Previously, we’ve discussed the history and reason for chambering. The actual effect of the chambering has not been mentioned, though. So what do the tone chambers actually do for your tone?

First let’s look at what tone actually is. The tone of a guitar can be the sound of the guitar when heard acoustically or through an amplifier. The pickups play a huge part in shaping the tone, and the amplifier plays a huge part in constructing it. If the pickups and amp are so important for creating the tone, then why should the wood matter? And moreover, why should the chambers matter?

All these questions have the same answer. As you pluck a string, it moves in a wave form: a standing wave. Sound is nothing more than an oscillation of air, and that oscillation is set in motion by a vibrating body – in this case the string. The wave produced by a string is a very complex sine that consists of many other waves. The base of the wave can be seen as the carrier for all other waves, and is called the ground tone. This is the actual note you play, so, if you play an A on your g string in the first octave it’s 220 hertz. That note is identified by the string length, string tension and the mass of the string.
There are overtones, though. You can hear those when you play an artificial harmonic like pinched harmonics or flageolet. These notes are always there in the signal, but when you play those artificial harmonics you are essentially dampening out the ground note, leaving only the higher overtones to be audible. There are many more harmonics and overtones, and those are being ‘shaped’ in frequency and intensity by the entire guitar.
Let’s assume that when you pluck a string, all possible overtones are being produced, but some are being nullified by friction, such as at the nut or saddle. Because the pickup ‘picks up’ exactly what the string is producing, any cancellation or nullification in the overtones will eventually be audible.
Each material with a specific mass and shape has a resonance frequency. The is the frequency with which the material resonates, i.e.: when the material amplifies the signal that’s put into it. Because different materials have a different resonance frequency, different materials will nullify different frequencies. That is where the material comes in play. Mahogany nullifies different frequencies than alder or ash, and because the entire resonance frequency of a piece of wood changes when it’s being hollowed out, chambering has a dramatic effect on the tone of the guitar, plugged and unplugged.
This is just an answer to why it matters to your tone, not to what tone chambers actually do for your tone. It is unfortunately very difficult to get a good reading on that. There have been very few experiments on guitars which started as non-chambered and where then cut open and chambered! Everything in that area is just speculation, but I think that chambering will change the resonance frequency (the frequency of an object at which it will strengthen its vibration) to be more like a lightweight piece of wood. Because the wood can now move easier under the vibration of the string, it can behave more like if were to be light. But because there now is so much more air in the guitar than before, I have the feeling that this influences the sustain negatively. Because the string is the only object on the guitar that physically moves, it is the string that transfers its vibration energy, through the bridge to the body. The body vibrates too, and will now have to make air pockets vibrate as well! The string has, simply put, more different kinds of material to move. All those extra items drain energy from the string.

This idea can be taken to strengthen ones belief that a single-piece body is superior to a two-piece body, but I think that this is an exaggeration, because in my point of view the loss of energy is only between an abrupt transition of two types of material with a completely different resonance frequency, and I believe that a billet made of two pieces will act like a single piece of timber. Just as a beam of light loses energy when it transfers from air to a prism but loses little to no energy inside the prism but loses energy again when it leaves the prism, the same can be said for the sound waves inside a guitar.
On the other hand, the vibrating air pockets in the guitar will act as a vibration source of their own, making the wood move and redirecting the vibration back to the string, creating some kind of feedback loop. But because it’s not the ground tone itself that’s being transferred but some overtone, this feedback loop will be heard as an overtone. In other words: feedback.

So to summarize, tone chambers are a way of lightening up heavy pieces of timber. They are unpopular with some players because they feel it isn’t true to the heritage of the guitars, but for others it makes no difference as long as the guitar sounds and plays fine. What the tone chambers actually do for your tone is a lot less clear. There is some research in the field of tone chambers, and a lot of information is circumstantial. What I have done was to search for a hypothesis congruent to what I know from working with chambered guitars and from the dry physics itself. After all, most of this is my opinion, and I don’t know how much of the hypotheses I put down actually go on in a guitar. What’s your opinion?