only for use with mono optical soundtracks. Due to the use of dbx Type-II noise reduction, MCA eliminated the standard Academy Filter traditionally used on optical prints, thus giving Sensurround an increased frequency response of 16 Hz to 16 kHz and a dynamic range of 86 dB, superior to 70mm magnetic prints of the time. It also allowed a mono optical track to have surround sound effects and MCA began to market the system to other studios and producers as a truly high-fidelity sound and special effects system. Dolby Stereo optical was just beginning to become known in the industry and MCA felt they had a viable competing format. While Warner Bros. and Paramount seriously considered adopting the system, in the end only Universal Studios ever released films using the process. Both Warner and Paramount later patented their own "special effects" systems to create Sensurround-type effects. Sensurround Mod-III Mod-III Sensurround was a further refinement of the system to allow more control over level, timbre and placement of effects. Instead of a simple wide-range rumble that could be felt and heard, Mod-III used more narrow band extended low frequency effects in the 16–25 Hz range, in addition to the higher frequency program sounds and surround-sound effect. Thus, scenes could have dialogue and other audio at standard levels, plus the effect of movement from the infrasonic rumble, creating sensations that had not been possible in earlier Sensurround films. Mod-III Sensurround was used in Battlestar Galactica in 1978. Sensurround was a highly successful theatrical sound system. By 1976, when Midway opened, there were over 800 theaters with Sensurround capability in the US. Worldwide, there were over 2000 Sensurround theaters. During the initial design of the system MCA figured it would be installed in a limited number of theaters across the US—perhaps 30 in all—and that smaller theaters, or theaters in small towns, would not want to bother with the installation or the loss of seating capacity necessitated by the large Sensurround horns. This was quickly disproved: Earthquake premiered with 17 Sensurround installations and by the end of its run over 400 theaters had shown the film in Sensurround. Midway opened with 300 Sensurround-equipped theaters. At first, MCA only rented Sensurround to theaters at a cost of $500 per week, but by the opening of Midway, theaters could purchase the systems outright and MCA had begun to ship the Model-M horns to theaters un-assembled.