Im building a (Portable) speaker. I have a design and most of the electronics done already, but i need some help with the enclosure. I'm not sure what to build it out of, since I've heard some conflicting Info. Some say MDF is the holy grail top quality speaker enclosure material, while others say it is the worst possible material. I want a decent sound to come out of this thing, so I also need dividing walls inside as there are more that one speaker in the box. What material should I use?
MDF has very good acoustic properties at a low price. But it is heavy and does not hold up well to being bumped around. Also doesn't do well in moist environments. It is not used for pro portable speakers for those reasons. It's a good choice for speakers that won't be moved very much.
Almost all professional speakers use void free Baltic Birch plywood. Baltic because, in theory at least, the most dense and consistent birch comes from Russian trees. But there are a lot of different grades of Baltic Birch out there. What you will generally get in a consumer store (home center etc) is sold in 4' x 8' sheets like regular pine plywood and is not really what the pro's use.. it may have voids (gaps within the inner layers). The good stuff is usually sold in 5' x 5' sheets. Check with a specialty wood supplier in your area.
If you are looking for something a little less expensive, Arauco Pine plywood is often used by amateur speaker builders.
In all cases, the speaker builder is looking for a material that is very stiff, dense and consistent.. with minimum resonance.. that is to say, when it does vibrate, it does not favor any particular frequency. The speaker cabinet should (as well as possible) be a perfect container which does not respond to the pressure of the sound waves within it.
MDF, being made of very small wood fibers that are mixed with resin (glue) and hardened under pressure, is very dense and consistent. There are no components within it large enough to resonate on their own.
Plywood is made from sheets of wood which are glued together flat. Because each layer is still a piece of natural wood, there will be some knots and other variations in the wood. The manufacturer of the wood has to choose the best (most consistent, with the least defects) wood to put in each sheet of plywood. They will also sometimes cut out defects and place another piece in that spot to fill in any gaps.
Since trees are not always cooperative in providing perfect wood, the manufacturer will sort the wood out and sell it as different grades, at different prices. For some jobs, low grade plywood with large numbers of inconsistencies will be fine. For other jobs it may not be. For example, for furniture building where the grain of the wood is visible, a builder would not accept wood which has any visible (filled-in or otherwise) defects visible on the outer layers.
In the case of speaker building, when plywood is used, plywood made from hard (dense) wood with a consistent grain, which is stiffer and has few resonances is desired. That is why void free Baltic Birch is preferred.
The Arauco pine I mentioned is used as a second choice because although pine is not as dense as baltic birch, this particular pine plywood is said to have less resonance than other plywoods, at lower price than high grade baltic birch.