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I was at the Healdsburg guitar festival and played Brock Polings fabulous sloped shoulder dreadnaught. It was exactly what I want for the D style I am about to start. It had a lot of headroom and really screamed to be played harder. The sound seemed to just open as you stepped on it. I would like to be able to strum and pick with some force and volume and yet not have the guitar disappear at lower volume.

It seems to me that to brace a little heavier in the lower bout area (including the X) and not make the top too thin would be important. At higher volume and force the base seems like it would fall apart so heavier on the base side of the X-brace? Someone care to illuminate me?

Thanks for the comments about my guitar.

I can tell you how I built that one if you are interested, but generally speaking that is pretty light. The top itself is slightly heavier than I normally build, the x brace is just a touch taller at the lap joint, and the rest of it are my normal approach.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

There isn't any evidence that I'm aware to support the idea that the bass side is involved with bass any more than the treble side. The same seems to hold true for the treble on the treble side. So, changing the bass side of the X might affect the bass, but only by virtue of having affected the whole top. The same effect on the bass could result from changing the treble.

Pat

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formerly known around here as burbank
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http://www.patfosterguitars.com

Brock, yes I would be interested. Let me tell you how I would approach it (given your information) and you could maybe tell me whether I should seek medication before this build or not.
1). make the top on the thicker side .115 - .120
2). X's .260 wide and .625 high at intersection
3). spread tonebars (so they are not parallel and cover more of the large open area on base side)
4). Voice normally (not sure about scalloping) keeping the tap a little tight but not too open
5). cap X
6). don't tuck lower X's under kerfing
7). pray for a miracle

Pat, I guess I haven't made the jump yet to thinking about the entire box as a whole. Thanks for the push. Given this information how would one go about using it practically. I know that volumes could be written about this and it seems to be subjective, but in this case (a dreadnaught looking for a particular sound) how would one approach opening up the base response while tapping and hearing a lack of base? Thanks

If you're looking for 'headroom', I'd suggest seeking out a piece of wood that's on the dense side. Don't make it too thick; it will have higher then normal long grain stiffness anyway, and it will end up being a little heavier than a top made of lighter wood at the same stiffness. I'll note that Red spruce tends to be on the dense side.

I also find that 'tapered' bracing tends to give better headroom then 'scalloped'. More mass and stiffness at the bridge location resists over driving, but won't give you the 'whomp' you'd get from scalloped bracing.

OTOH, if Brock tells you something different, listen to him: he built the thing!

Alan, thank you very much. That helps a great deal. Haven't heard from Brock yet. I assume the "whomp" of scalloped bracing would be the brightness of attack or maybe thickness of tone in the lower resgister?

No this is on the money.

That top is Red Spruce in the 9 gm/in^3 range, I thinned it to slightly less than my normal deflection -- so it is thinner than most folks use. The bracing is 1/4" wide and it is profiled into a triangular shape and tapered (not scalloped). The lower legs of the x are not tucked. The upper fingerbraces orginate under the edges of the bridge. The tone bars are not parallel and try to drive as much energy as possible into the lower bout. The upper tone bar makes contact with the bridge plate.

My bridge is very stiff across. I don't have wings, but a domed pattern.

Does that help?

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

Brock, it helps hugely. Thanks a ton. It makes sense to me too. Now I just need the miracle!

Hey Brock-

how about some pictures of this guitar please? Thanks for the info on its' voicing and bracing.

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John Lewis
Wannabe builder owned by 2 crazy dachshunds

Brock:
You wrote:
"No this is on the money. "

Small minds in the same gutter, if you'll pardon the expression. Seriously, it's nice to have my ideas confirmed in practice by somebody else out in the trenches.

9 gm/cubic inch! You're as bad as I am for mixing units!

If I used my handy-dandy conversion table right, that's a specific gravity of about .550, or 550 kg/meter^3. That's indeed on the high side for density, and should correspond to a lengthwise Young's modulus of around 17,000 megaPascals, plus or minus about 10%. That's abnout as high as spruce gets, and is higher than some rosewoods I've measured. I'm sure you could go to .100" or even a bit thinner on a top like that.

Now there's a question. Did you go less than .100 on that top?

Yes Alan, I definitely mix my units. Probably because my balance in grams and I measure in imperial - my physics profs will probably hunt me down . I was equally impressed that you could zero in on that guitar from the theory.

I don't have specific notes on how thin that top was (I thin to deflection and rarely pay much attention to the final thickness), But I am sure that it was in the .10 or maybe even slightly less range. I have a batch of very dense Adi tops. Spruce usually comes in 6 - 8 gm/in^3 and every one of these tops is in the 9 - 9+ range, and crazy stiff in the long grain.

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Brock Poling
Columbus, Ohio
http://www.polingguitars.com

I think if you keep track you'll find that your density readings will pretty well predict the deflection numbers.