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Acoustic-only bass guitar build

#21
T_Bone_TL said:
As someone who actually plays full acoustic in a full acoustic, no amps at all band, may I suggest that you simply buy or build an upright bass? It works. It's not constrained by trying to be a guitar. It can keep up, un-amplified, with fiddle, mandolin/mandola/guitar/flute/whistle.

If you insist on building a guitar, figure out how to put about 3 cubic feet of air inside the body. Or look at the "Kickass Bass" design, which puts those 3 cubic feet of air in a bass drum, as the body.

I can make more volume by bowing than I can plucking, so once again, I suggest an upright...
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Yes, uprights are awesome, but, sadly, they don't quite fit the kind of music I do (mostly because they are not optimal for chordal playing and have low sustain, if not bowed), or the practical realities of my life (I can't haul an upright through dense vegetation for hours every day).

It will have to be a guitar - but a huge one. A minimum of three cubic feet of air is sound advice.
 
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#24
Regarding body depth - why are deep-bodied acoustic basses virtually inexistent on the market?

I have a pretty standard-sized acoustic bass. If the body was twice as deep, I could still play it comfortably (I actually experimented with simulating a deeper body by putting objects of various thicknesses between my belly and the guitar).
Wouldn't deeper bodies make the sound much more powerful? So why are acoustic basses, in general, barely deeper than the average guitar?
Is it to avoid feedback issues?
To keep them more playable in a seated position?
To keep them light and more affordable?
A combination of all of these factors?
 
#26
I've stayed silent on this, but it's also a rabbit hole I fell down years ago. The end of it for me was converting a guitarron with a 34" scale 5 string neck, which was the last failure I could tolerate. :(

I no longer play with the band that I went through all of that stuff for, but in the end, I bought a Roland Micro Cube Bass RX and used it with a short scale fretless. It was the best solution, and probably not what you wanted to hear. :D 12"x12" and 20 lbs or so, but was more than enough to provide the low end to several acoustic guitars, banjo, mando and fiddle. Nothing else I tried was audible in that mix, not even my double bass, really. I sold it a while back and regret it because they no longer make it and they are not easy to locate where I live.
 
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#27
Beej said:
I've stayed silent on this, but it's also a rabbit hole I fell down years ago. The end of it for me was converting a guitarron with a 34" scale 5 string neck, which was the last failure I could tolerate. :(

I no longer play with the band that I went through all of that stuff for, but in the end, I bought a Roland Micro Cube Bass RX and used it with a short scale fretless. It was the best solution, and probably not what you wanted to hear. :D 12"x12" and 20 lbs or so, but was more than enough to provide the low end to several acoustic guitars, banjo, mando and fiddle. Nothing else I tried was audible in that mix, not even my double bass, really. I sold it a while back and regret it because they no longer make it and they are not easy to locate where I live.
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Damn, sounds like a hefty ensemble. Maybe it was simply a situation where more than one bass instrument was needed. After all, if an upright wasn't enough for the job... I haven't had the chance to hear your basses, but, IMO an acoustic bass is hardly a "failure" just because it can't single-handedly counterbalance such an ensemble.
Do you think the results were unsatisfactory in and of themselves? Or were they unsatisfactory because the goal was so high?

I'm convinced it could work for my purposes, if the body is big enough. It only has to counterbalance 1-2 voices, light percussion, a guitar and a bagpipe-like instrument that mostly holds drones. And all these almost never play all at the same time.

As you've been down this rabbit hole, any advice you could give would be very valuable.
 
#28
Filip Sever said:
Wouldn't deeper bodies make the sound much more powerful? So why are acoustic basses, in general, barely deeper than the average guitar?
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That's a common misunderstanding. It isn't the depth of the body, or the cubic inches of air inside that make the sound output louder. The deflection of the diaphragm (the top) is what actually pushes the air forward and back, and creates the sound. The farther the top deflects, the louder the sound will be. And the lower the frequency, the greater the top deflection you need.

Think about speaker cones. When a speaker is putting out high frequencies, you can barely see it move. A bass speaker kicking out a bass note will move visibly, like 1/4". That's the physics of making loud low notes. You gotta push a lot of air to go low.

The main reason why an upright bass is so much louder than an acoustic bass guitar isn't because it has a large volume of air inside, but because the diaphragm (the top) is so much larger. A thin wood top has structural limits on how much it can bend and deflect before it will break. A larger size top can deflect farther without breaking, and therefore it can pump more air and make lower frequencies louder. An acoustic bass guitar's top is much smaller in square inches, and can't deflect as far without breaking. Pluck a low note on an upright, and the top will deflect as much as 1/8". The best ABG's have soft flexible tops, but they still can only deflect 0.040" or so. So they have about a third of the output volume of an upright.

The other part of the equation is that you have to apply enough mechanical horsepower to make that diaphragm deflect that much. An upright bass has more clearance under the strings, and you have to pluck it harder to drive that top. An ABG needs higher action and heavier plucking to push its top deflection to the limits. That's why a Guitarron is pretty darn loud for its size. It has a very flexible top, and it's designed to be plucked really hard.

Those are the limits when you design an acoustic bass guitar as a slightly larger acoustic guitar. Top deflection and the mechanical horsepower of plucking. You may get a good sound profile, but it isn't going to be very loud.
 
