Having watched films and read books on the cold war antics of the submarines of various navy`s, they lead you to believe that they can pick up and identify the sound of another Sub from hundreds if not thousands of miles away whilst submerged. Would this not be the same with the black box locator or is that a different situation all together? Just curious.
Submarines listen to low audio frequencies, which can travel very long distances underwater.
The pinger is at a much higher audio frequency (37Khz) which is attenuated (reduced in strength as it travels) much more quickly. It might not even be detected from the surface in a deep ocean, much less at distances of many miles.
Also, as far as is publicly known, submarines are not equipped to even listen at the high audio frequency. Of course, actual sonar capabilities are highly classified.