Subwoofers - What You Need To Know

EMP Tek Cinema 7 - E10s Powered Subwoofer - Quad View Photo
EMP Tek Cinema 7 - E10s Powered Subwoofer - Quad View Photo. Photo © Robert Silva - Licensed to

How do subwoofers affect your Home Theater experience? What is a subwoofer, anyway?

Subwoofer Types and Characteristics

Buying a subwoofer is becoming more and more necessary when it comes 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. In home theater, this is often referred to as LFE (Low Frequency Effects.

The surround sound channel that is dedicated to the subwoofer is referred to as the .1 channel.

With the popularity of home theater sound systems resulting in specialized speakers for center channel dialog, main soundtracks, and surround effects, the need for a speaker to reproduce just the deep bass portion of a movie soundtrack is all the more important. Although these subwoofers are not quite as "thunderous" as the subwoofers employed at the local movie theater, these unique loudspeakers can still shake the house down or annoy the downstairs neighbors in your apartment or condo complex.

Subwoofers come in two basic types, Passive and Powered.

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 configurations in which the characteristics of the amplifier and sub woofer are optimally matched.

As a side benefit, all a powered subwoofer needs is a line output from an amplifier. 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.

For more on the differences and how to hook-up Passive and Powered Subwoofers, read my supplementary article: Passive Subwoofers vs Powered Subwoofers.

Additional Subwoofer Characteristics

Additional subwoofer design variations include Front-firing , and Down-firing, and the use of Ports or Passive Radiators.

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. In addition, some enclosures 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.


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


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 pin-point 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. As a result, the subwoofer 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. There are more installation tips in the conclusion of this article.

Subwoofer Alternatives

Since the subwoofer experience entails more of what we can feel than what we can hear, using a loudspeaker-based design is not the only approach that can be used to reproduce low frequency information. For some interesting alternatives to the traditional subwoofer, consider the following:

The Buttkicker

More than just a subwoofer, the Buttkicker is a low frequency transducer that not only puts more feeling in your bass, but....Kicks Butt! Using a unique "suspended magnetic system" to reproduce sound waves that are not air dependent, the Buttkicker can reproduce frequencies down to 5HZ. This is well below human hearing, but not below human feeling! Variations of the Buttkicker are found in professional settings, such as movie theaters, and concert halls, but have been adapted for use in your own home theater.

Clark Synthesis Tactile Sound Transducer

Don't just hear sound, touch it! With a very compact transducer design, the Clark Synthesis Tactile Sound Transducer can be placed inside (or on the bottom of) chairs, couches, etc... to produce deep bass response that is both intimate and effective (others in the room will wonder what is getting you so excited!).

Crowson Technology Tactile Transducers

The key technology employed in Crowson Tactile Transducers is Linear Direct-Drive. Instead of vibrating air, like a subwoofer, or employing a piston that vibrates inside housing that indirectly transfers the shaking sensation to a chair, such as a bass shaker (both of which take of energy), Linear Direct Drive transfers sonic vibrations directly through the chair itself via its feet, which is similar to techniques used in direct hearing via human bone conduction. Thus, if someone is sitting in the chair, they will feel the direct effect of the linear drive process on their body.

This method requires much less energy to produce vibration effects than other methods, thus enabling a more dynamic effect with faster response times. In other words, the Crowson Tactile Transducer can capture the subtle vibrations of a car driving on a country road to the big boom of an atomic bomb explosion.

Bass Shakers:

Bass Shakers are another type of transducer device designed to reproduce inaudible low frequencies, designed to give an extra "punch" to your sound system. The Shaker is usually attached directly to the object to be "shaken", such as a chair (similar to the Clark Tactile Transducer) in order to realize its effect. Bass Shakers can be used not only by themselves, but in conjunction with a traditional subwoofer setup.

Some examples of Bass Shakers are listed on

One final note on these subwoofer alternatives. Although very effective in home theater setups for effects that contain a lot of inaudible low frequency information, such as explosions, earthquakes, gun blasts, rocket and jet motor effects, Shakers and Tactile Transducers are not very effective in the typical home music listening environment. A good, traditional, subwoofer is more than adequate for the lowest musical effects, such as bass drums.

Subwoofers - Shopping and Installation Tips

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.

In addition, make sure you find out the return policy of your dealer, just in case the subwoofer doesn't perform well in your listening environment. Place the subwoofer in various parts of the room, using the owner's manual as a guide, to find out what sounds pleasing to you.

The subwoofer should not sound "boomy", but deep and tight. This is especially important if you intend to use your subwoofer for music listening. Many subwoofers are great for Blu-ray Disc or DVD movies, but may not perform well with the subtle deep bass in music performances.

When installing your subwoofer, experiment with the crossover settings. In addition, most AV receivers have internal crossover settings for your subwoofer which depends on whether your other speakers are large or small. In this way your subwoofer can either take the entire bass load or split the bass load with large main speakers, with the subwoofer only producing the very lowest bass frequencies.

Also, if you live in an upstairs apartment, a down-firing subwoofer may disturb your downstairs neighbors more easily that a front-firing design. Lastly, in some cases, integrating two subwoofers into your system may provide a better option, especially in very large room.

For some additional subwoofer installation tips, read the following articles from Stereos: How to Get the Best Subwoofer Performance, How to Connect a Subwoofer to a Receiver, Processor, or Amplifier, and The Benefits of Using Multiple Subwoofers.

To get you started in finding a subwoofer that may be right for your system, check out my list of  subwoofers and subwoofer brands.