If you went to see Earthquake (1974) at a cinema, chances are that it was in “Sensurround”.
The Sensurround system was designed to envelop the audience with special audible and low-frequency infrasonic effects. The audience experienced the illusion of participation when they felt the movement of air generated by powerful Sensurround horns, designed to send vibrations against the bodies and ears.
All this really meant was that the seats vibrated . . . and lots of women left the cinema with flushed faces at the end of the movie.
In Earthquake, the rumbles were intended to simulate the tremors of the quake and were played at 110dB to 120dB and ranged from 16Hz to 120Hz – the exact waveform of the 1972 Sylmar earthquake.
Doctor’s claimed this new effect damaged your eardrums, but it sure was fun.
The full list of movies featuring a Sensurround soundtrack is Earthquake (1974), Midway (1976), Rollercoaster (1977), Battlestar Galactica (1979) and Zoot Suit* (1981). The effect was retired thereafter.
* I can understand why you would want bowel-rumbling effects with the first four – even the titles sound a bit sensurround-ish – but why the hell would you need Zoot Suit in tackle-wobbling sub-Woofer vibration?. Just thought I’d ask . . .
PS: You can re-create this effect at home by sitting on the washing machine while watching the TV.