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Neg-X Bracing Prototype
http://w-ww.luthiersforum.com/forum/viewtopic.php?f=10123&t=40795		 Page 1 of 1
Author:  JEguitars [ Thu Jul 04, 2013 4:13 am ]
Post subject:  Neg-X Bracing Prototype
Usually electric builders when building a semihollow guitar will route out a huge chunk of the wood to accomplish the acoustic sound. This takes away from the tone of the guitar and does not allow the wood to ring out. Acoustic makes will brace the guitar in certain areas to produce certain sounds.

I have integrated the best of both worlds, where I allow the guitar to have it's tone accentuated through veins I will be routing out in the guitar. I believe this will produce a nice full sound, lighter guitar, and the ability to ring out throughout the guitar. I have originated this idea and am the only one out there doing it (AFAIK)

Enjoy!

Image
Author:  Shaw [ Thu Jul 04, 2013 10:11 pm ]
Post subject:  Re: Neg-X Bracing Prototype
What about feedback? Many semi hollow body electrics suffer from feed back issues at high volumes. So i can imagine this will suffer from it too. Probably a lot. And acoustic builder don't necessarily brace a guitar to acquire a certain sound. It's to keep the guitar top and back from collapsing under the strings pressure. Yeah it can give it a different sound but the main and most important thing is support. Over the years various method have been used. It was found that an X bracing or modified X bracing pattern did a better job for steel strings. Fan bracing was popular for the lighter pull of nylon strings and so on. If guitar builders could come up with a method to make a top that needed no bracing at all they would if they could
Author:  elspringer [ Thu Jul 04, 2013 11:06 pm ]
Post subject:  Re: Neg-X Bracing Prototype
In my understanding... Depending on how bracing is connected, its stiffness, and placement all determine the way the face plate of an acoustic vibrates (dipole, monopole, or cross dipole). Each causing very different sounds. Therefore being highly important to the sound of an acoustic, I can't comment on how that translates to a semi-hollow body electric, does the face of the Semi-hollow body guitar really have the freedom to vibrate therefore allowing the bracing to affect the sound of the hollowed guitar? I honestly don't know.
Author:  Dekka [ Fri Jul 05, 2013 6:05 pm ]
Post subject:  Re: Neg-X Bracing Prototype
Jimmy, In a very simplified way, for the guitar to behave acoustically it needs to behave like an air pump; where the top is free enough at the bridge's point of attachment to rise up and down. (The acoustic police will be onto me for that, I know). Unless you are removing enough material to allow the top to act like a free moving membrane, then it is likely that routing your channels will do little more than make the body lighter.
The other thing to remember is that if you choose to have less 'meat' beneath the bridge, you will have less sustain.
In arch-top guitars you tend to get a loud note that decays fairly rapidly but that is what most jazz players want.
In small body semi-hollow electric guitars that I have made, the chamber does produce a little more sound via the sound-hole when you play it unplugged but I think the impact it has on pickups is negligible.
The flexibility of a Stratocaster pick-guard is likely to have more effect on an electrified sound (particularly on un-potted pickups) because the pups are suspended from it and not anchored to the wood.
Author:  abarson [ Mon Jul 08, 2013 3:25 pm ]
Post subject:  Re: Neg-X Bracing Prototype
Rick Turner's Renaissance guitars and basses implement something of this concept. The top is free to vibrate, yet there is still a center block. There used to be pictures of the internal construction, but I can't seem to find it anymore.
As far as I understand acoustic construction, much of the bracing has to do with countering string tension. Depending on how you anchor your strings, you may not need as much bracing as a typical acoustic.
Author:  Rodger Knox [ Mon Jul 08, 2013 4:05 pm ]
Post subject:  Re: Neg-X Bracing Prototype
Acoustic guitars are_different than electric guitars. They have different mechanisms to produce sounds, and these mechanisms are for all practical purposes mutually exclusive.
Acoustic guitars make sound by vibrating the top. Electric guitars make sound by sensing the string movement with pickups. This is an extreame oversimplification, but it illustrates my point. A guitar that works as an acoustic will need some alteration to work as an electric, otherwise it will feedback excessively even at low volume because the top has been constructed to vibrate freely and the output from an amplifer is adequate to drive the top.
edit: The usual modification is to plug the soundhole, which virtually eliminates the main air resonance.
Author:  hugh.evans [ Mon Jul 08, 2013 6:42 pm ]
Post subject:  Re: Neg-X Bracing Prototype
The Martin D-18E was never particularly popular, and it's solid evidence of what an acoustic guitar sounds like with a pickup. This design is essentially a step down from their approach. What you will most likely find is that the end result will lack sustain and will feedback at the drop of a hat.

