I purchased a 5.1 speaker system recently and i need to upgrade the subwoofer asap. I am mostly going to be playing music and blu ray movies. The room is about 15x20. I am willing to spend around $300, the problem is the sub currently seems to not handle loud volumes well without making the "popping sound" ....tried tweaking the amp and sub. Any help with a decent sub i can purchase that can handle the yamaha 473 receiver ? Thanks.