The 12-inch woofer is selling by unit(s). It is a part specially designed for Better Music Builder and Nissindo speakers, and may serve as a part for other speakers. However, please make sure that this 12-inch woofer can be used by your speaker. If not, you may need to buy a crossover for this woofer. The 12-inch woofer is in premium grade for speakers that are made of piano woods for high quality sound for music and vocal singing. SoundTek Music, Inc. is a distributor of parts for both Better Music Builder and Nissindo products.