Yeah, I have a borescope. It has been interesting, but the jury is still out on whether it is very useful. The camera is hard to control to get pointed exactly where you want, and the view area is so small, that it can be difficult to understand what you are seeing. Kent On Feb 17, 2011, at 10:21 AM, David M. Porritt wrote: > Speaking of looking under plates to find noisy objects – and I know we’ve all spent too many hours looking at our little dental style mirror and aiming our light where it really won’t shine – has anyone tried something like this? I’ve seen these and thought of buying one just for these occasions. > > dave > > From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Encore Pianos > Sent: Thursday, February 17, 2011 10:05 AM > To: pianotech at ptg.org > Subject: Re: [pianotech] Sub Harmonic "buzzing" in Treble Intervals > > Hi Jeff: > > I’ll bet you dollars to donuts that it is a foreign object on the soundboard under the plate. Long story short, the first board I put in in my shop had a very similar sound to everything you are describing. It drove me nuts for several days. I inspected the glue joints all over this piano with an electron microscope – all good. Belly rail glue joints were good. (Did you check that? When they fail, they can make nasty (un)sympathetic vibrations.) Looked at the board under the plate with a strong light and mirrors. I couldn’t see anything. A few days later I looked again, and I could just see a little ridge of something. Reaching it with a soundboard steel and air compressor, I got it out. It was a very thin steel washer. Suddenly the horrible buzz was gone. Whew!! > > So look, look, and look again. Blow under the plate with air if you can or reach with soundboard tool with a magnet on it or cloth to move things around. > > I can’t guarantee that this is the problem, but I think it is a contender for sure. > > Will Truitt > > From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Jeff Atkisson > Sent: Thursday, February 17, 2011 10:00 AM > To: pianotech at ptg.org > Subject: Re: [pianotech] Sub Harmonic "buzzing" in Treble Intervals > > Hi Joe, > > Yep, I don't think I'm dealing with sympathetic vibrations. > Because it happens with just about all of the intervals within the range I am hearing it. > A particular sympathetic buzz would only only respond to it's harmonic relatives - right? > Plus I tried the test you suggested - with no response from the culprit. > Also the tone/buzz I am hearing is at the frequency you described (i.e. the difference between the fundamental frequencies) > Problem is the tone/buzz is not pleasant or supportive to the sound. > It is sort of hoarse and spurious with an slow oscillation dying out quickly. > In some cases it can be quite loud - actually interfering with the sound of the chord or interval. > I'm pretty sure I don't hear it much on other pianos - although I don't have one to run to at the moment. > This seems like something that would be quite familiar to a lot of tuners if it was any kind of common issue ... > I'm starting to suspect my own ears, or does the piano have some kind of strange ailment??? > > > Thanks > > Jeff > > > > > > On Feb 16, 2011, at 11:36 PM, Joe DeFazio wrote: > > 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/20110217/6ec439c4/attachment-0001.htm>
This PTG archive page provided courtesy of Moy Piano Service, LLC