Official Luthiers Forum!

My partner and I are starting our first build, each doing a guitar individually but together in my shop based on Kinkeads book and whatever else we can find. The OM is based on Martin which is just over 4" depth. I want to build that size, I think it's perfect. But I can't help but think I want to increase the depth to say 4 3/8". Seems I would get more volume. Spruce over Honduran Hog. Mostly a picker but enjoy fingerstyle. Any thoughts or experience would be appreciated.

_________________
Just a box with strings https://www.facebook.com/wadesguitarshoporcas

You'll likely lower the air resonance a bit by increasing the depth of the soundbox but I doubt you'd increase the potential volume of the instrument by doing so. I'd probably just follow the plans for the first few and experiment as you gain more knowledge.

I would second that. Follow the recipe the first time for a baseline, and adjust to taste next time…

Welcome to the OLF Wade.

First guitars are really much more of a learning experience than a successful run at making one's ultimate guitar. And most here will tell you that they did not stop at one. My first I once put out with my Sunday night trash and I propped it up thinking that someone might like it, see it, take it, etc. The next morning it had been removed from the trash, checked out and thrown in my yard...., face down..... Everyone is a critic I tell ya....

So if it were me I would see these first efforts as 1) fun, 2) productive in what we learn and 3) putting us on a path to make a great guitar.

Is it possible to make a great guitar on the first pass, sure but in my experience it's not very common.

So maybe follow the plans so that on subsequent instruments you can isolate variables such as the box depth and then be able to compare what you accomplished to the last one you built.

When I was still building with each instrument I identified three things that I wanted to improve and I isolated those things. Acoustic guitars and how they function, exactly is not perfectly understood by anyone in my view and they are still a bit mysterious to many and that's part of the fun.

The book you are using is a good supplement but it's dated and most of us learned from a combination of books, kits, plans, forums and friends.

Welcome aboard and feel free to let me know if I can ever help you out.

Hi Wade
My first build was a OM, following the Kinkead book. The OM design is pretty classic and works really well. You can do your own thing but deeper is not necessarily better or louder. Also, a deeper guitar can be a bit harder to get your right arm over, not as comfortable to play. My second build was a Gibson L-00 just like that pair that Hesh built and has in his signature photo. There was a famous and popular version of L-00, the Nick Lucas model, which was unusually deep for a small body guitar - four and a half inches. I built those dimensions and the guitar is good, sounds nice, but some people comment that it is less comfortable to play because of the thicker body. I agree with the recommendations to stick with the standard plan for your first go. Then go nuts with a jumbo, cutaway, arm bevel, multiscale, fan-fret, falcate braced flamenco cross-over (or whatever your heart desires - the Wade Lucas model) for number 2 after you know it all.

Hi Wade and welcome to the obsession. Keep in mind that if you change the size of the box too much it probably won’t fit in a standard case.

_________________
Steve Smith
"Music is what feelings sound like"

My experience has been that increasing the depth of the body on small bodied guitars seems to improve the bass notes some. The OM is not a small bodied guitar. If built to plan they tend to be well balanced. I have built some with deeper bodies, and they work O.K., but as mentioned, can be hard to find a case for (I used to find a Taylor case that they kind of fit - don't remember the model)
Mario Proulx went the opposite direction - he built some Dreadnaughts with a shallower depth.
Building a guitar from a book is like cooking from a cook book; it will give you the recipe and some guidance on the steps to assemble things, but the final flavor is still up to the cook. If you are willing to risk failure, go ahead and throw in that extra handful of cayenne pepper!

OK, that made me laugh. Thanks Hesh!

Make sure to consider the depth of the case


Sent from my iPhone using Tapatalk

Two people have already mentioned building to fit an available case. My third guitar was an OM sized 12 string, I got the bright idea of making it a bit deeper. The custom case for it cost $300 (fifteen years ago) and took 4 months to get to me.

Since then I have built a number of OM's at 4-1/8 inches, they fit in TKL cases and sound wonderful.

I've built a couple of dreadnought depth 12 fret 000 guitars--both Hawaiian square necks built for lap style playing so the extra depth isn't uncomfortable, and the deeper tone works great for this style guitar. I have also found reasonably priced cases that fit designed to fit deep bodied resophonics. There are some "deep bodied 00" cases available that will fit a Nick Lucas or a deep bodied L-00 type guitar too. But I learned a long time ago not to build something I couldn't buy a case for. Custom cases are $$

I've built some pretty odd sized banjos that required special cases, but building a "coffin style" case isn't hard, and at least with banjos it's considered to be an appropriate style of case.

