How Do Subwoofers Work?

You know that a home stereo setup has left and right speakers, but you may wonder how do subwoofers work as a third speaker. It is the job of speakers to faithfully reproduce sound from their source, whether it be from records, CDs, tapes, or TV. Subwoofers enhance the audio so that the listener can actually "feel" the low frequency components of the sound.

  1. Connect a subwoofer to a home stereo receiver or to a home theater stereo receiver by using the mono line output jack marked "subwoofer" on the back of the receiver. A stereo receiver will have jacks or screw terminals for a left speaker and a right speaker, and a jack for the output to a subwoofer. A home theater receiver may also have outputs for rear and side speakers, if it supports surround sound.

  2. Position a subwoofer at home in between the left and right stereo speakers. The subwoofer works by reproducing the low frequency content of the music or audio material. While traditional stereo speakers used for the right and left channels reproduce low frequencies, these frequencies require additional amplification to "move air" in the room and give them sufficient volume. Subwoofers have amplifiers built into their cabinets to increase the volume of the material they reproduce. When purchasing a subwoofer, the amplification section will be listed in watts, with about 100 watts being typical, but upwards of 250 watt subwoofers are available.

  3. Low-pass filter circuitry is also contained inside a subwoofer’s cabinet. This filter only allows the low frequency content of the audio signal to be amplified. This band of frequencies typically ranges from about 150 Hz down to 15 Hz. With the extra volume given to the sound in this range, reproducing material such as explosions and earthquakes often found in action movie soundtracks, the listener not only hears the sounds but can physically feel the vibrations coming from the subwoofer. This enhances watching movies, adding another sense to the audio and visual experience.
  4. Choose a subwoofer with a large speaker for best performance. Although subwoofers are available with speakers as small as 6-inches in diameter, a 12- to 18-inch speaker is optimum for reproducing low frequencies, due to the physics of loudspeakers. These can also handle more volume, increasing the sound pressure level (SPL) needed to drive the sound throughout the room.
  5. Subwoofer cabinets are also part of the design that makes subwoofers work best at reproducing low tones. Some cabinet enclosures are sealed air-tight, while others use a ported enclosure design. Both are engineered to give excellent sound, and you can purchase either type and be confident about getting good performance.
  6. Subwoofers for cars and trucks are also popular, but due to space limitations, they are not feasible for all vehicles. Because of the small listening environment in a car or truck cab, subwoofers with high wattage amplifiers are not really necessary, although many vehicle owners like to hear music at concert levels.

Our generation of music technology today contains a wide spectrum of audio frequencies, and subwoofers work to make that music more exciting.



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