Is it acoustic or acoustical?

The only material differences that I can see are that "acoustic" can be used as a noun as well as an adjective, whereas "acoustical" is only adjectival. The usage of "acoustical" is also more common in N America than other English speaking countries.

What is the meaning of acoustical?

1 : of or relating to the sense or organs of hearing, to sound, or to the science of sounds acoustic apparatus of the ear acoustic energy : such as. a : deadening or absorbing sound acoustic tile. b : operated by or utilizing sound waves.