I've had some dreadnoughts that I've absolutely loved the sound of, but hated playing them because of the depth. I could play a wider bodied archtop with its thinner body and be completely comfortable. My arms just don't go around big deep bodied guitars very well. My wife has one of the "Women in Music" model Martins that they made in the 80's or 90's. It's a 14 fret dreadnought depth 00 body, and is actually very comfortable to play and sounds really good. Better low end than a regular 00 would have, and the body is narrow enough that the extra depth doesn't make it unplayable for me.

Dave

'Way back in the '70s, Fred Dickens did an experiment where he built a very deep guitar and cut it down. He made Classicals, but the principles are the same. He started out with sides 6" deep, built the guitar up, and checked it out. Then he sawed off the back, reduced the height of the sides by an inch, and glued it back on. He kept doing this until he couldn't make it any shallower: it may have actually been due to the top and back braces touching.

One of the measurements he made was the Helmholtz-type 'main air' resonance. This is what you hear when you blow across the mouth of a wine bottle, and on the guitar it's the lowest pitched resonance that can actually make sound. If you make a wine bottle shallower the air resonant pitch rises, and that's what he expected to see. It did, but not by much: reducing the side height from 6" to (maybe) 2" (?) caused the pitch of the 'air' resonance to rise by (drum roll) 7%: just over a semitone.

In the low range a guitar acts like a 'bass reflex' speaker cabinet. Air moving in and out of the hole changes the pressure in the box, and that pushes on the top/speaker. Movement of the speaker/top pumps air in and out of the hole. The top and the air have to work together, and each one has an effect on the pitch of the other.

Rossing, in his (and Fletcher's) 'Physics of Musical Instruments' describes experiments he did with Martin. He buried guitars in sand to deaden the wall vibrations, and left the holes open to measure the 'real' Helmholtz air resonance. It ended up being somewhere around 125 Hz, iirc. A guitar body with no back, but the edge of the rim stiffened up (and thus no Helmholtz air mode) had the low top resonance at about 170-180 Hz or so. When you put the box together, and the air and top interact, the Helmholtz mode gets pushed down in pitch to around 100 Hz, and the top pitch rises to around 200 Hz. The amount the pitches get displaced is a function of how strongly the top and the air 'couple'; how hard they push on each other.

On Fred's guitar making the box shallower meant that a given amount of top motion produced a larger pressure change in the box: the coupling got stronger. By itself this would have the effect of pushing the 'air' pitch downward. However, making the box shallower (the bottle less deep) would also raise the air pitch. In the real world the two more or less canceled out; as the box got shallower the 'air' pitch rose a little, but not much.

When Fred told me about this experiment I didn't know enough to ask the right questions, and he's been gone for some time (alas). What I didn't find out was how the timbre of the guitar might have changed, and, also, whether the loudspeaker-like 'top' mode (up around 200 Hz) also changed in pitch. I've done a few experiments of my own since (but not the same one Fred did) so I can offer a couple of opinions on what to expect.

If you look at a spectrum chart of a guitar, there will be a peak at the low pitched 'air' frequency. All else equal, with a deeper box the 'air' pitch stays pretty much the same, but the peak gets a bit lower and wider. The 'air' resonance, instead of reinforcing one note, get's spread out over a couple of notes, but it doesn't reinforce them as much. The 'total available horsepower', the area under the curve of the spectrum, seems to stay about the same, so there's no cost or benefit in terms of power.

It's possible, again, all else equal (and it seldom is), that the 'top' pitch could be pushed up a bit. I suspect the change would be 'small' for any usable depth increase (you didn't plan on 6" sides, right?).

In terms of timbre, I do feel that the shallower box tends to give a more 'forward' sound, while the deeper one is 'rounder'. Deeper might seem 'bassier',and shallow more 'treble', but in terms of sound output that doesn't seem to be the case, at least in the lower range of the sound. It would be a fair amount of work to really nail all of this down.

Alan Carruth wrote:
"In terms of timbre, I do feel that the shallower box tends to give a more 'forward' sound, while the deeper one is 'rounder'. Deeper might seem 'bassier',and shallow more 'treble', but in terms of sound output that doesn't seem to be the case, at least in the lower range of the sound. It would be a fair amount of work to really nail all of this down."

I'm thinking changing the depth of the box may affect the strength of the upper partials we hear. Some may become more prominent and some more muted - similar to how plucking different parts of the string will change the timbre.

