Subwoofer Reviews

Piece of cake, thought I. All I needed to do to review Wilson Audio Specialties' smallest active subwoofer, the LōKē ($8950 each in standard finish), was describe how low a pair goes in my room and how cleanly they woof.

As I was soon to learn, though, there was a lot more to reviewing LōKēs than that. Why? Because a pair of LōKē subwoofers does more than reinforce the already deep bass extension (footnote 1) of the Wilson Alexia V loudspeakers with which they are now paired in my system. Therein lies the tale.

Behind the woof
"Wilson Audio has a long history with subwoofers," Wilson CEO Daryl Wilson (footnote 2) explained during a Zoom conversation that also included Blake Schmutz, director of the Wilson Audio Special Applications Engineering (WASAE) division (footnote 3). "If you go back to our original WAMM, which was low frequency limited, my father complemented it with two large woofer towers. Then, later, for people with space issues, he released the passive WHOW [Wilson High-Output Woofer] as an option. After that came the active POW WHOW, with a built-in amplifier. Fast-forward 15 years, to right after the X-1 Grand SLAMM was introduced, when my father asked Chief Engineer Vern Credille (footnote 4) to create the huge XS (footnote 5), the ultimate subwoofer for home theater."

Since peaking in size with the XS, Wilson subs have gotten smaller and smaller, responding to dealer and consumer demands. When Wilson employees added their voices, expressing a desire for an even smaller subwoofer for their own setups that was reasonably priced by Wilson standards, the LōKē was born.

As with other Wilson products (including the aforementioned XS), "LōKē" has several meanings. In Norse mythology, LōKē is the mischievous little brother of the great god Thor, for whom the much larger Thor's Hammer is named. So "LōKē" seemed appropriate for Thor's diminutive sibling. But in the world of puns that, for better or worse, spins circles around Wilson's CEOs and associates, present and former, Daryl indicated that LōKē also signifies that the company's smallest subwoofer is intended "to hit low keys while kind of hiding, 'low key,' in the corner."

LōKē was conceived of to pair with Wilson's smaller loudspeakers and other speakers of similar size. Its 10" woofer, housed in a relatively small enclosure, was never intended to put out huge home-theater SPLs or to descend to 5Hz. Depending on the room, LōKē could put out "some decent SPL" down to 20Hz, Daryl told me. In my 20' L × 16' W × 9'4" H listening room, Daryl thought it would deliver energy to "well below 20Hz."

Daryl and Blake classify LōKē as a WASAE product, as in Blake's title (see above). A WASAE product is one that does not fit Wilson's "standard" loudspeaker model. Why? First off, the LōKē differs from other Wilson subs because it has limited output power that is sufficient only for smaller spaces.

It's an outlier in another way as well. In designing the LōKē, Wilson was able to make only certain modifications to its outsourced amplifier. "We were able to make some changes to the amplifier, but change requests were limited by the manufacturer," Blake said. "We didn't have the ability to do everything we may have wanted. We could have spent a couple of hundred thousand dollars developing an amplifier that was customized just for Wilson Audio, but that didn't make sense when we were able to find an amplifier that checked all the boxes ... after some relatively minor modifications." That said amplifier is built by a US company—Dayton Audio—that builds its products in Taiwan was an additional enticement.

Wilson also chose to work with Dayton because their amplifier, according to Daryl, is "virtually bulletproof." "These units have a 98% reliability rate," Blake noted. And if an amplifier were to fail, Daryl noted, the electronics are easily serviceable.

Subwoofers are often called on to extend the bass of a smaller "satellite" speaker. The LōKē can do that when paired with a TuneTot or any other limited-bandwidth speaker. But all of Wilson's larger speakers, from SabrinaX up, run full range or close to it; used with size-appropriate mates, including the Alexia V, the LōKē can reinforce low bass.

Low bass is LōKē's raison d'être. "In my large room, we cross over our subs at 44Hz," Daryl said. "We don't ask them to produce sweetness in the midrange or harmonic expression in the high frequencies. We ask them to push air very effectively."

Even so, integration with the main loudspeakers is very important. Integration means several things. It means getting the subwoofer volume right. It means making sure music signals at every frequency in the range where main speakers and subs overlap arrive at the listener's ears at the same time. And it means, according to Daryl, that it has to be fast. "If a subwoofer can't integrate well into a system and contribute to the reproduction of music in a believable way, it won't have any Wilson or WASAE badging on it," he said. "A sub has to be fast and create the space in the music in a believable way. If it can recreate large spaces such as the Concertgebouw or the Musikverein, and accurately convey the thud of the timpani or the roll of the drum on the skin, then it will take care of anything that is thrown at it."

When I asked what Wilson had done to ensure smooth integration with the main speakers and avoid bloated bass, it was Blake who answered. "We examined resonance control and were very careful about our driver selection. To avoid the muddy feel, the woofer has to be nimble, move fast, and recover quickly."

What does it mean for a subwoofer to be fast? The answer to this question came from Vern, via Blake: "If we put energy into a driver that is below its natural mass-controlled region, we see a 'quickness' in the subwoofer bandwidth."

Addressing the cabinet, Blake said, "You can also get a lot of smearing if the baffle is modulating. You've got a lot of mass in a subwoofer, so the enclosure has to be heroic. This is where our X-material shines. If you're trying to save on material cost and skate the line between good enough and just good enough, you do detriment to the design. X-material enables the enclosure to be rigid, stiff, and able to handle the pressures created by the woofer without contributing its own resonances to the sound." That curve on LōKē's side isn't just cosmetic; the material is thicker in that region to help dampen the enclosure and provide additional rigidity.

