Question about braces

[Matthew Tucker]

i don't feel that the back plate works in the same way as the top plate. I'm not sure that it has to vibrate in the same way.

[Eric Rene Roy]

I'm not saying it does or needs to vibrate like a top. I'm saying why reduce its own resonant capabilities.

[Ken McKay]

There have been studies showing how flat back and carved back plates vibrate. There is a big difference! However, interestingly though neither experts nor non experts could successfully tell the difference between the two in blind listening tests.

iirc the difference is that properly graduated, carved violin style bass back plates have even resonances that are equally space apart while flat backs with cross braces have distinct peaky resonances from the braces stiffening effect.

Keep in mind though that these listening tests were the same model basses with either a well made carved back or a well made flat back bass.

My take on this is that a carved back has the smoothest, most even response but the flat back can be constructed in a way that has evenly spaced resonances by bracing it to flex in a similar way.

Smoother or more even resonances are not superior to a more "reedy" or peaky, viol sounding bass, only different.

I try for evenly spaced resonant back. I use thin, light braces that are X shaped and curved to a radius, resulting in the back being dome shaped which create about a half inch of curve from end to end and side to side. Even the area above and below the break angle is curved in the dome shape. The reason is to mitigate against cracks and to create a flat back that behaves like a carved one.

[Matthew Tucker]

Originally Posted by Ken McKay

Smoother or more even resonances are not superior to a more "reedy" or peaky, viol sounding bass, only different.

Right.

... curved to a radius, resulting in the back being dome shaped which create about a half inch of curve from end to end and side to side. Even the area above and below the break angle is curved in the dome shape. The reason is to mitigate against cracks and to create a flat back that behaves like a carved one.

... similar to my approach, and to the construction of a roundback, you are making quite a rigid shell, inhibiting "pumping" vibration very strongly. very different to the top plate with its inbuilt flexibility at the edges. It may feel like the back is vibrating, but I think this will be largely the resonance of the whole, via the ribs. The endpin material, density and weight of the bass (inertia) will affect how much vibration is felt through the back, and how much impedence there is in the shell.

But the outcome is, as usual, hard to predict!

I feel that the back, like the bridge and neck, has a filtering and reflecting effect more than an emitting effect. No proof of this though, just a feeling. The laws of conservation of energy and momentum say that for every movement there is an equal and opposite movement, and you can't create something out of nothing, so I would think that the MORE the back is a moving component, the less the top will move for any given energy input.

If the free vibration of the back is that advantageous, I'm wondering why anyone hasn't built a bass with identical top and back plates; identical materials, grads and arching?

[Ken Smith]

Originally Posted by Ken McKay

Keep in mind though that these listening tests were the same model basses with either a well made carved back or a well made flat back bass.

I had 6 modern basses here one day, all the same model with roundbacks. No two sounded alike and they were quite close to each other in wood and measurements. A flatback on one would be as different. You cant compare different basses and point to the back style as the reason for anything. It's only one component.

The first basses made in Brescia 400 years ago were flatback with an angle break. What kind of basses they were we don't know for sure but now they are Double basses and each costing more than my house.

Like I said, my opinion is that each bass made or repaired should be looked at individually and not as a model to be done one way unless you are making production basses in plywood or even carved.

I have 5 flatback basses right here in my office. Two English, two Italian and one German. Three of them have angle breaks. No two of these 5 basses have the exact same bracing system. Only one of them would I change anything inside and that is only because it was repaired a long time ago. The other 4 were all recently re-braced one way or another.

[Matthew Tucker]

That's why I love basses so much

[Ken Smith]

Originally Posted by Matthew Tucker

That's why I love basses so much

What does what? Who knows.. It is easy sometimes to gauge too much or too little in thickness and builds but which way to go to get the right stuff done is always interesting.

My Cornerless bass was/is ultra powerful and the back is a gradual taper with some gentle bend in the upper back, not an angle break cut. When I got it I glued up all the cracks that were open mainly from the outside just to keep it going till the restoration. It would shake itself apart and you could see daylight thru the F-holes coming from the back cracks. Other than fixing all that's loose and re-doing EVERY previous repair, we are leaving the bass alone. What's done was done and with old basses, over modifying is not always a good thing.

Why did that bass sound so good and so loud? A combination of things. How much of each we don't really know but it had the right stuff! It had its own internal can of whoop-ass!

The copy bass will have a gradual taper from block to block as well BUT a shallowish round back with a center brace. Three of my roundbacks currently have center braces as well. The Panormo School which is very old if not original, my Candi which was partially put in for a repair and to strengthen the softer maple used for the back and my Martini which is the same soft wood but thicker made in 3 piece. The partial brace in that is to protect the joint on the soundpost side. The two that were just done recently slightly improved the projection of the bass as far as speed of sound or it feels like it. The other is older than time but for a huge bass, not a bad idea.

Back designs, bracing systems, sizes of basses, the species or wood used and the thickness of the woods. All of these factor in.