Tech: Mandolin Bridges

Subject: Tech: Mandolin Bridges
From: dick greenhaus
Date: 02 Nov 09 - 08:04 PM

I never thought much about mandolin bridges (until mine broke yesterday). Ordering a replacement was easy enough, but I've been wondering why the typical new mandolin bridge happened--the two-piece model with two knurled nuts to adjust the string height. It would seem to me that this design is inherently heavier---and therefore a better mute---than a thin single-piece bridge would be.
    Are mandolins more demanding of precise string height adjustment than, say, fiddles or guitars or banjos? Or is some degree of muting considered desirable? Or what?
    I know that I could find out for myself by carving a simple one-piece bridge and comparing the sound, but I'm not that curious, and fitting a bridge to an arched top is the kind of thing I used to do in my youth, before I got lazy.

Subject: RE: Tech: Mandolin Bridges
From: The Fooles Troupe
Date: 03 Nov 09 - 12:14 AM

I picked up a couple of such instrument at the 2nd hand shop for a total of $5 - will need strings, bridges and tuner pegs...
SO will watch this discussion closely...

Subject: RE: Tech: Mandolin Bridges
From: The Fooles Troupe
Date: 03 Nov 09 - 12:15 AM

Actually, maybe they are ukeleles...

I'm a keyboard player, right?

Subject: RE: Tech: Mandolin Bridges
From: mandotim
Date: 03 Nov 09 - 02:48 AM

Red Henry started making one-piece maple bridges for archtop mandolins, and there are others on the market now. They look a lot like fiddle bridges.

Subject: RE: Tech: Mandolin Bridges
From: JohnInKansas
Date: 03 Nov 09 - 02:52 AM

Because of their short length, mandolin strings are considerable "stiffer" against the fingers than is the case for longer strings. The stiffness is sufficient that single-course strings would literally slice the ends off your fingers. The double-course strings are to "spread the load" in the manner of a bed-of-nails. If one pound of pressure against one sharp edge would hurt, one pound against each of two identical closely spaced sharp edges may be "tolerable."

Because of the pain factor, mando players like to have much more precise adjustment of the clearance of the strings off the finger board, and - if they're really fussy - like to have some degree of adjustment across the strings, so that the "high" strings have a pressure requirement compatible with the pressure needed for the "low" strings.

Again primarily because of the short string length, the amount of "stretch" in the string when it's pressed down to a fret is relatively larger than for longer stringed instruments, so relatively large amounts of "compensation" are needed in the bridge. The open string length is actually different for each string so that mid-fingerboard tones will be close to pitch. The "staggered" blocks of the bridge^* provide the required compensation.

Mando design is by now sufficiently "standardized" that it's seldom really necessary, but the sloped sides (notches) of the "block" for each string do provide a way to relatively easily tweak the compensation in the rare cases when that's needed - without making the bridge ugly (uglier?).

^* An alternative design uses a curved/arched bridge similar to a fiddle to achieve somewhat similar compensation, but to my ear it doesn't do quite as well as the traditional "blocks" and especially "up the string" it requires some practice to accomodate the very slightly different string heights. Tried one once. Didn't much care for it.

Once again due to the short string length, the "down force" applied to the bridge by the strings is - relatively - very much higher than for longer-stringed instruments. Only the best (hardest) woods suffice, and a "sturdy" structure is necessary.

On one occasion when a bridge broke during a festival, and no replacement was available, a piece of a wooden clothespin was the only wood I could find that was hard enough to whittle (actually Dremel grind) a replacement that lasted more than a few minutes. That one did last me for about three years before I found a "real" bridge locally - although toward the end it also broke in a way quite similar to the fracture of the original. (Its hard to find a clothespin with "properly aligned grain.")

John

Subject: RE: Tech: Mandolin Bridges
From: mandotim
Date: 03 Nov 09 - 04:36 AM

Hi John; while double courses certainly do help with spreading the load on fingertips, that's not really the primary purpose. Mandolins generally don't have a lot of sustain, so tremelo is used a lot, especially in classical mandolin playing. Double courses means that each string is able to 'ring' for slightly longer on each pair of 'up/down' pick strokes, giving a smoother tremelo and the impression of long sustain.
Red Henry has a development page on his site, with lots of detail about his experiments with solid maple bridges.
here

Subject: RE: Tech: Mandolin Bridges
From: Nick
Date: 03 Nov 09 - 06:05 AM

I broke the bridge on my (cheap) mandolin and was advised to superglue it and it's been fine ever since

Subject: RE: Tech: Mandolin Bridges
From: deadfrett
Date: 03 Nov 09 - 11:16 AM

Dick- I've been making my own bridges for several years now. I usually use bebinga as the material of choice. I starteed on banjos and moved to mandolins. A scroll saw is really helpful in the initail stages but there is still a fair amount of hand work. It's really worth it when you string it up and listen to it ring. There is usually someplace like the YMCA or a Senior Center where you can find a lot of free tools to use. Hope this is helpful. Dave

Subject: RE: Tech: Mandolin Bridges
From: deadfrett
Date: 03 Nov 09 - 11:18 AM

Dick- Sorry forgot to add that I use a A Model Gibson Bridge as a starting point as the solid piece gives a better sound. Dave

Subject: RE: Tech: Mandolin Bridges
From: BTMP
Date: 03 Nov 09 - 12:25 PM

I fitted a Brekke bridge to my vintage Gibson A4 about 4-5 years ago and was very happy with the sound, although it was not as nice as the one-piece original bridge. The Brekke does offer wood on wood sound transmission, as opposed to the wood thru metal post transmission of the traditional Loar bridge.

