Archtop bridge science/nonscience

[ksdaddy]

A couple years ago I built an 17" archtop from scratch. I wanted to say I made the entire guitar, or at least as much as humanly possible. So I made the tailpiece, pickguard, bridge... I think the only things I couldn't make were the pearl dots, frets, and tuners. It was a 'principle' thing more than 'I can do it better than the parts sellers'. Not trying to reinvent the wheel or claim I'm better (neither is true), I just wanted to lay claim to making as much as I could in the actual building of it.

 

I made the bridge out a piece of maple, non adjustable, which meant a little more fitting. Actually this is #2 because I had cut curlicues out of the first one, kinda violin-like. It collapsed under the downward pressure of the strings, quite quickly and with no questions as to it's DNR status. #2 is one solid piece but small and thin (see pic).

 

The tone on this guitar is 'okay'. It's hard to do an A/B comparison because there's only some laminated electrics here, no carved tops. This morning, on a lark, I swapped the bridge out with a POS unknown thing with an ill fitting base, adjusting wheels, and a Gretsch-esque solid bar on top. It was like I hit the loudness button on an old Pioneer receiver. It opened up, loudened up, and it sustains forever. I can't believe it's the same guitar. And I didn't change strings, so that didn't affect it.

 

So what now? I've explored the science a little, just enough to steer me off into the wrong direction. In the past I've replaced rosewood bridges with ebony, replaced plastic saddle inserts with metal, made other bridges from scratch, and have come to no predictable results. Different guitars just sound better with different bridges; you can't say a harder material will yield better tone, as I've seen it go both ways. Does mass/size/footprint come into play? I would have thought a bigger, heavier bridge would absorb a lot of the string's energy, at least to the point of transferring less to get the top vibrating.

 

I'm kerflummoxed here. I now want to make a new bridge but given the amount of time and fitting, I'd like to have some semblance of a plan. If it's just a matter of another maple bridge with more size and mass, that's easy enough. If I should just go nuts and make an adjustable bridge like the one pictured, I'm okay about that.... well, shaping the top will be a challenge but I'd muddle through it. I might even make it from brass just to be different.

 

Help me with the big blonde. Throw some ideas at me.

 

[L5Larry]

I think you may have hit on something with the "footprint" theory. But I would also think that there is a point of diminishing returns.

 

I always think of an archtop guitar as a giant violin. Although a violin bridge does seem to have a very small footprint, if it was proportionately increased in size to the larger area of a guitar "soundboard", what size would the base be? Just thinking out loud here. Logically, I would also assume a solid bridge would transfer better than a multi-piece adjustable.

 

Just for your information I have measured the bridge bases of my L-5 and L-7. These are, or course, full contact hand carved bases.

 

L-5: 145mm x 15mm, ebony base with tune-o-matic bridge on thumbwheel posts.

L-7: 136mm x 15mm, rosewood base with rosewood compensated bridge on thumbwheel posts.

 

Another odd type bridge to look at would be the type on the guitars that Django played. The bridge base goes most of the way across the lower bout of the guitar.

[BigKahune]

I think you may have hit on something with the "footprint" theory. But I would also think that there is a point of diminishing returns. ... Logically' date=' I would also assume a solid bridge would transfer better than a multi-piece adjustable. ...[/quote']

 

+1

 

BTW, ksdaddy - glad to hear you've stumbled on a solution, because that's a real fine lookin' piece you built. It's nice that the sound now measures up to the looks of your 17" self-built beauty.

[Hoss]

It's all about footprint. Looking at your original, I'm amazed that you heard anything when you played the guitar!

 

There may be a point of diminishing returns, where you can get the footprint too large. I'm also thinking that it would be difficult to ever get a 'giant' footprint seated correctly on the guitar surface.

 

Anyway, I am certainly no expert- I have the good fortune of living in an are with a number of exceptionally talented and competent repair persons/luthiers. (And I also had a discussion with Ren Ferguson about this years ago!)

[ksdaddy]

I did a little experimenting but nothing much gained. I cranked out another solid maple bridge like the original, except a little taller. I didn't do any fancy fitting, just bandsawed it out and roughed it into shape. I shoul mention the original has a thin ebony cap, just enough to strengthen the bearing surface. I tried the new rough bridge just as maple. It sucked all the highs out and wasn't robust like with the junk bridge. I then added a thin bone cap. No better. I then slotted the top and added fret wire as a bearing surface. Minor improvement but no cigar.

 

One thing I noticed on the junk bridge was that it had two feet as opposed to a solid fit across it's width. I then took the original bridge and added two pieces of 0.120" thick rosewood as feet. I left them oversized and while the glue was wet I installed it and put tension on the strings so the feet will conform to the top and underside of the bridge. A quick check showed it's too tall and no real improvement in tone.

