NHT SuperZero loudspeaker & SW2 subwoofer Review
I know this because I just spent a whole weekend watching the Beavis and Butt-head Marathon on MTV—two full days of the clearest, most incisive social commentary since Charles Kuralt stuffed himself into a souped-up Winnebago and hit the road searching for the naked soul of this strange and dangerous country.
As everyone now knows, Beavis and Butt-head’re two 13-year-old, brain-damaged, dysfunctional cartoon snot-noses who sit on a couch and critique rock videos when they’re not out playing baseball with live frogs and shooting down Boeing 747s with shotguns.
What makes someone a good hi-fi reviewer? A fine critical sensibility? A good technical background? Ears? Eyes? Nose? Throat? So many different people are reviewing audio gear these days that it’s downright impossible to characterize a good reviewer. But I do know that Beavis and Butt-head would make killer hi-fi reviewers!
Naturally, Beavis and Butt-head have become my Supreme Gurus.
See, Beavis and Butt-head are Real People. I know because I was Beavis and Butt-head. Maybe I still am. I hope I still am, because Beavis and Butt-head know what’s really important. When they watch rock videos, they don’t lament the lack of plot focus or plausibility—they want babes in tight shorts, fire, babes in tight shorts, ugly, longhaired, devil-looking guys hunched over electric guitars, and babes in tight shorts.
Beavis and Butt-head are God.
Man, I’d love to see Beavis and Butt-head start reviewing affordable loudspeakers! I just know they’d have the right hierarchy when it comes to the things that Real People want from their hi-fi:
Butt-head: Listen to these $1000 high-end minimonitors…like, where’s the bass, dude? They suck. Huh-huh, huh-huh.
Beavis: Yeah…huh-huh…they suck! Expensive speakers that can’t kick ass suck! Huh-huh, huh-huh.
Butt-head: I bet they were made by somebody who’s old. And a wuss. Huh-huh, huh-huh.
Beavis: Do these speakers come in Morning Wood finish? Huh-huh, huh-huh.
Butt-head: Huh-huh, huh-huh.
Beavis: Huh-huh, huh-huh.
When I picture a speaker that would win the approval of even Beavis and Butt-head, I see a speaker that really kicks ass—one that offers true high-end, full-range sound, all for under $1000. A speaker that’ll not only play your music as loud as you want, but remain clean and clear under the most trying conditions. Not surprisingly, there isn’t a single speaker in the entire High End that can fit this bill.
Now Hear This
Which brings me to NHT’s new SuperZero loudspeaker. Forget about “small” speakers, “bookshelf” speakers, “minimonitor” speakers. The SuperZero is just plain li’l! Which happens to give it certain advantages over larger speakers. Because the SuperZero’s cabinet is so small, it’s much more solid and rigid than most speakers. And what cabinet vibrations the SuperZero does have are much higher in frequency—and lower in amplitude—than those from a larger cabinet made from the same 3/4″ MDF material. The SuperZero’s tiny front baffle also endows it with the imaging superiority of such classic imagemeisters as the BBC LS3/5A and the various Celestion babyspeakers.
The smallest speaker made by NHT used to be the original $199.95 Zero. I bought a pair several years ago for use as Real World monitor speakers in the production studio of the radio station where I used to work. Not because it was a killer li’l speaker, because it wasn’t—it had no bass, the mids were very colored, and the upper mids and highs hardened pretty severely when you played them even semi-loud. No, I bought the Zeros because I wanted a small pair of speakers that sounded par for the course in terms of the station’s target audience—mostly young, mostly female, and mostly non-audiophile. If the station sounded good on the Zeros, I knew it’d sound good in the listeners’ homes and cars.
But that was then and this is now. Ken Kantor, NHT’s designer/founder, has totally redesigned his smallest speaker—the cabinet is the only thing left from the older Zero—giving it high-performance drivers, a better crossover, and real speaker connectors. And while NHT never claimed that the original Zero was anything but a decent budget speaker, they’re calling the SuperZero a true high-end component that just happens to cost very little.
I first heard the SuperZero when NHT introduced it at the 1993 Las Vegas WCES along with their new flagship 3.3 ($4000/pair). But while the 3.3 really knocked me out, the li’l SuperZero wasn’t far behind. Having become very familiar with the original Zero’s sound, I couldn’t believe the level of sound quality I was hearing from the Super version. I promised you in my Show report last April that I’d review the new NHTs as soon as I could lay my hands on a pair. Hey, I may lie, cheat, steal, swear, expectorate, saunter, and push over sleeping cows in the dead of night, but a man’s only as good as his word.
Whut’s the guts?
The NHT SuperZero is a true minimonitor—the speaker’s 5.5″ front panel is barely wider than the 4.5″ paper-cone midrange/woofer. This acoustic-suspension driver is mated to a 1″ fabric-dome tweeter. The new mid-woofer is a better-behaved driver than that of the original Zero, with a smoother response at the top of its band. The 1″ fabric-dome tweeter—the same driver used in NHT’s $1095/pair 2.3a (footnote 1)—replaces the original Zero’s inexpensive 3/4″ polycarbonate-dome tweeter. The crossover has also been upgraded to better integrate these higher-performance drivers. Unlike most inexpensive speakers, both drivers were designed by NHT from the ground up, then made by Japanese OEM driver manufacturer Tonegen to NHT’s specs.
The drivers are crossed over at 2.2kHz with a minimalist crossover consisting of just two small electrolytic capacitors (5µF/50V and 10µF/50V), three resistors, and one inductor. The low-pass feed to the SuperZero’s woofer is a second-order 12dB/octave filter, while the tweeter is crossed over with a first-order 6dB/octave slope. Thankfully, NHT has replaced the original Zero’s lousy spring-loaded speaker connectors with high-quality, five-way speaker posts that are actually better than the ones that came on my $1275 Spica Angeluses.
Unlike most speakers in the NHT’s price range, the SuperZeros have a very high level of fit and finish. Although they cost only $230/pair, their piano-black finish gives them an elegant appearance that suggests expensive black-lacquer-finished furniture. For a time at my abode, the NHTs sat atop a $4500 Pioneer Pro-76 projection TV whose own finish is high-quality gloss-black, and the SuperZeros’ finish melded seamlessly with the expensive Pioneer. The SuperZero’s elegant appearance is miles ahead of the typical plastik-wood “near-veneers” and other cheezy finishes usually found in the Lower Reaches. I saw a similarly priced Boston Acoustics speaker recently that had a “finish” consisting of a piece of woodgrain-print wallpaper glued around the speaker cabinet. The edges were coming loose around the cabinet’s corners—the perfect addition to any fine mobile home. Like Charles Kuralt’s, maybe.
