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Hello all. First post and first visit to the forum. I'm a guitar tech and luthier from the UK.

I have a build on the go for a customer of mine that requires some body chambering.
The guitar is based loosely around a Musicman JPXi 7 string.
I've never done any body chambering before, save for the odd thinline tele etc. However this is not a semi.
My question is to those of you experienced in chambering solid bodies.
There must be a formula or guide lines of how "tune" or do it. For if one removes too much, you end up in the semi area.

I'm just a little in the grey about what is the appropriate amount to chamber, and what pattern etc.
Does the arrangement of the chambering make a difference on sound? Gibson, I know, have a series of circular holes cut away in the lower bout bass side of their LPs from 2000 onwards

Here is a video of the JPXi being made, You can see, that the chambering is in a linear fashion.
Now they can't have got it right 1st time, there must be some sort of "plan" to follow, on how to get the best out of chambering.
http://www.youtube.com/watch?feature=pl ... erIO5bDCqM

Hope this isn't too vague, any response welcomed!
Simon

Hi again,
Sorry. The Topic should read "Solid Body Chambering"

http://www.recordingproject.com/bbs/vie ... hp?t=40311

Can you hear a difference in the two takes?

Note in the pic.....this is the chambered inside of one of the guitars featured in the sound clips. The other guitar is solid. The two guitars were made from the same billets of wood throughout.....all the way throughout....including the fretboards and the headstock facings. Which is to say I imagine there has been no better example of two guitars built identically for the purpose of examining the "chambering" effect.

My chamber walls are .3" and the chamber bottom and face panels are .175". Simply put, six vibrating strings generate nowhere near the amount energy required to resonate a panel that is .175" thick and is fixed at every edge. It would require an immense amount of energy to do that.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

I don't know if there is a specific formula or any effect of doing it a certain way as the body isn't acting like a sounding board the way an acoustic guitar top does. I chambered my LP DC that I'm making currently though, and I decided to chamber it with an eye towards balance, and therefore removed material on the bass side lower bout, of slightly more volume than was removed from the electronics cavity. Just because, and I have no evidence whether this will do anything, I removed sections loosely based on the golden ratio http://en.wikipedia.org/wiki/Golden_ratio.

I didn't get too crazy with my math here, I just divided each section into a length of 62% and 38% respectively. I've used this in the past making speaker enclosure structures and figured why not?

Here's a pic of what it looks like:


I chambered mine purely for weight concerns, I don't like having a boat anchor around my neck. I haven't played enough chambered guitars to be able to say I can hear a difference, and I've found enough conflicting evidence of this on the internet to be a bit skeptical that it does. It seems like with an electric all of your sound is coming from the pu's and unless you're using a piezo, any vibration of the body itself doesn't translate.

This is my first guitar though, and I am very far from being an authority.

Hi guys, thanks for your replies. A couple of things....
Zlurgh, I understand what you are saying that 6 strings could never produce enough energy to move a 6mm guitar top. But there must be a point where it does have a detrimental effect on the guitars tone. Think of the difference between a thinline tele and a standard.
Granted in your sound clip there is very little difference, but where is the cut off point? how do you know when enough is enough? I don't believe its purely a weight thing. It is going to have an effect on the sound of the guitar.
Also, how did you choose upon the design for your chambering pattern? It certainly looks like a thought and planning process has gone on here. Why did you settle on this design?

John, thanks for the reply. Again it looks like a though process when into the decision to make 4 separate chambers. Why not one large one? I have to disagree though, while its true a lot of the sound does come from the pickups, tonewood selection is a major part in shaping the overall sound, otherwise we'd all be making guitars from plywood.

And to throw another spanner in the works, Yes this guitar will also have a piezo loaded saddle.
Thanks for the link to the wiki page, but sadly after 2 minutes looking at the page, my eyes fell out and my brain turned to mush. Not so good with the algebra! Thanks anyhoo!

Sure it does. That's why when you strum a guitar and put it on a table or against the wall, it gets louder. I personally think there's a distinct difference between the two, most noticeable on the attack. The first one has a quick, sharp attack, and the second one is a bit more mellow on the attack and towards the end of the note. When you originally did this, I think I ended up guessing that the first one was chambered based on the quick attack and overall edgier tone. I will grant you, though, that it's probably a much subtler difference than most people would expect. I suspect that the stiffer the wood is to begin with, the less of an effect you'll see. For example, if your guitar body was made out of solid steel, I wouldn't expect that chambering the steel would make any significant difference until you took away a HUGE amount.