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#30
Another reason why you don't see ABGs with deeper bodies is that people won't play them. One of the big complaints we see about ABGs is that they're uncomfortable. This is especially the case with people who try to hold and play them the way they do an electric FSO.

When Ernie Ball was building the Earthwood bass, one of the iterations was 8 inches deep. Most were 6. The majority of the production ABGs now run about 4 or 4.5 inches. While I won't disagree with the physics in previous posts, I will say that you really do get better volume out of a bigger body.

My Mota bass, the Earthwood clone in my pic above, gets played weekly in an Old Time Jam circle, with a couple fiddles, a banjo, a guitar, and a hammer dulcimer. The guitar player says he can't hear me....but everyone else, including spectators across the room, can.

I have the strings up pretty high, and use the side of my thumb, not my fingertips. Plucking right up cl;ose to the neck helps. And I work at it. My hands are fairly tough, but I did raise a small blister last week backing up a fiddler on Orange Blossom Special. It doesn't kick listeners in the chest like an EB, but it's not supposed to. It's an environment where a DB would actually be preferable. But what I have works, and I don't want to pay for or schlep a DB.

So...for the use you describe, I'd say an ABG can be fine. I don't even know if you'd need a custom. I think there are some used ones out there that would do, for a lot less money.
 
#32
yeah, comfort is an issue. no comfort=no sales for production mfg.

typical abg string gauges can drive a fairly deep body generating a bit of air that needs to get out of the box otherwise you start quenching the body.

fwiw, 3.75" to 4.25" body depth at the tail block is pretty common on acoustic guitars. 6.0" is a handful on an abg. feedback from long term acoustic guitar players (20/30+yrs) indicates a high incidence of chronic shoulder and wrist pain. although when you look at mexican folk instruments, those things get pretty deep indeed. it all depends upon the player's ability to handle the girth.

were the op's situation mine, i'd consider a "normal" abg like a used thunderchief or a micheal kelly and outfit the saddle with a piezo or have a mic system installed. drag around a small amp as needed. no shame in using electrical devices to boost volume imo. if you're into the roots/traditional scene, maybe an upright bass is where you need to be.
 
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#33
They make acoustic basses.
They make resonator basses.
They make banjo basses.
What I can't find, is a bass that is a combo of all 3.
A bass that is designed like a typical AB, but with a banjo head as the resonator and a tuned port. Seems that would be the best combo for volume.
Something like this, but with a banjo head instead of a metal resonator.
kwjidego8ku5csaruk9v.jpg
 
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#34
I feel your pain. I played an ABG almost (almost) exclusively in a number of projects accompanying acoustic guitars (and in some cases piano, and/or drums). Live, or at an impromptu jam I couldn't be heard without amplification.
The best sound I ever had was through an old Fender Princeton, low volume, a little reverb, with tapewounds.
 
#35
RichterScale said:
They make acoustic basses.
They make resonator basses.
They make banjo basses.
What I can't find, is a bass that is a combo of all 3.
A bass that is designed like a typical AB, but with a banjo head as the resonator and a tuned port. Seems that would be the best combo for volume.
Something like this, but with a banjo head instead of a metal resonator.
View attachment 4375200
Click to expand...

Banjo heads can flex more than a wooden top, but they still have limitations in how much they can stretch and deflect. There are plenty of Bass Banjos out there, which have heads in the 12" to 16" size range, and are played horizontally on a strap. They are usually louder than an ABG, but not as loud as an upright bass.

If you haven't seen it, I have some personal experience with banjo heads and basses:

IMG_3677B.jpg


Banjozilla has a 24" head. Plucked hard, it travels more than 1/8" at the center. It's about as loud as an upright bass, but without the low boom of the air chamber.
 
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#36
Bruce Johnson said:
If you haven't seen it
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Oh, I've seen it. Matter of fact, if you Google banjo bass, there's a few pics of you with it that come up within the fist few dozen images.
Bruce Johnson said:
Banjozilla has a 24" head. Plucked hard, it travels more than 1/8" at the center. It's about as loud as an upright bass, but without the low boom of the air chamber.
Click to expand...
Right! So, if you shrunk it down to maybe 16-18", framed it into the bigger body of a typical AB and made a tuned port, it would have to be relatively loud, no?
Someone needs to build it.
 
#37
Bruce Johnson said:
Banjo heads can flex more than a wooden top, but they still have limitations in how much they can stretch and deflect. There are plenty of Bass Banjos out there, which have heads in the 12" to 16" size range, and are played horizontally on a strap. They are usually louder than an ABG, but not as loud as an upright bass.

If you haven't seen it, I have some personal experience with banjo heads and basses:

View attachment 4375342

Banjozilla has a 24" head. Plucked hard, it travels more than 1/8" at the center. It's about as loud as an upright bass, but without the low boom of the air chamber.
Click to expand...

I have had the pleasure of playing this thing, it plays and sounds great. Kind of suprised there arent more of these around, I have to think the larger top and cubic inches gives it a bigger volume than a more traditional sized banjo
 
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#39
RichterScale said:
Is the bridge supported by the skin alone, or is it making contact with the internal brace?
Click to expand...

More complicated than that. There's a wooden shoe contacting the head under the bridge. The shoe is on two big steel coil springs that are adjustable in height. Those springs are a big part of shaping the sound. The deeper engineering story here on Banjozilla's web page:

Bass Banjo
 
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