The LōKē's amplifier includes controls that allow listeners to delay the signal and correct for distance discrepancies between the main speakers and the LōKē so that launch and wavefronts reach the listener simultaneously. "When they do, everything synchs up and the subwoofers disappear," Daryl said.

Phase, space
According to Wilson Brand Ambassador Peter McGrath, who journeyed to Port Townsend with his wife, Elizabeth, to set up a review pair of LōKēs, "Wilson always constructs and sizes its subwoofer enclosures to allow the driver or drivers to operate at a natural Q, ie, to operate in a linear fashion throughout its range." "Q" is Quality Factor, a measure of the width of any resonance. JA often mentions it in his loudspeaker measurements. "Natural Q" means doing what most loudspeaker designers would do: put an appropriate, high-quality driver in a well-designed enclosure. That may not sound especially fancy. However: "From the time of Bob Carver on," Peter continued, "people have forced subwoofer drivers to do a lot of unnatural things by putting them into enclosures that typically do not allow for natural Q and then applying high levels of power and equalizing the signal. But whenever you apply equalization in the analog world, you shift the time domain of the driver." Frequency-dependent phase shift. Avoiding that is what Peter means when he says "operate in a linear fashion throughout its range." (footnote 6)

There's another factor at work here. Like some but not all other subwoofers, the LōKē digitizes the incoming signal. In the digital realm, you can manipulate the signal with less impact on phase than is possible in the analog realm.

"When you add a subwoofer to a musical system, as when you add a LōKē to an Alexia V, Sasha V, or Sabrina, you're working with a speaker that already has extended low frequency response," Peter said. "That results in an overlap between the output of the subwoofer and the output of the main speaker. The subwoofer and speaker must remain in exactly the same phase during the overlap to make the main speaker seem to descend even lower naturally while avoiding the introduction of such bass anomalies as a slightly blurred sound or a subwoofer that sounds like a subwoofer rather than naturally blending. When that goal is achieved, you not only gain bass; you also gain space."

Gain space? That's a claim I'd heard Peter and other Wilson reps make during demos of speaker-sub combinations. Every time I listened, space depiction and air seemed natural. But that didn't mean that the subwoofer was responsible for some of the realistic air I heard. The only way to tell for certain was to turn the subwoofers off and on and listen for myself. Until I was able to experience the difference, I greeted this claim with a healthy dose of skepticism.

Peter was not able to supply a definitive reason why subwoofers increase air. I don't know if anyone can. "My belief is that it's because you've got another pair of drivers in a different position that allows them to get past and break up some of the locked-in room modes that are characteristic of every room," he surmised. "In the digital recordings I make, bass descends to 3 or 4Hz because that's what the microphones I use are capable of capturing. You don't hear that subharmonic low bass, but you can sense it. You normally don't miss this information until you have a subwoofer that can supply a sense of its presence in the room.

"When I apply Wilson subwoofers to studio recordings of pop music, you also get an additional sense of space. Perhaps the phenomenon is connected to breaking up room mode anomalies and making the bass more evenly distributed in the room. Whatever the cause, a very good subwoofer design with natural Q, properly implemented and applied to a natural-sounding full-range loudspeaker, will result in a significantly improved sense of air and reality."

Are two subwoofers necessary to achieve this effect? "A more dimensional re-creation of space is possible when two subs are used in an audio system that sends the left channel LF information to the left sub and right channel LF information to the right sub," Daryl said, but one sub may suffice if left- and right-channel LF information are summed, as in the LFE (low frequency effect) audio tracks transmitted via Dolby, DTS, and other home theater sonic schemes (footnote 7).

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Footnote 1: Wilson Audio measures the Alexia V's frequency range as 19Hz–33kHz ±3dB Room Average Response (RAR).

Footnote 2: When we spoke, Wilson Audio was gearing up to launch its new active Submerge and passive Subsonic subwoofers, revisions to its Mezzo center channel and Alida wall-mount/surround/Atmos speakers, and several Special Applications Engineering offerings.

Footnote 3: In this review, to make it clear when I'm referring to Daryl Wilson rather than the company, I'll call him Daryl. For consistency, I shall refer to all Wilson personnel by their first names.

Footnote 4: Vern has worked at Wilson Audio for 30 years and is frequently credited for his work on drivers and crossovers.

Footnote 5: Wilson insists that XS was a phonetic play on the word "excess," and I believe them, but I can't look at those two letters together without thinking, with irony, of "Extra Small." The XS, which was retired in 2005, weighed 750lb.—Jim Austin

Footnote 6: In a follow-up email, Chief Engineer Vern Credille elaborated. "When a subwoofer is designed appropriately, with sufficient volume in the box for the driver, there is no need to manipulate the driver's acoustical or electroacoustical behavior with an EQ or other means. There is a common trend to have large drivers in small boxes, where an EQ is required to manipulate the throw of the driver to maintain pressure inside the box, which results in phase anomalies in the selected bandwidth of the subwoofer. In the LōKē, because the box was designed for the driver, the phase characteristics in the subwoofer bandwidth are linear."

Footnote 7: I would add "or more," as in "two or more," because when it comes to subwoofers, there's nothing special about the number two. At the frequency ranges we're discussing (approximately 40Hz and below), sound isn't directional, so as long as you can adjust the phase so that the music from the subs arrives at your ears at the same time as the music from the main speakers, you can use as many as you like and put them wherever they work best. More subwoofers is better because, first, you reduce the demands on each one (an excess of which could result in audible distortion), and second, with more units, you have more options for energizing the room.—Jim Austin