What Makes Your Seat Shake in the Movie theater? Subwoofers Explained
You don’t just hear the soundtrack at a movie theater. You feel it. It rattles your seat and hits you in the gut. Since their first use in the 1974 film Earthquake, subwoofers are now an indispensable component of home theaters and live public address systems.
Subwoofers are speaker enclosures using 8 to 21 inch drivers dedicated to handling only the lowest part of the sonic spectrum, which explains why they are so large. The bass signal is routed to the subs through a crossover, which prevents the subwoofer from trying to reproduce the higher tones and the main speakers from trying to reproduce the deep bass tones intended for the subwoofer. Since the subs are carrying the bottom load, the main speakers can be smaller.
Subwoofers require more power than the main speakers because they have to push more air, which explains why subwoofers frequently have their own power source. This power source can be either built in (powered), part of the main system, or a stand-alone component to the main system (passive). Powered subs have the advantage of not drawing from the total power output of the main speakers.
Satellite home theater speakers systems usually have one omni-directional sub woofer and 5 satellites speakers with 4 to8 inch drivers. They are placed in the 4 corners of the room and directly in front of the television screen, giving a realistic stereophonic experience. Subwoofers have rigid, heavy cabinets that resist vibration to prevent hearing the box and not the speaker.
To paraphrase Chubby Checker, how low can they go? Very low, thank you. Home subwoofers cover a range from 20 to 200 Hz. Subs used for sound reinforcement in nightclubs cover the ultra low and painfully loud sub-100 Hz tones. THX-approved systems for movie theaters solely cover the range below 80 Hz.
Subwoofers were first used to add bass response to high-end stereo systems. Vinyl recordings had a built-in limit on bass output. The signal could only be as loud as the tone arm and needle could handle. Reel to reel tape systems and CD’s enabled the bass signal to go far lower and be much louder, which required subwoofers to handle the low tones.
Car stereos are notorious for their subwoofers that are built into the trunk or backseat. The small interior dimensions can make it painful to endure the volume and in some cities, the stereos violate noise ordinances. The limited space led to the invention of square speaker drivers for subwoofers.
Subwoofers make entertainment more vital and inclusive. Three dimensional video and subsonic, seat-shaking audio create a truly unique viewing experience at the Cineplex. Home theaters boast a professional feel. And, when you hit the dance floor, you’ll never lose the beat—not when it’s pounding a tattoo on your gut.
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