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Hi. I have a question regarding acoustic bracing. In most X braced guitars( per Martin/ Gibson, etc)there is one , or more commonly, two diagonal braces that span the "belly" of the top, past the X braces. The last two braces on the top, attached to the treble side leg of the X brace just before the heel block.

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Mike

The only thing nescessary for evil to thrive is for good men to do nothing.

Tonebars.
They strengthen the top in an important area, but more importantly they help define the sound.
There is a decreasing area of stiffness as they head southward, leaving more of the bass side looser, while nudging up to the X brace on the treble side they help stiffen that area for treble response. And angled like they are, there is the probability that help will be given where help is needed. I.E., behind the 6th string is the maximum amount of unbraced area, while the 1st is the stiffest. And it graduates betwixt the two.

Does that help?

Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

Thanks, Steve. That's a very concise description, and it gives me everything I needed.
I sort of intuited the purpose by looking at the top, but did not know what they were called. Your explanation was perfect. Thanks.

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Mike

The only thing nescessary for evil to thrive is for good men to do nothing.

Mike, let me beat this horse closer to death if you would:
Notice that the tone bars are splayed...closer together at the treble area, and further apart as they travel bass-ward. Same theory as already stated.
Also, note what many call the "Musser" brace, right behind the bridge pad.
These function wonderfully, evening out the string-to-string response.

The top you pictured should sound great.

Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

Thanks, Steve.
The top pictured is a Martin top. I just grabbed it because it was the easiest picture I had to explain what I needed.
The reason i asked is because I am building what you'd probably term a "hybrid" instrument. A hollowed out electric guitar body, with an acoustic top. I'll be using an SBT pickup and Fishman Powerjack preamp. I'm trying to get an electric sized instrument(at least in body thickness) that i can plug into an amp or PA and get a decent acoustic type tone out of.
I had originally decided to use two rather heavy, parallel braces, similar to what Taylor uses in their T5 model, but decided that I wanted a bracing scheme more akin to an acoustic. I need to make sure that the top will vibrate enough to let the SBT pickup amplify the tone. Too thick of a top, or too stiff of one, will negate that, I think. I needed to know why before i could do that. I ended up with a sort of cross between the two, which I think(hope) is going to turn out to do what i want it to.
I took the size and shape of a Gibson L-OO, transferred it to a solidbody blank, and hollowed it out.



I moved the bridge and bridge plate forward(toward the neck) to give me a neck joint at the 16th fret, like an electric. That removed the possibility, at least at my current skill level, of an X braced top. So i ended up with a bracing scheme somewhere in between a twin parallel bracing pattern and a more acoustic type. Here's the bracing pattern I ended up with.





The top is approximately .118" thick. Thicker than a standard acoustic, but i think probably needed. The two main braces, and the cross brace in front of the bridge, are 5/16" thick. The two main braces taper from 1/2" tall, down to about 1/8" at the ends. The cross brace is 1/2" tall, and the tone bars I asked you about are 1/4" thick, 1/2" tall at the highest point, and taper to almost nothing. Since the sides are 1/2" thick, I did away with the tone bars you normally see on either side of the bridge. I think the added stiffness of 1/2" sides, as well as the new location of the bridge, will give me plenty of stiffness there without those bars. The two main braces will be glued to the neck block, but nothing else will be notched into the sides. They'll end right before reaching them. I think the 1/2" sides will probably also give me plenty of stiffness without that being necessary, as long as the gap between is not too large.
It's a simple bracing patten, but I think that it will work. If it doesn't, I'll start over until i get it right.
Thanks again for the information/education.

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Mike

The only thing nescessary for evil to thrive is for good men to do nothing.

You might want to check out this thread for some ideas as well:

viewtopic.php?f=10101&t=21005&st=0&sk=t&sd=a&hilit=John+Watkins%27+Acoustic+Les+Pau

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

Yeah, Andy, thanks. I saw that build. It's lovely. I had originally contemplated something like that myself, but I think there's a whole lot more bracing there than is actually needed for what I'm looking to do, although his top actually floats on top of them(way cool!)..
I'm nowhere near the craftsman a lot of folk around here are. I'm just trying to keep this as simple as possible. I think what I'm doing will work well. We shall see.

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Mike

The only thing nescessary for evil to thrive is for good men to do nothing.

I thought the most interesting thing about John's build is that from the pictures it looks like the bridge is actually glued to the body and it's only the rest of the top that "floats". Apparently this still results in an instrument that sounds like an acoustic.

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http://www.birkonium.com CNC Products for Luthiers
http://banduramaker.blogspot.com

If I recall correctly, you are right. However, he's using an Undersaddle Transducer pickup( B-Band, i believe), so he's getting more of the vibrations of the strings across the bridge rather than the vibrations off of the top, IMHO. I've put quite a few of them in quite a few different acoustics. They all sound pretty good, even in a cheap, heavily braced acoustic.
I'll be using a Soundboard Transducer pickup, which is attached to the soundboard behind the bridge plate, and picks up vibration directly from the top itself. Which is another reason I went with the bracing scheme i did. I think they're probably two different animals.

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Mike

The only thing nescessary for evil to thrive is for good men to do nothing.

Looks very interesting, Mike.
Full report when strung up?

Steve

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From Nacogdoches...the oldest town in Texas.

http://www.stephenkinnaird.com

Yep. I'll definitely keep you all posted. Hopefully this'll work well the first lime, LOL.

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Mike

The only thing nescessary for evil to thrive is for good men to do nothing.

So as not to be confused, some call them the 'lower face brace'

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Joe Beaver
Maker of Sawdust

thanks, Joe. Good to know.

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Mike

The only thing nescessary for evil to thrive is for good men to do nothing.