Side Braces

[Super72bb]

Greetings,

Just a question regarding side braces. The "popcicle" style braces some put along the inside of the sides. I can appreciate there is a number of ways to do this but there is a slight variation that I have noticed among builders. I understand that these braces are intended to be side reinforcements to prevent the sides from splitting. I have also read that some feel that these braces, if done correctly help transfer back vibrations to the top? Bill Cory recommends this in his book shows an example of using them but when I look inside of my Martin D41 there are only 4 that they used. They are about 2 times the width as a popcicle stick and I think they are rosewood. They are placed under the shoulder brace and the other two are in the middle of the lowers bout. This is what was supplied in the kit as well.

Just looking for a few opinions if it is worth running a series of popcicle sticks every 10 cm or would it be best to copy what is in the D41? It is a D28 kit that I have rosewood back n sides.

Thanks,

Curtis

[MaineGeezer]

I've just put them on as side reinforcement to prevent cracking and bowing. As far as transmitting vibration from the back to the soundboard...I dunno. Any vibration originates from the soundboard, so I don't quite see how vibration from the back to the soundboard would work. If anything, I think transmission of vibration would tend to go the other way, but what do I know (not much...)

If the behavior of my recently-constructed bass dulcimer is any indication, side braces may help transfer vibration to the back. The sides are quite thin -- 1/16" -- so I put on a lot of side braces, maybe a total of 12, to reinforce the thin sides. The back of the dulcimer vibrates like crazy. If you put it on your lap, strum it, then pick it up, the increase in volume and richness of tone is striking when the back is not damped by being on your legs.

How much does the liberal use of side braces contribute to that behavior? No idea. I wish I knew!

[Super72bb]

Mainegeezer, thanks for the reply. I would say if there is any benefit in the way the guitar transfers those vibrations it is likely going to be subjective.

I am mostly just looking to confirm if 4 braces total on both sides is enough? Many builds I have read use more.

Cheers

[johnnparchem]

As a quick answer to your question the range of sizes and numbers of sides brace discussed would do little to change sound of the instrument.

For a longer answer ...

Air pressure changes transmit vibrations from the top to the back not the sides.

Instead of thinking about vibrations being transmitted first think about energy. Once a string is plucked it will not get anymore energy until it is plucked again. If you want an efficient guitar (one that is good turning that energy into sound) then you want to make sure that anything moving as part of the strings vibrations is good at making sound. Sides are not good at making sound so if they can move a lot when the top is moving the sides are stealing energy from the top without making sound. Stiff sides would be more efficient than floppy sides. However there is a trade off between sound and ergonomic factors like weight. Having solid linings or reverse kerfed linings on the top would have the same effect. Basically it increases the impedance from the top to the sides so that the energy is reflected back toward the top instead of the sides.

When the top is pumping the resulting change in internal pressure will move the back. Some build the back so stiff and with enough mass so that it does not move in response to the changes of air pressure so once again the energy stays in the top.

The back can produce great sounds that color the overall voice of the instrument so if care is taken with the selection of the back wood, its thicknessing and the brace patterns the back can nicely be a good producer of sound.

It is also possible to have an active back that is out of phase with the top and dampen the sound.

[MaineGeezer]

Thanks for that explanation John, it all makes sense. I braced the back of the dulcimer very lightly -- maybe too lightly -- and the wood is thin, 3/32" so it moves a lot in response to the top moving.

[tippie53]

that is right think more like a drum. I don't believe the vibration is transmitted by the sides it is more of the air wave generated by the strings. Johnparchem is on the money.

[Super72bb]

Johnparchem thanks for that, very informative and it makes complete sense.

I have decided to use only what came with the kit for the side bracing.

Should be glueing the top on soon.

Thanks again all.


Curtis