A subwoofer is a speaker designed specifically to deliver bass for all the other speakers in a home theatre or stereo system. Bass is important for many reasons. It adds layers of massive sonic impact as well as subtle, even delicate sound that draws us in and makes all our music, movies, and TV shows more thrilling and immersive. Bass allows you to literally feel a musical note or sound effect in a movie — it sets the mood in a soundtrack, and it provides pacing for the rhythm and melody in music. Bass creates the foundation of the rhythms that make you tap your toe or nod your head when a favorite song comes on.
Unlike choosing speakers, which is a subjective decision based on many factors (appearance, voicing, form factor), choosing a subwoofer is a more objective one. Why? Because when it comes to subwoofers, we can more easily judge them by their ability to do 5 basic things. The best home subwoofers all share these five performance qualities, which are easy to catch if you know what to listen for.
Incredibly low frequency extension.
Many subwoofers don’t have the ability to reproduce the deepest bass notes or tones. In more technical terms, this means they’re unable to reach notes at or below 20Hz (the threshold of human hearing). So, they attempt to make up for it by exaggerating the mid-bass performance to hide the missing notes. This results in boomy, single-note bass, creating a less believable experience that robs you of feeling what the artist or director really intended to present in the lowest frequencies. The best subwoofers deliver the deepest bass with clarity and grace, sometimes creating frequencies so deep they can’t even be heard — only felt!
If you’re looking at a spec sheet, it’s important to know that these are written based on test results in an anechoic chamber (a room designed to completely absorb sound). This is unfair for subwoofers, as they rely on sound reflections in your room to create clear, powerful notes. As such, a subwoofer may only be specified as going down to 30Hz, when in reality it dives much, much deeper.
What you should listen for:
Look out for subwoofers that seem to run out of steam on very deep bass notes. Put on your favorite EDM bass drop, and you might notice that as the bass falls lower and lower in pitch, the volume starts to drop as well, too. World-class subwoofers will maintain output levels the whole way down.
Low frequency output at the highest sound pressure levels (SPLs).
That’s a mouthful, but the concept is quite simple. A world-class subwoofer plays effortlessly loud and distortion-free, no matter how deep or demanding the source material. Unlike passive speakers, subwoofers usually have their own internal amplifiers and DSP engines so they can make their own on-the-fly volume adjustments when a home theater or stereo system is cranked up. Lesser subwoofers use amplifier limiting, which artificially reduces the volume of the biggest slams of bass bursts to protect the amplifier from being overworked. The result: the bass “disappears” at the very moment you want it to kick in the most, like an action movie explosion or an EDM bass drop. This is an important feature, meant to save the subwoofer from damaging its driver or amp, but it creates a deflating experience. A world-class subwoofer generates enough energy to perform effortlessly with massive SPLs well beyond reference volume, without bottoming out or simply quitting at those critical moments.
What you should listen for:
Pay attention to how much energy and chest-thumping power it creates with the very deepest bass notes. If you can’t experience it in person, it’s good to talk to someone who has, like the product experts. You can also check the wattage, which tells you how big the internal amplifier is.
Accuracy in frequency response.
The best subwoofers produce the exact amount of bass you’re supposed to hear at the exact right pitch with complete faithfulness to the movie, music, or other source content. This is perhaps the biggest factor in creating a believable home theatre experience because it reflects what the artist or director intended for you to hear and feel — without any extra frills or distortion added by the subwoofer failing to perfectly recreate the sound.
What you should listen for:
Is the sound clean, clear, and powerful like it should be? Or is it unclear, flattened notes that sound warped and inaccurate? Bass should not be boring thuds, but rather an extension of the sound your speakers are producing.
Pinpoint speed in transients.
This is frequently described as the subwoofer's ability to “stop and start on a dime.” A great subwoofer has extremely fast impulse or change in momentum (accelerating and decelerating). When these changes don’t happen at lightning speed, extra notes get produced during those impulse times, and the sub is unable to keep pace with your speakers in an audibly pleasing way. For this reason, lesser subwoofers have difficulty keeping up with full range speakers when complex bass lines, aggressive action scenes, and other full range content is presented. The result? A loss of detail. With lesser subwoofers, the bass can take over the sound field in an unnatural and distracting way. World-class subwoofers stop playing bass at the precise moment they’re supposed to and kick back in at the perfect moment, so the sound is indistinguishable from the speaker output and everything plays in perfect unison.
What you should listen for:
How the bass integrates with the other speakers. Does it take over and dominate the sound in aggressive, but sloppy way? The transients are slow. The subwoofer should seem like a part of your speakers, seamlessly blending with their sound and broadening the performance, not overwhelming it.
Blend seamlessly with full range speakers.
No one wants to only hear bass in their home theatre or audio system. Proper home theatre audio is about creating a total experience where the subwoofer lays the sonic foundation, but never draws attention to the bass alone or its location in the room. Bass is omnidirectional and a subwoofer should energize or pressurize a room without overwhelming the soundstage or revealing its placement and presence in a distracting way. A world-class subwoofer adds a powerful and tactile sonic element that can’t be ignored, but always remains complementary to the system as a whole.
What you should listen for:
Just like the previous tip, pay attention to how the bass integrates with other speakers. The subwoofer should sound like it’s part of the rest of the audio system, not stealing the show.
by Gary Yacoubian