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Understanding Your Subwoofer

  • 7 min read

To experience great home theater audio, you need a subwoofer. The subwoofer’s purpose is to complement a speaker system by reproducing the lowest audio frequencies that add dramatic bass impact in movies and bring the beat to your music. If a speaker system includes a subwoofer, it is generically referred to by the term .1. For example, there are 2.1, 5.1, and 7.1 speaker setups

However, when referring to surround sound formats, such as Dolby Digital 5.1 or DTS 5.1, the .1 more refers explicitly to an LFE (Low-Frequency Effects) channel. Movies and select programs are usually mixed with specific low-frequency information that is pre-assigned only for the subwoofer to reproduce. 

The Relationship Between the Subwoofer and Other Speakers

Before digging deeper into the subwoofer, here is a quick summary of what other speakers in a home theater system do. 

The Center Channel speaker is designated for dialogue or music vocals. It’s the most active speaker in a system. In a movie or TV show, if the only thing going on in a portion of a movie or program is the main dialog, the other speakers and subwoofer may be silent. 

TheLeft/Right Front Channel speakers direct the main part of the soundtrack to the listener. The center channel information is not placed in these channels if a center channel speaker is in use. If there is no center channel speaker, most home theater audio setups allow you to assign the center channel sound to the left and right front channel speakers. This creates a Phantom channel in which the center channel information appears to come from the space between the left and right front channels.

TheLeft and Right Surround Channel speakers are mainly for sound effects and ambient sounds present in select movie scenes and musical performances. In some cases, sound effects may move from the front channel speakers to the surround channels or vice versa. Surround channels add more depth and immersion. Surround back and surround height channel speakers may also be included for additional sound effects, depending on your setup.

What a Subwoofer Shouldn’t Sound Like

A subwoofer should not be so loud that it overwhelms your other speakers, and should not be too boomy or muddy. 

If you are hearing boomy bass it means instead of producing the loudest bass at the lowest frequencies the subwoofer is producing the loudest bass at upper bass frequencies that may also bleed into lower mid-range frequencies. 

If it is too muddy, that means the subwoofer isn't separating the tiers of low-frequency sounds so that they are well defined. For example, an earthquake sounds different from an explosion or a thunderstorm and acoustic bass sounds different from an electric bass.

If the bass is too loud and/or boomy, it can cause listening fatigue, as well as ear damage. Although there are times where the bass can (and should) get very loud for dramatic effect, the impact is usually intended to be momentary or alternates with less impactful bass sounds (such as rolling thunder and heavy vehicles passing by). Throughout an entire movie, program, or music the bass frequencies should be low, tight, distinctive, and not always at the same volume level.

Low-Frequency Drop-Off

A problem you may encounter with subwoofers (especially cheap ones) is excessive low-frequency drop off. A good subwoofer can reproduce deep bass. When buying a subwoofer look closely at the frequency response specifications.

However, just because a subwoofer may be listed as having a low-end frequency point of 25 Hz or 30Hz, you have to look at the dB qualifier, which tells you how loud it will be in relation to a set volume level at that frequency. 

For example, if the Subwoofer specs state that it is -3 or -6 dB down at 25 or 30Hz, that means at that frequency point, the sound output is a lot less than it would be at 50 or 60Hz or higher frequency the subwoofer may be assigned reproduce. This can be a cause of boominess as frequencies approaching mid-bass are louder than the lower frequencies. 

Although you can increase the subwoofer volume of the lowest frequencies, you will also be increasing the volume of the higher bass frequencies, which contributes to a subwoofer that will be too boomy. Increasing the subwoofer's volume too much may also result in distortion if the amplifier and the speaker can't provide enough power for higher volume levels at the lowest frequencies. It takes more power to produce the same volume for low frequencies than mid-range and high frequencies.

Subwoofers Only Produce Sound When Needed

Another thing to keep in mind is that the Subwoofer is not always producing sound, nor should it be. For example, in movies, the subwoofer is only active when there are deep sounds - such as explosions, loud motors or vehicles, thunder, spaceship engines, something heavy is dropped, etc... If the only thing that is going on is dialog or low volume background noise, the subwoofer is most likely going to be silent.

On the other hand, depending on the music performance, a subwoofer may be active either intermittently or continuously, such as with acoustic bass, electric bass, kettle and bass drums, and the lower tuba and pipe organ pedal notes. Also, if the content doesn't have frequencies low enough for the subwoofer, then the subwoofer won't reproduce them.

