[pianotech] Additional Information Regarding False Beats

[Richard Brekne]

Hi Paul

        ricb at pianostemmer.no writes:

        I'm also  aware that many believe that false beats are caused by
        rust on strings,  general termination problems, variations in
        string thickness and  density... etc. etc.

    Etc. indeed. The phrase "general termination problems" is of course
    too  broad. Have you decided that the condition of the "termination"
    is  not part of or one of the causes? Please elaborate.  :-)
     
    P


I suppose "general termination problems" is a bit broad... but that and 
the other etc's mentioned were not really the point.  And one has to 
remember in these discussions what kind of "falseness" we are talking 
about. Wavering unsteady falseness that displays no clear period is not 
what I am referring to. It is that classic false beat... clear and so 
identical in sound to the beating two strings that are slightly out of 
tune display.  One also has to define closely what the "termination" 
really is.  Many would have it that the termination at the bridge is 
simply the bridge pin. I don't subscribe to that idea. The bridge pin 
and bridge surface form a combined clamp that terminates the string.  
For that matter it is entirely possible that the end acoustic result... 
that is to say what is accepted of the strings vibration by the bridge 
and soundboard assembly and sent out into the air, is significantly 
affected by the condition of the wood components involved at critical 
points relative to any given string. Remember we are talking about 
extremely small out of phase movements here needed to cause an audible 
false beat. Just where those occur in the entire chain is in my opinion 
an unanswered question.

All my experiments tell me that the false beat we "hear" is the result 
of a combination of events in which the bridge itself is most definitely 
involved. It seems quite possible, if not outright probably to me that a 
string, isolated from the soundboard and bridge producing a false beat 
does not necessarily result in an audible false beat when coupled to the 
bridge and soundboard assembly. Conditions at the pin / notch and for 
that matter the wood immediately surrounding the pin along its full 
length... anything that can contribute an out of phase condition where 
in one phase one frequency is transmitted further on in the system and 
in another phase another frequency is transmitted can affect what in the 
end comes out into the air.  Sometimes these things could cancel each 
other out... other times enhance each other or even cause multiple false 
beats... which is also observable btw. Everything stated here is 
perfectly in line with theory of coupled vibrating systems.

All this is in line with the basic train of sound production as 
described by a couple of the authors in the 5 lectures and other related 
studies.  Its easy to simply look at the string itself, or the bridge 
pin itself as the soul support and thereby the cause of this phenomena 
and assume the soundboard assembly faithfully reproduces everything 
exactly as it hits the bridge pin. But this is an oversimplified 
perspective in my view to begin with... and secondly we actually do know 
the soundboard / bridge assembly does not necessarily always do this.  
We just haven't looked  closely enough at that side of things to see how 
it can get into the classic audible false beat.  Given the statistics 
I've run into... and the basics of how vibrating components all combine 
to produce any given output for a complete vibrating system.... it seems 
to me that the reigning theory (ie the loose pin flag polling postulate) 
is simply not nearly complete enough and doesn't match the observable 
results of controlled experimentation.

Cheers
RicB