This is a multi-part message in MIME format. ---------------------- multipart/alternative attachment I should have said stiffness in the panel versus stiffness in the assembly. I mean that in terms of acoustic properties.=20 =20 David Love davidlovepianos@comcast.net=20 -----Original Message----- From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On Behalf Of David Love Sent: Saturday, February 12, 2005 8:35 PM To: 'Pianotech' Subject: More CC vs RC questions was RE: Killer Octave & Pitch Raise =20 Another very basic question about these design elements: Is there a difference between tension in the panel and stiffness of the panel? I mean that in terms of the physical properties of the panel. Intuitively, it seems that the CC board would be under greater tension owing to the crowing process. While the same amount of stiffness might be achieved by how the board is loaded and the amount of bearing, does tension (whatever that is) play a role in tonal output? =20 Another question is this: A CC board, as we=92ve discussed, runs a greater risk of compression set and cellular wood damage due to the fact that it bears some of the load that is born by the ribs to a greater degree in a RC board. Do I have that right? If that=92s the case, how = do we know that it isn=92t the fact that the panel bears more of the load that contributes to the tonal output. While the ribs may bear the load and spare the panel to some degree, is there not a tonal price to be paid for that. Which isn=92t to say that an RC board can=92t be made to sound acceptable or good, they obviously can, but will it sound different by virtue of the type of crowning and what is that difference, if any? I think that=92s an important question. =20 =20 David Love davidlovepianos@comcast.net=20 -----Original Message----- From: pianotech-bounces@ptg.org [mailto:pianotech-bounces@ptg.org] On Behalf Of Overs Pianos Sent: Saturday, February 12, 2005 6:45 PM To: Pianotech Subject: re: Killer Octave & Pitch Raise =20 At 1:54 AM +0100 12/2/05, Richard Brekne wrote: =20 Udo Steingr=E6ber and I got into a conversation about this in Helsinki a couple years back on the only opportunity I've had to sit and chat with him. It was part of a discussion where he was explaining why he felt compression soundboards were the way to go. =20 You've mentioned this before on the list, but the question I asked at the time of your original post, "has Udo done any modelling experiments with both types of construction?" remains unanswered. Would you ask Udo this question, since you have already established a relationship with him? =20 I have done modelling with both types of construction. I have built full size models and tested them on the bench. For those who might be interested to see an image of our experimental setup, go to our second web page on my I-rib development. =20 http://overspianos.com.au/iribbd2.html =20 Regardless of the sound board construction method chosen, the maximum stress on the sound board assembly will be directly under the bridges, if the ribs are of a uniform cross-sectional area. When RC construction is employed, the depth of the ribs under the bridges can be increased to reduce the stress point under the bridge. Our I-ribs are flat on the bottom flange and crowned on the top flange, so they will be relatively stronger in the middle where they are deeper (standard solid RC ribs can be profiled in the same way). Rib feathering allows for all boards to be appropriately weakened at the edges where there is less stress, to allow for greater sound board activity. Our I-ribs are tapered also in the width of the bottom flange (we call this secondary feathering), which allows us to further vary the strength of the rib along its length, creating a sound board which deflects more uniformly under the downbearing load. The same result can be achieved with a solid RC rib, by varying depth along its length. Terry Farrell has shown some excellent images of RC ribs which had significantly greater depth in their mid sections. Would you like to post a couple of links, Terry, to show the troops what you and others are doing? Varying the strength of the ribs along their length is, I believe, the way forward in sound board design. I can't imagine how similar rib strength variation could be achieved with a CC board, unless the builder is prepared to forgo crowning in the proximity of the bridges, since a deeper CC rib will prevent the re-hydrated panel from forcing the board into a crown. =20 He mentioned something about the so called K point (I think this is a Klaus Fenner coined term), which as I understood it was that point on the soundboard where crown from both along the grain and cross the grain intersect and is at its highest point. This area is exactly (and always) in the area typically refered to by american techs as the <<killer octave>> area, and of course varies somewhat from piano to piano. =20 The highest point of the sound board, from the instruments I have measured, is somewhat further down the long bridge towards the middle of the board. =20 The killer octave, for most 'conventional' designs, is the grossly overloaded part of the sound board. They also are often overloaded directly under the bridges. Try placing a 150 mm steel rule under the bridge, almost anywhere, on the underside of the panel of any CC boarded piano. The rule almost always will rock, which indicates that the crown has reversed directly under the bridges. I have observed this many times, even with pianos which were under one year old. Quite a number of the new grand pianos exhibited at last year's Adelaide piano technicians convention had reverse crown directly under the bridges. And this observation was not limited just to the lower priced pianos either (the checking with rule was done late in the night to avoid upsetting various exhibitors - some examples already had 'nicely developed' killer octave zones - Ron N was party to these observations also). =20 It is then also the exact point then that is most vunerable to failures. =20 How do you arrive at this conclusion? The only part of any sound board which is prone to failure would seem to be those areas that are under-engineered and overloaded. =20 Udo was of the position that along the grain crowning was every bit as important as cross grain crown. =20 I would have expected this