transverse bracing vs X bracing

matthew · Post by **matthew** » Sat Nov 10, 2007 8:59 am

I'm trying to come up with a design for the back bracing of my new bass.

Usually doubles basses use three or four transverse braces. That's what I used on the last bass. But some makers are using a long X design running from upper bout to lower bout, with the ends of the braces joined with a transverse bar at either end.

This is sort of what I am considering, probably combined with some slight radiussing of the lower bout area.

Can someone do me a laymans summary of the pros and cons of traditional transverse bracing against the full lapped X style bracing, as it relates to guitars? perhaps I can glean something useful and apply it to my bass.

Cheers

Craig · Post by **Craig** » Sat Nov 10, 2007 9:19 am

Sorry to say this Matt , but there's only one way to find out,,,,,,, build both and compare ! . Cruel ain't it !

A number of guitar builders have swapped from ladder bracing their backs to cross bracing . Maybe some of those guys can give you better advice .

Do you want the back to move and help pump air out the soundholes ? ,, or do you want a firm back to act as a reflector.

The firm backs tend to make the instrument louder , but the tone is somewhat changed.

I see we now have a cello builder with us ! Welcome here Jasmine ! Hopefully more of the bowed instrument builders will join in as well . I'm certain you people have a wealth of information we can all share and adapt to meet our own type of instruments. (This thread is a very good example ) Has any one built a cello with a soundport yet Jasmine ?

Cheers , Craig Lawrence

matthew · Post by **matthew** » Sat Nov 10, 2007 9:58 am

I want stability - no splits please

I want resonance, volume, strength

Heck, I want it ALL and I WANT IT NOW!!!!!

This is what I am drifting towards:

have a look here for more. great website.

http://www.stringrepair.com/Double_Bass ... _Klotz.htm

Hesh1956 · Post by **Hesh1956** » Sat Nov 10, 2007 2:15 pm

Matthew buddy here is what I see in the guitar world.

Ladder bracing is the traditional way to do it and it provides a good, stable dome for the back across the grain.

X-bracing on a back will provide the back with a better dome both along the grain and across the grain.

But which is more desirable depends on home much you want your back to pump.

With ladder bracing I was able to manipulate the lower bout to be less stiff and more of a bellows while making the upper bout ladder braces taller to add stability in the neck joint area.

X-bracing ties the entire back together better but limits any attempt to have the back function differently in different areas.

Which is better? Who knows and I agree with Craig's comments fully too.

I noticed that what you are proposing to do has very wide and low braces in an X pattern. If excess mass and weight are not good in your style of instruments why not make the X braces narrow and taller?

OTOH everything that sticks up very far inside a guitar or any musical instrument can act as a baffle. Perhaps this is why you are using low and wide?

For guitar tops ladder bracing is less stable over time and can tend to potato chip according to some of the more knowledgeable or so they say...... on another forum.......

Craig will understand my indiscretion here......

matthew · Post by **matthew** » Sat Nov 10, 2007 2:29 pm

This is traditional bracing:

lower and middle brace has a slight curve built in so the back bow outwards.

Centre brace is wider as it has to support the soundpost pressure, but I don't see why it has to go right across.

Hmmmm.

Craig · Post by **Craig** » Sat Nov 10, 2007 2:55 pm

Ahh ! now your talkin' matt . This is the sort of thing that greatly interests me and others I bet. It doesn't seem all that different than conventional guitar ladder bracing except on a giant scale . Some guitar builders are not tucking their back braces into the liners , and I figure that'll help the back move a bit more ,,,,,, that's if you want the back to move more !

If I were to scale you bass back down to guitar size though , I d say that the back is very heavily braced . Lets see if others agree . I do note the middle one having to be wider for the soundpost.

If you were to crossbrace it , would the soundpost rest on part of the cross . To my thinking , that would distibute the vibrations across the back plate in a different way to ladder bracing . Good thing or bad thing ??

Cheers Craig

matthew · Post by **matthew** » Sat Nov 10, 2007 3:29 pm

This is a useless forum no-one knows ANYTHING!

I come here for answers an' all I get is questions!!!!!!!

Only kidding.

yes the post will sit on the brace. I don't like the idea of tucking in the braces.

I'm thinking WRC cedar cos light, stiff and stable, about 10mm x 70mm, tapering in width and height at the tips, which finish a few mm short of the ribs. Cross brace lightly bowed.

Across the upper bout at the bend, some chunky cleats to minimise cracking due to differential stretching.

Not sure what to do across the lower bout, perhaps a single ladder brace like the Solano bass I showed before.

Look, I don't know what I want to achieve really. This is only my second bass. Some say don't mess with it, just use ladder bracing as it's tried and tested. I don't even know if I want a stiff back or a resonant back.

talking about it helps.

If you were making a tas oak guitar with a wrc top, what would you do?

Allen · Post by **Allen** » Sat Nov 10, 2007 3:44 pm

I agree Craig, those are some massive braces even scaled to a guitar size. But then I know squat about Double Bass's. They're obviously built to that size for a reason.

I switched to 2 tall and reasonably thin upper transverse braces on my guitar backs and then a X-brace for the lower bout. The only reason for the change initially for me was that I had used low fat ones on my first guitar, and I was really dissatisfied with how it did not hold the dome on the lower bout. The X-brace definitely does a much better job of it.

I've been inletting my back braces into the linings, and I would say that I'm getting a fair bit of "pump" from the back. If I hold the guitar back from my body the tone is much louder than with it against my body.

I may try not inletting the lower legs of the X-Brace on the next guitar to see what happens there.

Here's a photo of my latest.

matthew · Post by **matthew** » Sat Nov 10, 2007 4:33 pm

OK so it seems your guitar uses mainly the lower bout as a diaphragm to mirror the top diaphragm. Your X brace covers that. The top braces are for stiffness.

