What to Build with an 18" set of Brazilian Rosewood

[Robert Filippi]

I recently unearthed a set of Brazilian rosewood I had stashed away in the early 90's. I was going to build a J-200 with it, but on closer inspection, I realize  I could easily make an 18 inch body. Is that too much of a good thing? Anyone have plans for a flat top steel string that large? The matching sides are 4-7/8" tapering to 3-7/8" (34" long). When I google !8" lower bout, I get a lot of discussions about arch tops which is expected, but little on flat tops. Suggestions?

[Robert Filippi]

Twelve string, Dave? Don;t get me started in that direction. Sounds like too much fun!

Thanks,Howard, this is good advice,generally. I am comfortable making my own plans. As a lifetime graphic artist, I have at my disposal several vector graphic programs (I use Corel mostly) and a 30" plotter to make full size drawings.
If you click on my avatar, you will see My Page which shows a J-200-ish I made in 1997. The drawings on the page are my own.

If anyone out there has similar drawings in cdr, ai, or other cad. for a large guitar, I would be interested.

Paul is taking this discussion more in the direction I would like it to go. I am principally concerned with features of the construction that are disproportional to say just blowing up a Jumbo design.

I was thinking about a 25.5" scale as that fits most people comfortably. The J-200 I built was 26"; I am personally comfortable with that except that bending notes is a little harder; on the plus side, it helps bring the bridge closer to the middle of top which I think helps to improve stability and response.

Other particulars:

1) I notice that some models in this size have proportionately smaller soundholes. (to control boominess ??)

2) Some models have very small upper bouts.They look like big pears!

3) Some models have shallow depths; 3 inch sides?

4) The Prairie State has a metal rod inside the body? (obviously not necessary, what was the thinking?)

5) How about a cutaway? Don't see them much on guitars this size.

[Paul Hostetter]

I am principally concerned with features of the construction that are disproportional to say just blowing up a Jumbo design.

I was thinking about a 25.5" scale as that fits most people comfortably. The J-200 I built was 26"; I am personally comfortable with that except that bending notes is a little harder; on the plus side, it helps bring the bridge closer to the middle of top which I think helps to improve stability and response.

It also helps with intonation, which is less important if you're bending notes!

Other particulars:

1) I notice that some models in this size have proportionately smaller soundholes. (to control boominess ??)

The common knowledge is that smaller holes increase low-end response. I'm not saying I personally believe that, but a lot of people do.

2) Some models have very small upper bouts.They look like big pears!

Like the early Super 400s? I actually like that look.

3) Some models have shallow depths; 3 inch sides?

That's another can of worms and deserves its own thread. Shallower bodies allow more player comfort, first and foremost. (Remember George Gobel.) There are other attributes, such as projection, which are very important but also very subjective.

4) The Prairie State has a metal rod inside the body? (obviously not necessary, what was the thinking?

Good question. Several people have done this, notably Larsons and Fenders. Advantages were ascribed. In my estimation, they didn't mean much. Take them out and nothing happens.

5) How about a cutaway? Don't see them much on guitars this size.

If you took an oversized 18" J-200 and put a 25.5" scale on it, and made the neck join at the 12th fret, a cutaway would give a good result.

[Howard Klepper]

"1) I notice that some models in this size have proportionately smaller soundholes. (to control boominess ??)

"2) Some models have very small upper bouts.They look like big pears!

"3) Some models have shallow depths; 3 inch sides?"

1) Complex issue. If other things are held equal, a smaller hole will yield a lower main air resonance frequency (Helmholtz resonance). But this is not the same thing as yielding more bass. Compared to a true Helmholtz resonator, the guitars main air resonance has a broad bandwidth; it supports frequencies on either side of its peak. If the air resonance drops too low (it's often around G on the low E string; rarely lower than F#) then its support for mid-bass frequencies can be reduced.

Also, the smaller hole will tend to make the bandwidth of the main air resonance narrower, and not as loud. Same potential problem. You might, for example get the low E sounding great, but the loss in the next higher notes results in a guitar that sounds weaker in the bass overall, as well as unbalanced.

But as far as boominess goes, I think it is less likely with a larger hole, not a smaller one, again because of the lowered and narrowed bandwidth of the main air resonance.

2) I think there is a connection between one's taste in this aspect of guitar design and one's taste in the form of human females. 'Nuff said.

3) Besides the ergonomic issue, the shallower guitar will hold less air and therefore have a higher air resonance frequency. But, this is far from a linear relationship, because the air couples with the top and back, and that coupling is weakened by making the box deeper. In other words, as you go deeper, you do get a lower air resonance, but not so much lower as you would with a rigid walled resonator. And as Paul said, it affects projection, another complex affair involving midrange frequencies and the directionality of the sound. It also tends toward boominess--hollow sounding bass lacking in mid frequencies overtones.

[Doug T]

#2, Howard - I inherited a body-shape designed by David Melly I think he called his "Modified Dread" but he referred to it as "Grandma Melly" everything slightly south-shifted.

I personally love the 25.5" for its clarity. I use a shorter string (24.625) length to emphasize more overtones whereas the longer for a snappier attack and more fundamental tone. The longer ones, unless on the multi-scale length where it's long on the bass and short on the treble, for my taste promote a more "stage grand-piano" sound than a guitar tone. With these bigger bodies, I think folks are trying to keep the air volume consitent while, as Howard says, developing projection. If you've got two guitars with the same air volume/sound-hole but make a smaller top and deeper sides for one, in general, you'll get more projection out of the shallower one, but you'll also effect tone and such, so it's a balancing game.

Sounds like a great opportunity to try something new. The other thought, (I think it was mentioned before) is build two parlor sized guitars. Those small instruments can be really sweet.

Doug