Subwoofers - What You Need To Know

All about Subwoofers, Bass Shakers, and Tactile Transducers

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

When you go to the movies, you are not only impressed with the large and colorful images on the screen, but the sound emanating all around you. What really makes the experience though, is the deep bass that shakes you up and gets you right in the gut. That deep bass is produced by a Subwoofer

What a Subwoofer Is

A subwoofer is a type of speaker that reproduces only the lowest of audible frequencies. In home theater, this is often referred to as LFE (Low-Frequency Effects).

Home theater surround sound is implemented by 5 or more channels, with each channel represented by a speaker. The surround sound channel dedicated to the subwoofer is referred to as the .1 channel.

With home theater sound systems requiring 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 a home subwoofer is not quite as "thunderous" as the ones at the local movie theater, it can still shake the house down or annoy the downstairs neighbors in your apartment or condo complex.

Types of Subwoofers

  • Passive: This type of subwoofer is powered by an external amplifier, in the same way as the other speakers in your system. If using this type of subwoofer, keep in mind that extreme bass needs more power to reproduce low-frequency sounds. This means an amplifier or receiver needs to be able to output enough power to sustain bass effects via the subwoofer without draining the amp. The amount of power depends on the requirements of the speaker and the size of the room (and how much bass you can stomach!).
  • Powered: Powered subwoofers combine the subwoofer speaker and an amplifier inside the same cabinet. All a powered subwoofer needs, in addition to AC power, is a line output (sub out, pre-out, or LFE out) from a home theater receiver in order to operate. 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. Most subwoofers used in home theater setups are the powered type.

For more on the differences and how to hook-up passive and powered Subwoofers, read our companion article: Passive Subwoofers vs Powered Subwoofers.

Additional Subwoofer Characteristics

There are also additional design variations and setting options employed in subwoofers to further optimize low-frequency performance.

  • 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: In addition to the speaker portion of the subwoofer, some enclosures have 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.
  • Passive Radiator: Some subwoofers utilize 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: 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. A typical crossover point would be between 80Hz and 100Hz.
  • Directionality: Deep-bass frequencies reproduced by a subwoofer are non-directional. It is very difficult for our ears to actually pinpoint 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. Due to the non-directional characteristics of extreme low-frequency sound, a subwoofer can be placed anywhere in the room where it sounds best in relation to room size, floor type, furnishings, and wall construction.

Subwoofer Installation Tips

Typically a subwoofer is placed in the front of a room, near the front left or right main speaker. However, they can also be placed on a side wall or in back of the room. Where it sounds best will determine the final placement.

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 to the settings available on the subwoofer, most home theater or AV receivers have crossover (also referred to as bass management) settings for your subwoofer as well. Using either crossover setting option, a subwoofer can either take the entire bass load or split the bass load with large main speakers.

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

For some additional subwoofer installation tips, check out our companion articles on Lifewire:

Beyond The Subwoofer

ButtKicker Advance
ButtKicker Advance. Image via ButtKicker

Since the subwoofer experience entails more of what we can feel rather than what we can hear, using a loudspeaker-based design is not the only approach that can be used to reproduce low-frequency information. If you really want to pump things up consider the following compliments to your home theater and subwoofer setup.

The Buttkicker: The Buttkicker in not a traditional subwoofer. It is a low-frequency transducer that not only puts more feeling in your bass but...Kicks Butt! Using a "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 some movie theaters, and concert halls, but has been adapted for use in a home theater environment.

Clark Synthesis Tactile Sound Transducer: Don't just hear the 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 a deep bass response that is both intimate and effective.

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. Examples of Bass Shakers included offerings from Aura Sound, Dayton Audio, and Soundshaker.

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 a 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. If someone is sitting in the chair, they will feel the direct effect of the linear drive process on their body. This requires much less energy to produce vibration effects than other methods, enabling a more dynamic effect with faster response times. Crowson Tactile Transducers can capture the subtle vibrations of a car driving on a country road or the big boom of an atomic bomb explosion.

Tactile Transducer/Bass Shaker Installation

Each brand/model of Tactile Transducer or Bass Shaker has specific installation requirements that are provided by the manufacturer, but in general terms, these devices are usually placed between the floor and a chair, couch, or furniture legs, or attached directly to them, and, in some cases, you can purchase home theater seating with such devices already built-in. Also, since these devices work below the range of human hearing, they should be used in conjunction with a traditional subwoofer, not in place of it.

Although transducers and shakers are very effective for effects that contain a lot of inaudible low-frequency information, such as explosions, earthquakes, gun blasts, rocket and jet motor effects, they 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.

The Bottom Line

When it comes to home theater, it takes more than just one component to deliver the full experience, and the inclusion of a Subwoofer is definitely a major part as it provides the punch that brings those great TV images to life.