If you have a strat neck laying around, Stu, build a solid vs chambered alder body for it, and rerun your test. I wonder if you'd see more of a difference? I'm curious what type of wood you used on yours? I have to say that it's nice to see someone doing testing on something like this.


re: though process behind chambering

I left a block down the center for structural reasons. Around the edges, I took out a good amount of wood but separated it into separate chambers. I ran into feedback problems when I used one big chamber. There was no real though that went into it except a little bit of experimentation.

Simon, I've read so many threads about the effects of tonewood on your sound, and whether it really changes things with electrics that simply break across both sides of the argument. Usually the evidence cited for whether the wood really affects or does not affect the tone is anecdotal, and very subjective. I can't say I know for sure that it has or hasn't any impact on the sound however I haven't seen enough compelling reasoning to suggest that it has very much impact on the sound. The pickups don't work like microphones, where a diaphragm is set to vibrate in response to soundwaves and air pressure, rather a magnetic field is disturbed by vibrating strings. I suppose an argument could be made that the reflectivity of the wood can enhance the sustain, through strings vibrating longer but I believe that the fit of the neck has more to do with this than the wood itself. My goal with putting my guitar together was to effectively join the neck to the body in a way so they act as one. Any slop in the neck joint translates to vibrational dampening which leads to less sustain.

As far as that wiki link is concerned, it was way over my head too! That's why I included the percentage in my original comment. If you have an overall length, you multiply that by .62 which gives you the bisecting line. Like I said I don't know if this has any impact on anything, but I've used it before. It's a proportion that has been observed repeatedly in nature, and is seen in many visually appealing works of art and architecture. I don't know why I didn't just cut out a big hole, I'm sure you could do that and it would be fine. I would have been comfortable removing more wood, but I would have avoided removing wood around where the bridge and tailpiece go, just for strength reasons. I removed an amount that left me with a guitar that felt comfortable to me. The only real rule I would follow is making sure that the side that points to the ground is slightly heavier than the one that points up, that way the guitar naturally wants to hang vertically.

Sorry I couldn't be more help, I don't have any experience with Piezo's, though I'm sure I will incorporate them at some point in the future.

I must say I meant something quite specific when I said there isn't enough energy to resonate those chambers.....I failed to really explain my thinking.

The chambers were designed with an expectation that failed to materialize. I had a theory that if I were to make nine chambers with distinct shapes and sizes then any resonance of those chambers would occur at different frequencies. That theory would have been validated, I still believe, if the chambers had actually resonated...which they never came close to doing. If they HAD each resonated, the result would have been a VERY nice tonal profile, since each resonate peak was at a different freq and was 1/9th the amplitiude of what a single chamber might have produced at a singular frequency.

The panels in each chamber of my guitars have NO potential to individually resonate with the amount of energy present. What was I thinking? Semi-hollow body panels are MUCH larger, requiring a lot less energy to move them...and they move very little.

New Theory:

What happens with chambering: as wood is removed by chambering, inertial mass is lowered on the body....allowing it to respond and move as a whole unit a bit easier than the solid body. Any increased punchienss (compared to a solid body) is not due to the initial response from the strings being louder...but due to the fact that the vibration returning from the body and getting back to the strings has a higher amplitude than with the solid body. The larger amplitude has a larger phase cancellation effect on the sustain....right after the intial "pluck". Also, the phase cancellation primarily influences the fundamental of the wave...so the realtive difference between the two guitars is that the attack seems more accute, the sustain seems less, and the overtones seem more pronounced on the chambered guitar. It's just a theory....I'm trying to figure a way to quantify all this without fancy equipment. I don't think I'll get too far without it though.

But these two guitars sound pretty similar....I think all would admit. This was very much a surprise to me to discover. I attribute it to the fact that the two fulcrums (the bridge and the nut) are similarly rigid on each guitar. They are both made mostly of Sapele....harder and denser than mahagony. There is a maple strip down the middle of both necks. I expected a profound difference but the only difference is precieve by clever ears. It ain't much.

