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FDP Forum / Guitar Mods, Repairs, and Projects / Cheap flat top with lifting bridge creates some 'out-there' thinking

Peegoo
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Aug 27th, 2019 11:00 AM   Edit   Profile  

I had here on the bench a cheap Ibanez acoustic guitar that belongs to a neighbor's daughter. It had a lifting bridge; the rear of the bridge was separating from the top. I removed the bridge, cleaned up the mating surfaces, and glued and clamped it back together, followed by a setup. Standard bread-and-butter work for a repair tech.

After I got the thing together, I was turning over in my head the fact that if the guitar does not get destroyed, it will at some other point in its life need another bridge repair. This is a fact of life about acoustic stringed instruments: they spend their entire existence being slowly and gradually distorted and disassembled by constant string tension.

Even expensive violins suffer from this. All fine stringed instruments are actually made to be easily disassembled and reassembled by a luthier.

But back to acoustic guitars. The way the strings attach at the bridge, they are locked into a thin plate (usually a hardwood like maple) underneath the top by the pokey ends of the bridge pins. It's this plate that grips and holds the string balls.

The part of the bridge you see on the front of the guitar does little to anchor the strings. Its sole purpose is to hold the saddle vertically and securely in place, and efficiently transfer the strings' vibrations to the top.

A acoustic guitar's bridge reacts the same as the string anchor bar on a Bigsby--or more easily visualized--a Strat's vibrato bridge. The string tension creates a rotational force (torque) that lifts the rear of the bridge away from the top. This is what causes acoustic tops to "belly" behind the bridge and "sink" between the bridge and the sound hole. It's also what causes a bridge to lift and separate from the top.

So I was looking at that Ibanez's bridge and wondering why there's so much wood behind the strings' pin holes. It would make more sense to have very little wood. The more wood there that's glued to the top, the more tension that's placed on the glue joint at the back of the bridge. And the faster the joint will separate over time.

I'm thinking about a different design for the wooden acoustic bridge. Less mass in the bridge also makes for a livelier top. I'm pretty sure a parallel change to the inside-the-box bracing would be necessary too.

There are makers that have developed alternative designs (see link for an example), but none have really caught on because they look a bit wacky to traditionalists, and they add cost. There's also the JLD Bridge Doctor, which is an aftermarket add-on designed to solve bellying problems and prevent the bridge tipping forward. Some makers incorporate the JLD in their production guitars.

There's got to be a better way that uses traditional methods and materials and is affordable due to low production costs.

Have you guys ever thought about this stuff?

Babicz design. Yeah, those are the strings.

(This message was last edited by Peegoo at 01:15 PM, Aug 27th, 2019)

Peegoo
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Aug 27th, 2019 11:37 AM   Edit   Profile  

This is what I'm talking about (link).

I could just be crazy. I mean, builders have already figured this out and have the best design, right?

Further study is needed...

Cal-Woody

USA/California

Why do I keep fixing things that work?
Aug 27th, 2019 11:55 AM   Edit   Profile  

Why not just use a trapeze type of tail piece to anchor the strings? They produce a nice jangle and allow the bridge to resonate the top of the guitar.
Wouldn't this be a good option?
The Babicz design is a little peculiar and would require longer string runs, although I can see how it adds to the overall design. But if you have the strings running over just the bridge with the trapeze tail piece, it doesn't place a lot of downward pressure on the top of the guitar and gives you more string sound with a little less body resonance but will have a longer lasting instrument.
It's all a trade off but the Babicz design is a little goofy. It would seem like a cool idea to have those leftover string lengths to be used as some sort of droning strings and be tunable!!
So many options but having the strings anchored to the guitars top is the best sound to me, as it causes the wood to be more vibrant and quicker acting to your picking style.

Peegoo
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Aug 27th, 2019 12:15 PM   Edit   Profile  

You're spot on.

In the 50s and 60s, makers of cheaper guitars (Kay, Harmony, Stella, etc.) did use a trapeze on some of their steel string flat tops. The problem is the flat top: it doesn't provide enough string angle (breakover) over the saddle to create enough force and transfer the strings' vibrations to the top.

These guitars, as a result, are not very loud and the tone is quite anemic compared to traditional flat top bridges.

Example

(This message was last edited by Peegoo at 02:42 PM, Aug 27th, 2019)

Leftee
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VA

Aug 27th, 2019 03:07 PM   Edit   Profile  

Gretsch still does it right!

Peegoo
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Aug 27th, 2019 03:14 PM   Edit   Profile  

Gretsch flat tops? They're pretty traditional.

But their archtops with the original skinny lightweight trestle bracing--that is a really great design. Their import stuff has fairly hefty trestle braces, but they work well.

Achase4u
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Aug 28th, 2019 10:31 PM   Edit   Profile  

Interesting topic I've never thought about.

