Most people would agree that the real goal of any audio system is an illusion of transport — the musicians to the listening room, the listener to the recording space, or both to another place entirely. I’ll tell you right now that NHT’s long-awaited Xd speaker system, though not without its flaws, is one of those rare products that lives up to this promise. In successfully applying advanced digital technology to an otherwise common bookshelf speaker, NHT and its partners have cooked up a magic brew that will quicken your heart and send your emotions soaring. Simply put, this system takes you inside the music and ultimately lets you forget the gear.
The product of more than four years of development, the basic Xd package includes a pair of 10-inch-tall bookshelf speakers called the XdS, a powered subwoofer designated the XdW, and an electronic component not much bigger than an old VCR. This box, the XdA, contains a digital signal processor developed by the Australian company DEQX (pronounced “decks”) and a multichannel power amplifier contributed by PowerPhysics, a California firm that specializes in digital switching amps. Digital amplifiers are extremely efficient — they pump out gobs of power from a small chassis while staying remarkably cool. Despite the XdA’s modest size, it houses four 150-watt amps, each powering just one of the drivers in the compact satellites. The subwoofer contains its own 500-watt digital amp, which is fed by the XdA’s line-level sub output.
NHT has used first-class drivers throughout, including a 5.25-inch magnesium-cone midrange and 1-inch aluminum-dome tweeter (with a powerful neodymium magnet) in the satellite and two 10-inch aluminum-cone drivers in the subwoofer. Both speakers have sealed cabinets that offer solid build quality, attractive sculpted styling, and an unusual blond and plum finish in furniture-grade lacquer and veneer that NHT calls Classic. A pair of matching, weighted stands come with the system.
Given the Xd’s unassuming presence, its $6,000 price tag could take your breath away, even after conceding that the power amp is included. And the real palpitations start when you move into home theater or multichannel music. NHT doesn’t offer a 5.1-channel Xd system or even a horizontal center-channel satellite. Instead, the company forces you to buy three stereo Xd setups for a 6.2-channel system priced at $16,500, the $1,500 discount reflecting the omission of one subwoofer on the thinking that a pair of these oughta do for most rooms (trust me, it will). Considering what’s not there — the 6-foot floor-standing towers in grain-matched Brazilian rosewood, the massive power amplifiers and all the metal they entail — it seems that most of what you’re paying for is the digital processing.
WHAT’S ON THE EDGE? All multidriver speaker systems have “crossovers” that separate the music frequencies into bands so the drivers will reproduce only the sounds they’re best suited for. Typically, these circuits slightly overlap the sounds coming from each driver. So, for example, in a simple two-way speaker with a woofer and tweeter, the woofer delivers a small portion of music that should ideally come only from the tweeter, and vice versa.
This overlap, though a necessary evil, creates distortions. Some parts of the musical spectrum may play at different volumes in the overlap area, causing frequency-response errors that can affect tonal balance. And since some notes are being reproduced simultaneously by different drivers, they arrive at your ears at slightly different times and with different audible characteristics. The individual drivers also introduce their own timing errors, as some frequencies will naturally lag behind others as the sound emerges from the speaker. Collectively, these errors undermine sonic clarity and the ability to accurately place instruments within a virtual soundstage.
Here’s where DEQX technology comes in. It’s applied in both the design phase and during playback. During design, the output of each driver in the XdS was measured to determine, among other things, its ideal frequency limits and which frequencies within its range were out of sync with the others. That information is later used in the XdA to correct the performance of the drivers and program the system’s crossovers.
The beauty here is that fixing these frequency and time errors in advance allows the designers to use digital crossovers that virtually eliminate driver overlapping and the bad stuff that goes with it. In technospeak, the crossover slope between the Xd satellite’s midrange and tweeter driver is set at 100 dB per octave instead of the typical 12 dB per octave for a conventional speaker. Fellow geeks can go to Deqx.com to learn more, but what’s important is the end result. There’s an improvement in the power handling and dynamic capability of each driver, allowing it to play louder without distortion. And the total system disperses the sound across all frequencies more evenly, which largely eliminates the “sweet spot” effect that favors listeners sitting precisely between the speakers. With the Xd, anyone in the room hears pretty much the same sonic image.
Best of all, the time corrections bring instruments and voices into sharper focus — you can follow them individually no matter how complex the music and hear the kind of detail that’s uncommon on all but the very best (and even more costly) high-end playback systems I’ve heard. That this is possible from a pair of small bookshelf speakers is nothing short of astounding — and precisely the point. In time, NHT hopes to use DEQX processing to improve the performance of relatively inexpensive speakers.
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The Short Form
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| DIMENSIONS (WxHxD) XdS satellite 6.5 x 10.25 x 8.5 inches XdW subwoofer 11.25 x 22.125 x 13 inches XdA processor/amplifier 17 x 2.875 x 15.75 inches WEIGHT XdS 13 pounds; XdW 57 pounds; XdA 17.5 pounds PRICE $6,000 MANUFACTURER NHT, nhtxd.com, 707-748-5945 |
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Plus
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| •Amazing image clarity and focus. •No listener fatigue. •No "sweet spot." •Small form factor. •Upgradable processing. |
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Minus
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| •Slight lack of "air." •Loss of shimmer on cymbals. |
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Key Features
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| •Powered subwoofer/satellite system •DEQX digital signal processing for crossovers and driver optimization •Outboard PowerPhysics digital amplifier |
Two notable connectors on the back of the XdA are a microphone input, which will eventually work with DEQX room-correction processing that’s still in development, and a USB port for downloading new features or updating the digital crossovers in the box. While I was testing the system, NHT e-mailed me a small file containing a set of updated crossovers. It took all of 15 minutes to install the software NHT provided for my PC and use it to download the upgrade to the XdA.
