"Back Tilt" on a Bridge

[John Flynn]

The "pressure on the top" thread got me to thinking: I have heard some people say that if you set up a bridge to "lean back" toward the tailpiece about eight degrees, it drives the top better. I have seen some mandos that the builders set up this way, inclduing my Parsons flat-top, and I believe Mike Compton has his mandos set up like that. My questions are:

1) What has been your experience with this? How much of a difference does it make?

2) Would the lean change the pressure on the top, given the same set of strings at the same pitch or would it just be more efficient in transferring vibrations at the same pressure?

[labraid]

To help visualize:
http://www.bfolk.com/bridgetilt.jpg
The upper drawing should show the force arrow beginning more to the right, right where the string makes it's "bend", but for clarity's sake...... Anyway, seems pretty reasonable to cut the string bend angle in half and to lean back the bridge by this much. Seems like it would more directly transfer the vibes, but maybe that's in an ideal world where everybody has opera singer ears and can tell the difference. Probably doesn't change much, but I never tried it... Anyone else?

[pathfinder]

Although a banjo's string tension is much lower (not to mention the top construction!), some banjo players do this too. #

Years ago, a guy set up my five-string with a Randy Smith or Randy Wood bridge. #Randy sands the base of his bridges on an angle, creating a noticeable back-leaning tilt when installed.

As was explained to me, the sanding creates more surface area where the bridge makes contact with the top. #This 'spreads out' the pressure being exerted downward by the strings, lowering the risk that the bridge will puncture the skin (which ain't graduated spruce, and has no tone bars or cross-bracing for support). #Moreover, it creates more surface area for the bridge to actually vibrate the banjo top.

Don't know how true this is, but made sense to me at the time, and it did seem to improve the tone. #Even for a bad banjo player like me. # http://www.mandolincafe.net/iB_html/non-cgi/emoticons/laugh.gif

Maybe the same principles hold true for tilting a mando's bridge?

[sunburst]

OldTymer,
Thanks for the drawings. Maybe not worth 1000 words, but worth quite a few.
I think a straight-up-and-down bridge is fine, and a tilted bridge is fine, as long as the center of force (similar to center of gravity) is not too far toward the edge of the feet. Your drawing explains this better than my words could have.

I use a tilted banjo bridge because it seems more stable and resists tilting forward better. On a banjo a straight-up-and-down bridge will often sound better, however, because the bridge feet end up farther from the center of the head. This reduces overtones in some banjos. I don't think that applies directly to mandolins.

[pathfinder]

Huh? #Why don't you get someone to translate that reply into English (and logical sense)?

[Mark in Nevada City]

Makes sense to me ;-) First the main reason for tilting the banjo bridge is to reduce the chance of it leaning toward the fretboard, not to increase area on head. I've actually heard "slap" of a fallen banjo bridge juring a jam, and its not pretty ;-) The strings need to contact the bridge in the same spot regardless of bridge angle--ie instruments scale plus a smidge of compensating intonation. Sunburst is just saying that for (some) banjos, there's an advantage to having the feet of the bridge further from the center of top (which happens with perpendicular bridges).

That said, it does make sense to me that "bi-secting" the breakover angle is more structurally sound, but I would defer to 'bursts experience that it doesn't really matter in the increments that we're talking about.

cheers, mmm

[MDW]

My Larry Muth F-5 has a distinct backward slant to the bridge. I haven't tried a more conventional bridge setup on it so I don't have anything to compare it to on this mandolin. But it seems to work well. I asked Larry about the slant and he said this, "The bridge should approximately bisect the angle formed by the strings, or a little back. This gives the maximum force of the strings onto the top." So he seems to be in the camp which says there is a more efficient transfer of energy.

Mark

[labraid]

There's really so many factors that affect all this anyhow. Some makers use pretty huge adjusting thumbwheels on their bridges, this extra mass only helps dull the soundboard vibrations (if you had equipment good enough to measure the difference MAYBE you'd find one). Or what about a bridge with ebony of a higher density? Does anyone measure the specific gravity of their ebony before saying yeah or nay it's good enough for a bridge?? And given that the density of wood even within a given tree varies widely, every bridge has slightly different sound perpetuating properties. Anyhow, if someone is going for serious "maximization of sound perpetuation by bisecting the string angle", that's ok with me. But back to my oft-quoted opera singer analogy, does anyone have ears good enough to appreciate the difference? (we're talking micro-measurements here) Hey, though, if it helps prevent the bridge from tipping, I'm all for it... Just my 4 cents (more than ye wanted? http://www.mandolincafe.net/iB_html/non-cgi/emoticons/biggrin.gif )
-Brian

[mandough]

I agree with you Oldtymer, there seem to be numerous factors that add to a bridge's efficiency to drive the soundboard.
I believe that one can greatly improve the sound of a dull sounding mandolin by maximizing it's efficiency. This may be one way to do it. There are other ways, like changing out those big thumbwheels, like you said.
The question becomes " how far do you go?" I've heard muddy Pacrim mandos sound tons better by bridge improvement. On the other hand, I've heard some great mandolins that IMO needed to back off a bit on driving the soundboard (a little too loud and harsh).
Louder doesn't always mean better, but sometimes it does. That's a bit confused sounding, isn't it.???

[Chris Baird]

The bridge to soundboard coupling is one of the most important and easily altered interactions on a mandolin. It doesn't take much of a bridge change for anyone familiar with the instrument to take notice. The strings/bridge/soundboard coupling largely effects the mid to higher register of the instrument. The problem that both the violin and mandolin have is that many of the overtones on the e and a string are above what we can hear. The "right" bridge will emphasive the lower harmonic range so as to bring out a "richer" e and a string. As mandolins vary considerably in modal couplings so will thier "right" bridge compositions and placements. The best way to figure out what works is to experiment and literally "play it by ear".