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Kyle and I are starting guitar #11, our larger body design (16" lower bout).

We have found that our guitars, as a whole, tend to have a very balanced sound to them - but we would like to understand some theory behind how to coax a little more bottom end out of them for future builds (as that seems to be what some of our customers say they want).

We use a fairly common 105 degree x-brace pattern with 2 tone bars and 2 finger braces on each side.

To this point we have not done deflection testing - but are realizing that for us to move forward this is one of the steps that needs to be included in our builds. This is not to say that this is a part of the "more bottom end" process - but it does give us a standardization that could be helpful in giving us some consistency.

So.... We are calling on the experienced builders here who can give us some guidance on how to get to our desired end. We would like to know what you do and how you do it, in a way that is instructional and constructive to us as still relatively new builders.

If you want more information, photos, measurements, we can provide those - but I thought this might be a good place to start.

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P A U L B U R N E R
Burner Guitars

Great thread starter!

I find that if I am building a guitar with a definite "tone target" in mind, I will early on begin thinking about the target as I am picking wood, and at each step of the build keeping the target in mind, and what to do to steer the tone to the target.
I know that sounds sort of "touchy-feely" but that is my best words to describe the process that I use.

As an example, I had a customer who wanted almost the opposite: a mahogany dreadnaught that emphasized the treble end. Of course, in a dread, the bass is almost a given, so no need to do anything special to get strong bass, but many little things were done by me to tighten up the treble, from choosing a stiff red spruce and leaving it slightly thick, asymetrical top brace carving, back stiffness, bridge weight, things such as that.

I think each guitar is a different animal, and building each one with its specific tone target in mind is important.
It's what guitar builders do!

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David,

Yes, wood choices are a given part of the formula. Our next guitars will be Black Ebony, Cocobolo, Walnut and EIR. So all of these should give us the opportunity for some good bottom end.

We're looking for what we can do in bracing, thicknessing, positioning (or braces, tone bars, etc.), thinning of edges, etc. to try to get us the desired results. We plan to use standard Sitka brace stock and either a Maple or Rosewood bridge plate.

Cheers!

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P A U L B U R N E R
Burner Guitars

I haven't built a guitar yet but I've played enough dreads including Martin D28s that I thought seriously lacked in bass response. Usually the 35s have it and my brothers custom martin has it. I don't even agree with the word "almost". But then I haven't played too many built by small builders. The ones I've heard, have it though. I imagine they're doing thing to insure it.

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Hutch

Get the heck off the couch and go build a guitar!!!!

Hey Filippo - once I have those numbers what do I do with them?

Is there a "formula" that tells me if I should be adjusting my soundhole size?

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P A U L B U R N E R
Burner Guitars

Hi Paul,

Check out the Dana Bourgeois articles at http://www.pantheonguitars.com/

He specifically touches on bringing out the bottom end about half way down his article "Voicing The Steel String Guitar". (American Lutherie #24)

Also, if you look at the title "Guitar Details" there is a pic of his dread bracing scheme.

Man makes some amazing instruments!!!

Ray

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Guitar Building = Continuous Improvement Process

There are lots of threads archived here talking about tuning the back to the top to accentuate the bass. Reading those would be a good place to start thinking about that relationship and how/if it could affect your own guitars.

Thinning behind the bridge can help as well but carries its own set of problems. In my experience guitars with bellies will usually always have a good bass note.

The best way to see how your guitars will work with any suggestions are to build some prototypes and take some risks. Those have taught me the most and shown me I still have a ton to learn.

There is no formula (i.e, with numbers) that I know of for soundhole size. The prevailing thinking that I have heard is that bigger equals treble balanced and smaller gives more bass (that is very simplified). In my own work I have found it to be not that simple.

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Burton
http://www.legeytinstruments.com
Brookline, MA.

As Burton suggested, try some searches on 'main air', 'main top', and 'main back' resonances. Al Carruth is the resident expert here--maybe he will reply as well. Here's what I've found doing FFT tap tests on various commercial guitars and my own:
Guitars with strong bass usually have the 'main air' resonance in the 90-97 Hz range. (For example, the regular D28 I tested was around 105 Hz, while a HD-28V was 97 Hz.) To get the 'main air' frequency in that low range, the usual strategy is to make the 'main top' and 'main back' freqs reasonably low as well (all resonances are coupled): 'main top' is usually 170-190 Hz, and 'main back' is usually 200-230 Hz. Some builders place the 'main back' just above the 'main top' for more power. In my experience, if the 'main air' is too low (below 87 Hz or so), then the low E and F notes will be strong but there will probably be a 'hole' in the perceived bass response around 110 Hz. Compared to other aspects of guitar tone, bass response is actually pretty straightforward to dial-in using quantitative methods.

