Keith, I saw the photograph of the bridge you posted and read about the problem you're having with a '"false beat beyond belief". From the situation you've described, it sounds to me like you have a real beat between two (or more) strings of a unison with different inharmonicities. In my opinion, it is not a false beat - it is a real beat. (For clarification, I'm using the phrase "false beat" to describe that throbbing sound one hears when only a single string is speaking). If I read your post and the subsequent replies correctly: You indicated in one of your clarfications that you're having a hard time locking in a solid unison for this note. You get beating no matter where you align the tunings of the strings in relation to one another. You also said the Pitchlock provided some help. The bridge notching looks horrible (among the assumptions that one could take away from this is that the speaking lengths could be sllightly different for the adjacent stings of that note. All else being equal, if the speaking lengths are different for that unison, the inharmonicity will not exactly match). And to summarize the replies so far... Some of the replies to your post appeared to be focused on the termination at the bridge pin being loose, or in some other way trying to guide you on how to fix a false beat in a single string. Other replies appeared to be offering suggestions on how to correct a problem between two strings not aligning into a unison, experimenting with Pitchlock configurations, and recapping the bridge to correct that horrendous notch. I think that the sum of the evidence points more toward two strings that do not share the same amount of inharmonicity - probably caused by the unequal string lengths due to the bad notch. One solution, already mentioned, is to correct the bridge notch, thus correcting the string lengths, thus correcting the inharmonicity of the notes - allowing for a unison to be tuned more cleanly. Big job - and it sounds like you want to avoid this level of corrective work. Another solution might be to change the inharmonicity of one of the existing strings... I have seen Marcel LaPointe, a piano tuner in Quebec, give a seminar on correcting/matching the inharmonicity of two wound strings of a bichord. (I know I've often had the problem of beating bichords no matter where I try and locate the unison). I don't know if the same technique would work for a plain wire string, but it might be worth a try. Further, I don't know if this technique is Marcel's invention or someone else's. I suggest you call Marcel to get a more detailed procedure. For the benefit of the list, I'll try and describe Marcel's procedure: Tune the fundamental of two of the unison strings together as close as you can get them. An ETD will get you pretty spot on. If you need to do this aurally, align the lowest partial you can hear to be as beatless as possible. Identify the string that has the greater inharmonicity coefficient/constant. One can accomplish this using an ETD that measures the inharmonicity directly. If you don't have an ETD that does this, you can do it aurally. You can pluck the strings very close so the termination with your fingernail, (you get that really nasally, twangy sound indicating a lot of partials are being excited). Make sure you pluck at approximately the same position on each string. Compare the sound of each of the plucked strings. One can hear that the "pitch" of one string is very slightly sharper than the other even though you've tuned the two strings' fundamentals to be the same. The string evidencing the higher "pitch" is the string with the higher inharmonicity. (If I remember right). This effect is clearly audible in the wound bass strings, but I'd guess it will be more diffcult to hear on a higher, plain-wire note. Add a miniscule amount of mass to the string that has the higher inharmonicity. Marcel used a drop of clear nail lacquer on the exposed core of the wound strings near the agraffe. Give it a few mnutes to dry and test again. Repeat as needed to align the inharmonicities of the two strings. Did you make a mistake and put too much clear nail lacquer on the string? Just scrape it off. The audible effect of this was quite pronounced on the wound bass strings that were the subject of experimentation in the seminar I attended. This seminar was revelatory to my ears - two misbehaving wound bichord strings were brought to a much better unison. Again, I don't know if this will work on plain wire strings, but my guess is that this process is a little bit cheaper that recapping the bridges and re-notching, and at least worth a try. I hope this has helped, Chris Storch, RPT -----Original Message----- From: Roger at Integra.net <rgable at integra.net> To: pianotech at ptg.org Sent: Fri, Feb 4, 2011 12:21 pm Subject: Re: [pianotech] Bridge pin locations help (image oops) Ron, Well, I guess we'll agree to disagree about the string seating verses loose pin. I believe the seating process is effective because the string is now laying flat against the bridge cap. I've found that false beats can be reduced or eliminated by seating, on both new pianos out of the crate that don't have loose pins and strings on 90 year old pianos that obviously have loose pins. This points to the cause of these false beats to be created by poor termination on the bridge cap. I believe most manufactures recognize the importance of the uniform termination by applying great care to ensure a perfect string and notch alignment. I must emphasize that I'm not discounting loose pins as the cause of false beats but pointing to other sources as trouble. As for the screwdriver test. Listen closely when applying pressure to the pin with a screwdriver. In those instances when a loose pin is not the cause, the false beat is reduced in strength and duration but not speed. I've found this to be the case on many Yamaha pianos. To acknowledge this effect may point you to something else, such as a poor termination on the opposite end of the string. That's the tree I was referring to. Roger Gable ----- Original Message ----- From: "Ron Nossaman" <rnossaman at cox.net> To: <pianotech at ptg.org> Sent: Friday, February 04, 2011 4:39 AM Subject: Re: [pianotech] Bridge pin locations help (image oops) > On 2/3/2011 11:22 PM, Roger at Integra.net wrote: >> Ron, >> I would have a tendency to disagree with your analyst. First, if a false >> beat was usually caused by a loose pin (which it frequently is) then >> there isn't a rational reason why string seating cures a major portion >> of false beats. > > Seating sometimes stops the beat because it jams the string against the > bridge cap hard enough to stop the pin flagpoling - sometimes. > > >>What seems more rational is that the seating process >> beds the string against the pin and bridge to create a uniform >> termination during the entire circular motion of the string -- remember, >> strings rotate, not just move up and down. In the situation pictured, >> the rotational movement of the string would indeed vary the termination >> length and/or create an "energy leak, or skip" past the termination >> sometime during the rotational cycle. That picture "screams" of an >> situation where the energy can't be uniformly reflected back into the >> string during the entire rotational cycle. > > Again, the pin is the termination in all directions of string termination > unless the notch edge extends into the speaking length. The string doesn't > slither up and down the pin except perhaps the first millisecond of the > attack impulse, well before the beat can be heard. The friction between > the string and pin doesn't allow it. The beat comes from the different > "effective" speaking lengths caused by the more rigid termination in the > vertical direction, and the springy termination in the horizontal. That's > why the screwdriver test works. > > >> Your mention of using a screwdriver to temporarily "stake" the pin for >> testing is, in my opinion, suspect many times. When the false beat seems >> to be reduced or disappear during this test, you will, with close >> examination, find that you are not always hearing the effects of a more >> solid pin, but only the result of a dampened bridge cap, giving you the >> impression that the false beat has disappeared. > > Close examination? What method do you use to indicate a "dampened" bridge > cap? And how do you get an impression that the beat disappeared if it > didn't? If the screwdriver "damps" the cap, then you can push directly on > the cap and get the same effect, or on the adjacent pin. This isn't the > case. Have you actually tried it? The beat suppression is a direct and > repeatable result of stopping the pin flagpoling, and it doesn't take much > pressure to do it. > > >>This is not to say that >> the screwdriver test is an invalid test, but is to say that you may find >> yourself barking up the wrong tree. > > No, I'm not. How about you inform us what, specifically, is a valid test > that barks up the right tree? > Ron N > > -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20110204/3df32796/attachment.htm>
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