Subwoofers are speakers designed to amplify low frequency vibrations. Their first widespread commercial use was in movie theaters for the 1974 disaster film Earthquake. Dubbed “sensurround,” this new technology consisted of carting subwoofers into theaters and feeding them frequencies low and loud enough to make seats shake. “Please be aware that you will feel as well as see and hear realistic effects such as might be experienced in an actual earthquake,” the poster warned. “The management assumes no responsibility for the physical or emotional reactions of the individual viewer.” At the time, New York magazine critic Judith Crist dismissed the rumbling gimmick as having “all the effectiveness of a drop-a-quarter-in-the-slot motel massage bed.” But audiences flocked to it.

Physical and emotional reactions to extremely low frequencies, or infrasound, have long fascinated military researchers as well as Hollywood special effects departments. In the book Extremely Loud: Sound as a Weapon, Juliette Volcler asserts that much of that military research is, like the warning on those Earthquake posters, probably bunk: Theories about how certain low frequencies could make eyeballs explode or the existence of a “brown note” which would reduce enemies to “quivering diarrhoeic messes” proved to be no more than twisted fantasies. (Sound weapons do exist—witness the Long Range Acoustic Devices deployed by police departments on both Occupy Wall Street and Black Lives Matter protestors—but operate under different principles than infrasound, chiefly volume.)

There is a medium where twisted fantasies need be no more than that: video games. The gaming industry’s use of low frequencies combines the cheap Hollywood effect of shaking your seat with the military’s dreams of violence, and its tremendous popularity is one of the reasons there are now so many subwoofers in American homes.

Still, none of this explains how subwoofers came to be seen as important to music. In the ‘70s, apart from an audio engineer who claims he built one to help mix the Steely Dan album Pretzel Logic (more twisted fantasies), subwoofers seem to have barely made an impression on the broad commercial music industry, via neither producers nor consumers.

One simple explanation for that is the LP. Long-playing vinyl records don’t do a good job of reproducing the loud, low frequencies that subwoofers are made to amplify, frequencies that can bounce the needle out of an LP’s microgrooves. Which meant that even Pretzel Logic—mastered and pressed as an LP—couldn’t benefit from the sound system it had been mixed on.

Twelve-inch vinyl singles, with their wider grooves, allow for more bass volume, and starting in the mid-‘70s they began to be used for disco, reggae, dub, and then hip-hop and bass-driven rock bands like New Order. Originally pressed expressly for dance clubs, these records—unlike the LP, or the 7" 45—can (and do) play to effect on systems with subwoofers, and it’s in those clubs that the intended “physical or emotional reactions” of such equipment first crossed with the world of music. At New York’s legendary Paradise Garage, the custom designed “sub-bass” speakers were even named for DJ Larry Levan: the Levan Horn.

Outside a disco, though, you wouldn’t find music playing on anything like a Levan Horn. The analog era ended with no one but Steely Dan hearing Steely Dan on a subwoofer.