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Would anyone be willing to cast an opinion on my bracing?

I'm building a 4 string bass guitar. The body shape is an OOO 12. The scale length is 28.6", and the total string tension will be very similar to a 6 string.

The top of the X is 13.5mm high. Then straight line down to 8mm, 75mm from the rim, then down to paper thin at the rim. The upper X arms will be inlet into the sides.

I've built a couple of archtops, and a flattop with a floating bridge, but this is my first flat top with a glued bridge.

I get the impression most people seem to think free plate resonances doesn't say much of any use, but it's 258hz....

I originally decided to do a tapered X brace because I thought it would be easier to add a scallop later, once strung up, if it was obviously necessary. But now I'm having doubts and thinking I should scallop a bit now....

Please feel free to throw mud, I can take it! But obviously, given it's a bass I want to try to make it as flexible as possible. The top is european spruce, 2.7mm.



Thanks!

Beautifully crafted John, great work.

Very clean work, John. It looks good to me. I often see photos of top braces that look a good deal heftier than needed, IMO. Yours don't look like that to me.

Do you plan to reinforce the x-brace joint?

I do have a question for other OLFers. Is there a consensus on whether or not to taper the upper x-brace arms? I don't because that's how I was taught, and it makes sense to me to keep the upper arms full strength because that's the area of the top that wants to fold in under string tension.

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Once in a while you get shown the light in the strangest of places if you look at it right - Robert Hunter

I taper the upper X arms but only because that is the way I was taught.

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Steve Smith
"Music is what feelings sound like"

Just curious! No sound hole reinforcement? No bridge plate? Or maybe this hasn’t been installed yet?
Your bracing looks quite nice, very clean work.

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Remember, there are no stupid questions, only stupid answers!

I'd add some soundhole braces. It will probably dip there due to the long distance between upper X legs and upper transverse brace.

The lower X legs could probably use some more carving, but you could wait until it's strung up and do that through the soundhole so you can hear the difference and measure the effect on bridge rotation.

Same. I only carve them down in the last inch or two before the linings, and notch in at about 1/8" tall.

Thanks Hesh

Yes, for the x brace joint I was going to use glue (epoxy) soaked linen, or similar. Would you normally do both arms, or just the one?

Thanks Cal. Sound hole reinforcement is on my to-do list, the bridge plate isn't. I'm going to do a pinless bridge, so my thinking is it's probably not needed. Do you think that sounds right?

Doing it through the soundhole once strung up is definitely the plan. Though I'll admit to never actually having done it before. I'm guessing a finger plane or 80/120 grit sandpaper, do you think that sounds right? Is it...ummm...hard?

Looks good!

The pic doesn’t quite show the full lower bout, will you tuck the X into the linings or taper it to zero short of the lining?

What is the radius of the top and braces? Are the rims radiused the same to receive the top or left flat?

Cool project!


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John—

This isn’t mud; more like a little cold water.

Can you tell us the setting(s) in which this instrument will be played, and whether it will have a pickup and amplification for regular performances? I ask because what you should do going forward may depend a lot on the answers to these questions. Acoustic bass guitars tend to be played in ensembles, and due to the limited size of the resonating chamber (compared to the notes being played on the lower strings), they tend to rely on pickups through amplifiers to be heard.

It does appear to be very clean work so far! Well done.

I would add a bridge plate extending in front and behind the bridge to help maintain the shape of the top. Otherwise the top could deform into an S shape, dipping in front on the bridge and rising behind it.
Nice clean work! I hope it’s a great success!

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Jim Watts
http://jameswattsguitars.com

They're tapered to zero below the bridge, and tucked in above.

The top/braces are radiused to 32 feet, and the rims are radiused to meet them. Which is definitely the worst job I've encountered so far....

It's designed to be played acoustically, for practise at home and possibly (just possibly) with a soft-playing guitar person. But as you say, a pickup is probably a good option to have....

So I'm going to build it without a pickup, to begin with. But..... Previous acoustic bass builds have had a Fishman UST and a K&K soundboard pickup. So for this one I was thinking of trying something like this:

https://schaller.info/en/oyster-d-s/1605-D

Basically a pair of stick-on transducers that I can move around to compare how the sound changes depending on location. I can then CA glue it to the inside once I've found the optimum location. That's the plan anway. (Probably coupled with an external preamp).

Thanks Jim!

And noted re the bridge plate. I'll have another think. I feel as though I've got decision exhaustion. Who knew one tiny guitar could demand so many critical decisions

I've built three ABGs, one had a pinned bridge the other two pinless. I referred to a plan by Mark Stanley for the bracing although the bodies were smaller than his plan (J200 and 0000 Martin). His plan had a substantial bridgeplate with a pinless bridge so that's what I used on all of them.

I would feel pretty uncomfortable without a bridge pin…

I think it doesn't sound right. The string tension on the soundboard is unchanged.

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Peter Havriluk

Bridge plate I meant…

A bass may be more difficult than a guitar since the soundhole may be smaller. Curved finger plane is probably best. I've only ever done it with a chisel, which is fairly difficult. Sandpaper (or better, a small piece of sanding belt) would be annoyingly slow, but doable.

As for the bridge plate, I don't think it will do anything worth doing except for adding stiffness, so if present it should be larger than the bridge footprint. Here's an image I made a long time ago to explain it (in real life there will also be a bend in front of the bridge, but it's usually not problematic):

But your first tone bar looks like it will already perform that function to a large degree. And bridge peeling is mainly a concern for thinner-than-average soundboards. What species and how thick is yours? Chances are it would be fine just like it is.

If you add a bridge plate, you could use softwood to save weight since you don't need string ball protection. You could also orient the grain the same as the soundboard to get much more stiffness in the string pull direction for a given thickness, or diagonally for something inbetween.

Ain't that the truth But the decision making is a large part of the fun for me.

My point in asking is that, since acoustic bass guitars tend to need pickups and amplification to be heard, I would favor structural stability over trying to get the most acoustic tone possible. We always are trying to balance between the two, and for this sort of instrument, there's only so much acoustic sound available, so I wouldn't do much more carving in order to try to make it sound better.

Hi Carl, Thanks for that. I've come across mention of the Stanley ABG plans a few times. I take it you don't still have them?

Well I've glued the top on, no bridge plate. Thanks everyone for the advice. As is always the case there are widely differing opinions, frequently opposing but always interesting! I can completely understand why the idea of no bridge plate makes people nervous. Me too! But there's only one way to find out....