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.
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