point to be a 'position', rather than a 'conclusion'. Crowning along the grain is something that will occur naturally in any sound board once it is fitted to the case, whether CC or RC crowning is used. However, the resultant crown along the grain won't really help a sound board to better withstand the downbearing forces. While it might appear to be beneficial, the span along the long bridge relative the section sizes of the materials used, will make it impossible for it to be of any serious assistance. =20 Something to do with along the grain compression due to downbearing having a stablizing effect on cross grain crown and strength. =20 I doubt it. Very slight soundboard compression will result along the grain as the downbearing is applied, especially since the bridge is located above the 'mounting-plane' of the inner rim, but it won't help or hinder the net ability of a sound board to resist sinking. Furthermore, it would be very difficult to build a sound board with compression crowning along the long grain, since the bridge would need to be dried before gluing it to the panel, and there would be insufficient shrinkage of the bridge, along its length, to achieve an alleged worthwhile crown along the grain. =20 The ability of a sound board to support downbearing is related primarily to the ability of each rib/board segment's ability to support the load to which it is subjected. =20 This, I think, ties in with Ron N's reply to Terry Farrell's original post; =20 At 6:41 AM -0600 12/2/05, Ron Nossaman wrote: At 5:22 PM -0500 11/2/05, Terry wrote: When I raise the pitch of a piano, typically I find that I need to pull an area of the treble, commonly around the sixth octave or so, a bit extra so that area does not end up flat when the pitch raise is completed. I use typical pitch raise overpulls - 20% in bass, 25% in tenor and 33% or so in treble - but that one octave or so in the treble needs to go a little further - maybe 35 or 38%. I find this to be true on most pianos. =20 My understanding is that one factor that may conspire to produce a killer octave (low volume and/or short sustain) in a piano is the fact that the killer octave area is also the area the long bridge is curved most - rather than having the downbearing supported in part by a straight (or nearly so) bridge (like in the tenor), the curved part of the long bridge in the killer octave area is more prone to rolling - I know, not rolling - actually soundboard deformation - but I'm trying to point out that it can rotate in this area more easily than other areas. =20 My question is - might these two phenomena be related? Is the killer octave area more prone to going flat because the bridge is rotating (I suppose in part due to soundboard not having enough support in that area)? =20 Thanks for any thoughts. =20 Terry Farrell =20 I think so. The tenor isn't heavily loaded, and the soundboard (usually) supports it, though it sinks some. The upper treble section is heavily loaded, and barely sinks at all because the bridge is very close to the belly at the top end. It's sitting on a brick, essentially. With the top end of the bridge as a fulcrum, any load put on the treble levers down to the curve in the bridge, where it loses beam support because of the curve. So the killer octave has to support not only it's own heavy bearing load, but gets additional load from both the tenor and treble by virtue of being at the end of two third class levers courtesy of that curve. =20 Exactly Ron N, and the situation in many cases is made even worse due to the lack of an appropriate sound board cut-off, in this area of the board, which causes the ribs to be way too long and way too weak to withstand the excessive forces under which they placed. =20 The soundboard deflects proportionally more at the curve, and the bridge rotates with it's center of rotation being a line through somewhere at the top end, and somewhere in the mid tenor. The part of the bridge furthest away from this center of rotation is the curve, where the killer octave is. This is also why it's possible to have both negative crown and negative overall bearing in the killer octave. =20 Well put Ron N. =20 And now, back to Mr Steingr=E6ber's claims. =20 He also meant that both these were needed to produce the kind of acoustical results he wanted from a soundboard. =20 Mmm? For those of you who haven't seen a sound board being glued into a case, the 'free board' doesn't even nearly conform to the profile of the inner rim. The sound board will always have to be clamped to the inner rim (which places it under some initial stress - which will occur regardless of the construction methods used). =20 I'm under the impression, correct me if I am wrong, that most of the rib crowned methods extoled on this list do not employ any purposefull along the grain crowning as part of how the panels are attached to the rim, and therefor do not have this vunerablity. It would stand to reason that they too are not able to create the same acoustical results.... (whether that is preferable or not is an entirely different subject). =20 I cannot see how it 'stand[s] to reason' at all. You seem to be implying that RC sound boards are not able to 'create the same acoustical results', but I don't see how Udo arrived at this conclusion. You seem to be implying that the RC school membership don't build crown into the board along the grain. It can't be avoided once the sound board is installed, regardless of which construction school you happen to be sitting. But you seem to go further by implying the crown along the grain is somehow a critical component of tone building. I am not convinced that it is, but even if it were, its an unavoidable result with both methods once the panel is fitted to the case. =20 I believe the important issue is that the majority of boards are grossly overload at the second top string section. =20 Ron O. --=20 OVERS PIANOS - SYDNEY Grand Piano Manufacturers _______________________ Web http://overspianos.com.au mailto:ron@overspianos.com.au _______________________ ---------------------- multipart/alternative attachment An HTML attachment was scrubbed... URL: https://www.moypiano.com/ptg/pianotech.php/attachments/c0/28/07/7f/attachment.htm ---------------------- multipart/alternative attachment--
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