NHT SW2 subwoofer
The SW2 subwoofer comes in two versions: one with an internal 130Hz 12dB/octave crossover, one without. The version with the crossover is meant for use with NHT’s larger speakers—such as the $500/pair 1.3a (footnote 2). and the $1095/pair 2.3a—to extend these speakers’ LF response to -3dB at 21Hz. Used in this situation, two SW2s are employed, one for each speaker.
The crossover-equipped version of the SW2 has four pairs of five-way speaker posts on a sunken cup located on the rear panel to interface the sub with the rest of the system. One pair, Sub In, takes the speaker-level signal from the system’s power amplifier; another pair, Sat Out, sends the portion of the music signal above 130Hz to the satellite speaker. The remaining two pairs of speaker posts are for using the SW2 with an external amplifier/crossover such as NHT’s MA-1. Normally jumpered together for passive operation, the SW2’s internal crossover may be bypassed for use with the MA-1 by removing these jumpers and driving the designated pair of five-way posts.
The SW2 I had on hand was finished in the same high-gloss, black-laminate finish as the SuperZeros, and looked just as boss—as long as I kept my grubby fingers off it. Even though the SW2 is a true subwoofer with response down in the lo twennies, it’s only a 16″ cube, and doesn’t really dominate a room the way many other subwoofers can. Even when I had two SW2s set up in the living room, their small size made them easy to position so they wouldn’t look ugly enough to send Dara after “El Diablo,” the heavy cast-iron skillet she wields like it’s a natural extension of her right arm.
NHT MA-1 amplifier/crossover
The MA-1 is an 80W solid-state mono amplifier expressly designed by NHT’s Ken Kantor to drive the SW2 subwoofer. Aside from the passive crossover-equipped version of the SW2 described above, the SW2 also comes without the internal crossover as part of a $650 package (called the SW2P) with the MA-1. This version of the SW2 has just a single set of five-way posts, which are driven by the MA-1.
The MA-1 offers two ways to mate the SW2 subwoofer with a pair of speakers, and was designed to allow the use of other manufacturers’ speakers as well as NHT’s own models. Via the MA-1’s speaker-level inputs and outputs, the signal from a system’s main amplifier is taken to the MA-1 and crossed over passively at 100Hz to the main speakers. The MA-1 also sums the two channels and sends the signal to the active low-pass crossover, whose feed to the subwoofer is then adjustable in terms of level via the front-panel level knob and crossover frequency—50Hz, 80Hz, or 110Hz (footnote 3). (The MA-1’s crossover has a fourth setting, Bypass, which removes the crossover from the circuit and makes the MA-1 a full-range mono power amplifier suitable for driving the center-channel speaker in a Home Theater system, etc.) While the satellite speakers are always crossed over at 100Hz, NHT recommends that the user try all three subwoofer frequencies to find the best balance between the SW2 and the main speakers for a given system and room.
The MA-1 also has a pair of RCA jacks that allow for line-level signal inputs, such as an external crossover or the subwoofer output from a Dolby Pro Logic surround decoder. In this case, no signal is sent to the main speakers. The input signal is simply sent to the subwoofer and crossed-over at 50/80/110Hz; it bypasses the crossover entirely if the surround processor has its own crossover.
The MA-1 has a Standby mode that turns the amplifier off if no audio signal is detected by the MA-1 within several minutes. Standby mode is indicated by a green LED on the front panel, which remains lighted until the MA-1 revs up again in the presence of an audio signal. For those who do not appreciate such anti-high-end tomfoolery and like to use up them kilowatt hours on a steady basis, NHT dealers offer a simple internal modification to defeat the Standby circuit.
Overall, the MA-1 looks and feels much the same as most $300 power amplifiers—like Rotel and Adcom gear, for example—and its internal construction looks about on a par with either of those brands. Instead of the Far East, however, the MA-1 is built in LA by Databyte. One aspect of the MA-1 that bothers me, though, is the use of cheap, spring-loaded speaker connectors for the speaker-level inputs and outputs. Ol’ Dick Olsher had it right in his review of the original Hsu Research subwoofer in Vol.16 No.3, p.86: These el-cheapo spring-loaded speaker connectors suuuuuuuuuck, and shouldn’t be seen on gear with high-end pretensions. Thankfully, the MA-1’s subwoofer output has a good pair o’ Heavy-Duty Judy five-way posts.
As with other affordable gear that I review, I listened to the NHT SuperZeros and SW2 subwoofer in both my He-Man reference rig and my Real World living-room system. The first rig tells me what a product sounds like in absolute terms, and the second tells me how much of that information matters in an environment more typical of what non-audiophiles experience. The Real World system also tells me how well a product can sound when mated to similarly priced gear, which is probably the most important part of the review.
For LP listening with the He-Man rig, the analog setup consisted of the Well-Tempered Record Player, the Sumiko Blue Point Special cartridge, and the Exposure XVII preamp (with a phono stage via its Rec-Out jacks). CDs were played with a Theta Data II transport linked to Theta’s Gen.III processor with Theta’s Single-Mode laserlink. My 8-track tapes were handled by a Curtis Mathes 8-track deck. The line-stage was my own buffered passive preamp; the amplifier was either Aragon’s 4004 Mk.II or the new Muse Model 160; cables were Kimber KCAG for interconnect and 4AG for speaker cable; and everything, including the NHT MA-1 amplifier/crossover, was plugged into API Power Wedge AC line-conditioners.
The Real World system included the JVC XL-Z1050, Rotel RCD-955AX, and NAD 502 CD players; my own buffered passive preamp as the line-stage; the Muse Model 100 amplifier; Kimber PBJ interconnects and Kimber 4TC or AudioQuest Type 4 speaker cable; and raw AC as the poweur du jour.
As the reader of this assertedly unbiased review, you should be aware that I have seen the designer of these products totally naked. It was in a Taipei bathhouse when we were both overseas last year for the Taiwan High-End Hi-Fi Show. In fact, I was totally naked, too, and sitting on a wooden-slat bench in a steam room with my totally naked butt this close to the designer’s own butt, which, again, was totally naked.
I like Ken Kantor. Even his naked butt. But I review products, not people, and I take my professional credibility very seriously. I have given highly negative reviews to products designed by people who, on a personal level, I like quite a bit. And I have given rave reviews to products from people who, on a personal level, I wouldn’t piss on if they caught fire.
