This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment Hi Don. I would be interested in the maths calculating the relative errors we do = when we measure downbearing with the carpet thread method and with the = Lowell buble gauge method. I have the feeling that these errors might = be enormous. Right ? Best regards, St=E9phane Collin ----- Original Message -----=20 From: Don Gilmore=20 To: Pianotech=20 Sent: Thursday, February 19, 2004 11:13 PM Subject: Re: what is downbearing? Hi Julia: I won't purport to be an expert on the subjective qualities of = downbearing, but purely from an engineering standpoint, calculating the = force of downbearing is fairly simple. I haven't been following the = other downbearing threads, so forgive me if this information is = redundant. Ideally, downbearing is proportional to the angle that the string = bends downward (toward the harp) after passing over the bridge. If you = can measure this angle, the downbearing force is simply F =3D T * sin A Where F is the downbearing force, T is the string tension and A is the = angle that the string dips downward. You can see that more tension = means more downbearing as does a greater angle. Note also that a = negative angle (upward) means a negative downbearing. If you don't have an accurate way to measure the angle A, you can also = calculate it by measuring the length of string between the bridge and = the next contact point (b) and how far the string has dipped down at = that point (h). =20 F =3D T * h / b Obviously, everything is fine until you realize that you need to know = the string tension...but how? Well, believe it or not, you can = calculate the string tension theoretically if you know the size of the = string and its musical pitch. If I did my math right, the formula = should be T =3D 0.0023 * (fLd)^2 Where f is the frequency in Hertz, L is the vibrating length (agraffe = to bridge) of the string, in inches, and d is the diameter of the = string, also in inches. The answer will be in pounds and the string = must be steel. The tension should come out to around 100 to 200 lbs or = so. Then you can use the other equation to determine the downbearing. Hope this helps. Don A. Gilmore Mechanical Engineer Kansas City At 11:11 AM 2/19/2004 EST, you wrote: >Greetings, >=20 > What exactly is downbearing? Does it affect the = sound of the >piano or is it a mechanical/ physics measurement for the = playability of the >piano? Why is it important to measure it? Can it be calculated = by a >formula(e)? What does it mean? >=20 ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/d7/f6/c4/dc/attachment.htm ---------------------- multipart/alternative attachment--
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