I have some Port Orford Cedar and Peruvian Walnut (light, stiff, and airy) guitars being finsihed at this time. Actually, I have twelve guitars in finishing....all made of different woods. I fully expect to draw some final conclusions about tone when I have the ability to make more comparisons between these guitars. I'm looking forward to hearing the Peruvian and Port Orford guitars the most. They are SO light. I expect the Peruvian to weigh in at 5.5 pounds....maybe even less...and just as rigid as you want.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

I think this probably very close to correct. I've obtained a copy of the complete proceeds of the Journal of Guitar Acoustics. It's still available for purchase, I believe. What's very interesting to note on acoustics guitars is just how whacky the top actually vibrates, AND how much sound actually comes from the neck. The coupling is very strong, and you can prove this to yourself by sticking a tuning fork on the bridge, and then sticking it in various spots on the neck. You'll find, or at least I did, that there are spots on the neck that couple nearly as strongly to the box as the bridge does. I was very surprised...I didn't expect that at all. I think I've convinced myself that stiffening the neck in the area of the heal with some carbon fiber rods made an audible difference in my builds, though I'm not really sure (I did it mostly to control where the relief comes in a bit more reliably).

I think where the shape of the chambers comes in is that the body does not just vibrate as though you were driving a tuned membrane. You don't just get a nice, spherical wave. You end up with all these nodes that move around with frequency, and I think the shape and location of the chambers can affect what you end up with, not because you're resonating a cavity but because you're selectively taking away bits and pieces where you would have had stronger vibration, driving that elsewhere or killing it entirely. In a former life I was an engineer who did a lot of robotics and optics work, and you see the same thing when you analyze mounts and structures under vibration. It can be very complex and rather whacky which parts wiggle and where.

Terry Mcinturff has hinted that he's done a lot of work in this area and has a better understanding of what's going on, but I think he's keeping his yap shut until he retires I don't understand it very well other than trial and error until I'm happy.

I've been meaning to pick up a scope, not just for this but for electrical work I do, and I'd love to measure strain vs frequency at various points around the bodies and map it out, just to see what's going on. Maybe you'll beat me to it and save me a whole lot of time and money. LOL.

In the acoustic forum we talked about the fretboard rolloff and this issue. The stress riser in that area HAS to contribute to an unwanted dissipation of energy...unless managed properly...as you appear to have done. Anything done to stiffen that area must produce more sustain by decreasing the relative movement of the fulcrums. In this scenario the energy losses are transfered more directly to the neck and body through the fulcrums. I can't put my finger on it but that just seems proper/efficient with any stringed instrument.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Interesting. I just read through that fall off thread. That makes a lot of sense. What I noticed most on mine is the low end got a lot punchier. The first couple of iterations seemed a bit dead on the low E string. Honestly, I don't know how much of that is voodoo and luck...maybe the CF rods are like the luthier version of a rain dance, but what you say about the fulcrum at that point make a lot of sense.

Seems to me there is some very good understanding of how the guitar body resonates and some pretty clear understanding of how the body resonances can effect the vibration of the strings thus altering the free vibration of the strings. I agree with most of what I have read here.

I think an important point is that the understanding, while interesting, can lead down a path to nowhere.

Here is my approach. I have done a lot of resonance testing, acoustic instruments are different than electric but I have done both. I have a set a impulse tests on a series of semi-hollowbodies that I have made. I have from this only determined that they are consistent because I used similar shape, construction and wood. I no longer need to test if I use similar materials and identical dimensions. By the way changing dimensions makes much bigger change in sound than changing materials. Still materials (wood) given tight joinery, does give another level of perception. Some will say better some worse given the same shape, but it truely has an effect. I copy or replicate an existing design that has been proven, trying to get it how I percieve it as best. I use similar materials as best as I can determine and reverse engineer. That's the way I do it.

What does the best semi-hollow or chambered guitar sound like?

_________________
Ken

Why....mine....of course.

_________________
I read Emerson on the can. A foolish consistency is the hobgoblin of little minds...true...but a consistent reading of Emerson has its uses nevertheless.

StuMusic

Glad to see this.
I've purchased a guitar that I love but has such awful neck-dive I'm having to take a serious look into not removing too much body weight from my own creations. I sure hate lifting while chording.

I haven't finished my model yet, but I'm told autocad can find the weight center of a model. Anybody do that?

I certainly don't doubt that a bit.

_________________
Ken

there is a fine line.

