Neutral Tension Bridge

EDITOR'S NOTE: I was awarded utility patent US 7,795,516 regarding the Neutral Tension Bridge design for acoustic instruments, on September 14, 2010.

This design is changing the way I think about building instruments. Neutral Tension Bridge — a bridge that places zero tension on the soundboard of an instrument. Every other existing instrument design couples string tension to the soundboard, whether longitudinal, tangential or lateral. Acoustic guitar strings attach to the guitar top. Classical instrument strings (violin, cello, bass, etc.) and archtop instrument strings pull the bridge against the soundboard. Even solid body electrics couple string tension to the soundboard (body).

Two significant problems are associated with conventional designs, especially acoustic instruments:

• Conventional soundboards must be designed to counteract string tension, through the use of bracing. Bracing adds mass (weight) to the soundboard. As strings vibrate, they must push against the combined mass of the soundboard + bracing + string tension in order to transfer energy and amplify sound. This mass slows response time (loss of transient detail and note articulation) and dampens sustain.

• Expansion and contraction of the soundboard due to temperature and humidity changes cause the soundboard — including the bridge — to change orientation angle relative to the neck. As a conventional acoustic guitar swells or shrinks with humidity or temperature, the action changes. String height above the frets is an ever-changing frustrating variable and a constant struggle affecting quality, design and warranty. Bob Taylor (Taylor Guitars) explains the problem in this series of videos.

Both of these issues are eliminated by the Neutral Tension Bridge.

Here's a simple sound clip of the test prototype. Note the test platform guitar is slightly larger than a Martin Backpacker — about 1/3 the body volume (size) of an average acoustic guitar. Prototype saddle is stainless steel (bright/crisp) and not intonation compensated.

UPDATE (12/2010): Sound clip dates from 10/2008. As part of my ongoing research, I recently created an additional sound hole "slit" similar to an "F" hole in the soundboard on the bass side of the bridge, resulting in approximately 1/3 more perceived bass response. The addition of this third sound hole in the instrument is also creating a very open and airy 3-D sound playing experience for the musician. The sound clip above does not include these recent changes.

I have absolutely abused this acoustic prototype made from cherry and spruce. It has never been in a case. I have never used a Dampit or any other humidifier. For the past 19 months I have traveled with and played the guitar in climates ranging from the swampy summer humidity of sea level New Jersey to arid (10,000'+) mountain ranges of Santa Fe, New Mexico. Inside. Outside. Winter. Summer. Even stashed inside a (black) pickup truck cab parked in the desert!

The action never appreciably changes. No splits. No cracks.

A whole world of design posibilities is opening, which is so exciting to explore. Please contact me for licensing opportunities.

Comments

[Joachim]

Wow, Rick, that's brilliant! You've got a real talent for challenging the conventions. Can't wait to see and hear where you're going with this :)

How does it sound?

[Jesse]

Once again fascinating, I can't wait to see the complete project!

[Fighting Windmills]

Congratulations on filing for the patent, Rick. It is gorgeous.

[Ola Strandberg]

I think that this will change more than just your way of thinking of building instruments! Awesome! I can't wait to see what's in store from the list of things there.

[Ian L]

It's very interesting to see more work in this area! Ned Steinberger and Steve Grimes did some work on a similar idea (see pat. no. 5,679,910). They include an interesting adjustable neck mechanism (length and tilt) as well as several manifestations of a "stress free" bridge system.

[Marcel Roy]

Great job! Nice shape! I'm an industrial designer and I'm without words! Very good innovation!

Mrcl

[Gorm Sverre Bruland]

Elegant design I have to say. I've sketched on a similar design myself. Although, in my sketches, it was kept within the looks of an ordinary bridge. Of course mechanical principles in action are the same. I came up with the idea when trying to figure out what Babicz had in mind with their bridge design. Your design takes away the forces on the soundboard. In contrary I guess the Babicz solution answers a question that nobody have asked.

I find your work very inspiring. Both asesthetically and in terms of technical solutions.

I'm going to build my first acoustic guitar at Totnes School of Guitarmaking early next year. I'm fascinated with acoustic instruments in particular. And I would like to design and build more ergonomic and still elegant guitars in the future. I'm also interested in improving the guitars efficiency in transforming sting vibration to sound. Your bridge design could be a key element in such guitars.

As a mechanical engineer I find the complexity in the function of traditional sound board brazing a bit confusing. Taking away the torque and stress of the soundboard should give room for more optimal sound transducer designs.

I wish you good luck with your work Rick

[Tyler]

How do you deal with intonation compensation? Do you have a way around this?

By the way, I think Bob Taylor wishes he was as clever as you are.

[Rick Toone]

Thanks, Tyler.

I've owned Taylor acoustics and they are fine production guitars. I have a lot of respect for Bob and the excellent work he's done both in advancing lutherie and associated ecological issues. Perhaps at some point we'll have an opportunity to work together.

Intonation is approximate on the prototype pictured above, equivalent to a production acoustic. Compensation for the B was simply a matter of filing the cross-member.

This prototype was only to test the concept. More advanced bridge designs — with intonation compensation — are under development in prototype form. I will be publishing additional information as I have time.

[John Maddock]

This is really good, nice job!

I'm assuming that there has to be no appreciable break-angle in order to ensure zero-pressure on the top? I'm asking because I was wondering if this style of bridge could be retro-fitted to a vintage instrument with a delicate top?

Regards, John Maddock.

[Jeff Wewers]

Beautiful design! Are the strings pulling up on the center crosspiece, as well as resting on the outer crosspieces? Love that tailpiece too!

[Rob Johnson]

This is a brilliant idea, not to mention stylishly executed, but there is very little that is new in the guitar world.

Take a look at the bridge on this guitar:

LINK | http://www.harpguitars.net/history/org_images/form1/lacote_9-stg-mfa_dangerous_curves.jpg

...Interesting, huh? That was built by Rene Lacote in 1827. He made at least one other (a seven string) with the same bridge. I assume he used this design to relieve the tension from the extra bass strings.

On a different note (no pun intended), your use of native woods is fantastic. It’s always nice to see someone making great instruments without using bits of what precious little rainforest we have left. Besides, cherry and walnut are easier to work and they don’t give you lung cancer. ;-)

[Rick Canton]

That is truly genius Rick.

[Jake Powers]

i really like your idea for the neutral tension bridge, yet im curious about the tone and projection of the instrument.

where i work, we put a lot of time and effort in to shaping all of the braces so the top resonates at a tone that sounds beautiful, but what really drives that is the tension from the strings, which also increases the projection and volume of the guitar.

it seems to me youd be trading one dragon for another, then again i havent heard your prototype. much respect.

[Rick Toone]

Jake — thanks for commenting.

You can actually hear the prototype on my website. It is a small test instrument, slightly larger than a Martin backpacker. I built it just to test the concept — prove that it works — before applying for the patent.

LINK | http://www.ricktoone.com/2009/02/neutral-tension-bridge-recording.html

I'm currently building a full size guitar using this technology. It will sound much bigger and deeper, of course. It will also feature a (very) different embodiment of the Neutral Tension Bridge concept, along with a body mounted (headless) tuning system that I've had machined.

Unlike current acoustic guitars with centuries of bracing refinement, I think of this idea as ripe for exploration. It is the beginning of a new branch on the tree of acoustic instruments.

[Roger Landes]

Very, very cool! I love the tailpiece. What is it made from?

[Rick Toone]

Roger — Thanks very much! The tailpiece is stainless steel.