So if the knowledge that I have seen the naked butt of these products’ designer undermines your opinion of my objectivity, I understand. But it’s one hell of a butt, this is one hell of a good speaker, and I think you should know about them both.
The NHT SuperZeros ROCK!! I don’t hear that many products that even meet the level of performance claimed by their manufacturers, much less set a new standard for sound quality at anywhere near the price of the SuperZeros. A $3000 amp that sounds about as good as many other $3000 amps? Zzzzzzzz. But a $230 loudspeaker that competes with high-end speakers costing $3000? Now that’s something to get excited about!
The SuperZeros aren’t perfect. Although they can play impressively loud for their size, they don’t perform miracles—drive them hard and the sound becomes edgy and hard, as can only be expected from speakers tiny enough to juggle. But what distinguishes the li’l NHTs from their similarly priced competition is that, rather than go for a budget design that “fakes” a real low end with a midbass hump, and otherwise balances a panoply of flaws into a reasonable facsimile of a real high-end speaker, the designer of the NHT SuperZeros has completely ignored the bass range and all the problems that it entails in a budget design. Ken Kantor has instead concentrated on getting the range from 100Hz on up as accurate and as coloration-free as possible—within the constraints of his design budget.
Footnote 3: The actual markings on the MA-1’s rear are “50Hz,” “100Hz,” and “200Hz,” but as Corey’s nomenclature coincides with the measured -3dB points, I’ve left them as is.—John Atkinson
You’re not going to get great sound from the NHTs unless you treat them like a “real” high-end speaker, though. Just because they’re cheap, don’t be fooled into thinking that all the high-end attention you lavish on “real” speakers is a waste of time with the SuperZeros. Chuck the grilles. Give the NHTs a good pair of solid, stable stands, with a bit of Blu-Tack under the speakers’ corners. Toe them in so they directly face you.
If you treat the SuperZeros like just another cheap speaker, that’s the kind of sound you’ll hear. But while most cheap speakers never really improve no matter what kind of attention you give ’em, the NHTs reward every bit of attention to setup detail with sound quality that has simply not been previously available anywhere near this price point.
So what did they sound like? Like true high-end speakers, except without any bass. They don’t have “some” bass—NO bass. Used solo, even on a good pair of solid speaker stands, the SuperZeros just didn’t have a real, or even implied, low end. I heard a slight emphasis in the upper bass around 150-200Hz that added a bit of chestiness to male vocals, but the NHTs didn’t have the kind of “quasi-bass” midbass hump found in small speakers (such as the PSB Alpha and LS3/5A) that can fake you into thinking you’re hearing real low bass. The NHTs were more in the mold of a true high-end minimonitor: neutral and accurate, with no attempt to do anything in the low end, and focusing their strengths on the range above 100Hz. As crazy as it sounds, consider the NHT SuperZero a budget Wilson WATT. After you listen, you won’t think it’s crazy at all.
By themselves, the li’l NHTs sounded extremely smooth and uncolored through the midrange, but with a bit of treble brightness (because there’s no low end to balance out their sound). Unlike the Spica TC-50, which achieves a good tonal balance by rolling off the high end to complement a similar rolloff in the bass, the bass-less NHT’s high end was unattenuated—in fact, the SuperZero had a slight treble emphasis that, while not an irritating overbrightness, served to further shift its tonal balance to the thin and forward. Without the SW2 subwoofer filling in the low end, the SuperZero sounded overly thin and wispy, especially with gritty-sounding budget electronics. The SuperZero is not a “cheap’n’cheerful” low-rez speaker that’ll smooth over the rough edges in a poorly matched budget system. Like the true high-end speaker it is, the NHT accurately reproduced the signal fed it, warts and all.
Yet even when used without a subwoofer, the first thing that stood out about the SuperZeros was their incredible sense of spaciousness and sheer, vivid soundscape portrayal. You just don’t expect a pair of tiny $230 speakers to sound like a giant wall of sound when you close your eyes, but the NHTs did. As absurd as it may sound, the NHTs disappeared as well as or better than the $3000/pair ProAc Response Twos I lovingly reviewed in Vol.15 No.7, p.109. I set up the NHTs well away from the rear and sidewalls and was rewarded with a vivid, boundary-free soundscape that floated in the air without any aural clues that it was coming from those two tiny black boxes on the other side of the room. Recordings with a real sense of depth and soundstage, such as Los Lobos’ Kiko (Slash 26786-2), or the great new Jeff Palmer organ-trio workout Ease On (AudioQuest AQ-CD1014), came across with a sense of ambient detail and lack of boxiness that I just don’t hear from many sub-$1000 loudspeakers, much less ones costing only $230.
In this regard, the SuperZeros aren’t merely great for the money, they’re great period. Kiko‘s “Wake Up Delores,” in particular, had as impressive a sense of palpable space around and between the hard-left and hard-right panned guitars at the front of the soundstage, with the drums at the rear, as I’ve heard in either of my two listening rooms. And the QSound-processed images from Roger Waters’s Amused To Death sound-effects CD extended way to the outside of the NHTs and in a 180 degrees arc in front of me. Contrast this with the $695/pair Vandersteen 1Bs I reviewed in September 1993 (Vol.16 No.9, p.98), which refused to image much beyond the speakers’ outside edges—they were more colored and congested through the midrange and presented an overall lower level of resolution across the band than the one-third-as-expensive SuperZeros.
That’s the word I’m looking for—resolution. The SuperZeros’ midrange smoothness and sheer resolution of recorded detail put them on a par with other high-end loudspeakers costing many thousands of dollars. This is no exaggeration. Compared to the pair of Spica TC-50s I had on hand, the SuperZeros had a higher level of resolution and a less “muffled” character through the midrange and low treble. The clear-as-a-bell gospel vocals of the Fairfield Four’s Standing in the Safety Zone (Warner Bros. 26945-2) sounded much more present and clear with the SuperZeros, the Spicas tending toward an overwarm and rolled-off character in the low treble that made them sound far too reticent and chesty compared to the NHTs. The TC-50s were my reference speaker for a time when I was first getting into high-end audio years ago, but if the SuperZeros had been around back then, I would have undoubtedly chosen them. Terrific-sounding as they are, the TC-50s do not have the coherence or neutrality of the SuperZeros. And while the TC-50s have much deeper bass extension and are extremely non-fatiguing to listen to, the SuperZeros are less colored overall and give a more accurate picture of the audio signal fed them.
