There are those who say Baltic Birch plywood is the best material for speaker cabinets. We have used it when requested by a customer. It is quite a bit more expensive and not quite as easy to work with as it does not machine as well. We have A/B'd it with speakers built with MDF and can't really say it made an audible difference. I won't say fans of Baltic Birch are wrong about this, in our tests we just haven't been able to determine that they are correct.
As funkmonkey pointed out, we are also exploring bamboo. Right now, it is very expensive at about 10 times the cost of MDF. But we built a pair of bamboo SongTowers last week and will be finishing that pair shortly (I'll post pics when they are done). It is certainly a sustainable, eco-friendly alternative. It is also nice to work with (machines well) and it can be finished naturally without veneering (something we find very attractive). Lower finishing costs may off-set the higher initial costs, so we find it intriguing.
We have also started working with 1" MDF, sandwiched 1 1/2" MDF and even sandwiched 2" MDF. These show a great deal of promise, especially at low frequencies where added mass can really be a benefit.
But in the end the most important thing, no matter what material is being used, is that it be well-braced. All of these materials benefit immensely when braced properly.
As for carbon fiber, my interest level is very low. I talked to one manufacturer who was crying the blues because the materials were in such short supply he could not deliver product. It is also very expensive and not the kind of thing you want to work with if you are concerned about your health.
There are also other materials we would like to explore. One is high-density foam. You can formulate these materials in virtually any density you would like - far denser than any of the above materials. And you can use forms to mold it into any shape you want. Of course, that would pretty much preclude a wood finish. Automotive finishes anyone?
- Jim
