Medium Density Fibreboard (MDF)...
...is the current material of choice for making speaker enclousres. It's quite sturdy, stable and as acousticaly inert as any other substance of a comparable thickness, and moreso than many. And, most importantly, it's quite inexpensive, easy to work with and takes a veneer quite well so it can look likeany wood you wish.
You don't have a heckuva lot of choice here, guy.
When you buy a speaker, you get whatever they made it with. If you're using the material of the enclosure to shop speakers, well, good luck.
Which speakers are you considering that aren't made of MDF?