The problem deals with a puzzle that was observed by Lord Rayleigh, so it is OLD! It deals with a peculiar behavior exhibited by pipe organs.
In 1877, English physicist Lord Rayleigh observed that when two almost identical organ pipes are played side by side, something strange happens. Rather than each blaring their own tone, the two pipes will barely make a whisper. But put a barrier between them, and they sing loud and clear.
You have to read the whole article to figure out the explanation for this. Fascinating!