Official Luthiers Forum!

Somogyi wrote an article that posited that the bluegrass crowd were basically mitigating the back and sides of their instruments by placing them directly on the torso and dampening their ability to vibrate and effectively reflect sound from the soundboard. I guess the classical crowd solves this by playing in classical posture thereby separating the persons chest from the back of the guitar.

These two different playing styles have hybridized to some degree, for example Dave Matthews unusual stance on stage in which he attempts to take advantage of both styles.

The primary problem is transferring energy efficiently between back and soundboard. has anyone considered creating a direct connection between the back and the soundboard similar to the sound post in a violins? Admittedly the violin sound post is also structural to prevent the bridge from collapsing the arch, but I also have a theory that thy are really transferring energy from the strings to the soundboards, and therefore the back and sides.

Food for thought.

Yes it has been tried before.
Bluegrass players don't want to sound like them there classical guys cus they got there own thing goin

_________________
Ken

A "soundpost" (misnomer) in a guitar would indeed transfer some vibration to the back, but at a much larger cost to the vibrations of the top. The guitar only has a little string energy to work with (from the pluck), so the top needs to be as light as possible. Inserting a post between top and back would more than double the effective mass that the strings need to excite, which would kill the sound. It would also completely change the vibration modes of the top, back, and air, so the result would probably not sound like a guitar. Violins, being bowed, have much more energy to work with and so can afford to couple the top and back via the post.

_________________
David Malicky

A better option would be a "double back", where the real back of the guitar is very stiff and more or less inert, but there's a third plate inside the box to perform the flywheel vibration effect.

It's also a good chance to use woods like wenge, padauk, movingui, and osage orange that have great mechanical properties for use as backs, but have huge pores that are a pain to fill and/or bright colors that don't quite fit the traditional aesthetic. Since the flywheel back is inside the box where you can't see it aside from looking through the soundhole, it's kind of a waste to use woods that sound AND look great, like a lot of the rosewoods.

One really interesting thing I read about violin soundposts one time (can't remember where), was that one of the main purposes of it is to translate the side-to-side (cross dipole) motion of the bridge into up/down pumping motion (monopole). Since the bow sort of holds the bridge down, while making the string move side to side, symmetrical bracing inside would mean that the vast majority of bridge motion is cross dipole, which doesn't put any pressure on the air volume inside the box (phase cancelling; one side is up while the other side is down, so zero net pressure).

By putting a post under the treble leg of the bridge, when the bridge moves side to side, one way causes the bass leg to press down on the top and compress the air volume inside, and the other way allows the bass leg to come up, but the post prevents the treble leg from going down, therefore reducing the pressure on the air volume. Air pressure increasing and decreasing = vibration/air pumping = lots more depth to the sound.

Guitars are quite different since there's no bow holding the bridge down, and the string is free to vibrate in all directions rather than just side-to-side, but I do still wonder if that effect is one of the reasons that asymmetrical bracing patterns are popular in guitars as well. Make the treble side a bit stiffer, and some of the cross-dipole motion goes into pumping the air volume.

Thanks for the input. I wasn't trying to slam bluegrass by saying it's bad, just commenting that it's different. Sorry if I came across otherwise. Thanks for the physics advice!

The Bluegrass guitar can be called the drummer. They generally looks for a loud projecting guitar with a strong bass. Mr. Martin and your D-18 and D-28 please stand up.............!!! Very important for some folks even though there may be better sounding guitars.
Tom

_________________
A person who has never made a mistake has never made anything!!!

Another possibility would be to make a "possum board" like some dulcimer players use. The structure of the guitar would be unchanged, and the back would be held off the players body.

Someone makes a cage like device that attaches to the back of the guitar to keep it off the chest/belly of the picker. I know a real good Bluegrass picker who has one on his guitar and seems to think it works.

_________________
Fred Tellier
http://www.fetellierguitars.com
Facebook page http://www.facebook.com/pages/FE-Tellier-Guitars/163451547003866

Somogyi(or anyone else that can be rather influential, for that matter) shouldn't write about subjects/musical styles that they obviously know little of. When you study the actual playing of the better Bluegrass musicians, you'll see that as far back as the Father Of Bluegrass music himself, Bill Monroe, it was customary to hold the instrument away from your body. Watch Monroe and other great mandolin players, and you'll see that they actually hold the mandolin at a slight angle to their body, to free-up the back. And those that don't/can't, use a device called a tone guard:

http://www.tone-gard.com/

The guitar players typically do the same, holding the guitar at a slight angle, and many will "turn" the guitar neck forward or raise the guitar a bit when accenting a passage/riff, again, to free-up the back. and yes, some guitar players will use a tone guard type of thing, and many others(Doc Watson being the more famous) also use a "arm rest" which is a small device attached to the rim to hold their arm off the top. To this extent, all the built-in armrests we are adding to guitars today are likely counter-productive to tone, since they encourage the player, no matter the musical style, to lay their arm right across the most responsive part of the guitar's top.

Carry-on....

Peter Rowan is holding his D-18 up to the mike away from his body for his lick, sounds pretty good.
http://www.youtube.com/watch?v=m0G9F-Bw ... r_embedded

Whats bad for you and Ervin may be good for me!

_________________
Another day, another dollar.

I tend to build with an 'active back', at least in the low range. One of my customers, who records a lot, pointed out that he can use back contact as a tone control, and many players probably do that, consciously or not.

DennisK's memory about the function of the violin soundpost is just right: it's a 'bellcrank', converting the crosswise motion of the string activated by bowing in to a vertical force at the bass bar. Carleen Hutchins told me that putting a sound post into a fiddle cuts the overall efficiency of the thing in half, but most of the loss is in a frequency range that is unpleasant anyway, and it does increase the output in the low range.

I've used sound posts in archtop guitars as a last resort to control feedback. They tend to kill the acoustic sound, but do add a lot of feedback resistance in the low end by nearly eliminating the 'bellows' motion of the top and back at the 'main air' pitch.

A friend of mine tried several sound post configurations in a classical guitar, and got some interesting results. Putting a post between the waist cross braces on the top and back had varying effects on the tone, depending on where it was, and, in some cases, could have been called an improvement.

The Torres 'tornavoz, a soundhole sleeve usually made of brass or copper sheet, was also generally made to couple the top and back, and thus acted as a sound post. Those guitars seem to have been made without the usual waist bar on the top, with the back stiffness supporting the top against bridge torque. With so many changes being made at one time, it's sort of hard to sort things out intellectually, but the thing seems to have worked reasonably well. It's interesting to note, though, that it was abandoned fairly quickly in historical terms, so maybe it wasn't so much of an improvement, or, at least, didn't fit with the way music was moving. There has been something of a modern revival of this feature, with all the usual claims being made as to it's 'remarkable' qualities. That's always a hard word to interpret: a foghorn in a Beethoven symphony would be as 'remarkable' in it's own way as, say, the tone that Yo Yo Ma draws from his 'cello when he plays Bach, but one would be much preferable to the other...

My guitars are so responsive that the player needs to muffle the back and top somewhat to keep things from getting out of hand!
And... I like .

_________________
https://www.facebook.com/profile.php?id=100008907949110

It's called a tone guard or Tone-Gard. Pretty much solves this issue. http://www.tone-gard.com/