Here are some recent discussions (my current database in the first):
viewtopic.php?f=10101&t=31330
viewtopic.php?f=10101&t=31178

Yes, doing deflection testing on the top would help to give a consistent bass response. More deflection --> lower 'main top' freq --> lower 'main air' freq.

A larger body volume or smaller soundhole will also give a lower 'main air' freq. The latter would be at the cost of overall sound output, though. The coupled resonances are too complex for a formula. Few successful guitars deviate much from the standard sizes, though a little tweaking is common. I've enlarged the soundhole to raise the 'main air' freq, but beyond 3/8" larger the overall tone became somewhat harsh in the 2 guitars I tried it on.

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David Malicky

While deflection testing in itself won't do anything except help make your tops a consistent stiffness (which you can also do by hand very successfully) you can start to use these stiffness offsets as a basis to begin with. Of course you can make a equally crappy guitar using deflection testing, or not. The reverse is true as well. It's all in your approach. I'm not nearly into the left brain as many guys like Al Carruth ect, ect. Not passing it off, I just work better using tactile methods. I do deflection test my braces, and tops prior to cutting out shape or soundhole, but this is only for consistency reasons. I've found certain target deflections that work for me and my system I've been working on for over a decade.

Now for the bass response itself. As I see it a better bass response comes from the monopole, or main air perhaps as techie guys call it (correct me please if I'm wrong). I'm not sure the terminology, but the main up and down movement of the face. One of many ways to do this is to not tuck your braces into the linings. Taper them (fast taper, long taper, scalloped or not..whatever works for you) off before they hit the linings. I do this for the tone bars, finger braces, and lower legs of the X-Brace. I normally tuck the upper legs of the X, but I've tapered them with success as well, I just don't know if I'm gaining that much by doing it, and I worry about the long term implications of not reinforcing that area, although admittedly I may be over cautious here. Of course the Transverse should be supported in some way.

So what you will have done by detaching the legs from the rim is free up the top around the perimeter to move as a whole better. Combine this with working a bit thinner than you might think and that is a good basis to start with. Although I warn you to make some prototypes to test out these design changes as they can be quite drastic, and possibly catastrophic if not done properly.

Another thing I've been finding, and perhaps this is not so much as bass only standpoint, but and overall efficiency standpoint, but when he top is working as a whole in unison rather than a collection of braces quality of tone improves.

As for the soundhole I've been pretty conservative about that as well. As a general rule of thumb the larger the soundhole the brighter, and louder it becomes....up to a point where then, from what I've experienced, it degrades. Guys who have been building guitars long before anyone on this forum was alive knew these things. They didn't arbitrarily select a soundhole size. I've been using 3.9-4" soundholes for almost my entire career. I've tried bigger, and smaller, but the look always is off putting and the desired tonal goal can be achieved in different ways and not have to make the guitar look funny (opinion).

Slightly denser/heavier bridge will dampen some of the highs and give a more bassy tone, although it's really more a less highs tone. Sometimes you get to decide on the bridge, and sometimes the customer will force their will on bridge material due to looks. In those cases match a individual weight/density piece to the guitars desired outcome.

Of course all this is "all things being equal" (which they never are) so I'm not taking into account body depth, or bout width, string gauge, ect. Of course these things can have a very large outcome on the bass and overall tone of an instrument.

Just a few of my ramblings. Hope it gives food for thought.

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John Mayes
http://www.mayesluthier.com

David and John,

These are really good posts that give us a lot of good information - this is the kind of input we were looking for. David - I'll do some searching of the archives later tonight - but really appreciate the 2 links as it gives us a place to start.

John, We totally "get" the "pumping" concept - and think we've been heading in that direction more on our latest guitars. I remember KG (Kevin Gallagher) telling us in class that he would thin the edges of his tops to get more pumping. I'm also assuming this is why Taylor guitars routes a rounded slot on the underneath of their tops near the edge. Gotta get that drumhead moving!

