Ken, I agree that controlling the moisture content of the wood, and gluing up in a low RH atmosphere helps, but there will still be problems if the bass lives in an environment where the temperature and humidity go through large swings. Not to mention the fact that gluing in the crossbars re-introduces water into the wood. Owners of flat-backed basses with crossbars (who live in temperate areas) should expect occasional loose braces and cracks; it's par for the course.

well
 

Here are some links of the Backs of some of the Basses that I have, have come and gone or are in restoration as we speak that have had Back Repairs/Restorations due to the reasons stated above. Depending on the Bass and the situation, the Bracing system was either done as before, modified to a different style or was modified already and just left as-is. Still, the repair history of every bass shown indicates that in the Northeast, a Flatback can be hazardous to its own health.

Here they are in no particular order.
one , two , three , four , five , six , seven , eight , nine , ten

A Bass can be 200 years old or brand new. Once it goes thru a Northeast Winter or two and has never been repaired or modified you will see what things are possible. Roundbacks do a little better but they move as well.

With all of that said, some of my favorite Basses are Flatbacks and I continue to buy them regardless.

One brace, X Brace?
 

I have seen a few flat back basses with only one brace in the back for the soundpost and they seem to have held up very well.
Also, I think the X Brace is supposed to help the cracking problem, but I haven't tried it myself. Didn't someone say that Prescott introduced the X Brace?
Generally I prefer flat back basses.

X's..
 

I have never seen a Prescott with an X-brace but I did hear of him doing this. Also, there are so many Yankee basses 'named' Prescott that in my opinion are just not. If one of these Prescott 'like' basses had the X then it would be possible that he was credited with something that he never actually did. On the Prescott theory, how many basses like this, Prescott or others still have their original Braces? Yes you can see scars of previous work but still, you have to make sure what's original before giving a maker a particular claim.

I know of two basic X patterns. One with a lap joint in 2 pieces in total and one without the joint, 3 pieces. The longer piece under the 'post being solid with 2 attached pieces forming the X.

Then, there is the quasi half-X. I have that on two basses now with a third in restoration getting it as well. One long single slanted piece and a smaller angled bar opposite it at the lower bout. Sometimes another piece at the top.

On the French Basses with the single 'step' like center brace these are theories about this. My Mougenot is like that but the center seam has opened up from the bottom all the way up about 2/3 of the way. Now, the Back has to be rejoined with possibly a center strip added. I don't think it will be a single brace when it goes back together.

On a roundback, a single center brace is nice to have as well. It helps to spread the sound across the back and takes the pressure off a single place under the post. In this case, if the Post gets tight in the winter, it will most likely open a c-bout seam on that side, top or back. I had two openings this winter. The back on a flatback and the top on a round back. No splits, just a seam and a sign to check the post fit.

:confused: How can you tell that the sound is spreading across the back?

because..
 

Because two of the Basses we added this brace to were in my possession before the brace was in and I know the sound before and after. Also, where else is the sound being transferred in your mind from this addition, the scroll?

Try it yourself with a few old Italian Basses with Oppio backs and get back to me. Make sure you know what the bass does before hand as well so you can make a good post brace audible assessment. Playing the basses in a symphony Orchestra before and after is the best test. Ask the concert master across the stage what he hears differently.

The concert masters I've met would reply, "I'm sorry - who did you say you were?" :D

oh?
 

In one Orchestra I play in I have received comments like 'that bass sounds good over here' or, 'I heard you tonight' meaning the sound was noticeably penetrating.

I can't tell you why you haven't been noticed! Come by and let me get you into a world class bass. I am sure things will be different afterwords...

Ken, I'm not contesting that a brace for a roundback is a good idea and can improve the sound of a bass. And I'm not contesting that you or a concert master (or a cloth-eared donkey for that matter) can hear a difference between a bass before restoration and the same bass after restoration.

I was just wondering about your specific comment that it helps to "spread the sound across the back."

My own instinct would be that the back brace stiffens the back, thus reducing the damping effect of flexible wood. Like a stiffer neck, this would result in more movement of the top for a given input energy, you could say that results in a louder or more penetrating sound.

But I don't understand the concept of sound spreading across the back and how that would translate audibly.

I find the rest of your comments a little condescending so I'll ignore them.:)

humm..
 

Well, was not trying to insult but you seemed to not believe me so I went in towards the deep end. Sorry if it came off that way. I do not know how much you really know about my experience with basses but it's well over 40 years now as a professional on bass in one way or another.

Now, as far as scientific spreading across the Back, I don't have that data. As far as the bass pushing out more clear tone, that I can feel and hear. Also, a Flatback has the brace and roundbacks usually do not. Adding it to the roundback can get you some of that flatback spread. The post on the back of a roundback pushes out the back over time. On one new bass of mine it was within a few years and the original post became too short. Another old bass of mine also suffered from a short post when I got if and looking down the back you can see the bulge from the post. If the back has a crack or a seam near the post area or within a few inches of it, the center brace can act as a post patch as well in the back. It doesn't have to be as big as the braces seen on commercial German basses but something shorter and not as thick will work. Also, having the back brace will help prevent the back from bulging and cracking as well in that area. I know two Luthiers personally here that build new basses with roundbacks with center braces in them.

How do I actually know it spreads the sound on the back? I don't but I do hear the difference and it is enough to make me believe that it does. My word should be good enough I think. It's not just a theoretical guess..

Bridge pressure on a bass top would be deadly if not for the arch, which provides strength while still allowing the vibrating plate to be relatively thin. The soundpost pressing on the back does not take advantage of the back's arch because the back is convex, not concave (in other words, the pressure from the post works against the back's arch). I install a "soundpost pad" in my roundbacks, so I can carve them to a thickness that vibrates nicely without the soundpost bulging or breaking the back. I have experimented with many sizes and shapes.

yes.

I have sketched out a plan for a bass with the back arching INWARDS for this very reason, to support the soundpost with a minimum back thickness. But it looked so weird, I haven't really thought about it much more. It also reduces the volume of the box a fair bit, and beefing up the ribs to compensate is impractical.