PERFORMANCE Right from the get-go, the little XdS satellite proved itself a brutally revealing speaker that takes no prisoners when it comes to recording quality. The bittersweet love song “Clarity” on John Mayer’s Heavier Things CD begins with a slow, rhythmic introduction paced by a four-note piano bit, a repeating drumstick thwack, some long trumpet notes, and guitar. The Xd spread these instruments before me with alluring precision, but it was quickly apparent how much artificial reverb had been added to Mayer’s voice. When the song reached its chorus and the tempo kicked up, I could follow every instrument against the pervasive electric guitar, but felt cheated by the record’s compressed dynamics. This type of thing was a regular occurrence with the Xd, especially with a lot of older popular music.
But with good recordings, the system was nothing short of amazing. Boogyin’ Swamprock Salsa & Trane is a superb production by A la Carte Brass & Percussion, a 17-piece band with real cajun soul. “Lucy I’m Home” — their romping take on the theme from the I Love Lucy show, starts with a minute and a half of pure percussion: clanking cowbells, stomped kick drums, rapped snares and congas, clicking wood blocks, dinging triangles — you name it. When the trumpets, sax, trombones, and sousaphone finally break in, you’re immersed in a riot of sound. The digital amp rose to this occasion as it did on every test track, playing plenty loud and clean in our 12 x 20-foot room. Here again, I could pick out any instrument and follow its line in the chaos. And at the same time that the Xd kept this cacophony from melting into a muddled mess, it faithfully delivered the natural blat of the horns without making them harsh or strident.
This was another suprise with the Xd. Despite long sessions with many potentially irritating tracks, I experienced virtually no listener fatigue. An example was Ricky Lee Jones’s cover of “Don’t Let the Sun Catch You Crying” from Flying Cowboys. Jones stretches her voice to the limits of its upper register, and her half-nasal falsetto — which can sound edgy on a bad speaker system — had a smooth, silky purity that I just couldn’t get enough of.
The subwoofer proved itself a real powerhouse, too, providing well-defined, pervasive string-bass lines and taut, solid impact on the drums. “Cherry Pie,” the bad-boy tribute from Jennifer Lopez’s Rebirth CD, starts out with synth bass and kick drum that’ll wake the dead. The XdW grabbed on tight, went deep, and wouldn’t let go. When the music stopped momentarily and J-Lo let out a breathy “Yeah you!” she was as good as in the room with me. (Okay, at least I can fantasize.)
Was the Xd perfect? I only wished. Although it had that near miraculous focus and a fairly wide soundstage, it couldn’t deliver all the image depth of the big, panel-style dipole speakers I’m fond of. More bothersome were a slight lack of air around the instruments, which stole some of the ambience of recordings done in natural spaces, and the way the satellites over-tamed the metallic shimmer of well-recorded cymbals. Both of these concerns were alleviated somewhat by the filter update but not completely removed. And the subwoofer’s fixed digital crossover made it difficult to get a perfect blend with the satellites. (See "Tech Notes," below.) But here’s the thing: none of this prevented me from falling in love with these speakers.
BOTTOM LINE I could go on and on about the NHT Xd system, because that’s what I did — disc after disc, song after song, hour after hour, searching for new gems among my recent music purchases and rediscovering all my old favorites in a new way. How ironic that a speaker system designed to sound great from anywhere in the room made me want to sit and listen.
Still, I’m guessing audiophiles will debate this system in the days to come. Some, like me, will latch on to what it does so right; others may focus on its perceived weaknesses. But if there’s one thing all will probably agree on, it’s that you have to hear the NHT Xd to believe it.
Tech Notes
All measurements were taken with the XdS satellite mounted on the supplied stand and with the boundary-compensation control on the XdA processor/amp set to the Away from Walls position. There were two key findings. First was the satellite’s limited output below 200 Hz. It measured 2.7 dB down in level at 248 Hz and dropped to 15 dB down by 105 Hz. Coupled with the subwoofer’s fixed crossover frequency, measured at 104 Hz (with a steep 40 dB-per-octave slope that effectively cuts off any output above that point), the satellite’s lack of low-frequency energy leaves a gap that may complicate system setup in some cases. Otherwise the XdS measured very flat and smooth in the middle to upper frequencies.
Also notable was the satellite’s incredibly uniform directivity. Although the system was reviewed for stereo, I also measured for average response across a ±45° listening window, typical of center-channel speakers, and a ±60° window, common for surround speakers. These response curves looked smooth and very much like the primary front left/right response (averaged over ±30°), with only a small dropoff in the extreme highs at the widest listening angles. The XdS satellite can serve in any channel position in a surround sound system.
The XdW subwoofer’s bass limits were measured with it placed in the optimal corner of a 7,500-cubic-foot room. In a smaller room users can expect 2 to 3 Hz deeper extension and up to 3 dB higher sound-pressure level (SPL). The sub had smooth response, measuring only ±1.9 dB from 32 to 104 Hz, and useful dynamic capability down to 20 Hz. Although it had very high output at 62 Hz (112 dB SPL), its linear SPL capability fell off at 13 dB per octave below that frequency. Average SPL from 25 to 62 Hz was 103 dB.
— Tom Nousaine