The SuperZeros obviously needed good stands to get them up high enough for serious listening. Unfortunately, most good stands cost more than the speakers themselves! While the SuperZeros are definitely deserving of as high a quality stand as you can find, I’m not gonna recommend that you buy stands that cost more than the speakers!!
So I builded me a pair of Aunt Corey’s Uneducated White Trash DIY Speaker Stands: cinder blocks, two per stand, stacked end to end. This gave me very massive, literally rock-solid stands 31″ high, which happened to be a good height for the SuperZeros in both of my listening rooms.
I found that the NHTs sounded best when toed-in and firing directly at the listening position. I also liked them best when they were positioned fairly high, so that my ears were level with or below the woofers. In addition to using the cinder-block stands, I listened to the NHTs on the excellent $200 heavy-metal 24″ speaker stands Merrill Audio has just introduced as an affordable alternative to the expensive imported British stands. (The $800 Target R2s, for example, are fine stands, but their price unfortunately reflects their overseas trek to your rumpus room.) Because the Merrill stands are shorter, the NHTs were placed upside-down to ensure the optimal listening axis.
I know what you’re thinking: “Cinder blocks?! My wife’d KILL me!!” Well, fine then—buy the Merrills. But for the rest of us Real World audiophiles, four 45-cent cinder blocks sprayed gloss-black with a $3 can of paint not only look tough, but the price is right (footnote 4). I’ve got ’em in my living room, and, so far, El Diablo has not reared his grim and fearsome head.
I was so knocked out by these li’l NHTs that I decided to compare them with a similarly priced babyspeaker that’s received a rave review in these pages: PSB’s $200/pair Alphas (footnote 5). Each pair of speakers was placed atop a pair of Aunt Corey’s Uneducated White Trash Speaker Stands, coupled to the stands with four small pads of Blu-Tack damping material per speaker, and positioned about 2′ from the rear wall. The NHTs were toed-in, but the PSBs were left to fire straight ahead, as recommended in the Stereophile review.
I found that the two budget speakers sounded radically different, each offering its own set of strengths and weaknesses. The vented-alignment PSB had a weightier, more full-range sound than the bass-less SuperZero. But while the Alpha had the deeper bass extension, it also sounded much more muddy and bloated than the NHT. The PSB definitely trades off clarity and tightness in the low end for some semblance of a full range, but I found this choice of extension vs transient purity to really thicken and slow the sound down—especially on rhythmically intense material such as Kiko. The Alpha definitely had deeper bass extension than the SuperZeros, but the lack of definition and the plodding, one-note bass kept me from really digging the music as much as I did with the NHT.
In virtually all other areas of performance, the SuperZero walked all over the Alpha. The NHT was more neutral in character, possessing a level of clarity through the midrange and highs that the PSB didn’t even hint at. While the SuperZero approached the kind of midrange quality you get from something like a ProAc Response Two, the Alpha had enough nasality—a “hootiness”—that it kept them from reaching the same level of sound quality as the NHT. The almighty Fairfield Four CD really showed up the difference in midrange coloration, the PSB adding a considerable amount of midbass heaviness and cupped-hands coloration to the voices.
But the most dramatic difference was in the speakers’ renditions of space. On records and CDs that have a good sense of depth and breadth, the SuperZeros consistently threw up a much larger, more detailed soundscape than the Alphas. The NHTs are so impressive in this area that I went into Space-Trippin’ Hyperdrive and yanked out all my neat-o “wide open spaces” records, such as the Ry Cooder/Vishwa Bhatt A Meeting by the River, the “Angels With Dirty Faces” track off Kiko, and Jimi’s “Still Raining, Still Dreaming” off Electric Ladyland (Reprise 2-2RS-6307). And if I closed my eyes and forgot about the lack of any real bass, there were almost no clues that I was listening to a pair of $230 babyspeakers sitting on a pile of cinder blocks.
All those boundary-stretchin’ sounds—the church acoustics and image placement of the guitars on the Cooder/Bhatt CD, the “outside o’ the speakers” hand claps and shaker sounds on the Los Lobos track, and the flying-around-the-room second-guitar solo on “Still Raining, Still Dreaming”—came through just as clearly defined in space and as detached from the black boxes as I’ve heard from far more expensive speakers, including the Spica Angelus, the ProAc Response Two, and NHT’s flagship 3.3.
Bottom line: If you’ve got 200 clams and want a small budget speaker that plays surprisingly loud and sounds fairly full-range, and you’re not too picky about imaging or ultimate midrange, the PSB Alpha is a fine choice. But if you want a speaker that trades off the PSB’s bass extension for an overall sound quality approaching multi-thousand-dollar audiophile speakers, the SuperZero is the one to buy.
Harbeth, I hear ya callin’
As JA was fixin’ to review Harbeth’s latest iteration of the classic BBC LS3/5A minimonitor (footnote 6), I asked him to ship them to me for a few days so I could compare the SuperZeros to a more refined babyspeaker than the $200 PSB Alphas. The little NHTs were so good, I wanted to hear how they fared against the $1000/pair LS3/5A, the time-tested king of the genre.
Well, I can tell you that the $800-more-expensive Harbeths put up a lot more of a fight than the Alphas. And I can also tell you that all the classic good-time ingredients that’ve made the LS3/5A one of the most enduring of all speaker designs—terrific imaging, low midrange coloration, and a warmly balanced sound that just almost sounds like a full-range speaker—are intact in the current Harbeth version.
Footnote 4: While the cinder-block stands were wobble-free on my living room’s hardwood floor, you might want to stick some of the large Tiptoe cones under the stands, points down, to increase stability on a carpeted floor. You might also Super-Glue the cones to the bottom of the cinder-block stands because the stands have a tendency to slide around on top of the cones when jostled.
Footnote 5: See Jack English’s review in the July ’92 Stereophile, Vol.15 No.7, p.117.
Footnote 6: JA’s review of the LS3/5A appeared in December 1993, p.189.
But I can’t tell you that the Harbeths creamed the SuperZeros—or that I’d rather own a pair of the “new” LS3/5As over the $230 NHTs—because I think the SuperZero is a more neutral, transparent speaker than the venerable BBC design. And it can play a hell of a lot louder without strain, too. True, the SuperZero doesn’t have the midbass hump that gives the LS3/5A its famous “li’l ‘un that can boogie” reputation. And the NHT’s high end is more extended and detailed than the Harbeth’s, which has that warm, forgiving character that sez, “It’s British and I paid a lot of money for it.” But if I had to choose between the two for an accurate, revealing reference speaker to do all my reviewing with, I’d definitely go with the SuperZero—and pocket the change.
