Topic by nowork

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Topic: Kawai Piano Resonance

Hi everyone!

I have a Kawai CA63 digital piano at home that exhibits the following behavior:
When I hold a key pressed silently, and staccato play a key right next to it [a semitone higher/lower], then I can hear the silently depressed key ringing.

I made a video, though you might need good speakers/headphones to hear the effect:
http://www.youtube.com/watch?v=xJreG6BF...e=youtu.be

I sent an email to Kawai and they said that the acoustic piano they took the samples from behaves exactly the same. I also posted elsewhere and Kawai acoustic piano owners said the effect is indeed present in their pianos as well. But other said this is not normal/this behavior is not present in their acoustic pianos.

And I'm intrigues by this behavior. I calculated the partials that C has in common with all other notes up to the 10th harmonic: https://docs.google.com/spreadsheet/ccc...DNtN0o5ZFE. It doesn't share any partials with B or C#! And indeed pianoteq responds according to this document. But does anyone have any idea why Kawai [maybe other?] pianos would exhibit the above described behavior?

Reply by EvilDragon

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Re: Kawai Piano Resonance

That's how pianos behave.

Hard work and guts!

Reply by sebion

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Re: Kawai Piano Resonance

When you strike a piano key the knock noise of the hammer and the action contains quite any frequency. This knocking sound can excite every string that is not blocked by a damper. The strength of this coupling depends on a lot of parameters like the hammer hardness, the hardness of the felt in the keybed, etc...
maybe this effect is too week on other pianos to be heard by the owners, or they simply didn't do the test right

BTW pianoteq shows the same behaviour, but it is very weak, if you strike adjacent keys, that do not share much overtones. You can only hear it when you increase the sympathetic resonance to its maximum and raising the volume of your speaker/headphone.

Last edited by sebion (11-09-2012 15:36)
DIY digital piano on salvaged piano action with homemade optical sensor bar: http://sebion.wordpress.com

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Reply by nowork

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Re: Kawai Piano Resonance

Ah, thanks! I didn't know Pianoteq shows this behavior, I'll try it when I get home.

Other have postulated the same thing, that it comes from the hammer knock noise, but I wanted some evidence, like a study or something of the sort. Because the effect is really pronounced for the key a semitone higher/lower, but not so much so for others.

Any other ideas why C responds sympathetically when C# or B is played, even though it doesn't share any partials with either of them*?

*up to the 10th partial

Reply by sebion

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Re: Kawai Piano Resonance

The hammer knock noise is transferred to the soundboard which is also coupled to the strings that are not damped. I would guess such a knock noise will affect the strings nearest to the source most, that would explain this behaviour.

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Reply by mooks

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Re: Kawai Piano Resonance

You can consider the adjacent undamped strings a bit like "driven harmonic oscillators". They WILL resonate with the frequencies of the struck note, just not very strongly. When the struck note is damped, the excited adjacent strings will shift to resonate at their natural frequencies. And this is the lingering sound you hear.

The amount a harmonic oscillator resonates due to being driven by some external oscillation depends on how close the driving frequency is to the natural frequency (hence this only happens for adjacent notes) and also on the physical properties of the oscillator (such as the "Q factor").

Reply by nightwatch

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Re: Kawai Piano Resonance

sebion wrote:

The hammer knock noise is transferred to the soundboard which is also coupled to the strings that are not damped. I would guess such a knock noise will affect the strings nearest to the source most, that would explain this behaviour.

Simply put, wouldn't this just be due to amplitude? If I line up 88 people with slightly different heights, and I shout out load, the ears of the two guys on either side of me are going to ring the most. In other words, the heights don't matter. It's just the fact that the lower frequency knock makes whatever is close to it ring because of amplitude. Simple as that, right?

Regards,
Steve Steele
stevesteele.com
Music theorist, composer, Vienna Ensemble Pro templates, YouTube channel (Mains: 2 Mac Pros, Digital Performer, Vienna Ensemble Pro, and an iPad Pro.)

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