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Asymmetrical body shape and balance

Mr Sensitive

Mr Sensitive

Guest
Feb 9, 2017
57
44
On the banks of the Mighty River Eno
#1
I'm an intermediate woodworker with some interest in designing and building my own bass, or at least the body of one.

I'm intrigued with the idea of a symmetrical body shape. Think the less tweaked side of a Rick 4001, mirror imaged.

I'm wondering, though, if the asymmetrical shapes, with the longer upper horn, serves a purpose in achieving balance. I would hate to design and build my dream bass and then find that it doesn't balance well on me.

Thoughts on ensuring a body design has good balance before I start cutting into expensive woods?
 
#2
As I've mentioned in a couple of threads (and I'm a wooddorker who reads a lot, not a luthier) having the strap attachment point out at the 12th fret (more or less) is a generally a good call for avoiding neck-dive. While there are various ways you can try to fight that, if you get it out there, you don't have to fight that. Designs that don't are around, and many of them have persistent neck-dive issues.

I did think that this Ampeg setup (neck-plate and strap mount extension in one) Bruce posted a picture of in #392 of 'glo's "speak of the devil" build was an interesting approach to it. Clearly not so far as the 12th, but then, that body has a lot of empty space forward and solid parts aft, so it won't be "typical" in its balance. And you could make a longer one, just be sure there's hand clearance and that the edges are not sharp. You could also make a different one without having to change the body if the first one seems "wrong."

img_2969b-jpg.jpg
 
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#3
The balance has more to do with where the center of mass of the bass as a whole ends up, and the placement of the strap pins. The total center of mass is influenced by every single component in the bass and it's therefore not really a matter of whether the body is symmetrical or not. Sure, adding or subtracting from the horns does play a part mass-wise, but my guess it's going to be pretty minor. The location of the strap pins are more likely to have a significant effect.

Perhaps a good way of getting a rough feel for the balance of the body is to take a bass body with a balance that you like, remove the neck and misc components and find the center of mass of it by trying to balance it on a point on the lower part of the body. Then cut out a template of the new body design you're making and see if the it balances somewhat similarly to the other bass you looked at. See if the balance point is the same distance from the strap pins or where your thigh would sit on the lower horn. If you end up using pretty similar shaped neck with the same materials and same components on the new bass, the balance should be about the same, assuming that the bodies themselves have the same balance. A bit tedious and definitely not foolproof, but it should give a decent approximation. If you choose a body wood type that is significantly heavier or lighter than your reference bass then it probably won't work as well.

Calculating the exact theoretical balance/center of mass of a complex shape like a bass is not a trivial task and can only really be done with CAD software, so without that I can't really see any other method than simple rough guessing and trial&error.
 
#5
Yes, "neck dive" is a new term to me, but makes complete sense. I can see that the center of gravity issue is a total guitar consideration. I was wondering if the long upper horn is a general approach since centers of gravity tend to be high enough to warrant it.

What CAD software to you guys use? I think I can have access to AutoCad at work...
 
#7
I really like symmetrical bodies (heh heh). Some things to consider:

- heavy body wood
- light neck wood or a chambered neck (!)
- lower strap button high on the curve of the lower bout
- lightweight tuners on a small symmetrical headstock
- bridge-side tuners with or without a vestigial headstock for aesthetics

Also, how you wear the Bass can have an impact. It seems that folks who wear it higher are more sensitive to neck dive than those of us who wear it lower.
 
#8
ctmullins said:
I really like symmetrical bodies (heh heh). Some things to consider:

- heavy body wood
- light neck wood or a chambered neck (!)
- lower strap button high on the curve of the lower bout
- lightweight tuners on a small symmetrical headstock
- bridge-side tuners with or without a vestigial headstock for aesthetics

Also, how you wear the Bass can have an impact. It seems that folks who wear it higher are more sensitive to neck dive than those of us who wear it lower.
Click to expand...
Good points, CT!

I like to wear my bass low (more DeeDee Ramone than Jaco).

I have pretty big hands, so I would look to a wider, heavier Precision-style neck. Sounds like I'd need to use heavy body wood, not chambered, and then not contour it much?
 
#10
For symmetry, maybe consider using something heavy like ash for the treble side of the body, and something a lot lighter like alder or basswood for the bass side. I think it should shift the center of mass of the bass down and back, toward the bridge and controls, at least a bit.

If you're painting it a solid color, the change would be invisible. Dingwall does this, but not for balance. They do it for MUH TOANZ!
 
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#11
A long upper horn is a safe design from a neck dive perspective. Neck dive usually happens if the upper horn is too short. So build your bass, attach the straps with duct tape, wire or whatever works (not marring the finish) and then drill the holes for the strap pins after you found a balance you like.
 
#12
I've built mostly chambered bodies that are lightweight, and have also put a long upper horn on them to help balance. It has worked in every case for me. The one bass I built that has some neck dive to it, had an upper horn that only reached to the 14th fret. For some, this does not matter, but for me, I like it to hang comfortably, and I also like being able to reach the first fret comfortably.

A little test I've done is to build the shape out of plywood first and see how it hangs. Plywood should be much lighter than your finished design, so if it hangs well out of plywood, it should hopefully also balance well when it's finished. I've gone so far as to put weights on the headstock to simulate a heavier head with a lighter body, and this has worked out well for me... :)
 
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#13
If headless - a symmetric body is a functional option, as long as ergonomics are also considered. Otherwise getting the upper peg at the 12th fret, unless the bass is unusually shaped, will assure proper 45degree balance. The lower horn for me is also critical in resting comfortably on one's knee when seated, and having full access to the lower frets. But for balance the 12th fret peg location is a functional design given for me followed by aesthetically pleasing ergonomics. Once that is achieved, I also like a bass that stands vertical on its own and is as light as possible. The trick is satisfying all those points delivered in an attractive (pre-finish) end product. Of course, a cool finish is the cherry on top. ;)

fullsizeoutput_4b3.jpeg
 
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#15
JIO said:
If headless - a symmetric body is a functional option, as long as ergonomics are also considered. Otherwise getting the upper peg at the 12th fret, unless the bass is unusually shaped, will assure proper 45degree balance. The lower horn for me is also critical in resting comfortably on one's knee when seated, and having full access to the lower frets. But for balance the 12th fret peg location is a functional design given for me followed by aesthetically pleasing ergonomics. Once that is achieved, I also like a bass that stands vertical on its own and is as light as possible. The trick is satisfying all those points delivered in an attractive (pre-finish) end product. Of course, a cool finish is the cherry on top. ;)

View attachment 1065411
Click to expand...
By the way, that is a pretty, pretty shape!
 
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#17
Mr Sensitive said:
Thanks to all!

It sounds like there are few truly symmetrical basses for a good reason. I will rethink and embrace the elongated upper horn.

Wonder what it is that allows guitars to be symmetrical much more often...
Click to expand...
I find that if you put the strap button on the treble side of the neck heel on a hollow body you don't really get any neck dive. Might be something to consider if you really want a symmetrical body.
Edit: like position 5 in this picture
ts0055a.jpg
 
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#18
Mr Sensitive said:
Wonder what it is that allows guitars to be symmetrical much more often...
Click to expand...
I have a 69 or 72 (can't remember) SG Special that balances perfectly and an SG clone that has severe neck dive (it still sound good though). The only difference is that is that the Gibson has a light, slim, delicate feel to the neck and the clone has a chunky neck and die-cast machine heads (tuners).
 

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