Solid vs. cutout bridge base

[BradB]

I have an F5 style mandolin (custom built for me by Peter Sawchyn) that sounds very good. It's not the loudest F5 mando I've played, but it does have good volume and a really sweet tone. A well-known mandolin player who plays a 1920's Gibson F5 tried it and liked it, but he suggested replacing the bridge, which has a cutout at the bottom center, with one that is solid all the way across the bottom. He said that this would bring out the midrange and improve the tone.

Has anyone here experimented with a solid base bridge (one long foot) versus one with a cutout in the middle (two feet)? If so, what did you find?

[cwtwang]

Brad,

I own a LaPlant F5 with a solid bridge bottom that is in full contact with the top. If I can remember correctly, Lloyd told me that he had used both the bridge bottoms with the slot and the full-contact bottom and he gets a better tone with the solid bottom. Lloyd has experimented with this for years and he has been building for decades.

However, most bridges and all the best Loar F5 fashioned ones, have the cutout. The theory behind the cutout (another member might explain this better) is that the cutout allows the sides to rock back and forth slightly which frees up the tone and also creates more volume.

I guess it can be said that most luthiers get better results
in tone and volume with the cutout while some get better results with the solid bottom.

Cheryl

[Paul Hostetter]

It's a fairly easy thing to try, and it won't break the bank. So try one and see what you think. Just make sure the base really fits the top of the mandolin. There are other bridge types to experiment with too, such as non-adjustable one-piece bridges. Listening to other people talk endlessly about it is simply delaying you from making the real determination that matters. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/smile.gif

[mandomadman]

I just went through this a couple weeks ago. I sanded out the middle of the bottom of the base between the two adjustable posts a couple of millimeters creating feet,and the result was excellent. Really made a noticable difference on my KM-Dawg. Much better bass response and punchier chop chords as a result. Just be mindful not to sand directly under the posts or the base may cave from the string tension. I hear drilling small holes into the bottom of the bridge and base will make the bridge assembly lighter and transfer string vibration to the top better. Have not done that yet though.I'm not a licensed professional so if you screw it up it's not my fault.:p

[cwtwang]

I have considered sanding out a very shallow section of my ebony bridge base on my LaPlant, but it is not a very deep one and the thought has occurred to me that it might collapse.

I think that the depth of the base must be considered. You can try a new quality bridge with a cutout. But if the base and/or saddle top is deeper (thicker) than your original, the action/wheels will have to be lowered quite a bit to make up for the depth.

Cheryl

[kww]

I suspect that a perfectly fit one-piece will work better than a bridge with feet, but a bridge with feet will survive warping better.

Picture, if you will, two flat surfaces in contact. If one surface warps into a convex shape, then it will make contact only at one point with the flat surface, resulting in really poor sound transfer. If you have feet, then it will make contact at at least two points.

This is just a thought experiment. I am not a luthier, nor do I play one on TV.

[John Flynn]

Both of the Old Wave Ovals I have had close contact with have had solid bridge feet. They sound great! Both those instruments are cross braced. I wonder if the bridge foot style has any inter-relation with the bracing or sound-hole type.

[Paul Hostetter]

The part of the typical adjustable mandolin bridge that usually fails and most affects playing is the top (or what some folks call the saddle), which tends to go swaybacked if it's not big enough. This has nothing to do with bridge contact with the top.

Mandolin bellies and bridge feet are never really flat. Or shouldn't be.

The arch of a top flattens under tension. Ideally anyway, the point of the two-footed bridge is that the center of the base has some flex which enables the feet to keep good contact with the top under tension.

http://www.lutherie.net/mandolin.bridge2.jpg

What complicates this, and many of us who have been dealing with archtop guitars and mandolins for decades will attest to this, is that the pressure on the thumbwheels tends to concentrate the pressure on the inside of the feet, while the outer ends lift a bit. Lots of dented old Gibsons tell this tale over and over. It’s a design flaw, if you will, and it’s very common. There’s a workaround, which you can view here (http://www.lutherie.net/mandolin.bridges.html).

