Hi,
Have you tried using earphones to check if there is audio in both L and R earphones?
If there is then most probably the internal speaker is faulty or has a loose connection.
Here is the Ifixit guide on how to access the speakers.
[guide|36868]
If not then perhaps it is a earphone socket fault, a motherboard fault, a speaker fault etc.
In any event the tablet will need to be opened so that the problem can be further diagnosed and then repaired.
Hopefully this is of some help.