Best Buy is selling what they term a "Celestion 200 Watt powered subwoofer" which is further described as S-20 for a hundred dollars. I need a powered subwoofer, and I do not have money to burn. Understand that I am not looking for ultra good bass reproduction, &c., I have cheap primary speakers and a cheap amp because my ears are not good enough to make out the nuances, I just want to be able to hear the sound. But by the same token, if it does not fulfill its function of supplying the low-frequency components my bookshelf-model speakers omit, it's no use to me. So: on those grounds, should I buy it? Anybody have any experience? Thank you.