[CAUT] More on Single String Beats

[Willem Blees]

Quoting David Skolnik <davidskolnik at optonline.net>:

> Wim -
> By coincidence, I was experimenting with just such a false beat this
> 
> morning on a newly rebuilt Steinway L fro the '20's.  On note C#7, 
> treble-most string had a beat of appoximately 6-7 bps.  There was no
> 
> change in adding mass (as screwdriver) to any other part of the 
> system.  In fact even touching the bass of the bridge pin with 
> varying amount of force and from different directions produced 
> virtually no change.  What did accelerate the beat rate was moving 
> the screwdriver up the pin towards the top.  The pin did not seem to
> 
> be loose.  It seems possible that some aspect of the pin sets up an 
> internal resonance that could interact with the frequencies created 
> by that string.  I'd love to try something like pulling the pin and 
> changing the length, or take complete measurements of weight, length
> 
> and diameter, and then alter one at a time.  Well, I mean note the 
> changes of weight and length.  What's interesting too, is that 
> sometimes, a blade placed on top of pin of a vibrating string 
> vibrates quite noticeably, and at other times, such as this, not.
> 
> As far as your theory, I'm not sure I see how that might work.  Care
> 
> to elaborate?
> 
> David Skolnik
> Hastings on Hudson, NY

David

I don't know how it works, per se, since I am not an electrical 
engineer nor a metalurgist, but I just took an inch by inch 
measurement of a #14 wire for about a foot, and found a slight 
variation in several spots of between .02 and .001. My therory is that 
it is this slight imperfection that causes "false" beats. 

Wim  

> 
> 
> 
> 
> At 10:30 AM 4/14/2007, you wrote:
> >There is one thing that Ric mentioned that gives me reason to
> believe
> >the reason there are "false" beats is because of the differences of
> >the diameter in the string itself. He said "the addition of mass to
> >the strings front bridge pin, or an area very close to same has an
> >impact on the speed of the beat.... and at some optimal degree of
> mass
> >addition (or even > subtraction perhaps) the beat disappears."
> >
> >When strings are drawn to size, it goes through smaller and smaller
> >holes. The strings are pulled by an electric motor. As with any
> >electric device, the speed of the motor changes as the amount of
> power
> >fluctuates. The surges in power are effected by other electric
> >appliance starting or stopping.
> >
> >My theory is that in the factory where string is made, there are
> >lots of large electric motors that stop and start constantly. It
> >doesn't take much to cause a small surge in any of the motors. As
> the
> >surge occurs, it slows down the speed in which the wire goes
> through
> >the hole. This, in turn, changes the diameter of the string. It
> might
> >be so small that it is undetectable, but it might be enough to
> cause
> >the string to change it's beating pattern.
> >
> >Am I way out of it, or is this a plausible cause of false bats?
> >
> >Wim
> >Willem Blees, RPT
> >Piano Tuner/Technician
> >School of Music
> >University of Alabama
> >Tuscaloosa, AL USA
> >205-348-1469
> >
> >
> >
> >Quoting RicB <ricb at pianostemmer.no>:
> >
> > > Hi Folks
> > >
> > > Several off list discussions with a few well known piano physics
> > > profs
> > > has recently confirmed a now long held suspicion that the idea
> that
> > > classic false beats or single string beats are caused by a loose
> pin
> > > is
> > > just plain way too simplistic and very far from complete.  In
> fact
> > > loose
> > > pins can only account for a contributing factor to the overall
> larger
> > >
> > > and holistic bridgepin / bridge / and soundboard termination
> area. As
> > > a
> > > consequence of this it should be expectable to find this kind of
> > > falsness in all registers of the piano, contrary to present
> popular
> > > belief that these are confined to the mid upper range of the
> piano.
> > >
> > > Closer examination of what the overtones of strings in all
> registers
> > > of
> > > the pianos does indeed reveal exactly this.  I am finding single
> > > string
> > > beating in all registers and these are of the sort that respond
> to
> > > the
> > > pressure of a screwdriver or similar tool to the side of the
> pin.
> > > They
> > > are quieter and harder to discern the lower you get in the
> scale,
> > > probably because of the wealth of overtones and amplitudes of
> these
> > > that
> > > are present, but they are indeed and no doubt about it very
> present.
> > >
> > >  From A0 to C8 one can find this kind of single string beat
> popularly
> > >
> > > called the false beat.
> > >
> > > One thing I find curious, tho I have not confirmed it yet... is
> that
> > >
> > > these beats seem to occur in range of 1500 hz upwards.  At least
> in
> > > the
> > > ones I've been able to identify in bass notes... they seem to
> convey
> > > a
> > > sense of being overtones in this range.
> > >
> > > In all cases so far, the addition of mass to the strings front
> bridge
> > >
> > > pin, or an area very close to same has an impact on the speed of
> the
> > >
> > > beat.... and at some optimal degree of mass addition (or even
> > > subtraction perhaps) the beat disappears.
> > >
> > > It has seemed to me for a long time that this whole area of
> sound
> > > problems needs quite a bit more close examination as to what
> really
> > > causes this single string beat.  And it also seems more and more
> > > evident
> > > to me that a cure, and one which bears with it other tone
> enhancement
> > >
> > > factors, lies somewhere in an <<optimal mass at the
> termination>>
> > > perspective as opposed to the idea that the pin simply needs to
> be
> > > tight
> > > enough.  Especially since loose pins can so often be absurdly
> present
> > >
> > > with no noticeable resultant single string beat.
> > >
> > > Cheers
> > > RicB
> > >
> > >
> > >
> > >
> > >
> > >
> 
> 


Willem Blees, RPT
Piano Tuner/Technician
School of Music
University of Alabama
Tuscaloosa, AL USA
205-348-1469