It doesn't need a lot of strength because there's nothing pressing on it; its stiffening and holding the radius in that area.

What is the corresponding top bracing like for that guitar? It'd be nice to see top and back side by side.

On a bass, both bouts are diaphragms. The sound post connects the front and back. On a carved "roundback" bass, there is no bracing at all. The high curvature of the back is generally enough to keep everything together, and the curvature means that shrinkage and swelling is not a huge issue.

On a flatback bass there is no inherent strength in the flat plate, so the braces provide that. But it needs to be light and stiff and able to handle wood shrinkage and swelling without cracking, or the braces coming unglued.

On my first bass, the whole bass resonates when I play it, front and back equally, and yes, it is significantly damped if I press agin the back with my body or knee.

If I made the back "stiff as", would the top vibrate MORE?? And would that be better. Of course, rhetorical question. Who knows.

I suppose I'm thinking that a cross-braced flatback with tapered braces may act more like a roundback bass that a purely flat back with ladder bracing.

What does it all mean? 42 I guess.

matthew · Post by **matthew** » Sat Nov 10, 2007 4:45 pm

Check this:

Seems to me there is a fundamental question to answer. Should the back vibrate, acting like a pump with the top ... or be stiff, to push all the vibrations out the top.

If you want the back to be stiff and "reflect" all the sounds out the FFs, then a stiff bracing, arching and heavy construction is probably needed. If you want the back to vibrate nicely, then a lightweight and flexible construction is desirable.

Some guitars are built so stiffly that only the soundboard resonates. These work well. But others are made so the whole thing vibrates in sympathy. The difference is sound quality I guess and not necessarily better or worse.

I like the concept of a really stiff neck because the strings are obliged to use up their own kinetic energy rather than that being damped by flexing elsewhere. Whether that quality is desirable elswhere I don't know.

Actually I don't really expect any answers, but its good to discuss.

Allen · Post by **Allen** » Sat Nov 10, 2007 4:48 pm

Here's a pict of the top on the same guitar. I've lowered and thinned the tone bars more than in this shot.

Allen · Post by **Allen** » Sat Nov 10, 2007 5:04 pm

Very interesting image. So that little oval pad is for the sound post I assume? That back has got to be resonating along with the top. Seems very lightly built compared to the shots you provided.

I could be way off base here (excuse the pun) but does the back really need a lot of strength to resist pressure from the sound post? Seems to me that the top and back would have equal and opposite forces on the sound post, so are in equilibrium. Just a thought, like I said, I know nothing about basses.

As for guitars, I suppose their are a few schools of thought. I like the back to be responsive, but I've heard of other builders (notably Smallman's) that are built incredibly stiff and these are terrific guitars by all accounts.

There is probably a fair bit of preference by the player for one or the other, depending on their playing style and type of music. Does this apply to double basses?

matthew · Post by **matthew** » Sat Nov 10, 2007 5:22 pm

"does this apply to double basses?"

HA! Do you expect me to give you all my secrets??

No actually, I have no idea

Actually the braces in the pic of my bass were thinned down a bit after that pic was shot. But that bottom bout is 700mm across, so it needs to be a bit hefty I think.

Also, double basses aren't cradled on one's knee with a light touch, and put away in velvet-lined hard cases after being polished with a silk cloth and kissed goodnight.

They are "lugged" rather than carried, man-handled up stairs and getting through your average doorway is a bit like playing croquet with a football.

So they need to be strong.

Allen · Post by **Allen** » Sat Nov 10, 2007 5:39 pm

So, good in a bar fight

Bob Connor · Post by **Bob Connor** » Sat Nov 10, 2007 5:41 pm

From what I understand of all this back business, a stiff back will give you a greater throw of sound. Smallman uses this theory with his classicals.

Similar to what Ervin Somogyi would call a long dipole response.

A more flexible back, I think, will give you a sound which envelopes the musician at the expense of volume at a distance.

With Smallman's classicals the throw is important for an instrument that is being played acoustically.

For a steel string guitar you can get the throw with a mic or a pickup.

We use the x-brace on the lower bout and feather the braces down to nothing where they connect with the linings. Or rather we have on the last few instruments and I like what it does. You can feel the back vibrating and pumping while you are playing it.

Don't know nuthin about basses but I would assume the the theory would be relevant.

Bob

Allen · Post by **Allen** » Sat Nov 10, 2007 5:53 pm

Have you noticed a difference in the "throw" with your guitars Bob?

Bob Connor · Post by **Bob Connor** » Sun Nov 11, 2007 7:42 am

I haven't checked Allen.

It's one of those things you would notice if you were playing on a stage in a theatre,

At the rear of the theatre an instrument with the greatest throw would sound louder.

If you stood on the stage next to the instruments, they MAY appear to be similar in volume.

Which is why Greg Smallman builds his classicals this way.

I like the concept of surrounding the player with the sound of the instrument, which is why we tend to the more flexible back.

Bob

kiwigeo · Post by **kiwigeo** » Mon Nov 12, 2007 6:57 am

Matthew,

Do you ever get problems with basses splitting along the back centre seam? Just curious.

Ive just started using a cross brace on the back of my steel strings and find it holds the arch much better than more conventional transverse bracing.

Cheers Martin

matthew · Post by **matthew** » Tue Nov 13, 2007 11:18 am

Yes, if the wood is not dry when assembled, further shrinkage will do that, or worse, crack the plate NOT on the seam. there's a lot od wood across a back and shrinkage can easily move the wood a mm or more.

that is why I have built a slight bow into the back, if it shrinks further it will tend to pull flat rather than apart. That's the theory anyhow.

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