Bridge caps

[Ron Nossaman]

>It really comes down to how energy efficient you want to the system to be. If 
>you want as much of the vibrational energy to go into the bridge/soundboard 
>system (impedance and all), the ideally the pin should be buried as deeply as 
>possible in the trunk of the bridge (not the cap). 

But the pin depth in the bridge is for mechanical support, not energy
transfer. All the energy stuff happens right there at the termination
point. That's not an impedance concern. The most common cause of wild
strings is that the pins are loose in the cap and flagpoling with the
string excursion. 


>Energy does bleed off into 
>the atmosphere from the tip of the pin, and more as the pin is extended.

That's just it. I haven't seen anything at all to support that assumption.
That's why I asked for an explanation. I've seen plenty of pins set at all
heights producing false beats in strings. Touching the top of the pin
clears up the beat. I've seen no cause and effect correlation at all
between pin height and false beats. I've also seen pins of all sorts of
heights with strings producing no discernable false beats or other obvious
problems. Again, no height correlation. Some do, some don't, but it's the
loose ones that produce the most noise.   


> When 
>someone gives me that half a million dollars to set up that research facility 
>that I've been waiting for, I'll get right on it, but in the meantime, 
>intuition if not hard science would lead me to think that system efficiency 
>is the issue. This will probably not be a satisfactory answer to your 
>question, but it's the best I can do for now.
>PR-J

No, it isn't satisfactory when the "intuition" is contrary to both logic
and observable effects. As I've said many times before when stuff like this
comes up, if it's that critical, it ought to be obvious or demonstrable.
Meanwhile, you don't need a half million dollar research facility to test
it. You have the means right there in the shop. Repin a bridge with the
pins of every other unison  sticking up from, say 5 to 10mm. That's pretty
extreme compared to no taller than the string diameter, and if excess pin
height is such a big energy drain, it ought to be immediately obvious. If
it turns out that you and everyone else can't hear the difference without
looking... 

Also, FWIW, I recently ran a test on a sample bridge section to see what
happens to bridge pin height during humidity swings. Cooked in a fishing
rod case with a DC heater rod for three days, the average pin height above
the bridge cap measured 0.126". After three days in a plastic container
with an open bowl of water, average pin height was 0.117". Better not file
those pins too low in the winter. 

PS, and to whom: At the same time the pin height went from 0.126" > 0.117",
the bridge height went from 1.091"< 1.119". 


Ron N