<!doctype html public "-//W3C//DTD W3 HTML//EN"> <html><head><style type="text/css"></style><title>Re: Tone near plate struts</title></head><body> <div>Phil, Ron and all,</div> <div><br></div> <blockquote type="cite" cite>> Ron Nossaman wrote:<br> >><br> >>It is, after all, a bridge. It's primary job is load distribution.<br> >>Stiffness affects assembly impedance, as is most obvious where a bridge is<br> >>notched to go under a strut, making that section of bridge below minimum<br> >>stiffness, and the tone quality of the unisons immediately on either side<br> >>of the notch are reminiscent of mini killer octaves. This lack of stiffness<br> >>is also evident at the low tenor, where the bridge (structural support)</blockquote> <blockquote type="cite" cite>>>ends, making the assembly more flexible than it is just a few notes up scale.</blockquote> <div><br></div> <div>Indeed, and while the practice of using a ring bridge is an attempt to alleviate this problem, it has the disadvantage of reducing the fundamental tone from the lowest bass notes. In the past few years we have been extending the low end of the long bridge to beyond the lowest tenor note, to provide support on the 'lower' side of the note. In our piano no. 003, it extends such that it terminates over an auxiliary sound board rib (one which does not extend to as far as the bass bridge or the inner rim on the straight side). This has the effect of forcing the sound board panel area immediately adjacent to the lowest tenor note, to move more as a unit. For many pianos, there is quite an area of sound board in the back-bass corner where there is little or no rib support for the panel. Very often the tone is found to be wanting here.</div> <div><br></div> <blockquote type="cite" cite>. . . But on pianos that do not have a cut down bridge there is still a deterioration, or at least a change, of tone adjacent to the plate struts or braces.  It seems to be worse on some pianos than on others.  What do you think is the reason for this?  I'd be interested in hearing some conjectures (or authoritative explanations if someone out there has some).</blockquote> <blockquote type="cite" cite><br></blockquote> <blockquote type="cite" cite>Phil F</blockquote> <div><br></div> <div>Phil, this is an interesting phenomena. We design the contact of the bridge with the sound board such that it forms a uniform curve as it approaches and leaves the immediate area under a plate strut<font color="#0000FF"> (I do not allow a dog-leg of bridge contact with the panel - dog leg contacts are certainly a no no on my computer)</font>. However, since I am not prepared to compromise the speaking lengths of the scale for any reason, the top of the bridge must therefore lay back, and then forward of the board contact as it goes down under a plate strut, particularly with regard to the second break down. Theoretically at least, we build the piano such that the percentage of breaking strain is uniform. Therefore, we would expect the tuning to be relatively stable also at the plate struts. However, while the stability is superior to those pianos of the straight bridge under the strut variety, some instability with temperature and humidity variations continue to occur - as it does also at the string gauge changes. Tonally, there seems to be more risk of variation if the note to not spacing across the strut is wider. Since the wider the space between the adjacent note centres (at the struts), the greater will be requirement for the bridges to lean over as they approach the struts. I believe it is important to minimise the bridge lean as much a possible.</div> <div><br></div> <div>Now while I hate to raise the topic of bridge rocking with respect to this matter<font color="#0000FF"> (since it has nearly been done to death over recent months)</font>, I believe it must be considered with respect to bridges leaning<font color="#0000FF"> (adjacent to plate struts)</font>. Let's assume that we have built the long bridge as described above, and that it leans back on the treble side of the strut and vice versa on the bass side.</div> <div><br></div> <div>Check the second top break on the overhead image of no. 003 at;  http://overspianos.com.au/OS003.html</div> <div>This bridge cap leans back significantly on the treble side of the strut. I have got better images showing the detail of leaning bridges, but they're not on my site at present.</div> <div><br></div> <div>As the bridge rocks during the cycle<font color="#0000FF"> (and if you don't believe that the bridge rocks then that's OK, but I happen to believe that it does)</font>, the rear leaning section will tend to increase sound board panel depression as the speaking length tension increases, while the forward leaning section will tend to reduce panel compression. This may indeed cause a difference in the tonality on either side of the strut. It should cause the board impedance to be lower on the treble side and higher on the bass side. Now I'm not saying that this is the magic factor which causes tone variability immediately adjacent to the struts. But I suspect that it might be an important consideration.</div> <div><br></div> <div>Any other thoughts on this matter? Its an interesting question Phil.</div> <div><br></div> <div>Ron O.</div> <x-sigsep><pre>-- </pre></x-sigsep> <div >           <span ></span>      OVERS PIANOS<br>        Grand Piano Manufacturers<br> _____________________________<br> <br> Web:    http://overspianos.com.au<br> Email:  mailto:ron@overspianos.com.au<br> _____________________________</div> </body> </html>