FW: Bi-Chords.....(recycling Ron)

[Lesher, Trent J.]

	Hi Dale,
	 
	You probably saw this already, but, just in case, Ron Nossaman touched on one example like you're talking about in a recent post talking about an upright with the break between C3 and C#3, that comes standard with all plain wires on the long bridge.  Ron said (emphasis added):
	 
	"For instance, that 38.75" C#-3
	with plain wire trichord will be at about 24% of breaking tension
	(regardless of wire size, within reason). That's pretty low, and will be
	very reactive to tension changes resulting from humidity fluctuations,
	meaning it will go out of tune quicker and farther than unisons farther
	up-scale, or down scale in the high bass. Tension will be determined by the
	wire size used there. For instance, unison tension with #20 will be about
	404 lbs, or about 369 lbs with #19. Going to a bichord unison, dropping two
	or three half sizes for the core, and figuring wrap to get back near the
	unison tension that was originally there will raise the break% to around
	40%. That's going to be a more stabile unison with humidity changes, and
	sound better too. The trouble is, that puts you at the bottom of the list
	of available copper wrap sizes, requiring about a 0.007" wrap to keep the
	tension down around where it was with the plain strings. Arledge uses as
	small as 0.006" for copper wrap. That takes care of C#-3, if the impedance
	and inharmonicity connects reasonably with the high bass. Now you'll
	probably want to go 2-4 notes higher with wrapped bichords to blend the
	impedance and inharmonicity into the rest of the treble. What happens? You
	maybe need 0.006" wrap for D-3, and smaller than is available for the next
	one or three. There's the problem, and the reason this doesn't always work
	that well, and the reason for transition bridges. The speaking lengths are
	too long at that pitch for wrapped strings. "
	 
	Maybe that'll help get your discussion going.   ( :  
	 
	Regards,
	 
	Trent

		-----Original Message----- 
		From: Erwinspiano@aol.com [mailto:Erwinspiano@aol.com] 
		Sent: Mon 11/22/2004 6:30 PM 
		To: pianotech@ptg.org 
		Cc: 
		Subject: Re: Bi-Chords.....
		
		
		
		  Hey Fast Joe
		  True enough in general except that this bass string maker also does scaling for his own rebuilds. That doesn't say if the scaling  program used is accurate or has a tension bias  toward conservative tension numbers. 
		    Also this a S&S B being discussed & the warts are pretty common knowledge right? My guess is someone with experience on list could chime in about the tensions involving plain wire verses BI-chord wrapped or tri-wrapped string & how the various tensions blend into the plain scale. Sounds like an invitiation huh? Whos got a string length handy?
		   Dale

			
			Dale said,
			I was told by my bass string maker that this spot on both pianos is  too 
			long for bichords"
			 
			Dale, 
			And, of course, these bass string makers are manufacturers, Scale Designers & Rebuilders? B.S. Unless they are in direct contact with each piano of question, they ought to keep that stuff to themselves, IMO! Of course, there are a few string makers that have fullfilled the criteria and can give good advice, but each piano is an entity unto itself, warts and all. The correction of warts is what most of us do. Sheesh!
			Joe Garrett, R.P.T.
			Captain, Tool Police
			Squares R I

		 



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