NHT SW2 subwoofer & MA-1 amp/crossover
And what of the SW2 active subwoofer? Despite its smallish size, the NHT SW2 is a serious subwoofer that gave plenty of usable output all the way down below 25Hz in both of my listening rooms. The SW2’s ported 10″ driver delivered amazing room-shaking output levels, even when driven by the 80W MA-1 (which I didn’t think was going to pump out the kind of seriously hardcore bass that the SW2 was capable of).
In terms of control and definition, the SW2 was very impressive, but not quite as tight or as “fast” as the $2750 Muse Model 18 225W active subwoofer I used for a time in my reference system. Strong basslines such as those from Stevie Ray Vaughan’s Couldn’t Stand the Weather (Epic EK 39304) were all there and then some, but the SW2 fell a bit short in terms of sheer tightness and clarity when compared with the much more expensive Muse. The SW2 was incredibly tight and well-defined, but didn’t quite match the Muse’s sheer clarity and transient purity or a really good sealed system like the 12″ acoustic-suspension woofer of NHT’s own $4000 3.3.
For only $650, I don’t know of a better subwoofer than the SW2—the only real sub even close in price and performance is the popular Hsu Research SW10, which costs $750/pair. However, that price does not include an amplifier to drive the Hsu subs, while the 80W MA-1 is included with the $650 SW2P package.
Taken on its own terms, the SW2 does an extraordinarily good job of reproducing the music’s bottom-most octaves—I was impressed enough with the SW2 that I bought one for my Home Theater system.
I’m gonna add so-ome bot-tum
As excited as I was about the NHT SuperZero, I have a hard time giving a blanket recommendation for a speaker that has no semblance of a low end. That’s why I had NHT send along the SW2—so I could hear if the marriage of the SuperZero and the SW2 would result in a world-beating $880 speaker system.
At first I tried using two SW2s in a passive configuration, with their internal 130Hz crossovers splitting the signal between each sub and SuperZero. NHT’s Ken Kantor told me that the SW2’s internal crossover was optimized for the larger NHT speakers and not for the SuperZero, but encouraged me to try the configuration anyway.
Well, I can tell you this: If the SuperZeros had no low end before, they DAMN WELL had it now!!! Ye gads!! Beavis and Butt-head would kill for a speaker setup like this! There was way too much bass with this setup, but I gotta tell you—the Butthole Surfers’ Independent Worm Saloon never sounded as almightily WOMPIN’! Man, I wish I’d had this setup when I was 13!! Cuz when you’re 13, you could give a rat’s ass about timbral accuracy and tonal balance—you want BIG, BAD BASS that’ll knock your dad clean off his feet and send him tumbling down the stairs when he has the gall to barge in yelling for you to turn that #$A$% down!! YEAH!! LATER WITH YOU, POPS!! WA-BOOOM!! This is the setup that Beavis and Butt-head would go for in a BIG way. If you’re 13 and reading this right now, you have FOUND the SOUND!
But for us over-13 audiowusses, using two passive SW2s isn’t really the way to go if you want to listen to anything but AC/DC’s Back in Black, which I have to admit has never sounded better in my house than with the two passive SW2s. Way too much bass, and the transition between the subs and the SuperZeros wasn’t very smoothly integrated, either—not surprising in light of the fact that neither the SW2 nor the SuperZero was designed to go together in this fashion.
Pre-pube ya-yas out of my system, I went about hooking up the SW2 the way NHT intended: just a single SW2 driven by the MA-1 amplifier, crossed over to the SuperZeros with the MA-1’s own speaker-level crossover. The output of the main amp, a Muse 100 was taken to the MA-1, and the high-pass-filtered signal was sent on to the SuperZeros.
While this configuration was far better in terms of tonal balance and low-end control, the SuperZeros lost a good deal of their clarity and focus. There was a layer of opacity now that wasn’t there when they were driven directly by the Muse amp. No matter how I adjusted the sub’s level and/or crossover frequency, running the speaker-level signal through the MA-1’s internal speaker-level crossover caused a considerable amount of degradation of the satellites’ sound—so much so that I don’t recommend this hookup method. Much of what the SuperZeros did so well was lost when crossing them over through the MA-1.
Aunt Corey’s Uneducated White Trash DIY High-Pass Filter
But I knew there had to be a way to mate these two terrific products into one awe-inspiring $880 loudspeaker system. I tried running the SuperZeros full-range with the Muse while sending my preamp’s output via a Radio Shack Y-adapter to the MA-1’s line-level inputs—so the SW2 could fill out the bottom end, even though the SuperZeros weren’t high-pass-filtered at all.
Now I was getting somewhere! This sounded much better than using the MA-1’s crossover. The SuperZeros remained clean and clear, and the SW2—the MA-1’s 80Hz setting gave the best blend in my room—really fleshed out the sound to make for a truly full-range speaker system with all the SuperZeros’ amazing attributes, but coupled with a real bottom end.
Still, the transition between the SW2 and the SuperZero wasn’t as smooth and transparent as I’d hoped for. And driving the SuperZeros full-range did nothing to improve their dynamic headroom and midrange purity—reasons to use a subwoofer which are just as important as merely adding the bottom octaves.
Like Martin Colloms, I can’t help messing with stuff. Martin bi-amps his Wilson WATTs/Puppies by inserting a passive first-order RC filter between his preamp and the amp that drives the WATTs, so I thought I’d try the same thing with the NHT system. I made up a couple of passive first-order 6dB/octave line-level filters: simple RC networks consisting of a series 0.1µF “Kimber Kap” polypropylene capacitor shunted to ground with a 15k ohm Resista metal-film resistor (fig.1). In conjunction with the Muse’s 51k input impedance, this gave a passive high-pass filter -3dB down at approximately 137Hz (footnote 7) (fig.2)—high enough in frequency to roll off enough bass in the SuperZeros to give them more headroom, but low enough to ensure a seamless transition with the SW2. I soldered these components directly to an unmounted RCA jack at the filter’s input, and to an RCA plug at the filter’s output. These filter modules were plugged directly into the Muse amplifier’s input jacks, and the interconnects split from the Y-adapter at the preamp output plugged directly into the filters.
Fig.1 Simple DIY passive high-pass filter for use with satellite speakers.
Fig.2 Amplitude & phase response of fig.1 filter when loaded with 51k ohms amplifier input impedance (2dB/vertical div.). Note polarity inversion of satellite feed due to series capacitor (footnote 8).
