Disclaimer; I'm not an expert and have no scientific proof beyond anecdotal experience. So far I've built 3 basses. 2 are chambered. My 4th bass has a HUGE cavity routed out of the middle of the body so I don't know how it fits in exactly.
Like others have said it comes down to a few things.
1. Weight; just remember though, you need to remove huge amounts of wood to have a real effect here. My first chambered bass is heavily chambered but still weighs 9pnds (aprox).
2. Tone; there are two things going on here really.
A. less timber holding the tension of the strings thereby allowing a little more flex in the body. The function of all bodies is flex/lack to change the sound in some way. As you probably know neck joint also effects this. Well chambering does as well. It effectively lowers the density of the whole body.
B. Actual resonance in the body chambers. To do this you need to think also about the thickness of the top as well as the size of the chamber. If the top is still 5mm thick and not actually supporting the strings, the ability for it to resonate is gonna be severely restricted. Thinning the top round the edges of the chamber will make a difference here I've found, but then you risk it being fragile. To give you an idea of the sound of the chamber here's a soundclip I recorded with an Ehrlund linear (contact) mic... http://soundcloud.com/simpleinnovati...ehrlund-pickup
Now the same bass with a piezo... http://soundcloud.com/simpleinnovati...orn-with-piezo
And finally with a combo piezo and mag pickup... http://soundcloud.com/simpleinnovati...ass-guitar-all
Bass in question
Internal chambering (before gluing)
And if I was to do it again, I'd rout out even more wood...
I'll just make a comment about sound-holes too. Both my chambered basses have soundholes. I found without them, it choked up any acoustic sound the bass had. I don't think it greatly matters the size of the port/hole, but if you wanna hear it, you gotta let it breath.