My wife had a new Alpine stereo/CD player installed for my B-day on Sat. She also replaced the 4 door speakers with some new Pioneers. There are 3 speakers in the rear, 2 small ones mounted in the ceiling and one round one on the right side. I tore those all out today B/C they do not work. My question is what is the bottom one/ I sit just a speaker or is it a Sub woofer? There is a transformer or something attached to it and it appears that maybe the two small ones from the ceiling are also tied into it. Has Anyone replace these? If so with what. Thanks