Yeah, Scientifical is considered a real word, but it would be a lot less commonly used and you will receive odd looks. Acoustical is a more specific word than Acoustic, but can actually be used in the same sense.
Acoustic refers to things related to sound, as does Acoustical, but Acoustical also refers to things relating to Acoustic... Yes, that's definitely something sounding weird, but remember that Acoustic can refer to the science around sound, so Acoustical actually more specifically refers to things relating to the science around sound and is very Rarely used except in very specific instances, or else when Acoustic could have been used instead.