This was the best-sounding configuration of all. With the high-pass filters providing a degree of bass attenuation in the SuperZeros, and the SW2’s own crossover set for 80Hz, the transition between the sub and the SuperZeros was much more seamless than when driving the SuperZeros full-range. And the system remained clean and clear at higher levels, too—much higher levels, in fact, than either the Spica Angelus or the ProAc Response Two, both of which cost a good deal more than the combined price of the NHT system, and neither of which approaches the full NHT system’s bass extension. I was surprised at how much this setup reminded me of the sound I enjoyed from my previous reference speaker system—the $3000/pair ProAc Response Twos mated with the $2750 Muse Model 18 subwoofer. In terms of finesse, musicality, and top-to-bottom coherence, the $880 NHT system came very close to the kind of sound I used to hear from that $5750 reference combo.
Depending on the room I used them in, the polarity of the subwoofer connection varied with the SuperZeros/SW2 system. In my He-Man listening room, I achieved the flattest measured response and smoothest blend between the sub and sats with the woofer connected in the same polarity as the SuperZeros. However, in my Real World listening room—my mild-mannered living room by day—I found that reversing the polarity of the connection between the MA-1 amplifier and SW-2 subwoofer gave the flattest measured response and the better integration with the SuperZeros. I determined the optimum subwoofer polarity in both rooms with the bass warble tones on track 16 of Stereophile‘s Test CD 2 and a $30 Radio Shack sound-level meter set for “C” weightin’ and “slow” needlin’.
NHT’s Ken Kantor agrees that there’s really no “right” subwoofer polarity, and that the user should try both in order to find the polarity that makes for the smoothest transition and the least excitation of room modes. This was certainly true of my living room, where a positive subwoofer polarity interacted with the pretty large bass hump in the 80-100Hz region. Reversing the subwoofer’s polarity nulled out this hump and gave a much flatter response through the whole bass range.
Bottom line: Try both polarities with various male vocal recordings (the Fairfield Four were ideal for this, as were Richard Lehnert’s spoken intros on track 1 of Test CD 2) to see which sounds more natural. The difference won’t be subtle, believe me.
I said before that if the $230/pair NHT SuperZeros had been around back when I bought my $550/pair Spica TC-50s, I’d’ve chosen the NHTs. Well, if the $880 NHT SuperZero/SW2P combo had been available when I bought my $1275/pair Spica Angeluses, I’d’ve gone with the NHT system. The Angelus is an amazing-sounding speaker, but it just couldn’t compete with the SuperZero/SW2P system in terms of bass extension or dynamic ceiling. And while the Spica has one of the most holographic soundscapes at any price, I don’t think the NHT system (hooked up the way I finally had it) lags too far behind. As with the Harbeth LS3/5As vs the subwooferless SuperZeros: If I had to choose between the Angelus and the SuperZero/SW2P combo as a reference speaker system for my reviews, I’d choose the NHT.
Footnote 7: To calculate the approximate -3dB point for a first-order filter like this, use the formula f = 1/(2PiRC), where Pi = 3.142, C is the value of the series capacitor in farads, and R is the combined resistance in ohms of the amplifier’s input resistance and the shunt resistor used. For the example CG gives: a 15k resistor in parallel with a 51k resistor gives a combined resistance of 11.6k ohms; the capacitor has a value of 0.1 x 10E-6 farads; the formula predicts a -3dB point of 137.1Hz.—John Atkinson
Footnote 8: In John Atkinson’s comments on the NHT SuperZero, he noted an apparent phase inversion imparted by a simple high-pass RC filter (fig.2, p.149). In fact, the capacitor cannot invert the phase—it causes a phase shift which only approaches 90 degrees at the limit and only shifts by 45 degrees at the nominal crossover point, 137.1Hz. On the graph, a 180 degrees phase inversion is shown, due solely to measurement presentation. Allowing for this, the graph does show the predicted 45 degrees lead at crossover. The corresponding low-pass network for the woofer could well lag by 45-90 degrees, according to the order of the crossover. The resulting system phase match is indeterminate, neither in nor out, and practical experiment with either phase connection is worthwhile to see which suits you and the listening room best.—Martin Colloms
Home theater use
The SuperZeros should also be considered a prime candidate for Home Theater systems that see double duty as music-playback systems. I tried using five SuperZeros for the Left, Right, Center, and two Surround speakers—along with an SW2P to handle the bass—in my own Home Theater rig, and was extremely impressed with their performance when playing high-quality laserdiscs. And unlike every video-specific Home Theater speaker I’ve heard—including THX-approved models from Fosgate, JBL, and even the Snell 500 THX system JGH reviewed in Vol.15 No.12, p.202—the SuperZeros didn’t offer reduced performance when asked to play non-soundtrack music CDs through my Home Theater rig. Video-optimized speakers may work well when playing soundtracks, but none I’ve heard has offered even minimally high-end sound quality when playing back non-soundtrack music. The SuperZeros are therefore an excellent choice for those who have room for only one audio/video system, or who wish to listen to a lot of music in their Home Theaters.
Three pairs of the SuperZeros and the SW2P cost $1040—and since you only need five SuperZeros, consider this package as a true audiophile Home Theater speaker system, plus an extra speaker you can throw at the next wiseguy you see wearing a “Back to Mono” button.
I was totally knocked out by the NHT SuperZeros, either by themselves or in conjunction with NHT’s SW2P active subwoofer. While there are several inexpensive speakers on the market that are good at presenting an illusion of near-high-end sound, the SuperZeros are true high-end minimonitors that I would feel completely comfortable using as my reference speakers above 100Hz. They are really that good.
Mated with the SW2P subwoofer and a pair of passive in-line high-pass filters like those I described above, the SuperZeros are capable of delivering the kind of audiophile-quality, full-range sound that bears close comparison with some of the most well-regarded high-end speakers on the market. The SuperZero/SW2 system is one of the best values I know of in a full-range, high-end loudspeaker system.
Highly recommended!—Corey Greenberg
Sidebar 1: Specifications
NHT SuperZero: two-way, acoustic-suspension minimonitor. Drive-units: 4.5″ paper-cone woofer, 1″ soft-dome tweeter. Frequency response: 85Hz-25kHz, ±3dB. Crossover frequency & slopes: 2.2kHz, 6 and 12dB/octave. Impedance: 8 ohms nominal, 7.5 ohms minimum. Sensitivity: 86dB/W/m. Power handling: 100W maximum, 15W minimum.
