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Chambering the body

#2
I myself usually just cut out anything I feel I don't need. You have to keep in mind that the more you cut out, the more of an upright tone you will get. I actually was just experimenting with a sort of question mark shape in the upperhorn of a single cut. I'm a bit curious myself as to see whether or not this shape will produce a "sound chamber" and alter the sound at all.
 
#7
I haven't actually built anything chambered, but I've got something in the works with 3/4" thick on the outside walls and separating one chamber from the control cavity, 1/4" thick "floor" of the cavities and chambers. As for the size of the chambers... I removed whatever wasn't needed. I thought the wall thickness + 3.5" center block would be enough for the glue. I could be wrong though. And remember, this is still on paper.
 
#8
I tend to think that everything IS rocket science and as soon as you believe it not to be, you are missing some details. Some things can be made more complicated than they should be but in this case I want more research. Does anybody know about patterns of sound. I was reading a while ago when I was building acoustic guitars about ?chandri? patterns the name; i'm not sure of. But when a piece of wood is resonated at certain frequencies different parts of the wood vibrate more than other parts. On acoustic guitars it's good to brace around these patterns. As far as chambering a body I wonder wether to create a chamber for resonation. Or leave the wood alone where it's most resonate. any thoughts?

paul
 
#9
"The first thing i have to say is that i'm not a scientist or an engineer of this stuff, so whatever i say i'm not even saying that it's true. i'm just giving my opinion. it really has to be qualified as an opinion. i'm not sure how to technically describe this, but there's a certain point where a guitar can't be too light and it can't be too heavy. the tone suffers if youhave a real, real heavy guitar - it's even more apparent in a guitar than in a bass, because you have the treble frequencies. if you have a really hard piece of wood for a solid body guitar (like heavy ash) the guitar will start to sound really brittle and have a hard attack and sound thin. if you lighten the wood, everything else staying the same, the guitar will start to develop more midrange and be sweeter sounding. what i found is that if you go even further and introduce hollow chambers, if you keep the center block solid, the vibrations begin to make a loop. *drawing an oval in the air with his finger* an acoustic guitar doesn't have that so you pluck the string and it dies out. the vibrations are absorbed into the body. if you have a solid center block that's rigid enough, you pluck the string and it doesn't absorb the vibrations, it keeps vibrating. i don't know exactly how to explain this, but when you add a hollow chamber, it's almost like it causes it to resonate different and there's some sort of feedback loop created. i'm guessing on that. all i know is from my experience from doing all the wood combining. i know what sounds good and what doesn't. so it's my experience that sometimes you can have featherweight instruments that can sustain longer than instruments that almost weighs twice as much. but you have to have the solid center block to get that. it has to have a rigid neck, have the right woods, and be constructed properly. it's not just about weight."
 
#10
It makes sense. Precision. The wieght is not my concern. It's the resonance. The idea of a "loop" is an interesting way to explain it. Brings to mind the idea of too much chambering would reduce the clarity of the instrument. hence my questions of size and shape. Great to hear that the center strip needs to be solid. I had thought of carving long thin chambers under each string. But after The interview excert(thank you teej) I'll probably keep it simple. I'll post in progress pics when I can.
 
#11
le bass said:
I tend to think that everything IS rocket science and as soon as you believe it not to be, you are missing some details. Some things can be made more complicated than they should be but in this case I want more research. Does anybody know about patterns of sound. I was reading a while ago when I was building acoustic guitars about ?chandri? patterns the name; i'm not sure of. But when a piece of wood is resonated at certain frequencies different parts of the wood vibrate more than other parts. On acoustic guitars it's good to brace around these patterns. As far as chambering a body I wonder wether to create a chamber for resonation. Or leave the wood alone where it's most resonate. any thoughts?

paul
Click to expand...

For acoustic instruments, various modes set up on the soundboard. The vibration which sets up is highly dependent on the geometry of the top. I was designing a xylophone with one of the PhDs in my lab and I remember running across a paper on the modes set up on a violin soundboard.. They were extremely complicated. It isn't too difficult to set something up to see what modes are setup on a given geometry with various hollowed out chambers, but you would require some modelling software to do it with any accuracy. Femlab would probably work well for that.

I remember modelling a drum in a calculus class. For its simple geometry the resulting modes were Bessel functions. I imagine that the irregular shape of the sound chambers that I've seen in most chambered solid body instruments would be too messy to do by hand.

I do not chamber for any sort of tuning. It would either require a significant amount of trial and error, or some pretty involved design. In the end I'm not sure what the improvement would be.
 
#12
le bass said:
I tend to think that everything IS rocket science and as soon as you believe it not to be, you are missing some details. Some things can be made more complicated than they should be but in this case I want more research.

paul
Click to expand...

That's pretty insulting. There are no details in my chambered basses that are important to me, that I am not aware of, and I didn't put there myself. When Fender designed the instrument that started it all, his approach was utilitarian. I want to take the same approach. Not much beyond common sense and basic luthiery accomplished that marvel and I figure keeping it simple is the most radical idea I can offer those cognizant enough to recognize it. ;)

And if you "want" more research dig it up yourself bro. You asked the question and I tried to give you a glimpse into my approach and keep it light. I wasn't debating the relative merits of one builders philosophy over another.
 
#13
There was no insult meant hambone. Like you said I'm not here do debate the merit of one builders philosophy over another's either. What i meant was that everything in this world makes a difference. Whether I can hear it or feel it is another story. Every piece of wood and every person is different. I wouldn't expect there to be a be all end all of answers, only opinions and experience. All opinions are welcome, appreciated and as valid as the next.

Thanks,
Paul
 
#14
le bass said:
Brings to mind the idea of too much chambering would reduce the clarity of the instrument.
Click to expand...

This needs more examining. hmmmm.... Well, let's look at the situation as a syllogism. If a body that is too thick, it will sound brittle, according to Rob Allen that is. If the body is thin, with a solid piece of wood under the strings and bridge, and has been chambered, it will sustain well, sometimes that is.

Hmm..not much of a syllogism. Let's see. Where was I going with this? (scratches head) :hmm:

Ok, I got it:
Thick instruments sound thin and brittle,
Thin and chambered instruments have a nice midrange tone and sustain
Therefore, very thin instruments must have a very long sustain and a "beefy" sound.

I think if you look at the difference between an electric, dare I say, guitar, and an acoustic guitar you can see the difference. Electric guitars sound, unplugged that is, very weak for two reasons. One, there is no amplification nad the sound waves are of very low amplitudes. In an acoustic the body's hollow shape allow for the sound waves to "reflect" and resonance results, increasing amplitude and increasing sustain.

I think in the case of chambering a bass there is an equilibrium that must be met. The wood is what gives tone, not empty space. Even in the case of chambers, it is the way the sound waves reflect off of the surfaces of the wood containing the chamber that alters the sound. If there was no wood, there would be very very little sound. It would just be strings striking atoms in the air, passing energy with, in theory, nothing to reflect off of. When too much wood is used, or too dense of a wood is used, the sound is absorbed more than reflected and refracted. The answer to this problem lies in finding the right balance of amount of wood. Enough to reflect sound waves, but not too much as to absorbe them all. In my opinion, Rob Allen has done this very successfully.
 

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