Designing an Experimental Guitar

[Paul Eisenbrey]

Hi folks.

I'm planning an odd duck guitar, and I'm looking for advice from anyone who has done anything similar. The guitar has to solve two basic problems:

1) It has to be load enough to hear, but quiet enough so that the person sitting next to me can still concentrate on whatever plot the TV is pumping out.

2) It has to handle amplification without feeding back. (requirement: no soundhole)

Currently, my design is for a very small body: 17" long by 13" (lower bout) and 11" (upper bout), with a 9.5" waist. Think Les Paul shape with a thick waist. And the whole thing will be around 2" in depth. That will help with the fact that I am circumferentially challenged, and I don't like to play side-saddle.

I am thinking of carving the body out of a solid-body guitar sized blank, and bracing it as if it were a parlor sized flat-top. The top wood could be any acceptable tone-wood: spruce, cedar, or whatever. Since I plan to stain the whole thing black, I don't care if the wood looks good or not.

I'll put a K&K mini under the bridgeplate.

So, my questions:

1) How thick should I cut the sides? Will 3/16" be too thin? Or can I safely go thinner?
2) Same question on the back. I will probably want to have a hatch in the back to allow access to the pickups and the bolts for the neck, so I can't go too thin. But it would be nice if the back was thin enough to resonate, too.

Any comments and advice are welcome!

--Paul

[Nick]

I once made (& used) a hollow body tele, thinline inspired & complete with bound F holes, that had the inside carved out of solid mahogany & a top similar to an acoustic. It had some acoustic volume, louder than a full solidbody & enough for a player to hear whats going on, due to the resonance of the chamber under the top but nowhere enough for a full concert recital It was my first 'attempt' into the acoustic realm so was way overbraced for it's size but probably helped with the fact it had zero feedback when pumped through my 60 watt Fender amp. Had two humbuckers & because I used an acoustic bridge, an undersaddle transducer with onboard preamp. I have some pictures of it finished & during manufacture if you are interested or looking for ideas, but they're on my puter at home (I'm at work at the mo) so will post them up later.

[charangohabsburg]

1) How thick should I cut the sides? Will 3/16" be too thin? Or can I safely go thinner?

I can't speak of hollowed out guitar bodies, but a charango body made of mahogany or a similar wood typically has about 6mm thick walls, and better not thinner than 5 mm. This minimum thickness is partly for structural reasons (but not only). Remember that a significant part of the figure of eight outline is endgrain! I have seen some charangos with a hollowed out rosewood body which were left as thin as 2 mm! Not very common though, and pretty fragile. However, near the neck the bowl is always left about 50% thicker than the rest of it (for structural reasons).

For controllable loudness you might consider fitting the bridge plate with a threaded insert for a mass loaded top, equivalent to Trevor Gore's mass loaded sides... Just kidding. But hey, maybe this would work...

[kiwigeo]

No sound hole? I can see a few problems.

[charangohabsburg]

No sound hole? I can see a few problems.

Which problems? A guitar with no soundhole works just perfect. Access to the interior will be granted by a back door anyway.

[kiwigeo]

No sound hole? I can see a few problems.

Which problems? A guitar with no soundhole works just perfect. Access to the interior will be granted by a back door anyway.

I'm thinking what happens when I block up the port on the ported speaker on my sound system....

[kiwigeo]

There are a few acoustics around without a soundhole...but not many.

[kiwigeo]

Is it an acoustic guitar...or an electric guitar?

[charangohabsburg]

I'm thinking what happens when I block up the port on the ported speaker on my sound system....

Then you've got a non ported speaker with all its consequences. But it's not going to be a problem. I have heard and played soundhole-less guitars and ukuleles that were built exactly the same as their soundholed twins - except of the missing hole. No drama, only muted and maybe a bit a duller sound. Just right for playing along with the news speaker on the TV.

[Paul Eisenbrey]

Thanks of the replies.

To answer the last question, it will be acoustic only. No humbuckers, nor anything in the body to attach them to . Leaving the soundhole out should minimize or eliminate feedback when I play amplified. And (obviously) if I cared about the thing's volume I'd make it deeper than 2".

