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Subwoofers received a great deal of publicity in 1974 with the movie Earthquake which was released in Sensurround.

Initially installed in 17 U. S. theaters, the Sensurround system used large subwoofers which were driven by racks of 500 watt amplifiers which were triggered by control tones printed on one of the audio tracks on the film.

Four of the subwoofers were positioned in front of the audience under ( or behind ) the film screen and two more were placed together at the rear of the audience on a platform.

Powerful noise energy in the range of 17 Hz to 120 Hz was generated at the level of 110 – 120 decibels of sound pressure level, abbreviated dB ( SPL ).

The new low frequency entertainment method helped the film become a box office success.

More Sensurround systems were assembled and installed.

By 1976 there were almost 300 Sensurround systems leapfrogging through select theaters.

Other films to use the effect include the WW II naval battle epic Midway in 1976 and Rollercoaster in 1977.