[CAUT] More on Single String Beats

[David Skolnik]

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




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
> >
> >
> >
> >
> >
> >