The wood could be purple heart but if these speakers are factory made then I doubt it plus based on the photo the color is not right. Purple Heart is expensive at $15 bd. ft. and very hard, machining and sanding takes forever.
Birch tends to warp, cup and tricky to stain because the grain reverses. Hard maple is just that - too hard. Not pine or fir either (no they are not the same wood).
A best guess would be a light colored, affordable, available in wide planks, tight grain without pores, easy to cut, sand and stain wood like soft maple.
