Official Luthiers Forum!

Hi Guys-excuse my ignorance ,but is there any reason why you couldn't put an upright brace between the top and bottom plates to help counteract the downward pressure from the strings? I was thinking about the fine line between a thin top, and sufficient structure on the soundboard and great acoustics. Cheers Paul

The general info is that this will deaden the sound in a guitar. It would be like putting your hand on the vibrating top, or worse. Violin family instruments have a post between the top and back, but those instruments are continuously energized by the bow, so they do not rely on the sustain of energy from the instantaneous string pluck, as does a guitar.

Yes. It would inhibit both the top's and back's ability to move in and out, which is the major volume producing movement.

There is no actual downward force on the top at this point that needs to be countered in a flattop guitar. That is a misunderstanding of the bending moment created locally due to the angle of the string break-over at the saddle, which tends to cause a forward rotation of the bridge. And a corrective action for an excessive amount of this rotation, which can result in a hump, is a device called a Bridge Doctor.

Isn't there some company that puts some contraption between the bridge plate and tail block?

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Pat

Breedlove.
JLD Bridge Doctor.

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The name catgut is confusing. There are two explanations for the mix up.

Catgut is an abbreviation of the word cattle gut. Gut strings are made from sheep or goat intestines, in the past even from horse, mule or donkey intestines.

Otherwise it could be from the word kitgut or kitstring. Kit meant fiddle, not kitten.

" I was thinking about the fine line between a thin top, and sufficient structure on the soundboard and great acoustics. Cheers Paul"

As you build more guitars you will find that a thin top is not truly desirable. Tops that are too thin sound "thin" and banjo like. Not a sound most people are looking for in a guitar. Thin tops can be louder, which people do desire in an acoustic guitar, so a compromise is needed.
Some of the best sounding amplified acoustics are pretty dead when they are unplugged. They tend to have thick tops (and/or finishes) On the other hand a highly responsive acoustic with it's thinner top can be difficult to amplify well. Small differences between notes become noticeable when amplified.
Making a top that is thick enough to sound good, thin enough to be responsive, and strong enough to last, is the balancing act we all try to do.

I remember years ago that Richard Brune (renowned classical builder) commented that he was surprised when he measured the thickness of tops on old Hauser I guitars and found how thick they were. Hauser was one of the old great builders.

Thanks Guys-much appreciated. I read this thread from another site and would appreciate your comments. I did have a 'dull sounding classical guitar and inserted a sound post just behind the sound hole and on the treble side and the guitar has improved dramatically, by becoming brighter and louder. The post is between the back and the transverse brace below the sound hole. The top was 2.0mm in the center.
http://www.acousticguitarforum.com/foru ... p?t=167776

Sound posts are made to suck some of the power off the top on a bowed instrument. without it - you can literally saw on them till they vibrate to pieces. Much harder on a plucked instrument.

Most of the time - a sound post ruins an otherwise decent instrument.

Thanks