So has anyone measured plate expansion and contraction with temperature changes? Wouldn't that be the most likely suspect given this newfound innocence of the soundboard? Jason On 3/7/07, RicB <ricb at pianostemmer.no> wrote: > > Hi List > > I see I sent the wrong post, a copy of one earlier sent. Please excuse. > What I meant to write was the following. > > > I've been running some numbers and thinking a bit about this traditional > idea that vertical deflection of the strings is the main cause of pitch > change and thought some of you might find this interesting. > > Given the following string lengths, all with identical back lengths > (50mm), and lengths from front termination to tuning pins (200mm) (to > make the example simple) and assuming a 1 mm string deflection as the > starting point for all strings (also for simplicity) and calculating for > a roughly 50 cent pitch rise we get: > > A string length of : > > 1400 mm needs 6 mm additional deflection which results in about 22 lbs > of downbearing. > 1000 mm needs 5 mm additional deflection -->19 lbs downbearing > 800 mm needs 4,5 mm additional deflection --> 18lbs downbearing > 500 mm needs 3,5 mm additional deflection --> 15 lbs downbearing > 250 mm needs 2,5 mm additional deflection --> 13 lbs downbearing. > 100 mm needs 1,75 mm additional deflection --> 13 lbs downbearing > 50 mm needs 1,2 mm additional deflection --> 13 lbs downbearing. > > As you can see neither the amount of deflection needed to exact the > actual 50 pitch rise to begin with, nor the resulting downbearing > figures are within reason... which leaves one no choice but to admit > that something else is primarily responsible for seasonal pitch change. > > Its also good to note that if we are starting with a 1 mm deflection to > begin with.. which btw yeilds reasonable enough string deflection > angles, then the absolute most downward pitch change possible is when > the panel flattens out and bearing becomes 0. In this case the same > string lengths yeild : > > 1400 mm length --> -1 cent > 1000 mm length --> -1,4 cent > 800 mm length --> -1,7 cent > 500 mm length --> -2,4 cent > 250 mm length --> -4 cent > 100 mm length --> -7 cent > 50 mm length --> -10 cent > > These examples are simply illustrative of the kinds of things that > actually has to happen if the soundboard rise and fall is to account for > most of the pitch change. I apply all the resulting change on the > speaking length itself and do not account for any friction. This is a > best case scenario. In reality the string will disperse some of any > change in tension caused by a change in vertical deflection... lessening > the frequency change and resulting downbearing... but necessitating even > more vertical change for any give change in pitch. > > I can not help but conclude... looking closer at the consequences.... > that vertical rise and fall of the soundboard simply doesnt have much to > do with the seasonal pitch change at all. > > Tension change, and hence pitch change can come from an altering of the > relative positions of end points to each other... i.e. hitch pin and > tuning pin. Pitch change can also happen without tension change if the > speaking length is somehow altered. Seems to me that ruling out > vertical deflection... one has to look to these to general conditions > for the explaination. > > Cheers > RicB > > > > > > > > > > -- =cell 425 830 1561= -------------- next part -------------- An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/20070307/f4a0d3db/attachment.html
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