For some reason, when I fitted a Brekke on my Flatiron f-hole A-model, the sound was softer and not as punchy as that with the Loar bridge, which I then put back on the Flatiron. Probably has something to do with the overall design and construction of the 2 instruments.

Subject: RE: Tech: Mandolin Bridges
From: dick greenhaus
Date: 03 Nov 09 - 01:38 PM

Innaresting. Any other opinions? And, since dimensions of mando bridges seem to be pretty much standardized, why can't one buy just a replacement top section? (spoken as a very lazy mandolin picker)

Subject: RE: Tech: Mandolin Bridges
From: PHJim
Date: 03 Nov 09 - 01:58 PM

Dick - Good question. When I replaced my bridge I only replaced the top, to avoid having to fit the new bottom to the top of my mandolin, but I had to buy both parts.
The same thing happened when I bought a bridge with a pick-up for my arch top guitar.

Subject: RE: Tech: Mandolin Bridges
From: Mavis Enderby
Date: 03 Nov 09 - 02:22 PM

I see there's already a link to Red Henry's site, but there's also some useful info on Frank Ford's site: a superlight mandolin bridge here and some info on fitting mandolin bridges here

It's well worth a look round the rest of his site too - very interesting and inspirational...

Cheers,

Pete.

Subject: RE: Tech: Mandolin Bridges
From: Songbob
Date: 03 Nov 09 - 02:26 PM

Well, the top sections aren't sold separately, for one thing. Another is that the 'standardization' is not, plainly, 'standard,' and a difference of .1" in the screw-post spacing is sufficient to make it impossible to use a top that doesn't come with a matching bottom.

That said, I have used new tops on older bottoms, with the result that I have at least two separate bottoms with no tops. The reason is that the curve of the feet must match the curve of the carved top exactly, and it's a pain to fit a new bridge when all you need is the top (breakable) section.

If you really want a problem with fit, try finding new tuners for a 1920s Gibson A-model. The modern spacing is off just enough that you can't use modern pegs, and I don't know of a source for ones with the proper spacing, other than really vintage instruments or parts which sell for astronomical prices. Sigh.

The difference between adjustable and non-adjustable bridges can be more than just the fit, too. There is a theory in bridge-making that says that you should NOT have a 'direct path' from string to top. If you look at a violin bridge, for instance, there are holes and 'partial' holes (the two outside strings are over holes with missing sides) under each string. Solid mandolin bridges without holes sound different from ones with holes. The adjusting screw kind, of course, have that gap under the top section that acts the same way. I experimented with the bridge on my flat-iron-style Mid-Missouri Mandolin instrument, and prefer the bridge with holes I drilled over the same style bridge without holes.

In any case, there are a lot of choices in bridges, some probably as expensive as a bottom-line instrument as a whole. I have several mandolins, from the old Gibson to a Harmony to the Mid-Missouri to a "The Loar" F-5 (no, not a "Loar F-5," but one by the Chinese company that's making pretty good copies of the "real deal"). I have mostly adjustable bridges on them, but may try a solid bridge on one or more, once I can afford any bridge at all. And I'll keep experimenting to see which combination fits which instrument.

And I'll also keep looking for old-gauge mandolin tuners, since the ones on the Gibson are starting to slip too easily.

Bob

Subject: RE: Tech: Mandolin Bridges
From: The Fooles Troupe
Date: 03 Nov 09 - 04:22 PM

"There is a theory in bridge-making that says that you should NOT have a 'direct path' from string to top. If you look at a violin bridge, for instance, there are holes and 'partial' holes (the two outside strings are over holes with missing sides) under each string. Solid mandolin bridges without holes sound different from ones with holes."

Ah - something I do understand.

The direct path uses 'compression wave transmission': the bridge with holes relies on using other vibration modes, the names of which JiK will probably advise, as I can't think of them just now. The different modes will transmit each of the various overtones in a different manner providing a degree of 'filtering'.

Subject: RE: Tech: Mandolin Bridges
From: The Fooles Troupe
Date: 03 Nov 09 - 04:25 PM

Oh, also, the more holes, the lighter the bridge, and the more mass, the more 'dampening', especially of the higher overtones. This is why violins sometime use 'mutes' - they add mass to the bridge, dampening the volume, and also affecting the tone by absorbing some of the higher overtones.

Subject: RE: Tech: Mandolin Bridges
From: dick greenhaus
Date: 03 Nov 09 - 08:01 PM

Well, I have an A-style, round-hole-archtop model (clearly copied from a Gibson of a half-century ago). Anyone have any experience in using different types of bridges on this kind of beast?