Passive Subwoofer Vs. Powered Subwoofer
By David James
Almost everybody loves loud bass. Whether it's the pounding bass that throbs throughout your favorite music, or the rumbling bass that bellows out from your surround system during the most intense scenes of your favorite movie, the bottom line is that you've got to have it. Buying a subwoofer is the most direct route to those sweet bass sounds you love so much. There are two types of subwoofers available: passive and active (or powered).
The Beginning of the Subwoofer
The inventor of the subwoofer is Ken Kreisel of Miller & Kreisel Sound (M&K). The first subwoofer was installed in 1973 by Kreisel as part of a three-speaker monitoring system in a recording studio, and was used for the mixdown of Steely Dan's Pretzel Logic album, as noted at Kreisel's own website. In 1974 M&K was officially founded in Beverly Hills, and by the '80s subwoofers became a standard component in home theaters and commercial movie theaters alike. Since then, there have been many advances in the technology of subwoofers and Kreisel has stayed on the cutting edge.
A subwoofer is classified as passive if it needs an amplifier to power it. A good example of a passive subwoofer is the kind used in cars. Essentially it is just a big speaker or group of speakers in a ported box. A passive subwoofer sometimes may have a built in crossover that prevents high frequencies from passing through the speaker's cone, but it doesn't have its own power supply. Most passive subwoofers only have connections for the speaker wires.
A subwoofer is classified as active if it has a built in amplifier and its own dedicated power connection. This type of subwoofer is more common in home theaters, commercial movie theaters and other surround sound systems. Active subwoofers are also frequently referred to as powered subwoofers. Usually, active subwoofers require line-level inputs such as RCAs or 1/4-inch TRS audio cables, although some designs allow for high-level inputs such as speaker wire.
When to Use a Passive Subwoofer
You can use a passive subwoofer if you need a separate amplifier for your bass, or if your surround system's receiver has a built in amplifier dedicated to the bass channel. The use of passive subwoofers is not very common in home theater systems although it may be beneficial if you plan on using multiple subwoofers in your setup, since you can connect them all in series using a single powered amplifier, and a single crossover if necessary. Following a similar concept, you can also run your main stereo inputs in series from your receiver to a stereo amplifier, then route the separate left and right channels from the amplifier through crossovers and on to passive subwoofers, thereby creating designated left and right bass channels, and a more separated bass surround sound.
When to Use an Active Subwoofer
Active subwoofers are quite commonly used in home theater systems because most surround sound receivers do not include a built-in amplifier for the bass channel. If you only plan on using a single subwoofer for your setup, which is often the case, it is more economical to purchase a single self-contained powered subwoofer than to invest in a separate speaker, amplifier and crossover. Aside from that, powered subwoofers have no need for special wiring configurations so if simplicity is your goal, active subwoofers can help you achieve it.
David James started writing professionally in 1990. He was first published at poetry.com, and his work now appears on eHow and Answerbag. His writing focuses on audio and studio engineering and music production. He is pursuing a Bachelor of Arts in electronics engineering from St. Petersburg College.