Have you consulted with your township's zoning board about noise
issues? Some communities have ordinances that can be brought into
play to help regulate nuisances such as the speakers blaring outward.
While those ordinances MAY not completely shut off the noise, it may
help by regulating the hours, the volume, and the direction of the
The store owner's assertion that the speakers are on their property
doesn't mean they can do whatever they want, if the output of the
speakers is pointed outside their property and invading the public
Failing that, how about gathering a coalition of the other merchants
who had established the "flavor" of the town centre as a quiet place
conducive to buying. Work together with them to create a campaign of
pressure that may be public or private, designed to help the invading
merchant understand that s/he is destroying the very purchasing
climate that attracted them to open in that space. Let them know it
won't be tolerated and that you will all help educate customers in a
boycott (if it gets that far) of their store in order to preserve
their town's character.
It's worked before, in other towns. People are beginning to come to
their senses and realize that there are spaces for aggressive,
brightly lit, garish retail emporiums, but that those spaces aren't
necessarily in their traditional town centers. They are beginning to
value the town center, with independent merchants, galleries, and
shops as a different experience that should be preserved as well.
Hopefully, you'll find this to be the case in your town, too.