Hard to understand what is happening with this particular iPad - when exactly was it purchased, what exactly is bad about the sound, what efforts have been made to get Apple to help? If it is current generation iPad Pro then it can't be older than 8 months - should still be under warranty.
I have been absolutely delighted with my ~ 1 month old 11" iPad Pro, in all respects and including sound quality compared to other lesser iPads we've owned. If I was experiencing a problem, I would either take it to the Genius Bar at my closest Apple Store, and/or initiate a support chat with Apple to get them involved.