Dimensions: 5.5″ W by 9″ H by 5″ D. Internal volume: 2 liters. Weight: 6.5 lbs each.
Finishes available: high-gloss black laminate, high-gloss white laminate, hand-rubbed oak veneer.
Serial numbers of samples tested: A410-0001000 & 0001001.
NHT SW2: 10″ woofer in vented enclosure. Frequency response: 21Hz-350Hz, ±3dB direct in. Crossover: 130Hz (passive version, built-in). Sensitivity: 89dB (2.83V at 1m), 200W maximum. Impedance: 8 ohms nominal, 6.2 ohms minimum.
Dimensions: 16″ W by 16″ H by 16″ D. Internal volume: 50 liters. Weight: 40 lbs.
Finishes available: high-gloss black laminate, high-gloss white laminate, hand-rubbed oak veneer.
Serial number of sample tested: A350-003237.
NHT MA-1 mono amplifier and electronic crossover: Power rating: 80W into 8 ohms, continuous (19dBW); 120W into 4 ohms, dynamic (17.8dBW). Dynamic headroom: 2dB. Frequency response: 20Hz-20kHz, ±0.25dB. THD: ±0.01%. Slew rate: 30V/ms. Measured output impedance: 0.09 ohms at 20Hz. Measured input impedance: 22k ohms. Measured maximum voltage gain into 8 ohms: 48.6dB.
Dimensions: 16″ W by 3″ H by 13″ D. Weight: 11 lbs.
Serial number of sample tested: 1189DOM9206.
All three: Approximate number of dealers: 250. Manufacturer: Now Hear This, Inc., 537 Stone Road, Suite E, Benicia, CA 94510. Tel: (800) NHT-9993. Fax: (707) 747-0169. Web: www.nhthifi.com.
Sidebar 2: Measurements
Fig.3 shows the manner in which the SuperZero’s impedance changes with frequency. The peak centered just above 2kHz is due to the crossover; that in the upper bass is due to the sealed-box woofer tuning. Reaching a maximum of 19.2 ohms at 120Hz, it indicates a complete absence of mid- and low bass in the speaker’s output. Overall, the SuperZero is a super-easy load for an amplifier to drive, which, coupled with a calculated B-weighted sensitivity of 85dB/W/m—highish for the size—means that it can be used even with inexpensive receivers (footnote 1).
Fig.3 NHT SuperZero, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
The NHT’s quasi-anechoic response, averaged over a ±15 degrees window on its tweeter axis, is shown in fig.4. The treble is commendably flat for such an inexpensive design, though the upper midrange appears to be a little forward-balanced, there being a 2-4dB energy excess between 1300Hz and 2300Hz. As expected from fig.3, the SuperZero starts rolling out above the bass region proper. The nearfield response in fig.4 reaches its -6dB point at 88Hz, just above the lowest note of the electric guitar.
Fig.4 NHT SuperZero, anechoic response on tweeter axis at 45″ averaged across 30 degrees horizontal window and corrected for microphone response, with nearfield woofer response below 200Hz.
In my listening room, the spatially averaged 1/3-octave curve (fig.5), calculated by averaging 20 individual measurements taken for left and right speakers separately over a 72″-wide by 36″-high window centered on the listening position, confirmed both the SuperZero’s rather forward balance and catastrophically lightweight bass. Overall, however, this curve is much smoother than I would have expected from a pair of speakers in this price region, particularly in the treble.
Fig.5 NHT SuperZero, spatially averaged 1/3-octave response in JA’s listening room.
This could readily be heard. Apart from a slightly “sniffy” quality in the high treble (this is almost a Ken Kantor trademark) which added some wiriness to the sound of violin and emphasized the crackle that accompanies trumpet tone, the SuperZero’s high frequencies sounded clean. The midrange, too, was remarkably free from coloration for a speaker this inexpensive. (Remember that if the SuperZero sells for $230/pair, NHT’s total parts cost for a pair can’t be more than $45 if they are to make a profit and stay in business.)
Unlike CG, however, I had a harder time getting past the speaker’s almost complete lack of low frequencies. It was very dependent on what kind of music I played. A lot of rock and small-scale classical music—string quartets, for example—emerged from the bass-truncation experience relatively unscathed, leaving me free to enjoy the NHT’s excellent sense of recorded space, good sense of pace, and clean midrange (as long as I didn’t play these tiny speakers too loud). But on large-scale orchestral music and power-rock with high-level low-bass lines, like Stanley Clarke’s new East River Drive album (Epic EK 47489), it all fell apart, leaving me marveling that I hadn’t noticed the emasculation of the music before. If choosing a minimonitor, and music with appreciable mid- and low bass contents is an important part of your life, you’d be better to choose the LS3/5A or (better) the Harbeth HL-P3 over the SuperZero. Or experiment with the NHT SW2 subwoofer, of course.
The SuperZero offers good dispersion in both lateral and vertical planes (figs.6 & 7, respectively, measured using DRA Labs’ MLSSA system with the Italian Outline speaker stand/turntable). Laterally, its top octaves do roll off more than 15 degrees off-axis, and a suckout at the top of the woofer range and a complementary peak at the bottom of the tweeter range appear at extreme off-axis angles. As long as you sit with ears somewhere in the vertical vicinity of the front baffle, you should receive pretty much the same tonal balance. Fig.6 does show, however, that sitting below the speaker tends to compensate for the on-axis forwardness in the upper midrange/low treble. Putting the speakers upside-down on shorter-than-usual stands would accomplish the same thing, which would also bring the two drive-units into a degree of time alignment, if that’s important to you. (The step response, fig.8, reveals that, on the tweeter axis, the tweeter’s output slightly leads the woofer’s.) The SuperZero’s waterfall plot (fig.9) reveals an impressively clean initial decay. Though a number of resonant modes can be seen as ridges parallel to the time axis, these are all at a low level.
Fig.6 NHT SuperZero, horizontal response family at 45″, normalized to response on tweeter axis, from back to front: reference response; differences 15 degrees off-axis, 30 degrees off-axis, 45 degrees off-axis, 60 degrees off-axis, 75 degrees off-axis, and 90 degrees off-axis.
Fig.7 NHT SuperZero, vertical response family at 45″, normalized to response on tweeter axis, from back to front: difference in response 15 degrees above tweeter axis; difference 10 degrees above tweeter axis; difference 5 degrees above tweeter axis; reference response; difference in response 5 degrees below tweeter axis; difference 10 degrees below tweeter axis; difference 15 degrees below tweeter axis.
