What is a subwoofer?
A subwoofer is a speaker that is designed to produce the lowest frequency range of audio range. (bass) 20Hz-200Hz.
Why do I need a subwoofer?
To add the frequency range that is not able to be produced by the speakers for a more full experience. Bookshelf speakers and even Floor standing speakers will produce some bass but very rarely you can find a speaker that can go as low a a dedicated subwoofer can.
While you may hear the bass from your bookshelf or floorstanding speakers, a subwoofer allows you to feel the sound. Listening to bass-heavy music like hip hop or EDM or watching a full-throttle action flick without a subwoofer leaves a lot to be desired. Plus, you’re not experiencing the song or movie the way the artist or director intended.
You might be asking yourself: I don’t listen to rap or watch action movies, so why do I need one?
Sure, a subwoofer is a bass-thumping juggernaut, but that’s only scratching the surface. A great subwoofer helps take away the heavy lifting from your loudspeakers, improving your overall system.
The dynamics are more compelling, the soundstage widens, and the stereo imaging becomes more accurate. Even if you prefer spinning folk records and watching dialogue-driven indie dramas, a subwoofer helps produce a more vibrant, all-encompassing sound.
Active subwoofers - this is the most popular kind of a subwoofer in a home theater/home audio world. Active subs will have an amplifier plate that drives the sub built in - see image below.
Passive Subwoofers -
These subs will require an amplifier to produce sound. See the back of this Klipsch THX-1200-SW below, it has an Neutrik connector for amplifier connection (KA-1000 amp is required for this subwoofer).
Passive subwoofer style is often popular in a scenario where having a power amplifier is not convenient or just not a good idea like - outdoor, in wall and in ceiling subs, professional applications.
See some examples of install subs from Klipsch - https://www.klipsch.com/custom-install/subwoofers
Subwoofer placement can greatly impact its performance! As the low frequency waves produced by the subs are large and most systems are setup in peoples living rooms with less than ideal acoustical properties for a sound system you may find some significant changes in how your subwoofer sounds in your primary listening position depending on where the sub is located in the room.
You do want to find a spot in the room that make the subwoofer sound best from your audience perspective. There are a few different techniques to find a good place for the sub and a couple things to consider as well.
Corner loading - subwoofer output will be amplified if it is placed near a wall or even more so if it is placed in the corner of the room. That being said that extra amplification may not be necessary, if you have a powerful sub and the room sounds a bit "boomy" You may want to pursue a tighter response by placing the subwoofer further away from walls/corners.
Since the subwoofer produces only the lowest frequencies that aren't perceived by us directionally, the sub doesn't have to be placed in a specific spot for proper imaging.
One of the better methods of finding a good spot for the sub is - place the subwoofer in the primary listening position and play test tone, or a track with consistent bass. Then - walk around the room listening to the track/tone looking for the spot where the bass sounds the best - most likely that will be an excellent spot to place the subwoofer.
Some active subwoofers will have a built in DSP to help optimize its performance for a particular room - Ex. Klipsch C series subs like the C-310aswi https://www.klipsch.com/products/c-310aswi-subwoofer-custom
How to dial in the subwoofer
A subwoofer works best when it doesn’t draw attention to itself. Your subwoofer and loudspeakers should act as one unit. The bass coming from the subwoofer should blend seamlessly with the rest of your speakers.
On the back of most subwoofers, you’ll find a low-pass crossover knob. Crossover is the frequency where your speakers begin to roll-off, and the subwoofer starts to produce bass notes. Set your crossover point about 10 Hz above your speaker’s lowest frequency range. For example, 34 Hz is the lowest frequency the Next-Gen Reference R-800F can handle, so you would set your crossover at around 45 Hz.
The 0/180-degree phase switch is another subwoofer control. The mechanics behind the phase can get pretty complicated. In layman’s terms, subwoofers and speakers perform best when their woofers move forward and backward in a synchronized fashion. When they don’t, the speakers and subwoofer are out of phase, which cancels out the bass. To dial in your phase, play some bass-heavy music, listen for a bit, and have a friend switch between both settings. Whichever one sounds better, leave it there. If you can’t hear a difference, set it at 0 degrees.
Should I get one or two subwoofers
A large subwoofer like the SPL-150 can take any home-theater setup to the next level. However, as your system grows, adding a second sub can help ensure the bass is evenly distributed throughout the whole room. Two SPL-150s increase your output capability by close to 6 dB, meaning everyone in the room can feel those powerful, low tones while watching action and sci-fi movies.
A pair of subwoofers can also minimize the seat-to-seat variance of bass response, offering an even coverage pattern of low frequencies throughout the room. Depending on room size and placement, one sub alone makes it challenging to deliver accurate bass responses at multiple listening positions. This is because the frequency response of an individual subwoofer tends to have peaks and nulls. A peak is an exaggeration of a bass note, while a null is the absence of bass. When paired together, two subwoofers smooth out those peaks and nulls, offering a more accurate frequency response at more locations in the room.
All in all, a subwoofer is an essential part of your system. If you’re on a budget or in the infancy of your home-theater development, start with just one subwoofer. As your system grows, think about adding a second low-toned beast to your setup. You’re adding more bass and evenly distributing it throughout the room. The results? Improved bass performance.
Connecting the subwoofer to a receiver.
Most receivers will have dedicated RCA jacks - Subwoofer outputs for 1 or 2 subs to be connected.
Connect the sub using a single RCA-RCA subwoofer cable of the appropriate length.
Although many subwoofers will have dual RCA inputs like these - you would typically want to connect just a single RCA-RCA subwoofer cable from the AVR to the subwoofer. It doesn't matter what input on the sub is used - red or white.
Some active subwoofers will other types of input sources -
See the back panel of C-310aswi -
Beyond the typical RCA inputs there are
Balanced line input - Female XLR input jack for a balanced connection style. Balanced connections offer a greater ability of noise rejection and can be a superior route but not often found as an output option in home audio world.
Hi-Level input - using the speaker level output of the amplifier. Not a very common connection route these days as most home theater systems will have a dedicated line-level sub. This connection method uses standard speaker wire connected to the amplified channel directly. This method is popular with 2 channel audio setups that involve an amplifier without a subwoofer out.
Wireless - some subs will have an ability to connect wirelessly to the audio source. That will typically involve a transmitter device to be connected to the source directly. Ex. - C-310ASWI sub and a WA-3 kit.