Spacers on the back of a guitar?

[Beate Ritzert]

Maybe that sounds strange, but at least some guitars have more volume or simply play louder if there is no contact (or as little as possible) between the bottom and the player's body.

That's the case with my cheap ABG - which is, btw, surprisingly loud and well sounding. I want to play the instrument without any amplification in an acoustic setup (accordion, soprano sax, bass) Which basically works well but i feel the need of being able to play slightly louder.

And one possiblity might be to add spacers to the back, of course only to its edges. Has anybody tried to incorporate something like this to the design of the instrument?

THX


Beate

[Alan Carruth]

One of the students in a shop I worked in about 25 years ago made up a 'rest' similar to the shoulder rests violinists use. Basically, it was a stick that was clamped across the lower bout (iirc) with a bit of air space between it and the back. I think it took him all of about a half hour to rig it up. He was playing Flamenco guitar standing, and this really reduced the damping of the back. The main problem with such a rig on the guitar is that the back on a fiddle overhangs the edge, so there's something there to clip onto, but it's not an insurmountable problem.

[Bob Gramann]

A couple of decades ago, I saw a player who had a plate with suction cups at the edges that attached to the back of his OM and held the guitar about 3/4” off of his belly. It made a big improvement in the sound of the guitar. He put the plate on the back of his guitar when he pulled it from the case before he went on stage. I’m guessing that he made the device himself. I don’t remember what the plate was made of.

[Beate Ritzert]

But that fortunately sounds as if my idea was not completely crazy ... encouraging.

[Alan Carruth]

The basic notion has been around for a long time, the issue is coming up with a generally acceptable way to implement it. Some 'double backs' are one effort in that direction; a false back spaced a small distance from the real one to free it up. The extra air space adds a lot of complication when it comes to the way the back vibrates, with the usual solution being vent holes on one or the other back. It seems to become like the cowboy who jumped on his horse and rode off in all directions, with most of the possible ways of doing it having been tried so far as I can tell. There's the added effort and expense too, of course; the outer back needs to look good and the inner one has to work well, so you need two nice pieces of wood, and the added structure. Selmer scrapped Maccaferri's double back almost as soon as he was out of the building. An added frame type of structure, such as the one our apprentice Igor made, moves the box out away from the player, which could be a problem with a deep guitar body. Combined with a Smith/Manzer 'wedge' it could be useful. You have to figure out how to stow it in the case.

I build with a 'live' back. One of my customers, who spends a lot of time in the studio, found that the ability to damp it or free it at will was really helpful in altering the spectrum of the sound. That's easier to do when you play sitting, of course.

[Marshall Dixon]

Depending on the finish of your guitar you could apply something like a thin vinyl material or double layer veneer with double stick tape. Make it a deep as needed. I've seen thin adhesive kitchen counter top edging material that might be layered by stacking it inside to outside to build up depth.

If it didn't work out be sure you can remove the adhesive with naphtha or acetone. I don't know how you can be sure you won't pull the finish off though! That would be a gamble.

[Beate Ritzert]

So here's my prototype - two stripes of poplar, the spacers made of XPS, and all temporarily fixed with double sided tape. It actually works as indended, and that's sufficient for testing and getting experience over longer time.

Quite interestingly, tapping the top shows pretty large stiffness in all of the upper part of the top (i.e. completely silent) and a stripe of cm within the edges of the lower part. So actually only a small part of the top does actually move significantly, a lot less than with my other acoustic guitars. Nevertheless, that instrument is loud, and it sounds well. But that also indicates, that there is still unused potential of such a body (Jumbo, 17" wide, 11-122cm thick). Well, that's a Harley Benton HB30 which cost me 75 € (new about twice that amount), so everything is fine. I'm actually quite impressed how well such a cheap guitar may sound if it is only done intelligently.

[Beate Ritzert]

The extra air space adds a lot of complication when it comes to the way the back vibrates, with the usual solution being vent holes on one or the other back.

Obviously. But anyaway: as soon as i move away the bass a few cm from my body, a similar situation arises there will be a gap which will of course affect the movement of the back.
The main difference to a partially doubled back appears to me the difference in reflectivity if ther spacers carry a wooden plate instead of the two stripes in my testing setup.

But anyway, a more porfessional looking solution could be something which is removable and possibly also adjustable, maybe something like an oversized violin shoulder rest.
In such a setup the beauty of the wood might even be less important because the thing will remain an addon. For now i tend to use beech plywood and just oil it with something like tung oil or probably clou hard oil (a thin oil laquer).
I am still a bit unsure wether it is acoustically better to leave the wooden surface intact or cut a large hole into it.

[Alan Carruth]

Certainly the proximity of the back to your body will affect the way the back vibrates to some extent, but it won't be as much as you'd see from actual contact. Practically speaking I'd say it would be negligible, or nearly so.

"... maybe something like an oversized violin shoulder rest."

That's pretty much what Igor made in our shop years ago. I think he even made it so that it could be stashed in a case, but I'm not certain of that.

[Mark McLean]

You could adapt the concept of the “Guitarlift”, which is a Perspex plate that attaches by suction cups. It is primarily designed to be a rest for classical guitars that sits on your leg and holds the guitar in an elevated “classical” position. However, it also has the effect of holding it away from the guitarist’s body as you are desiring. If you cut it down in size it could just serve the second function without lifting the neck (for more typical steel string playing position).
https://www.youtube.com/watch?v=ehWnm9Ac-ts