Interesting point about the heel area of the body being thicker than the rest. That sounds like a good idea, I'll add it to the plans.

--Paul

[kiwigeo]

From reading Paul's original post it sounds like he's describing a Godin.

[kiwigeo]

I'm sitting here with a stinking head cold.....guitars without sound holes are just too much for me in my current state of health

[Clancy]

Didn't Bob knock up something that generally met these requirements?

[Bob Connor]

I did and I'm still experimenting with it.

It originally had a spruce top but I whipped that off and now have a blackwood top on it and it's almost complete.

You might be surprised at how much volume you lose (or more to the point) you don't lose by not having a soundhole.

I've done three mandolins with no soundhole and they are almost as loud as my Ray Black f model.

The testing I did while the spruce top was on the guitar showed it was quiter than a mormal "soundholed" guitar but not by a lot.

I run an EMG UST plus a K&K mini in it.

I'll try and get some pictures of it during the week.

[Paul B]

You guys comparing guitars with or without sound holes to ported speakers, or ported reflex speakers, reminds me that I have a book somewhere on speaker design that says for speakers without a port, you need drivers with much softer cones, or that spongy bit around the edge of the speaker cone can be softer and allow greater "throw" because the trapped air inside the enclosure stiffens it up by adding resistance to movement of the cone as a whole. It kinda bounces off the trapped air in the speaker enclosure. Perhaps a guitar without a sound hole could be built to take advantage of this? The book said that both types of speaker design were equally valid, but each offered differing advantages and drawbacks.

Shit bought that book at least twenty five years ago, knew it would be good for something. I'll see if I can dig it up, might offer something interesting...

[Paul Eisenbrey]

Godin, huh? I'd never actually heard one. I had a listen out on youtube to three, and they don't sound bad -- I could do worse .

But the ones I saw were solidbodies. That may not be a huge difference, as with 6mm sides and back, mine is sure to be a heavy sucker, but mine should be acoustically better than that...

I found Bob's stage guitar thread. As this will only be my 5th (or 6th) guitar, depending on when I get to it, I have no hope of that level of quality. But it is good to have goals!

Thanks for the advice, I'll post progress notes when I ramp up on the project.

--Paul

[Dennis Leahy]

... for speakers without a port, you need drivers with much softer cones, or that spongy bit around the edge of the speaker cone can be softer and allow greater "throw" because the trapped air inside the enclosure stiffens it up by adding resistance to movement of the cone as a whole. It kinda bounces off the trapped air in the speaker enclosure....

How about the opposite: stiffen up the top, put an undersaddle (or maybe soundboard transducer) pickup, and use headphones. As Bob said, the ones without soundholes are still kinda loud, they are just a bit muted and (I assume) have a different, higher resonant frequency.) She will still tell you to go in the other room, unless you kill the top from moving much (and then, it will still have the higher frequencies.)

Oh the hell with it! Unplug the TV and get her a cowbell!

Dennis

[GregL]

Hi Paul,

Following on what Dennis said, why not get a wireless headphone setup for the TV? Then you can play a "normal" guitar, and the person sitting next to you can still hear the TV (through headphones - better stereo!)

Thanks,
GregL.

[nnickusa]

I can hear it now....."HEADPHONES! What and mess up my hair?!?!?!?!"

[Paul Eisenbrey]

HA!

I think I'll increase my chances of staying married and not suggest any of that.

--Paul

[kiwigeo]

When we were doing our last lot of renovations the boss had a horn on for an ironing board that slid out from under the kitchen bench. I wasnt keen on bocking off access to the kitchen everytime ironing had to be done. When I asked the boss why she wanted the slide out ironing board so badly she stated that she wanted to watch TV while doing the ironing. When I suggested I put a TV in the laundry she wouldnt talk to me for a week.

[nnickusa]

Actually, Paul, it sounds alot like a Godin for sure...Leonard Cohen plays a nylon version....Trot on over to the local muso shop and see what they've got on the wall to fish for ideas. I know a few guys very happy with their Multiac's

They make pretty good guitars....for Canadians.....come to think of it I know a Canuck or two who make pretty nice pieces....