> From: Jeff Atkisson <jeffkiss at sonic.net> > Date: February 16, 2011 12:42:22 PM EST > > Hi, you all don't really know me - but maybe you have a quick answer for me. > > It's a Stenway M. > Octave 6 and 7 (mainly) > Play a fourth or a fifth say from E6. > Strange (to me) "buzzing' or humming sound at a lower harmonic (i.e. at approximately E5 when playing E6-B6). > Piano is in tune. (does it with single strings) > Only does it it with intervals (not single notes). > Lasts for around a second or two ... > Does it with most of the intervals played in this range (not in high treble or below about C6). > It muddies the sound of chords and intervals there. > > It seems like its the board but I can't seem to stop it by pressing on ribs - although I haven't done extensive searching in this regard. > > You all know what this is? > > Please don't tell be its my ears or my imagination ... > > pretty sure I could catch it with a mic if I could post the sound clip. > > Thanks > > Jeff Hi Jeff, You are probably hearing a difference tone. Sum and difference tones are tones that are produced at the sum and difference between the frequencies of two simultaneously sounding tones. Of the two, only the difference tone is often heard in pianos, and it is often most audible in the mid to upper treble with perfect intervals, somewhat as you describe. As an example, let's for a moment forget inharmonicity just to make the math easier (think of an organ instead of a piano if that simplification offends you). The note A4 is at 440, with partials at 880 (A5), 1320 (E6), 1760 (A6), and so on, as you surely know. Now, if you play E6 (1320) and A6 (1760) together, you will (or may, depending on the strength of the fundamentals of those two notes, and on your aural perceptiveness, of course) hear a difference tone at: 1760 - 1320 = 440, or A4. That's a difference tone. It is real (measurable and reproducible); it is not a psychoacoustic effect. Now, it is entirely possible that in your particular case the difference tone itself is, by coincidence (I guess that's sort of an unintentional bad pun), exciting a sympathetic buzz in some other object in the room or in the piano, but that would be unlikely. You can rule that out by playing the note that you hear as a difference tone (in the example I gave, you would play the note A4). If that note does not elicit a sympathetic buzz, neither will the difference tone, in which case, the low humming sound that you are hearing is the difference tone itself. You may be interested to know that a next generation of highly directional speakers based on difference tones is in the works. Since high sounds are highly directional, a tweeter produces two sounds above the range of human hearing that create a difference tone within the range of human hearing. This difference tone may even be a low note, but it will be highly directional (you will only hear it if the tweeter is pointed right at you), even though low sounds are usually non-directional (thats why you can put your subwoofer almost anywhere, and why you hear the subwoofer in some hearing-damaged kid's trunk even when you can't hear the rest of his "music," (fortunately, most likely)). Joe DeFazio Pittsburgh -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20110216/c04381bb/attachment.htm>
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