Piezo could yield an interesting result, but I would wager that the effort put into the bracing would be better spent on other areas of the build. However, one test is worth a thousand expert opinions... So good luck, have fun, and let us know what happens.

To explain my pessimistic outlook for this approach: sustain on an electric guitar relies on minimizing the vibrational energy loss from the strings to the rest of the instrument an surrounding environment. Acoustic sound production has competing needs compared to solid body designs. The anticipated end result is that the top will rob the string of energy and the pickups will have significantly less to work with. This is exactly why I brought up piezo as a potential remedy, particularly if it sounds awful or strange with electric pickups.
Author:  theguitarwhisperer [ Mon Jul 08, 2013 10:02 pm ]
Post subject:  Re: Neg-X Bracing Prototype
Are you saying that you are going to route the body into an x-brace and glue the top down to that?
That means the "braces" will actually be anchored to the back, limiting the top vibration anyway.
I'm betting it will be more like the Warmoth "hollow" routed guitars. They sound okay but are extremely neck heavy. If you don't put an f-hole (or whatever hole) feedback shouldn't be an issue.
I for one am interested to see and hear the result!
I'm not as pessimistic.
Author:  Bob Garrish [ Tue Jul 09, 2013 11:17 am ]
Post subject:  Re: Neg-X Bracing Prototype
theguitarwhisperer wrote:
Are you saying that you are going to route the body into an x-brace and glue the top down to that?
That means the "braces" will actually be anchored to the back, limiting the top vibration anyway.
I'm betting it will be more like the Warmoth "hollow" routed guitars. They sound okay but are extremely neck heavy. If you don't put an f-hole (or whatever hole) feedback shouldn't be an issue.
I for one am interested to see and hear the result!
I'm not as pessimistic.


His idea is the opposite: he's cutting out the negative of a set of X-braces to make the guitar more flexible. He's cutting (slotting, actually) a hole in the shape of acoustic bracing.

The logic is faulty, though. Just because a truss makes a thin plate stiff, doesn't mean cutting the negative of a truss out of a thick plate will make it flexible. Even more so in that there's going to be another plate glued on top of it, which will stiffen the structure right back up. In the end, it'll vibrate like you'd expect if you glued a whole load of thick blocks onto the bottom of a guitar top.
Author:  hugh.evans [ Wed Jul 10, 2013 4:57 pm ]
Post subject:  Re: Neg-X Bracing Prototype
Okay, now I'm even more confused about the actual proposed plan being discussed here... Perhaps some detailed diagrams/CAD/sketches of some sort could be posted?

One point that has been bothering me in this thread relates to the use of f-holes to prevent feedback. What is the proposed logic behind this? If the instrument experiences vibrations induced by its amplified signal feedback will occur with or without f-holes, ports, or anything else that un-seals the box. Decreased mass from the addition of chambers is increase the propensity for such induced vibrations. Is there something to the contrary that I am missing in my understanding of vibration and feedback?
Author:  Rodger Knox [ Thu Jul 11, 2013 12:05 pm ]
Post subject:  Re: Neg-X Bracing Prototype
theguitarwhisperer wrote:
Are you saying that you are going to route the body into an x-brace and glue the top down to that?
That means the "braces" will actually be anchored to the back, limiting the top vibration anyway.
I'm betting it will be more like the Warmoth "hollow" routed guitars. They sound okay but are extremely neck heavy. If you don't put an f-hole (or whatever hole) feedback shouldn't be an issue.
I for one am interested to see and hear the result!
I'm not as pessimistic.


The logic is that without f holes, the will be no "main air" resonance which would induce feedback. I believe it would make little difference, the top is too heavy and stiff even if it's not coupled with the back. If the top is connected to the back, it's esentially a solid body.

A typical acoustic top is spruce and is less than 1/8" thick. Compare that with a 1/4" thick maple cap. Maple is heavier and stiffer than spruce, and stiffness is proportional to the square of the thickness, so the maple cap is more than 4 times stiffer and more than twice as heavy as the spruce top. This pushes most of the resonant modes beyond the range of a guitar. Good for and electric, bad for an acoustic.

edit: after rereading your post Hugh, you are correct. With enough power coming out of the amp, anything will feedback at any frequency, even a non-chambered Les Paul. If the guitar has a resonance in it's useable range, that frequency will feedbback at a lower power level than other frequencies.
Author:  Bob Garrish [ Thu Jul 11, 2013 5:40 pm ]
Post subject:  Re: Neg-X Bracing Prototype
hugh.evans wrote:
Okay, now I'm even more confused about the actual proposed plan being discussed here... Perhaps some detailed diagrams/CAD/sketches of some sort could be posted?


Imagine those lines drawn on the blank in the third image as slots routed into the body blank. He's essentially taking a set of bracing and doing a Boolean subtract on the body blank.
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