 

If this doesn't work, I may just go nuts and make another with a fitted base and a bigass brass cap. Or maybe I'll just crank out yet another with a bigger footprint and see how that goes. Larry, thanks for the dimensions. I pulled out my Emperor and saw it has a good sized footrpint as well. Maybe this is something that was 'found out' decades ago and I shold just follow suit. I'm okay with that, as stated, I'm not trying to reinvent the wheel.

 

I had no idea some little thing would have such a huge impact. Well, I guess I did, but needed to be reminded.

[TommyK]

Just a machine shed mechanic here with a blacksmith mind set, but here goes:

 

Mandolins have mostly wood bridges, some adjustable, some not. They seem to usually have two feet like a banjo bridge. Mandolins don't, in my opinion, have a lot of sustain like a big dreadnought guit tar. Having said that, a metal saddle may be the way to go.

 

As far as mass... Maybe with sufficient amount of mass, the strings set the bridge into motion and the mass of the bridge acts like a flywheel. Instead of spinning it is vibrating up and down. Have you ever seen on of those HUGE pendulums they have at museums? They call them Foucault pendulums, (pendulae?). They have a lot of mass and once set to swinging, they will swing for hours, maybe days on end. Once you set it to motion, it will sustain that motion for a long time. Again, there is probably a point of diminishing return. If the saddle is massive enough, the poor old strings might just have a hard time setting the 'flywheel' to jumping.

[Red 333]

Here's some food for thougght and discussion. It's an excerpt about archtop bridges from Robert Benedetto's Making an Archtop Guitar:

 

"The traditional two-piece bridge with its...obvious convenience of fingertip height adjustment...is a feature most archtop players are...not willing to forfeit. However, the result of the metal adjusters is undeniably a compromise in sound. On amplified guitar, this compromise may be hardly measurable; however, on the purely acoustic model, the metal adjusters simply do not belong...

 

The function of the bridge is to hold the strings in position while transmitting the strings' vibration to the top plate. It should be strong and lightweight...traditionally, the base portion...is fitted to conform perfectly, its entire length, with the arch of the top plate. If the R&D people of years ago had continued to make refinements, I'm sure they would have designed a completely new, one-piece bridge. Again, some violin or cello influence would be in order. A one-piece maple bridge with two fitted feet, its center trimmed away leaving only the enough mass to withstand the string tension is acoustically superior...A massive bridge...will have a dampening effect on the intrument's voice."

 

Red 333

[ksdaddy]

I made yet another bridge, more or less like the original but larger. It's too high right now but I can always remove material. It looks freakishly large but it's no bigger than a standard issue archtop bridge, I'm just not used to it. I also didn't fit the bottom yet; it's too concave and the outer edges are all that are contacting. I'm thinking I might go with the two-foot idea, just to give it a try.

[jaxson50]

I think it's the size of the footprint. But speaking of material, Martin and many other guitar makers are using Micarta for bridges and fret boards on flat top guitars. Why couldn't you use that for a bridge on a arch top?

[L5Larry]

I've got this rosewood two-foot bridge on a non-Gibson archtop, each foot measures 48mm x 15mm.

 

http://www.stewmac.com/shop/Bridges,_tailpieces/Archtop_guitar_bridges/Archtop_Guitar_Bridge.html?actn=100101&xst=3&xsr=4480

[jaxson50]

Or you could rock out with something like this;

http://www.fishman.com/products/details.asp?id=4

 

or this;

http://www.bluestarmusic.com/pickups/acoustic-guitar-pickups/archtop-guitar-pickups/shadow-sh-980-archop-ebony-bridge-pickup-jack.html

 

http://www.bluestarmusic.com/pickups/acoustic-guitar-pickups/archtop-guitar-pickups/schatten-at-02-archtop-macaferri-guitar-bridge-pickup.html

[jgwoods]

Lots of stuff about bridges in the mandolin world- take a look here http://www.murphymethod.com/redbridge.html

[ksdaddy]

Yep, my first bridge that collapsed was a ripoff of his 'winged' design. I think I may have made it too delicate.

[Red 333]

By the way, ksdaddy, your archtop looks beautiful. I admire your craftsmanship, and your persuit of completing it with as many hand-crafted components as possible.

 

Red 333

[jjulch]

KS Daddy- if the cheap bridge works, use it... You've done an excellent job with the archtop you've made. Those cheap bridges are copies of not so cheap bridges. They were all designed over years of trail and error. I wouldn't re-invent the wheel just because I can....