It has two "12-inch woofers and two horn tweeters". Virtually every loudspeaker today uses Villchur's innovations&colon; Acoustic Suspension Woofers and Dome Tweeters. Modern tweeters are typically different from older tweeters, which were usually small versions of woofers. The drivers that produce the sound are referred to as tweeters, midranges, and woofers. A rigid construction is necessary to optimize the working environment for both woofers and tweeter. Cone mid-range drivers typically resemble small woofers. Image Dynamics speakers, JL Audio woofers, and Alpine head units were also featured. The surround arrays are bass managed by woofers suspended from the ceiling. Sometimes the woofers have a cardioid characteristic. They featured 10" or 12" woofers and often twin mid-range drivers in a ported enclosure. There have been good and bad woofers made with every type of cone material. Hz; such drivers are commonly termed "mid woofers". High fidelity woofers were also vulnerable to damage from extreme low frequency signals. In concert sound, Showco began using ferrofluid in 1979 for cooling woofers. Less common types of drivers are supertweeters and rotary woofers.