Thanks so much.

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P A U L B U R N E R
Burner Guitars

#11 is what we call our MS size. We have built this guitar multiple times and I personally always have wished it had a bit more bottom end to it. 16" lower bout, 12" upper, 9.25" waist, 4.625 at the butt end and about 1" less at the neck. 25' radius of the top and 15' radius of the back. I will try to look up some of the thicknesses we used but don't have them at my disposal right this minute.

We have used EIR/Redwood, Bocote/Capathian, Waterfall Bubinga/Carpathian, Tiger Myrtle/Redwood, and recently Hormigo/Carpathian.

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P A U L B U R N E R
Burner Guitars

Paul;
I graduate (taper) top thickness.
The taller the brace the stiffer it is.
So work on the height of the X especially.
Weight -heavy braces & a to thick top make for treble -unless the body is way deep.

Only the brace above the s.h. is let into the linings.
The rest are carved to nothing at the linings.
This allows the edges of the top to move.
Picture a speaker-the edges are flexible and the center is stiff.
Make the center of the top able to handle string tension(without bridge lift) and make the edges flexible so the top
can pump some air.

Mike

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Mike Collins

John mentioned monopole. That is the ticket. You want the whole top to be able to move to have good bass.
If you want bass, you have to reduce mass because acoustic guitars have very little energy available to drive bass - which requires much more energy than highs. More mass requires more energy to move. You also have to free up the top to move up and down as a whole.
Choose your poison carefully!

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"An adventure is only an inconvenience rightly considered. An inconvenience is an adventure wrongly considered." G. K. Chesterton.

Using less top radius will reduce stiffness and allow the top to move in monopole mode easier. Maybe increase the radius then spring the top onto a flat (non-radiused) rim. Besides not inletting the lower legs of the X-brace into the rim, taper the tail block so that the top only glues to it for the width of the lining. This won't be a big change but seems it would move the monopole node line slightly which would increase the moving area slightly thus more volume. As previously metioned, thinning the top will help........and you can thin only in the lower bout if you have structural concerns.

I'm curious, what is everyone's opinion on how reducing waist curvature affects bass. Does this increase bass or only cut treble?

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Formerly known as Adaboy.......

Paul,

I am interested in knowing what differences you noticed between the Carpathian and Redwood tops. Also, did you brace them all the same way, and what method did you use to determine how thin to make the tops? In other words, did you thin them to a predefined "number" or did you thin them to a certain "feel?"

Thanks,
Dan

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Dan

I'm with Darryl. The first thing I would do looking for more bass is to make a flatter radius, or no radius. (Assuming your using a radiused top). Humidity control, both during the build, and during the guitars life is more important with a flatter radius though. Not tucking the lower legs of the X and tone bars works too. I've never tapered the tail block, but it make sense also.

Reguarding the waist, I believe the distance from the waist to the center of the sound hole is the key. Moving the sound hole toward the neck block a fret of so seems to have the same effect as a flatter, wider waist. My ears can't decide if it's increased bass, or decreased treble though.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

This is all so GOOD!

Thanks to those who have commented - as this is giving us much to think about as we move forward with our next builds.

Keep those comments coming. I greatly appreciate the support in helping us become better builders.

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P A U L B U R N E R
Burner Guitars

I'll add, build a test guitar to mess with. No need to finish it. (Maybe get the neck finished) Start with your "normal" stuff. Try different bridge designs, reach through the soundhole and carve on the braces, then try different tops. Make recordings of each configuration so you can go back and compare.

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I didn't mean to say it, but I meant what I said.
http://www.brackettinstruments.com/

Woody,
When you suggest moving the soundhole, are you moving only the soundhole, or are you moving the x's along with it?

You could try getting the guitar to have a baby. That certainly gave my wife more bottom end!

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http://www.CostaGuitars.com
PMoMC

I may just be an okie, but I'm smart enough not to touch that one!

Joe

Speaking of x's...
have you tried a forward shifted x pattern? Stewmac has a recipe in one of their newsletters...

I about fell out of my chair when I read this one

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Formerly known as Adaboy.......

Word of warning ! Just dont let her read that ! Usally ends up causing pain somewhere !

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Same here! But at the same time, my mid-range was enhanced to the same degree. Somehow my wife's bottom end has gone back to what it was before, while my mid-range has retained its enhanced "tone".