String coupling

[Roger Jolly]

I
>I personally would think that one measurement for each would be sufficient,
>contigent upon measureing many pianos over time, an "average" or "tendency"
>should show itself anyways.

Hi Richard,
                One measurement is not good enough, as I have observed
differences in the ratio of partials with changes in the following parameters.

Centre pinning, very clearly audible in the killer range with a variance 4
to 8 swings,
Jack height, lost motion between the jack and the knuckle, 

Both poor pinning and jack regulation will produce a sharp but weak
sustaining fundamental,
and weaker partials.

>From slo mo film, the flight pattern of the hammer shank is not a clean
trajectory, it wobbles around like a drunken sailor, so therefore, is not
predictable in a scientific sense.
Now if the hammer flight, (Tone generator) is not consistent, the best we
can do is to average a set of results.

Most of the serious experiments on string behaviour that I have read about,
have been conducted on a bench type set up, thus removing the up thrust of
the board.
I think what Ron is saying, and my intuition agrees, instead of down
bearing of 2-6lbs per string, we need to reverse our thinking, and think of
the bridge termination as being non fixed. I think this why we can measure
and hear the differences of 1+2+3 strings of a unison.

Measurement with any device that cannot measure the partials simultaneously
is not valid due to the poor reproducability of hammer flight.  Kent Webb
and I did some quick comparisons both using different Pianolyser's. While
the trends were the same, we both obtained different results due, we think
to the differences in Mic quality and preamps.

The major problem as Ron is pointing out, is to define what we are trying
to measure, the cause is a whole different story,

No answers again.
Roger
Roger Jolly
Saskatoon, Canada.
306-665-0213
Fax 652-0505