Well, math isn't a great part of my vocabulary so count me out of that one. Changing the pressure bar obviously changes tension, pitch and all that. The point I was thinking about was not how it affected the termination, deflection and impact on the bridge but, how little the screws needed to be turned to get that change in pitch. Same for the nose bolts as you mentioned. It stands to reason for me anyway, for whatever that's worth, that a whole lot less sound board movement is actually needed than is being reasoned out to change pitch drastically, no? Jer From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of David Love Sent: Monday, April 05, 2010 10:43 AM To: pianotech at ptg.org Subject: Re: [pianotech] Pitch Change One could do a fairly simple bit of research. It would be easiest in areas where large humidity swings occur. Carefully measure the downbearing on several notes through the piano. Six months later when you come back at a different seasonal time and the pitch has shifted, measure the downbearing again. You will be able to calculate the change in relative bridge height to the plate terminations using the change in downbearing. Measure the pitch change and you can calculate the amount of pitch change for that amount of change in bridge height and working backwards you can calculate the change in tension required for that particular change in pitch. One complicating factor is that when the tension increases or decreases the contraction of the plate changes. As we see with pitch raises and lowerings that's usually influences the pitch by a factor of about 25% in the midrange, a bit higher in the treble and bit lower in the bass. So if, for example, there's a pitch change of 10 cents for a calculated bridge rise of 1 mm, you probably should factor in the plate contraction such that 10 cents change would represent (in the midrange) 75% of the change that would occur for a change in the bridge height alone if there were no plate contraction. A 1 mm rise in the bridge height would also, of course, impact the downbearing to a lesser or greater degree depending on the length of the string and the backscale. So you would expect that the same 1 mm rise in the bridge would make less difference in the bass than in the high treble. I'm sure there are other considerations as well. David Love www.davidlovepianos.com From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of George F Emerson Sent: Monday, April 05, 2010 7:02 AM To: pianotech at ptg.org Subject: Re: [pianotech] Pitch Change Any pressure brought to bear on a tensioned string increases the tension, whether it be the bridge rising, pressure bar screws tightened, or indirectly, by altering a nose bolt setting. The reverse of any of these, relieving pressure on the string, would decrease the string's tension. The effects of any of these conditions would just as surely change the tension, as turning the tuning pin. The error of RicB's calculation is that it focuses on the deflection of the string and the downbearing on the bridge, which is only a small vector component of the string's tension. In his conclusions, he says something about the string tension remaining the same, theoretically. That's the problem: the string tension does not remain the same, theoretically or otherwise. It is not clear to me how he arrived at a difference in frequency of only 0.1 Hertz by adding 1mm of bridge rise, but it is clear to me that this cannot possible be accurate. I'm not sure how you might mathematically calculate the change in tension from 1mm rise in the soundboard/bridge assembly, but it is clearly wrong to assume that there is no change in tension. I had an Uncle who was never "quite right" after returning home from the War. He was a brilliant mathematician, and could produce reams of paper with flawless calculations, concluding that a meteorite was destined to crash into his house at a specific time and date. Not to associate Ric with my crazy uncle, but the math can be perfect; it just take a faulty assumption to make the conclusion total wrong. (The meteorite never struck my uncle's house). Frank Emerson ----- Original Message ----- From: Gerald Groot <mailto:tunerboy3 at comcast.net> To: pianotech at ptg.org Sent: Monday, April 05, 2010 7:49 AM Subject: Re: [pianotech] Pitch Change (was: Grey market pianos,seasoned pianos, etc.) Would lowering tension say, 1/8 turn on each pressure bar screw on verticals also be considered doing a simliar test as you mentioned below for comparison? Doing this would produce a very substantial drop in pitch with a very slight change in the height of the screw and pressure bar in relation to where it was originally at. Or, am I making a different type of comparison? Jer From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of David Love Sent: Monday, April 05, 2010 12:56 AM To: pianotech at ptg.org Subject: Re: [pianotech] Pitch Change (was: Grey market pianos, seasoned pianos, etc.) It's not perfect, but if you pull the plate down and the bearing changes you've effectively raised the level of the bridge relative to the termination points at the plate. Any change in the tension at all changes the stresses on the plate. It's more an experiment to show that small changes in the plate height which can be translated as soundboard/bridge rise and fall will make fairly substantial changes in the pitch. I don't remember Ric B's analysis but what was he talking about in terms of pitch change? To me a change of 10 cents is substantial and it doesn't seem to take much more than a fractional change at the nose bolts to produce that. David Love www.davidlovepianos.com From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf Of Ryan Sowers Sent: Sunday, April 04, 2010 9:25 PM To: pianotech at ptg.org Subject: Re: [pianotech] Pitch Change (was: Grey market pianos, seasoned pianos, etc.) But doesn't changing the nose bolts also change the stresses on the plate? Any pitch change could be caused more by that then by the string height relative to the bridges. On Sun, Apr 4, 2010 at 12:25 PM, David Love <davidlovepianos at comcast.net> wrote: It's not hard to do a simple test of bridge height change and accompanying change in pitch using the nose bolts of a given piano that has them. By lowering the plate a measured amount you can effectively calculate a change in the in the bridge height (using bearing measurements as well) and then measure the change in pitch. It's not a perfect test but it can give some idea. While I can't comment on Ric B's calculations not having done them I can say that even modest changes to the nose bolts create quite a difference in pitch when compared to the normal seasonal change we experience. I'm not convinced that the soundboard/bridge rise and fall isn't a significant part of the pitch change even if it is not the entire story. Certainly compression soundboards change enough during seasonal swings as to impact the tone, that they should impact the pitch would not be unexpected. For purposes of client communications and simplicity I think it's not an unreasonable offering. David Love www.davidlovepianos.com -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://ptg.org/pipermail/pianotech.php/attachments/20100405/60e4d354/attachment.htm>
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