Baritone Design

[angusa]

Im in the process of building my first guitar but am starting to plan the no. 2 build. Im planning to build a baritone acoustic but i can't find a plan that suits what im looking for so i am looking to create my own. The first guitar is based ( mostly! ) off the Kinkead OM plans included with his book, i am hoping to build a baritone from the same body shape ( but maybe with a cutaway?!?) as i quite like the shape and i could reuse some jigs and moulds. I have a load of questions im hoping some of you may be able to answer...

1. OM is probably smallish for a baritone, is it going to be too small to carry the bass?
2. Im thinking of a scale length of 27.55 inches ( 700mm - im a metric kind of guy... ). This seems to fall in the middle of the range and is close to whats used on some commercial baritone guitars. Does this sound reasonable?
3. Bracing! Obviously the forces on the soundboard are going to be much greater, should i consider different bracing patterns (double-x?) or just increase the dimensions of the bracing? Would it be a good idea to leave the top thicker?

Thanks!
a

[Golffishny]

First of all, I have no build experience or knowledge personally of how to build. That being said, since you're looking to build an OM size I would look into the bracing of a Walden B-1, It's the same size. From what I found while researching it, the soundhole is moved to the upper bout for 2 reasons. That placement supposedly enhances the bass response, and it allow for the top to be braced stronger through the center to compensate for the additional stress of baritone strings. As I said, I know nothing about building, but this sounded reasonable to me. Hopefully someone with actual experience will give you more information. Good luck with your build.

[Alan Carruth]

IMO I think you'd be happier with the sound basing a bari on a different platform, but an OM can work. A longer body, such as a 12-fret 000, would help to bring up the bass. A cutaway has a similar effect to makiing the box shorter, so I'd avoid that.

Back when I took voice lessons my teacher said that the way to make your low notes sound better is to work on the high ones. All of the stuff they usually tell you to make a bari, like thinning out the top and making the box deeper, tends to work against clean trebles, and this just makes the bass fuzzy. This is not to say you should be making a uke and then putting bass strings on it, but simply that you can't lose sight of the high end while trying to get the lows to work.

With a long scale you can use 'normal' strings to get a low tuning with 'normal' tension. I made my first bari two frets longer in the scale than I usually use, so it carries a normal tension when tuned to D. The owner used to run it down to B with normal intervals, and then go to drop D or DADGAD intervals from there succeesfuly. He did run somewhat heavier strings on it, but at the low tunings the tensions were still pretty normal. So there's no need beef up the top a lot.

Even if you are going to run higher tension you don't need to add all that much material. Keep the 'cube rule' in mind: the stiffness of the top or a brace goes as the cube of the thickness/height. If you want to double the tension you only need to make the top about 25% thicker, and the bracing 25% taller, and use the same layout, with the braces maybe a little wider to give more gluing surface. I've used this on 12-strings, and they hold up fine. With twice the power in the strings and only maybe 30% more weight, they're cannons. Tops don't usually fail because they are not strong enough, but becuase they're not stiff enough.

One change you can make is to drop the pitch of the 'main air' resonant mode. This is the lowest resonance that can produce sound, and is responsible for a lot of the 'fullness' of the bass notes. On most flat top guitars this is pitched anywhere from F# to A on the low E string. Getting it into the same relationship with the tuning you're going to use will help.

One thing that 'should' help, but doesn't do as much as you might think, is making the box deeper. The physics gets complicated, but basically making the box twice as deep likely won't drop it by much more than a semitone, and it will be hard to play. A deeper body also 'spreads out' the peak of the resonance. This helps in that more notes benefit, but it also makes the timbre 'fuzzier'.

Making the sound hole smaller will drop the 'air' resonant pitch, but, again, less than you might think. It also has some of the same drawbacks as making the box deeper. Moving the hole up into the upper right corner of the upper bout will drop the 'air' pitch a lot, but sacrifices some of the 'guitar' timbre IMO. There is less benefit from the 'added soundboard area' than you might think. If you want to do that I'd suggest making the UTB into a wide 'X', with the crossing under the end of the fingerboard. Be sure to use a really good wood patch over the joint; there's a lot of down force there.

All told I've had the best luck with keeping the sound hole size pretty normal, and making the box a little deeper by using a 'wedge' shape: keep the rim height normal on the bass side and make it 1" or so deeper on the treble, gaining about 1/2" overall.

Which brings up a point: don't be an idiot with a pepper shaker. It's easy to reason that if a little pepper makes the food taste good, a lot will make it taste great! Wrong. Rather than do a lot of one thing that will bring up the sound you want, like making the box deeper, find a number of things that all tend in the same direction, and do some of each. Wedging the body, moving the hole up into the corner, but making it bigger, using a bit longer scale with slightly heavier strings, and beefing up the top only as much as you need to handle the extra tension, should get you all the bass you might want without losing the clarity and sparkle in the high end that make it 'interesting' and 'colorful'.

Hope this helps.

[angusa]

Thanks to both of you, a lot of good sounding advice to digest!

Interestingly i was looking at guitars with sound holes on the upper bout a few days ago and was thinking it would be fun to try at some point although i had that pegged for an all out experimental guitar.

I will look into moving to a larger body but will certainly look into wedging the body to increase depth.

[yellowesty]

I'm now building a baritone guitar (27" scale, Gibson J-185 body) and have a couple of thoughts that you might find useful:

Using D'Addario Baritone strings (EXP23) on a 27" scale will give a total tension of 185 lbs. tuned B to B, 165 lbs. tuned A# to A#, and 147 lbs. tuned A to A. The Martin Baritone string set (MSP7700) gives total tensions that are about 10% less. A 27" scale may be a bit floppy tuned A to A, but none of these tensions are outside the range of typical 6-string tensions. A 27.55" scale will require about 4% more tension than a 27" scale for similar tuning.

Moving the sound hole to a corner of the upper bout has some advantages, both sonically, as Alan notes, and in allowing more flexibility in bracing patterns, but, unless you have very flexible arms, can make some of the later steps in building the guitar quite a challenge.

[Alan Carruth]

I can't beleive I forgot one of the most effective ways to drop the 'air' mode pitch: loosen up the back. For the most part the back steals energy that could be more effectively turned into sound by the top, so you generally want it to be 'reflective'. The one place where it seems to actually contribute to the power output is in the 'bass reflex' range. Getting the 'main back' tap tone close in pitch to the 'main top' resonance drops the pitch of the 'air' mode, and makes it stronger. Generally speaking you want the 'back' pitch to be higher than the 'top', and no closer than a semitone. Shaving the back braces is less troublesome structurally than taking down top bracing, and works better acoustically.

[tadol]

Im not a builder, but I love and have a couple baritones - my 2c would be that an OM soundboard is too small to adequately create the bass response you really want from a baritone, and that extra body depth can make them sound thick without sounding rich, and can muddy up the trebles really easily. I’m happy with my 27” scale, but a 27.5 would be fun without adding too much to fret spacing. The soundhole placement should be directly related to the main X brace position, which is directly related to the bridge position, which is directly related to the where you join the neck to the body and scale length. Lots of variables, lots of ways to squiggy things around -

[angusa]

Thanks folks.

I have taken the body size on board and will try to scale things up a bit. Don't want to really go to big as i don't really enjoy playing 'big' guitars. I will make things a bit deeper but will be sparing of the pepper!

I will also look into 27" over 27.5, i don't really need the extra scale length and the trade off from having to deal with more tension is worth avoiding.

I will have a play in CAD and see if i can come up with a sensible solution to the sound hole and bracing.