Are basses with convex back plates superior in sound to...

[Blazemourne]

basses with flat back plates?

[Eli_Upright12]

I predict alot of opinions on this one, but we shall see. I've never played a flat back, but what my friendly neighborhood luthier tells me is that flat backs are more likely to crack. and thats all i know about flat backs.

[flint]

from what I've heard, that is really too broad a generalization as there are too many variables from bass to bass.

The only way to test it would be to have a single bass and make two backs that you could try out. And even then you would really only know the answer for "That" bass. and I believe that another bass with the same graduations and same shape may behave differently in that test.

It is my opinoin that this is in large part due to the large vibrating mass of the top plate (and sides, back, etc..) and the variabilities between different cuts of even the same spruce filch. but that's just my opinion and is probably worth what you paid for it

[Peck_Time]

Flatbacks are more likely to crack, but some of the modern manufacturers eg Shen and Christopher, are using an 'X' shaped bracing in the back instead of the old horizontal bracing.

My Christopher has the X bracing and no cracks!*

* Knock on wood, YMMV etc

[Steve Swan]

I've gotten lots of flatback and carved back versions of two models by Calin Wultur, in Panormo and Carcassi models. My impression is that the flatback is more responsive to pizzicato playing than the carved back, with a quicker rise and decay to the note. The carved back versions tend to respond more smoothly and maybe a little more powerfully on long arco notes. The carved back seems to be a little more even note to note and string to string.

We have a very mild climate in the San Francisco Bay area, so I've never had a back crack or seam separation.

[jsbarber]

Believe it or not, someone did their Ph.D. dissertation on the differences between these: "An Acoustical Comparison of Flatback and Roundback Double Basses" It is a very interesting read. If you go to this website,
http://www.awbmusic.com/acoustics/index.htm
look at Link 2 towards the bottom of the page.

My recollection is that the vibrational modes in the top plates of the instruments is different between the two. I think this is caused by the bracing in the flatback that is required for structural support. The flatback is more like a viola and the roundback is more like a violin, in this regard . The acoustic radiation pattern of the roundback is uniform whereas the flatback is not, (I think it has a dip somewhere in the 360 degree pattern - he plots 2D pattern).

I was told by a prominent luthier that the flatback has slightly nicer tone but it may require more repair work in the long term, since the bracing and back can shift relative to each other. (The grain of the bracing runs side-side and the grain of the back is up-down.) But he also said that the use of stable, aged wood can reduce this. There are plenty of old flatback basses around after hundreds of years.

As to your question of superiority: I believe that the builder and wood selection (and condition, in the case of an older instrument) are more significant attributes than the flatback/roundback aspect.

Jim