In a one-piece base, the pressure is telegraphed from the strings to the face of the instrument in a more rigid condition, hence the entire top settles under that load with no choice but for the continuous contact to be maintained.

Lest you think I’m advocating a continuous base, I’m not. I only advocate a base that really fits, at rest and under load. I think the two-point-contact base sounds perhaps a wee bit better, but I’m not that doctrinaire about it. I have heard a number of types of bridges work well, and acknowledge that what’s best for one player may be entirely different in the ears of another.

[8ch(pl)]

I always thought that the center was removed for 2 reasons. One, a bridge with 2 feet will compensate slightly for an uneveness in fit. The other reason being to not make contact on the top at the location of a longitudinal brace. I may be wrong on both counts.

[Amandalyn]

Although this is on violin acoustics, I found the info on bridge design very interesting and could apply to mandolin bridges:
http://www.josephcurtinstudios.com/news....heights (http://www.josephcurtinstudios.com/news/tech/journal_vsa/principles.htm#ideal_heights)

[Amandalyn]

P.S. the link starts a ways down the page- scroll up for the beginning of the article. It's interesting that he tap tunes his bridges for different results.
Teri

[Paul Hostetter]

Glen -

A bridge with two feet will adjust slightly for an uneven fit if the center of the base is thin enough to flex, and if the whole thing is engineered to direct string pressure from the strings so the feet don't become splayed out. Having them fit pretty well at rest is no guarantee whatsoever they'll fit at all under load. As I point out in the linked page above, sometimes (often, in fact) it goes from bad to worse. The feet don't automatically adjust to the top, they do what the string pressure makes them do, depending on other considerations. And it's a rare mandolin that has any brace right under the bridge in the center of the top.

Joe Curtin's comments, linked above, are 11 years old. Here's where he's at with violin bridges today:

http://www.lutherie.net/curtin.bridge.jpg

This does have two feet.

[Rick Turner]

While two foot bridges may be right for both violins and mandolins, the mechanism by which sound is produced is quite different given the role of the sound post and bass bar in the violin and the nearly constant side to side rocking motion imparted by the bow. I can't imagine that a full contact violin bridge would work very well at all. Interesting to note that Curtin's new bridge maintains the traditional design of "no direct path" down from the strings to the top.

[Paul Hostetter]

The "rocking" model has become almost a cliché. I don't dispute it, but the received interpretation package is such old news. Nothing has come of that realization beyond the notion that those hoary old dudes in the 16th century and even earlier found the real stuff. As you say, the lack of a soundpost and everything a soundpost implies kind of cancels the value of the violin model as any kind of information for plectrum instruments.

Joe Curtin made his name for his ability and success in copying great historical instruments, including their sound. Then he won a MacArthur Genius Grant. He’s using that to explore the nether reaches of scientific inquiry as it pertains to violin (not mandolin, not guitar) physics. I’m inclined to wait another ten years after his grant is used up to see what he really came up with—the jury is not only not even still out, it hasn’t heard all the testimony yet. But I know one good thing he came up with along the way so far—which is also not news—is the benefit of more mass in the area of the top where the soundpost touches. But it has absolutely no applicability for plectral instruments. Dang.

If you understand Curtin's take on bridge physics, which I happen to agree with, then this new one of his pictured above, isn't so new, except in its aesthetics.

[Rick Turner]

Paul, I had a very interesting conversation with Curtin about five months ago, mostly about his use of balsa in instruments. I read his bit on adding some maple to the top where the sound post contacts, too. So what I'm picking up is that he is redistributing the basic recipe for mass, stiffness, etc. in order to try to get a more responsive instrument that still maintains warmth. This is akin to what Smallman started in classical guitars. Have you seen what our near neighbor Gil Carnal is up to these days? I just saw a lattice braced classical that knocked me out. Very impressive.

