I just bought this sub and it seems weak to me. Not sure if it's something with the settings or the unit is defective. I'm connected through the sub out on my Yamaha RXV671 receiver to the line in on the sub. Crossover is set at 80 on receiver and sub. Sub is selected on receiver. I need to turn the volume all the way up and crossover all the way up to hear any rumbling. Everyone else is saying that there PSW111 is pretty strong for the size. Not looking for anything earth-shattering, but I think the sound is pretty weak. Any suggestions or advice? Thanks.