Question about braces

[Matthew Tucker]

Originally Posted by Eric Rene Roy

I'm not sure if there has been any Chladni studies on bass plates the way they do violins...but I have to imagine the bend making a pretty big disruption to the lines of the plate.
Thoughts?

my be wrong but that thesis "round back vs flat back" floating around a few years ago probably did this.

My thoughts on this are that chladni patterns of a braced bent plate would probably be just as good/bad as an unbent braced plate, except that the the plate would be effectively shorter. But that said, you're not going to easily get the common modes 2 and 5. And it all changes when you attach the rim of the plate to the ribs, eh.

I'll try to find a picture of the chladni pattern of my ladder-braced bent back on my first bass. As I recall it was almost a perfect circle mode centered around the lower bout. Above the C's there was very little resonance at all, perhaps if there was no break there would have been a circle mode there as well at a higher freq. But what they all mean ... that's the big secret isn't it?

[Matthew Tucker]

Last page of Andrew Brown's research project on the matter. The paper was highly technical, and I think the conclusions were ... inconclusive!

[Ken McKay]

The papers I have read on vibration patterns of basses are on assembled instruments using lasers. This is a bit different from the free plate patterns which show the area of vibration of the plate only.

I think you are absolutely correct Eric, and Matthew. Bending the plate pretty much stiffens it enough to make it rigid so it only vibrates at higher frequencies in the area of the back above the break angle cross bar.

I think the major important factor of understanding this whole back stiffness concept is in the way it effects the bass response to bowing.

edit, thanks for putting that up Matthew, I am a big fan of Andrew Browns thesis work. I really think using the knowledge learned from his work has resulted in me making a better bass. In addition, I can't apologize for understanding the "technical" nature of the thesis. And it certainly doesn't imply that a maker has to understand what's in it to make a good sounding bass...obviously!

[Ken Smith]

Lasers, patterns, frequencies, research.... VOODOO

What ever happened to listening and feeling?

Unless you take the EXACT same Bass and keep remaking it with various backs and bracings you are Pissing in the wind.

You cannot compare Backs or bracings on different basses. There is that 'different bass' factor you are forgetting about.

I own many basses that were altered from one system to another, flat and round back. In this way we can tell BUT, even so, other restoration work was performed as well. Still, the other work performed had somewhat predictable results as it was not new science added into the bass so I am fairly certain I know what I am hearing when I listen to the changes.

Changing a bass from a 3, 4 or 5 piece brace system to a single 1/2 X brace with a bottom left angles bar (I have some like that) frees up the back in two ways. One, it can move easier with the weather and two, the sound spread up the back is aided by the long singe brace. The bottom angled Bar forms a an inverted 'V' pattern at the bottom with the longer brace to stabilize the wider lower bout.

On one of the basses like that it has an angle bend but is covered in sheer cut linen. It was left alone, unbraced or modified from the maker in 2007, England. The other is Italian about 30 years old, Cello-like un-tapered ribs, no angle break. Both of these basses were set up and played before the modification was done. Only set-up work was performed mainly other than the back work and some repairs that came about after the sound was evaluated.

I don't do this work myself but I do play the basses and my ear is pretty good.

I have two other basses in restoration that will be modified as well. One is an Italian round back and it will get a center brace. The back is fine but I like the idea. The other is an old Flat back pedigree (can't tell you for business reasons) and it had normal bracings before. It will get the modified X as mentioned before and what ever else it looks to need after all the back cracks are repaired and evaluated.

One other bass I have in repair is a large French bass with a single wide center brace. That will be modified to a normal center brace, one lower centered at the bottom bout and one upper brace just above the upper corner.

My Hart is a flatback with only a center brace and a lower brace. All braces other than center or X are shaped like a bassbar, never the wide flat ones you see in normal basses. The angle break has linen and vertical finger patches spaces along the bend.

Each bass got what it needed. No patterns here, just careful thought.

[Arnold Schnitzer]

There are two schools of thought about bass backs: 1) The back should be stiff and thick, so the top does the majority of the vibrating, and the bass will be more powerful; 2) The back should be treated like the top in that it vibrates and resonates freely, and the whole instrument will vibrate and the bass will be more powerful.

Several prominent bass makers carve their backs quite thick, and the tops fairly thin, adhering to school #1 above.

[Matthew Tucker]

So lets go for the more powerful one!

Interesting in Browns results is that the observation that the player is often able to mask or compensate for the difference in response between roundback and flatback so the differences are un-noticeable. I suppose if the back is contributing significantly to tone and volume you have a built in tone filter available with your left knee.

My observations of a free plate oscillating at a low resonant frequency, where the edges and centres of the plate can move by a centimeter or more, lead me to believe that a flexible rib structure helps allow the top to move, which is essential to transform string energy into movement of air, thus sound. The controlling factor is the strength of the box which must stay intact under high tension and compression. So you can see how both the schools of thought can work. But for me I think the back has a structural priority while its resonance is a by product of what's going on elsewhere.

Understanding its role in tone production I agree is not science yet!

[Pino Cazzaniga]

Put me in the second school, as I don't like heavy instruments, but top is moved mainly by bridge, back by soundpost (forgive the coarseness), and we have to consider the difference.
On flatbacks, sometimes I thought that a broken bend was due to the weather movements of the bend brace wood, locally stressing the groove.

[Brian Gencarelli]

Originally Posted by Arnold Schnitzer

There are two schools of thought about bass backs: 1) The back should be stiff and thick, so the top does the majority of the vibrating, and the bass will be more powerful; 2) The back should be treated like the top in that it vibrates and resonates freely, and the whole instrument will vibrate and the bass will be more powerful.

Several prominent bass makers carve their backs quite thick, and the tops fairly thin, adhering to school #1 above.

Maestro,

Which school do you subscribe to?

Brian

[Ken Smith]

Originally Posted by Brian Gencarelli

Maestro,

Which school do you subscribe to?

Brian

Is there a Column 'C' (school 3)?

[Arnold Schnitzer]

I personally treat the back like a secondary soundboard. I want resonance, and I also want some stiffness in the soundpost area. My back graduations (on roundbacks) would be considered thin by some.