre...Piano.html

My interpretation:

Initially the string heating system is turned ON.

The first key element is that the strings are warmed by applying a current to the tuning pins, which flows through the strings; the plate/frame is the common ground.  The strings have resistance, and warm up when heated.  Heating causes expansion in length which lowers the pitches.

When the system is on and the strings are warm, the piano is tuned in the standard manual method to whatever pitch and temperament is desired.

The second key element here is that the strings are warmed up to about 35C/95T.  The strings now elongate and their pitch drops.  BUT note that they are tuned when warm, so will be in tune only when warm.

The third key element is that the system can record the exact pitch of each individual string and store it in memory.  So whatever pitch and temperament the piano is tuned to is the reference for subsequent tunings by the system.

Now suppose that a string or strings slips - which lowers the pitch making it flat.  Turn on the system, the strings warms, a little device at each string induces vibration into the strings while other devices measure the frequencies which are then compared to the base frequencies.  The system discovers that those strings are flat, and lowers the voltage of the offending (flat) strings which permits them to cool, and raises their pitch to the correct value.  The piano with its warm strings is now back in tune.  Apparently this process only takes a minute or so.

If a string goes sharp (this often occurs in climates when humidity rises causing the sound board to arch more raising the tension and the frequencies in the mid range), any offending string/s will be warmed more than the others to lower their pitch.

Every time the piano is to be played, the system warms the strings, vibrates them, checks their frequencies, and adjusts the voltage/current to a temperature that will put the strings in tune.

During playing, the warming system remains on.

Glenn

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Reply by jcfelice88keys

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Re: The Self-Tuning Piano

Glenn NK wrote:

Interesting concept.  Not easy to understand right at first unless one pays attention, and exercises "reading comprehension" ( unfortunately not always well exercised).

http://www.pianoworld.com/forum/ubbthre...Piano.html

My interpretation:

Initially the string heating system is turned ON.

The first key element is that the strings are warmed by applying a current to the tuning pins, which flows through the strings; the plate/frame is the common ground.  The strings have resistance, and warm up when heated.  Heating causes expansion in length which lowers the pitches.

When the system is on and the strings are warm, the piano is tuned in the standard manual method to whatever pitch and temperament is desired.

[ ... ]

During playing, the warming system remains on.

Glenn

Hello Glenn,

I agree with your interpretation of the concept.  Something that concerns me is the practical application of such a system, especially in a system of reasonable cost and maintenance. 

There are approximately eighteen (18) individual wire gauges spread across the 88-note key range in the average piano.  I believe if a single voltage source is applied to the strings, and it relies on the steel frame as a common ground, I question the reproducibility of maintaining elevated temperatures throughout the entire lengths of all 200+ strings.

Restated, a change in +/-6% in string tension results in a semitone's worth of pitch change (100 cents), either upward or downward.  In order to keep the strings tuned within, say, 2 cents requires voltage and temperature control within 1/50th of 6% (or 0.12% accuracy).  Although this can be attained in theory, I question if such accuracy can be attained at reasonable cost.  Ironically, when listening to the YouTube video, the supposedly "in tune" notes were not tuned as precisely as I would do in practice -- some low-frequency warbling of overtones were perceived.

Cheers,

Joe

Last edited by jcfelice88keys (30-01-2012 04:20)

Reply by Glenn NK

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Re: The Self-Tuning Piano

Joe:

The way I understand it is that different length/diameter strings receive different voltages at the beginning - resistance varies directly with length and inversely with cross sectional area (true for DC, and low frequency AC - ultra high frequency is a different matter - the current flow is primarily around the perimeter in this case).

It's not a difficult calculation to ascertain the required voltage for a given length/diameter to achieve a given pitch drop.

In the video at 2:09, there is a still photo of part of the electronics and written on the photo are the words "Tuning accuracy +/- 0.001 cents."

The warbling has been pointed out by others in the thread, but I haven't seen a reply to this.

Near the end of the thread, about questions of electrically insulating the strings, he mentioned that a material called PEET is used.  One of the problems is that different pianos have different requirements.  Some have agragges, while not all do (at the keyboard end)- others have what I would call a steel bridge (I know this is incorrect), so the solution will vary with the piano.  There is no one-size-fits-all solution.

I was at my friend's piano shop last week and there were variations between a Yamaha C7, an older Steinway 5'-8" (don't recall the model), and a third (I think it was a Pramberger).  Then throw in duplex/triplex scaling (some pianos have it at both ends of the strings), and it becomes a nightmare.  Thankfully the (true) bridge is wood.

Practical in terms of cost?  This is when I'm from Missouri as the saying goes.

Glenn

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Reply by jcfelice88keys

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Re: The Self-Tuning Piano

Glenn NK wrote:

Joe:

<...>
In the video at 2:09, there is a still photo of part of the electronics and written on the photo are the words "Tuning accuracy +/- 0.001 cents."

The warbling has been pointed out by others in the thread, but I haven't seen a reply to this.
<...>
Practical in terms of cost?  This is when I'm from Missouri as the saying goes.

Glenn

Hello Glenn,

It is always very pleasant to have intelligent conversations with you and others in this forum. 

I do recognize from the video that the tuning accuracy was described in terms of +/- 0.001 cents.  Of course that is the initial tuning accuracy when the strings are at their optimum temperatures, and the tuning has been just completed.  My personal concern has to do with the repeatability and reproducibility of that tuning accuracy, as a function of maintaining the optimum string temperature. 

+/-0.001 cent tuning accuracy  <===> warbling overtones

Something does not compute!   It remains a fascinating subject, as I hope a self-tuning piano will become a reality in the near future.  I am always amazed at the cleverness that inventors reveal when they present technologies such as these.

I did perform a Google search on the PEET covering.  Nothing seemed to turn up right away; I speculate that such a coating sprayed onto the strings must give their surfaces some type of dielectric quality.


Cheers,

Joe

Reply by Glenn NK

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Re: The Self-Tuning Piano

Joe:

Sorry, I was sloppy or forgetful - the material is PEEK. But I'm not sure just how the material is used or formed into agraffes (for example).

http://drakeplastics.com/More_On_PEEK.h...Qgod1kPyuQ

http://en.wikipedia.org/wiki/PEEK

I too wonder about the ability of the system to achieve a repeatable tuning.

Glenn

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Reply by tractor_music

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Re: The Self-Tuning Piano

If it works (& I suspect that it probably does) then it is probably one of the things that I would want to not do to an acoustic piano.

It is ONLY at tuned tension when switched on and warmed up for playing, the rest of the time all strings are "cold" (room temperature) and over tensioned. 

I think it would be bad to subject a piano to such daily tension excursions for several months of winter.