consistent downbearing measurements

[Ron Nossaman]

>As I understood it, listening to Tom Lowell describe the proverbial 
>drawing on the napkin, the purpose of the gauge was as much to be able to 
>isolate the front and rear components constituting net bearing.  Maybe I 
>misunderstood.

No, you didn't, but that sidesteps my point. Measuring overall bearing with 
a bubble gage, you get a reasonably accurate picture of overall bearing, be 
the strings wrapped, or plain wire. With a dial or stick gage, your overall 
bearing will have to take into account the vertical offset across the 
bridge from front and back bearing (which you don't know), as well as 
deviation of the back scale from the plane of the speaking length where the 
gage is resting - all of which is dependent on the length of the gage and 
width of the pin row spacing. And what do you do with wrapped strings? The 
bubble gage eliminates all that and gives you a direct reading of the 
difference in plane between speaking length and back scale regardless of 
front and rear bearing, or whether or not the string is wrapped. It also 
allows you to take measurements of front and back bearing by adding the 
third measurement of the segment across the bridge. I know, Tom says to 
start on the bridge segment, but I disagree. I say zero on the speaking 
length, get a good accurate reading of the back scale, and then fit what 
you can get from the bridge top in between the two. It's easier to measure 
that way, less error prone, and you aren't working from the least reliable 
measurement of the three as you are when you start with the bridge top.


>  Whether or not it makes a difference whether we achieve a given net 
> bearing with a front and rear positive or with a mixture of positive and 
> negative, is a sub-question of soundboard loading, apart from the issues 
> relating to termination.  This, apropos your statement above  "... (the) 
> load the strings are putting straight down on the soundboard".  Do you 
> have any thoughts regarding possible acoustic differences (effect on SB 
> impedance) between a (basically) neutral load (positive front and rear 
> bearing) and one which introduces distortive potential ( positive / 
> negative)?  This would be another reason for measuring the individual 
> components.

Yes, I do. Front and rear bearing are termination issues, not soundboard 
loading issues.


>>>Still, the challenge of accurately measuring and conveying  the nature 
>>>of a particular piano's string deflection, including the bridge, is, to 
>>>me, a separate question from how much or little there should be or how 
>>>it does or doesn't affect the instrument's qualities.
>>
>>You'll never get an absolute answer to that one.
>
>This wasn't meant as a question.

You said it was a question, but then what I gave you wasn't an answer either.


>In other words, I should be able to relate the net downbearing I measure 
>with a bubble gauge with what I would get using a Hartman stick.

Ok, how? How do you measure overall bearing with the stick? How do you take 
pin row spacing, and vertical offset from the bridge top angle into 
account, and how do you do wrapped strings? With the bubble gage, I zero on 
one segment, and read the angle from the other. Explain to me the process 
of using the stick.

Ron N