Clay S. wrote:
"I'm thinking changing the depth of the box may affect the strength of the upper partials we hear."

Could be. Again, with a shallow box you'd tend to get stronger 'air' resonances. From what I've seen much of the high-range sound (2-4 kHz) comes off the top, but some certainly does come out of the hole. The size of the hole is probably a factor there, too.

One 'air' resonance that would certainly be changed is the 1/4 wave resonance set up between the more-or-less parallel top and back. This is usually a fairly broad peak (because of the taper of the box) at around 1500 Hz or so, and the pitch would rise on a shallower box. Most of the other air resonances rely on the shape of the box, and should not change much, if at all. This can get complicated, since at some point the 'air' resonances are no longer like surface waves in a guitar-shaped dish, but become three-dimensional. That probably sets in seriously an octave or so above the 1500 Hz resonance, and by then you're well into the 'resonance continuum', where it's impossible to sort things out.

Mr. Breakstone touched on the purpose of a first guitar, but to re-state and extend: your first guitar affords an opportunity to understand the order of build (i.e., what gets done first, second, last; what step must necessarily lead or follow another step; what steps may be safely left for later or advanced in order) and some exposure to methods and tools by which those steps in the process might be accomplished.

That the completed instrument is playable or handsome is of secondary importance to understanding the overall method and a subset of techniques to accomplish that task.

Given this purpose, build to plan and leave the fine-tuning for subsequent instruments... and there are always subsequent instruments. Time spent agonizing over headstock shape, iconic logos, interior decoration, or expensive, rare materials or components is time spent away from understanding the process, tools, techniques, and pitfalls.


Kinkead is quite dated as to tooling such as jigs, fixtures, forms, and the like, so as recommended here, consider some exploration of the following to update things:

- Side bending
- Shape control for the body
- Neck joint
- Finishing with neck on/neck off

In the shop where I worked, the order of build documents were fairly explicit on method, tools, etc., but alternative methods were always at least demonstrated if not incorporated in to the build process (e.g., hot pipe corrects to blanket bender-bent sides; hand-cut dovetail neck trial on scrap wood and neck block versus router-milled).

Good luck with the project!

_________________
For the times they are a changin'

- Bob Dylan

Not to pile on to what has been said but I wanted to come at it from a slightly different angle. It is common to have the idea that you are going to build yourself a guitar and make it the guitar your "ideal" guitar. It will be all the things you want but can't find off the shelf in one guitar. The truth is, by the time you get through the growing pains and are able to make a guitar you are happy with, your idea of what you thought you wanted has changed.

I make a few non guitar stringed instruments before I attempted my first guitar. I thought I was ready. I look back at that guitar now and even tough it is playable and sounds nice, it has a lot of geometry issues that I didn't understand at the time. It will be difficult to make the adjustments it will need to stay playable over its lifetime.

Looking back, It took me more instruments than I care to admit to graduate form making playable woodworking projects to making guitars.

_________________
Bryan Bear PMoMC

Take care of your feet, and your feet will take care of you.

Appreciate all the replies, I keep getting repairs dribbling in but I really want to dive into this build. I'm using some less expensive woods knowing it's a learning curve. I will stick with the plans. When I say less expensive I have a bunch of off Quarter spruce tops from my friend Bruce (olga tonewoods) love that guy and some hog, cherry, etc, B/S off Ebay should get me a handful of projects. Doesn't mean I can't make some cool stuff to start. I've been obsessing on guitar tinkering for 15 years now, and it just gets better (worse?) Appreciate the offer for help.

_________________
Just a box with strings https://www.facebook.com/wadesguitarshoporcas

Well.... The one place I wouldn't skimp on is structure is the soundboard. I would get good vertical grain and stiff.

The place where you could compromise is cosmetics. Wide, streaky grain, knot shadow, sap pockets, even non-book-matched orphans will have zero effect on tone (all things being equal) and that you could get for cheap would all be better than off quarter grain in my opinion.

Pat

_________________
Pat

How far "off quarter" are the tops? If they run from vertical grain to slightly off quarter then you could join the vertical grain edge and let the off quarter grain go to the wings. I haven't dealt with Bruce Harvie, but he has been dealing in tonewoods for a number of years, so if it was sold as soundboard material, "off quarter" might not be too far off.
It appears Bruce retired and is selling his remaining stock - so for those of you who are into resawing:
http://www.radiofreeolga.com/tonewoods/
He updated his remaining stock as of 1/14/23