Fig.8 NHT SuperZero, step response on tweeter axis at 45″ (5ms time window, 30kHz bandwidth).
Fig.9 NHT SuperZero, cumulative spectral-decay plot at 45″.
Footnote 1: I find it interesting that, with the appearance of inexpensive multi-channel receivers for Home Theater use, Consumer Reports appears to have abandoned the testing of receivers into the more revealing 4 ohm loads. One could be cynical and say that if CR continued to test receivers into taxing loads, they would be forced to point out to their subscribers that they just can’t get high continuous powers into loads below 8 ohms with a six-channel receiver without expecting to pay a lot more than they used to for a good two-channel receiver. And that, given their parsimonious philosophy, I am sure they would never do.—John Atkinson
Corey talked about the SuperZero’s tiny cabinet being more rigid than a larger one constructed from the same material—all things being equal. This will result in resonant modes that are higher in frequency and will therefore have less damaging effect on the music. Fig.10 shows that the mode highest in level lies at a very high 492Hz, or just below the B on the center line of the treble staff. Other modes are all much lower in level.
Fig.10 NHT SuperZero, cumulative spectral-decay plot of accelerometer output fastened to back of enclosure above terminal panel. (MLS driving voltage to speaker, 7.55V; measurement bandwidth 2kHz.)
Moving on to the SW2 subwoofer, fig.11 shows the impedance plot with the subwoofer’s jumpers removed for use with the MA-1 crossover amplifier. With minima a hair over 4 ohms, the subwoofer will not be too difficult to drive, though I feel that Corey’s use of two SW2s in parallel, which will give a 2 ohm impedance in the upper bass, is asking a lot from the MA-1. (The MA-1’s subwoofer outputs are marked “min impedance 6 ohm.”) The port tuning is revealed by the broad saddle in the magnitude trace centered on 25Hz. When the internal passive crossover is used, the SW2 becomes a more demanding load—fig.12, made with the high-pass outlets open-circuit—and its minimum impedance now drops to 2 ohms. With the passive low-pass filter, the SW2’s overall output is a bandpass centered on 50-60Hz, as can be seen from fig.13, which also shows the individual nearfield outputs of the port and woofer. The -6dB point of their combined output lies at 35Hz, which will be extended in-room.
Fig.11 NHT SW2, active crossover mode (jumpers removed), electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
Fig.12 NHT SW2, passive crossover mode (with jumpers), electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
Fig.13 NHT SW2, low-pass filter in-circuit, individual nearfield responses of woofer (curve with minimum at 23Hz) and port (bottom curve at 60Hz), with complex sum of nearfield responses (top).
The NHT MA-1 amplifier’s low-pass crossover functions, implemented using 4558 dual op-amp chips, are shown in fig.14. The flat curve is with the unit in “Bypass” mode. The passive high-pass feed from the MA-1 to the satellite amplifier has a -3dB point of 120Hz and a rollout slope of 6dB/octave, while the three low-pass settings for the subwoofer have -3dB points of 51Hz, 82Hz, and 110Hz, each with an ultimate slope of 12dB/octave.
Fig.14 NHT MA-1, Bypass, high-pass, and low-pass frequency responses (2dB/vertical div.).
If there’s one easy job for an amplifier to do, it’s driving a subwoofer. With a bandwidth limited to three or four octaves at most, a low-pass filter that suppresses the higher-distortion harmonics, and a speaker whose impedance is generally benignly behaved, it might be thought that a subwoofer’s designer could relax the specs a bit. Yet Ken Kantor’s design appears to be a respectable little amp. (Though it did get very hot after the one-hour, 1/3-power preconditioning period.) It uses a single output pair of devices and a series inductor, yet its output impedance was low, at 0.09 ohms between 20Hz and 1kHz; its input impedance was a reasonable 22k ohms. The maximum gain in Bypass mode, with the volume control wide open and an 8 ohm load, measured a rather high 48.6dB. The unweighted, 22Hz-22kHz S/N ratio was 79dB (ref. 1W into 8 ohms), with some very low-level 60, 120, 180, and 240Hz power-supply harmonics noticeable on an FFT-derived spectrum (not shown).
Overall distortion was very low, generally lying below 0.01%. Though it did rise at higher frequencies, this will be of no concern to its subwoofer-driving owner. The distortion spectrum itself was dominated by third harmonic (fig.15), though “dominated” is perhaps hardly the correct term when this only reached -69.6dB with respect to the level of the 50Hz fundamental (0.03%). The fifth harmonic was the next highest in level, with the seventh lying below the second.
Fig.15 NHT MA-1, spectrum of 50Hz sinewave, DC-1kHz, at 80W into 4 ohms (linear frequency scale). Note that the third harmonic at 150Hz is the highest in level, 69.6dB below the level of the 50Hz fundamental (0.03%).
Finally, the manner in which the distortion/noise level varied with output power for a 117V AC source voltage is shown in fig.16. The amplifier gives its lowest distortion into 8 ohms (bottom trace), with the approximate clipping power into that load (defined as 1% THD+noise) being 72W (18.6dBW). Into 4 ohms, 96W was available (16.8dBW), and into 2 ohms, 110W (14.4dBW), though the amplifier’s distortion into this low impedance was significantly higher than into 8 or 4 ohms. These figures are a little below spec, perhaps due to my use of a 100Hz test signal rather than the more traditional 1kHz. (I think that 100Hz is a more appropriate signal for a subwoofer amplifier.)
Fig.16 NHT MA-1, 100Hz distortion vs output power into (from bottom to top at 10W): 8 ohms, 4 ohms, and 2 ohms.
Regarding the sound of the MA-1/ SW2 combination: In absolute terms I would have liked a little more low-bass extension. It could also add a rather plodding, one-note signature to the sound unless you were painstakingly careful in choosing the woofer’s placement, polarity, and crossover settings. (I’m always nervous about blanket recommendations for subwoofer/satellite systems, given the difficulty even experienced audiophiles have in achieving the optimal blend in-room between sub and sats.) This was much less noticeable with orchestral music than with rock, however, and—its slight treble wiriness apart—the combination of the SuperZeros and the SW2 reproduced large-scale classical music with aplomb.
I agree with CG that the NHT subwoofer system is an excellent value at $650. Using Y-adaptors with passive high-pass filters in series with the main amplifiers, I got a well-integrated, almost full-range sound that allowed the SuperZeros to sing in a most effective manner. At $880, the combination of the SuperZeros with the SW2/MA-1 is a shoo-in recommendation.—John Atkinson