Wood has a direct effect on music. When used as a guitar speaker, wood imparts tone, character and volume to the guitar. Speaker sound is related to wood density just as it is in a piano soundboard, or a guitar body. There are many types of wood you can use for guitar speakers including composites or manufactured wood.
Medium Density Fiberboard
Medium density fiberboard or "MDF," is widely used for guitar speaker construction. MDF is extremely dense and consistent, making it a good choice for any speaker. MDF is affordable and can be cut cross-ways, sideways or lengthwise, making the optimisation of material easier. MDF is completely flat, without warps, deviations and it is easy to build with. The dense quality of MDF and it's reflectiveness add to the loud volume produced by MDF speakers. One detraction: MDF can impart a brassy sound to guitar speakers.
Waferboard and Particleboard
Waferboard and particleboard are distant relatives to MDF. The two composites are manufactured materials, but they are much lighter with less than half the density of MDF. Waferboard and particleboard are actually good choices for guitar speakers because of their bass response. They are lightwieght and very affordable. When these two composite materials are covered with Tolex (a light, thin vinyl), or even carpet, they become strong enough to withstand even the worst abuse.
Hardwood plywood such as oak, birch, ash or mahogany are exclusive and more expensive than most other guitar speaker woods. Hardwoods impart a rich, solid tone to guitar speakers and can add more tone than either MDF or particleboard speakers. Other qualities of hardwood include the beauty of the grain. Hardwood guitar speakers can be finished with stain and lacquer to an almost furniture-like quality. Hardwood speakers are a good choice if you have extra money and want only the best speaker boxes.
Fir plywood is the most popular guitar speaker wood. It is semi-hard, and imparts just the right amount of bass and treble response while delivering mid-range that other speaker woods lack. It is the all-around favourite. It is lightweight, but very strong and can resist moisture to a certain degree better than most other alternatives. More than anything else, the tone of fir plywood suits guitars best. It is also a relatively affordable option.