UL-115 Subwoofers,The Peavey UL115 features 1000w program power and 1 x 15" Black Widow sub woofer bass speaker, Bass subs or bass bins are used in conjunction with smaller speakers often called satellite speakers. The sub bass bins handle all of the lower frequencies and the built in x-over routes the mids and tops frequencies to smaller satellite speakers . This is a 2-way or two way passive cross over PA system. A 2 way PA speaker system is extremely efficient. The low frequency bass sounds use a lot of power and need a larger speaker to reproduce the sound. Using a sub bass bin speaker cabinet means that the larger slower moving speaker in the sub bass bin is optimised for bass frequencies. The smaller and lighter satellite speakers can then handle the mid range and tops frequencies more efficiently because they are much smaller.