I made two and one has a heavier neck and and it dives the other is like magic and has a lighter no rod neck. Same guitar size, weight etc...of the body

_________________
Ken

Zlurgh
That is the first time that Ive listened to your soundclip and I have to say I could hear a distinct but subtle difference, much like John C said in attack - but slightly in timbre as well... Im sure there is a very real difference in how the guitars play, as well, even if it too... be slight.
Ive always thought that mabye the way the pickups drink in the sound on the 2 different types of instruments mentioned might be minimal, compared to how the strings actually attach to the guitar in cases of chambered and non chambered instruments... It just seems to me that the traditional bridge design for a solidbody isnt exactly adequate for a chambered.. for instance if a bridge were seated on or actually attached/glued (i.e. wooden bridge base with adjustable saddles) to the top of a chambered electric, I imagine that there would be better vibratory transferrance, and ultimately top resonance. However Im just talking out my butt as I havent had a chance to experiment with any non traditional designs as of yet....
So I'll leave the rest of the discussion to you gentlemen...
I dont mean to change the subject but I would be interested to hear what some more experienced luthiers had to say about the idea I floated forward ...
if anyone knows of any seated bridges on chambered electrics Id love to check out the site or thread in which they appear..
Chers
Charliewood

Sounds similar to what I did with this thing. It is hollow under the bridge, about 1/4" material, the chambers extend into the wings. Before I put in the electronics, the control cavity has some acoustic tone coming from it, I would like to try an F hole on this idea. I have no idea how this effects the tone of anything though. The Baggs T bridge elements sound great though, I don't know if the hollow makes them any more acoustic sounding though, doubt it.
Rob

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Here's my take on it.
Stuart opened up all of our eyes/ears with his sound comparison (thanks Stuart!)
I've built a few (10?) solid body gits.
I am a tone monkey musician (hobby).
I'm 58 years old .
So, I think it doesn't matter how much you take out or leave.
Weight, and balance are important.
I think that in the chain,
the amp is most important,
the pick-ups are second,
the wood is third,
and the chambering is 4th,
and probably not noticeable,
except when unplugged.

[/quote]
Sounds similar to what I did with this thing. It is hollow under the bridge, about 1/4" material, the chambers extend into the wings. Before I put in the electronics, the control cavity has some acoustic tone coming from it, I would like to try an F hole on this idea. I have no idea how this effects the tone of anything though. The Baggs T bridge elements sound great though, I don't know if the hollow makes them any more acoustic sounding though, doubt it.
Rob[/quote]

Rob,
Yeah thats exactly what Im talking about - thanks for chiming in,
what I was getting at was > that a traditional tuneomatic style arrangement would transfer less vibration to the top wood than perhaps this sort of idea you've created here... now a Fender style bridge while seated (hardtail) still transfers vibration through metal saddles that have thier connection to the bridge plate via micro adjust screws for bridge height, in the front... and intonation screws in the back of the saddles. a vibrato system of the same sort and there is even less transfer area...
In both methods tuneomatic or Fender(either) the vibration is transferred to the saddles and then through metal posts/various attachments then into the wood.... It just seems to me that the resonance of wood would be higher than metal - so the more metal between the strings vibrating and the wood to resound - the more loss of potential vibratory aspects of the top .. as it "would or perhaps could" contribute to overall sound...
I know that the p/u's and the amp have the most to do with the sound, and Im sure there are luthiers out there who wouldnt even dignify my comments with a response... I'll admit they (my words) are unqualified remarks....
However Ive trolled alot of luthierie sites over the last ten years and I find that the deductions arrived @ that the body doesnt come into the sound picture so much as the electronics, are mainly based on examples that have either type of bridge mentioned above....
One idea I intend to tinker with, after numerous repairs to Strats and playing experience with my own Strat ... and noticing the effect that the tremolo springs have on the tone of the instruments ...... is that I would like to take a chambered electric and attach springs to the bottom of the bridge saddles directly and then into a resonance chamber beneath the bridge....sort of like an organic reverb...(in theory)
of course Id like to make the spring tension fully adjustable via the back of the instrument... has this sort of thing been done does anyone know?
My reasoning is that if the adjustment of brace mass can radically alter the sound of an acoustic than perhaps something similar could be achieved in electric instruments... via spring tension on bridge saddles ... just an idea right now.
Blah blah blah right - Im going to go to work now - one day I hope to show the results here...
Cheers
Charlie

I did this for string spacing, not for tone, and being a woodworker and not a metal worker, this was easier. I have considered putting a mic type pickup in the chamber under the bridge to see if I could get some more acoustic tone blended with the piezos, I am guessing it will be more cost and trouble then it would be worth. The hollow idea was for weight.
I agree with Allen on what will effect tone, under amp though, effects needs to be a sub category. The "sterile" EMG blended with a piezo into a tube amp, or as my friend has been using it, stereo effects into 2 small tube amps. Sounds great, but meaningless without the cool A B comparisons that Stuart did.
Rob

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