Before You Buy A Subwoofer

Martin Logan Dynamo 700w Wireless Subwoofer
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Subwoofers are crucial to the home theater experience. When you go to the movie theater, you marvel not only at the images projected on the screen, but the sounds emanating around you. What really grabs you, though, is the sound you actually feel; the deep bass that shakes you up and gets you right in the gut.

A specialized speaker, known as a subwoofer, is responsible for this experience. The subwoofer is designed only to reproduce the lowest of audible frequencies.

Passive Subwoofers

Passive subwoofers are powered by an external amplifier, in the same fashion as other speakers in your system. The important consideration here is that since extreme bass needs more power to reproduce low-frequency sounds, your amplifier or receiver needs to be able to output enough power to sustain bass effects in the subwoofer without draining the amp. How much power depends on the requirements of the speaker and the size of the room (and how much bass you can stomach!).

    Powered Subwoofers

    To solve the problem of inadequate power or other characteristics that may be lacking in a receiver or amplifier, powered subwoofers are self-contained speaker/amplifier units in which the characteristics of the amplifier and subwoofer are optimally matched.

    As a side benefit, all a powered subwoofer needs is a line output from a receiver. This arrangement takes a lot of the power load away from the amp/receiver and allows the amp/receiver to power the mid-range and tweeters more easily.

      Front-Firing and Down-Firing Subwoofers

      Front-firing subwoofers employ a speaker mounted so that it radiates the sound from the side or front of the subwoofer enclosure.

      Down-firing subwoofers employ a speaker that is mounted so that it radiates downward, towards the floor.

        Ports and Passive Radiators

        Some subwoofer enclosures also employ an additional port, which forces out more air, increasing bass response in a more efficient manner than sealed enclosures.

        Another type of enclosure utilizes a Passive Radiator in addition to the speaker, instead of a port, to increase efficiency and preciseness. Passive Radiators can either be speakers with the voice coil removed or a flat diaphragm. Instead of vibrating directly from the electrically transmitted audio signal, a passive radiator reacts to the air that is pushed by the active subwoofer driver. Since the passive radiator complements the action of the active driver, it helps to increase the low-frequency response of the subwoofer.


          The crossover is an electronic circuit that routes all frequencies below a specific point to the subwoofer; all frequencies above that point are reproduced the main, center, and surround speakers. Typically, a good subwoofer has a "crossover" frequency of about 100hz.

          Gone is the need for those large 3-Way speaker systems with 12" or 15" woofers. Smaller satellite speakers, optimized for mid-and-high frequencies, take up much less space and are now common in many home theater systems.

            Deep Bass is Non-Directional

            In addition, since the deep-bass frequencies reproduced by the subwoofers are non-directional (as frequencies that are at or below the threshold of hearing).

            It is very difficult for our ears to actually pinpoint the direction in which the sound is coming. That is why we can only sense that an earthquake seems to be all around us, rather from coming from a particular direction.

              Subwoofer Placement

              As a result of the non-directional sound that is reproduced by the subwoofer, it can be placed anywhere in the room. However, optimum results depend on room size, floor type, furnishings, and wall construction. Typically, best placement for a subwoofer is in the front of the room, just to the left or right of the main speakers, or in a front corner of the room.

              Also, many home theater receivers provide two subwoofer outputs - which provides more flexibility if you find that one subwoofer does not provide the results you are looking for or have a large room.

              Wired or Wireless

              A growing number of powered subwoofers offer wireless connectivity. This makes a lot of sense as powered subs have their own built-in amplifiers, and it eliminates the need for a long connection cable between the subwoofer and home theater receiver. A wireless-enabled subwoofer usually comes with a transmitter kit that can be plugged into the subwoofer outputs of any home theater receiver.

              The transmitter connected to the home theater receiver transmits the low-frequency audio signals to the wireless subwoofer, and then the receiver built into the subwoofer allow built-in amplifier in the subwoofer to power the speaker driver to produce the needed low-frequency sound.

                The Bottom Line

                Despite all of the technical specifications and design factors of subwoofers, the type of subwoofer you choose for your system depends on the characteristics of the room and your own preferences. When you go to a dealer, take a favorite DVD and/or CD that has a lot of bass information and listen to how the bass sounds through various subwoofers.

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