Subwoofers - What You Need To Know

Klipsch Reference Subwoofers
Klipsch Reference Subwoofers. Image provided by Klipsch Group

What a Subwoofer Is

When you go to your local movie theater, you marvel not only at the large and colorful images projected on the screen, but the sounds emanating all 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, referred to as a subwoofer, is responsible for that deep bass 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, surround, and sometimes even height 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.

Buying a subwoofer is a necessity when it comes to the home theater experience.

Types of Subwoofers

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 inside the same cabinet, in which the characteristics of the amplifier and subwoofer are optimally matched.

As a side benefit to the combining a speaker and an amplifier in the same cabinet, all a powered subwoofer needs is a line output from a home theater 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.

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 are employed to further optimize how frequency performance. These variations include the use of Front-firing and Down-firing speakers, as well as the use, in some cases, 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. This type of ported design is referred to as Bass Reflex.

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.

Crossovers

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.

Directionality

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 these types of sounds are 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 od the omni or non-directional characteristics of extreme low frquency sound, 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, that can really shake things up consider the following:

The Buttkicker

More than just a subwoofer, the Buttkicker is a type of 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 a home theater environment.

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 Amazon.com.

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 acoustic bass and bass drums.

Shopping 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.

Installation Tips

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 home theater or 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, check out our companion articles on Lifewire:

To get you started in finding a subwoofer that may be right for your system, check out our listing of Subwoofers and Subwoofer brands.