Subwoofer Sound Should Be Non-Directional

Deep-bass frequencies coming from a subwoofer are non-directional. It's more difficult to pinpoint the direction of the sound as frequencies get lower as frequency waves are much longer (sometimes as long as the room). That is why we can only sense that an earthquake seems to be all around us, rather than coming from a particular direction. 

Due to the non-directionality of extreme low-frequency sound, a subwoofer can be placed anywhere in the room where it sounds best in relation to the room size, floor type, furnishings, and wall construction. If you can detect where subwoofer sound is coming from, it means that the subwoofer is producing frequencies that are too high for its role. This may require resetting the crossover frequency.

The Crossover

Subwoofers have an electronic circuit (referred to as a Crossover) that sets a point that tells the subwoofer what frequencies to reproduce. Frequencies above the crossover point are sent to the main, center, and surround speakers. 

A typical crossover point is between 80Hz and 100Hz. The crossover optimizes frequency distribution so that there is a smooth transition between the frequencies produced by the subwoofer vs frequencies produced by the rest of the speakers. Depending on the brand/model of a subwoofer, the crossover may already be set to a fixed point or might be adjustable via a crossover control.

Subwoofer Placement 

Where you place a subwoofer in a room also plays an important part in getting the best performance. You may encounter a "dead zone" where low frequencies are minimized. Improper subwoofer placement can also contribute to boomy or muddy bass. 

Although a subwoofer is commonly placed in the front of the room, you may find that it sounds the best midway along a side wall or in the back of the room. 

When placing a subwoofer, don't put it right up against the wall. Allow several inches of space between the subwoofer and the wall. If you have a front-firing subwoofer make sure that the speaker is facing into the room and not into the wall. 

Subwoofer Listening Checklist

When choosing and setting up your subwoofer, keep the following in mind.

  • Does your Subwoofer sound tight and punchy, delivering the proper texture and impact for low frequencies?
  • How low does your subwoofer go without a significant drop off in volume?
  • Does the subwoofer respond quickly?
  • Does the subwoofer recover quickly if there is a series of low-frequency content coming at a rapid pace?
  • Does the Subwoofer blend well with the rest of your speaker system?

If the answer is Yes to the above questions, you have a good subwoofer that is placed properly.

If the answer is No to one or more questions, and the issue can't be corrected by better placement or setting adjustment, then you have a subwoofer that is lacking.

Types of Subwoofers

When considering a subwoofer (or an additional sub if you already have one), don't just let price be the deciding factor. Design variations and setting options help optimize low-frequency performance.

  • Front-firing Subwoofer: This type of subwoofer uses a speaker that radiates sound from the front of the subwoofer cabinet into the room. 
  • Side-firing Subwoofer: Instead of the front, this type of subwoofer may have a speaker mounted on one or both sides of the subwoofer cabinet.
  • Down-firing Subwoofer: This type of subwoofer uses a speaker that radiates sound downward, toward the floor which spreads the sound throughout the room. In a sense, the floor becomes part of the subwoofer.
  • Subwoofer with Port: Some subwoofers have a port in addition to the speaker. The port supports the speaker by pushing out more air from the cabinet. This increases bass response more efficiently, but the result is not always as precise. 
  • Subwoofer with Passive Radiator: Some subwoofers have a passive radiator rather than a port to increase bass output without adding another speaker in a subwoofer cabinet. If designed well, this is more precise than a port. Passive radiators oftentimes look like a speaker with the voice coil removed but may also be a specifically "tuned" flat diaphragm placed where a port would normally be.

Enclave Audio Subwoofers

Enclave Audio provides two wireless home theater systems (CineHome II and the THX Certified CineHome Pro) where all the speakers and subwoofer are matched. This means that the crossover points have been predetermined to provide the smoothest transition between the subwoofer and the rest of the speakers so you don’t have to guess where to set it. They provide tight, punchy bass for movies and clear bass for music.

Enclave Audio also provides a control app (iOS, Android) and CineSync for select TVs, projectors, and other devices. Enclave Audio can also be integrated with Roku TVs via the Roku TV Ready™ feature. These options allow you to set the speaker distance and sound output levels so that the speakers and subwoofer are optimally balanced for your specific room. 

The CineHome II subwoofer features an 8-inch down-firing speaker, whereas the THX-Certified CineHome Pro subwoofer features a 10-inch front-firing speaker. Both subwoofers are WiSA-certified and incorporate Class-D Digital Amplifiers.

In addition to the subwoofer that comes packaged with each system, you can add up to three more subwoofers. To dig deeper on how to determine if you can benefit from multiple subwoofers as well as additional subwoofer placement tips, check out our reference article: 5.1 vs 5.2

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