Though my Eastman looks like it got knocked up by the mailman. Hmmmm.

twangdoodles

michigan usa

Aug 29th, 2019 05:27 AM   Edit   Profile  

You have to think of the bridge as being one part of the sound board. It, the top, bridge plate, and bracing all form a system of sorts that transfers the sound. Guitar makers that produce consistent results most likely are choosing bridge blanks that fall within a fairly narrow weight range. A big change in bridge design would necessitate changes somewhere else to achieve similar results.

I built an acoustic guitar at a school where we incorporated some fancy science that included, among other things, tuning the top to a specific frequency. This was achieved by shaving the wing braces with a small plane. It only takes a wee bit of weight change to alter the tone of a guitar. So you can imagine what difference the bridge can make, sitting there in the middle of the sound board and all.

I suspect that the extra meat behind the pegs is to help prevent splitting there.

hushnel
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Aug 29th, 2019 10:01 AM   Edit   Profile  

I’m thinking the instrument it pretty well thought out, balancing all the fundamentals including the tone wood and bracings in an effort to get the best possible sound and life expectancy is pretty amazing.

Some guitars do it well with great tone and a century worth of use, is a good indicator that old school luthiers have a pretty good handle on it.

With all the physical attributes of the woods, bracing, kerfing, body size, internal volume, change one thing the rest has to change too. I imagine that for these builders the wood is crucial, if a selection is off even slightly, the other aspects of the tone will have to be re-engineered.

Comparing between the steel string flat top and the gut/nylon string classical is a great example of how tone is achieved with two different platforms. My uneducated opinion is an inexpensive classical is a bit more viable than an inexpensive steel string. The bracing and anchoring for the steel string produces much more stress, demanding finer tolerances, when done right you get the great volume and tone, still the top tiers of each are comparable in value.

The thing I think about is why among stringed instruments does the guitar not have a sound post, and how does radiating bracing compare to convex tops and back with a sound post compare.

This stuff keeps me awake at night “o)



SonicBlue

Sunbury-on-Thames

Aug 29th, 2019 02:06 PM   Edit   Profile  

It's to do with the plane(s) of string vibrations. Guitars don't need sound posts to make a useable sound, bowed instruments do.

Why guitars don't have sound posts

Peegoo
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Aug 29th, 2019 04:31 PM   Edit   Profile  

Good article!

"A big change in bridge design would necessitate changes somewhere else to achieve similar results."

I've built several acoustic guitars and ukuleles using traditional designs and methods. Tap-tuning is part of my process, and I figure if I built a guitar with a radically changed bridge and bridge plate, the internal bracing would have to be altered to compensate for the redistributed forces across and through the top.

hushnel
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Aug 30th, 2019 11:43 AM   Edit   Profile  

I agree, and it makes sense. It didn’t occur to me that the vibration bias would be so radical between the two.

Thanks for digging that up.

Peegoo
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Aug 30th, 2019 12:51 PM   Edit   Profile  

A guitar string oscillates in two planes 90 degrees from one another. If you have access to a tunable strobe light you can see this in action. in a dark room.

You can also hear it. Try this: plug in an electric guitar and turn up the amp; get a nice clean tone. With the guitar in the normal playing position, strum a chord. While holding the chord and letting it ring, quickly flip the guitar face up. You'll hear a difference in the tone because the strings continue vibrating on the same plane even as the guitar is rotated.

You can do the reverse too: strum a chord with the guitar face up, and quickly rotate the guitar to the normal playing position.

hushnel
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Aug 30th, 2019 03:29 PM   Edit   Profile  

It’s interesting, the tones decay can be different in acoustics some sound better than others, probably just an spect of good engineering, or sympathetic with good design. Scale length would have an affect on this too. Probably why scale length of similar stringed instruments are semi standard.

hpete
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Aug 30th, 2019 07:00 PM   Edit   Profile  

My Takamine doesn't have bridge pins it's top mount. It was old when I bought it 23 years ago and so far no belly bulge.

Peegoo
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Aug 30th, 2019 08:08 PM   Edit   Profile  

Ovation made guitars like that too with pinless bridges. I see very few Ovations requiring bridge re-glues.

I think the big reason is Kaman has always used advanced materials and adhesives. They were one of the first makers to mass-produce guitars using non-standard materials and production techniques.

Glenn Campbell (RIP Maestro) was their highest-profile endorser in the early 70s. I remember seeing him on the Carson show, and Johnny asked him about his weird-looking guitar with the round back. Campbell replied that the material used for the backs of Ovation guitars was "the same stuff they make helicopter blades out of." Kaman built helicopters as well as Ovation guitars.

That very cool description stuck with me and is one of the reasons I got interested in guitar building and repair.

FDP Forum / Guitar Mods, Repairs, and Projects / Cheap flat top with lifting bridge creates some 'out-there' thinking




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