[Paul Hostetter]

The guy who's pioneered balsa and CF instruments is Douglas Martin. Curtin is one of the directors of the Oberlin summer workshops where he's met Martin and tinkered with those instruments. There has been some conversation about them on another thread here, since this somewhat clumsy NY Times piece (http://www.nytimes.com/2006/11/28/science/28acou.html?ref=science&pagewanted=all). Bohmann was making lattice braced guitars in the 1880s and thereafter. Made for steel strings, decades before Martin (and certainly Smallman) got there. A great idea, also not big news, but I'm glad to see the notion surviving and being carried on.

[sunburst]

Hmmmmm... just how does one get one of these MacArthur Genius Grants? I can think of a lot of things I'd like to play with...

[Antlurz]

Paul...

I noticed in your post with the bridge illustration, your thoughts, but I also noticed the arch on the bottom of the bridge heavily favors the bass side of it. My initial thought was someone was tinkering with that location to enhance or minimalize some aspect, but that doesn't mesh with your accompnying statements.

I'm left to believe that bridge cutout illustration is an artists freebasing of graphics, rather than anything revealing deep dark accoustic secrets? http://www.mandolincafe.net/iB_html/non-cgi/emoticons/tounge.gif

Izzat correct?

Ron

[Paul Hostetter]

Freebasing is not an activity I engage in. And I'm not sure which bridge illustration you refer to - the mandolin or the violin. The violin bridge isn't mine and it definitely "favors" the bass side since violinists bow with the right hand. That's how violin bridges are always arched.

The mandolin bridge above is simply a much-messed-with shot of a Gibson, and the base looks pretty symmetrical side to side to me, though some earlier real Gibson bridges tended to have more meat at the bass end, where the patent stamp was.

Here's a current Gibson bridge. Notice how the end of the base is lifted. And it's even a one-piece base.

http://www.folkofthewood.com/Images5/gibsonbushbridge.jpg

This, in my book, is one substandard bridge. The slots look bad, the action was adjusted by applying a pair of pliers to the thumbwheel. But it could be corrected without too much trouble. But before it gets fixed, it'll leave the typical divots in the top and it won't sound quite right.

[Antlurz]

Whew. That last picture is kinda scarey.

No, the one I was referring to was the mando bridge. I guess from your reply, it's merely sloppy graphics..

..and I'm with you on the freebasing. http://www.mandolincafe.net/iB_html/non-cgi/emoticons/tounge.gif

Ron

[oldwave maker]

I've been using the solid for years, but thanks to Paul and Rick, can see the issue of how that will affect top shape. A friends loar has a stable top crack at the inside edge of the bass foot with a 2 footer,, and I see a slight bulge outside the bridge on both sides of a onefooter with softer redwood tops. One thing I've learned from hacklingering good mandos is how wide that thicker area under the bridge is, before quicly thinning at the recurve, somewhat counterintuitive to gradual graduation change.

[Fretbear]

Reischman's Loar had a problem with it's top that Todd Philips effectively addressed by installing a full-foot bridge. Sam Bush uses a full-contact one as well. They are not easy to find if you don't want to sand a two-foot bridge down. I use a single-foot radiused "Tall Boy" bridge that Steve Smith at Cumberland Acoustics made for me. He makes mighty fine mandolin bridges.

[Paul Hostetter]

The image above is a new stock Gibson Sam Bush. Again, a full foot is guarantee of nothing. Steve's bridges are great, I use them routinely, but they still need to be fitted to the top.

Ron - I'm not sure what your point was with the re-do of the bridge photo, or what your question was.

[mandolooter]

all very interesting thoughts but this sez it all...
Listening to other people talk endlessly about it is simply delaying you from making the real determination that matters. I tried a full contact on my Givens and didn't notice much if any difference at all so I went back to the original one. On my mandola/octave I tried a full contact and noticed a definite change for the worst. I found the best sound with a banjo bridge I fitted to the top! It has way less mass and 3 feet on the top.

[mandolooter]

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[mandolooter]

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