July 2006NHT Xd Loudspeaker System
by Doug Schneider
NHTs Xd speaker system is one of the most intriguing audio products to be released in some time. Its a compact and stylish active satellite/subwoofer system that features DSP-based crossover technology from DEQX in Australia and digital-switching amplifiers from PowerPhysics in California. Its priced at $6000 USD for the whole shebang (more if you want to have three additional speakers for home theater), complete with cabling.
NHT discovered the work of DEQX some time ago and was smitten by the possibilities that digital crossovers allowed; to make the system work, though, NHT needed amplification, and while the company probably had umpteen dozen choices, they selected the PowerPhysics technology. This makes the NHT Xd active speaker system a three-company technical tour de force, and all three contributors are bent on providing state-of-the-art performance in a compact, high-style package.
The Xd system has three main parts: the XdS satellite speakers, the XdW subwoofer, and XdA amplifier/crossover.
The XdS is a sealed design that uses a 1" dome tweeter and 5 1/4" midrange. Because the crossover technology is DSP-based and located in the XdA, no components other than the drivers and connectors reside in the speaker cabinet. This helps keep the speakers small and light -- each XdS measures 8 1/2"W x 11"H x 8 1/2"D and weighs 13 pounds.
At 11"W x 22"H x 13"D and with two stout 10" aluminum-cone woofers flanking each side, the XdW is the largest and heaviest component of the bunch. It weighs 60 pounds, but its not that bad to move around. As youll find out below, I didnt have to fiddle with the XdW's placement at all to make the system sound great. Unlike with the XdSes, there is an amplifier inside the XdW that NHT rates at 500W.
The XdW and XdSes are styled identically and look sharp. Their curves and slopes one moment seem futuristic and at others a touch retro. I particularly liked the color scheme of the system sent to me. The XdW and both XdSes had a light-colored wood finish that contrasted with maroon on the XdSs curvy baffle and the XdWs rounded underside. I love the look; in fact, I think the Xd is one of the best-looking speaker systems on the market today. A bit of trivia: When I was at the NRC measuring the speakers, a Swingline stapler on a desk was the exact same maroon color. Coincidence? Perhaps. Or did NHT have one of those around their offices when colors were being chosen? The Xd speaker system is also available in a deep-red/piano-black combo.
Finally, theres the silver-and-black XdA, which measures 17"W x 2 5/8"H x 16"D, and seems to weigh hardly anything at all (12 pounds Im told). Although its not as slickly styled as the speakers -- you can only do so much with a black-metal chassis and a black-and-silver faceplate, even if it has blue LEDs -- its lightweight and easy to configure. Inside are four independent PowerPhysics amplifiers, with each amplifier powering one driver in each XdS. You need one XdA for two XdSes, but one can actually drive two XdW subwoofers.
As I mentioned, the PowerPhysics amps are digital-switching amplifiers -- all the rage today, mostly because of their small size, low weight and low cost -- so they can deliver quite a bit of power yet help the XdA remain small in size and allow it to run relatively cool. NHT says that each amp can deliver 150W. However, while these digital amps are small and efficient, theyre also quite noisy -- more on this later.
Also inside the XdA is the DEQX processing engine, which handles the crossover tasks as well as other speaker manipulation. Now this is quite cool and, frankly, what most of the fuss is about with regard to this speaker system.
The XdA is fed line-level signals (it accepts singled-ended RCA or balanced XLR) that are digitized once they enter. Once the signals are in the digital domain, superior crossover manipulation can be done, which wouldn't be possible if the signals remained analog. For example, do you think 24dB-per-octave (fourth-order) crossovers are steep? NHT is claiming that DEQXs engine can produce 300dB-per-octave slopes (the crossover slope between the midrange and tweeter in the XdS is 108dB per octave, with 48dB per octave between the XdS and XdW). These steep roll-offs at the crossover points (the XdS midrange crosses over to the tweeter at just above 2kHz, and the transition with the subwoofer appears to be at 120Hz) result in greatly reduced driver overlap, which can improve dispersion and increase power handling.
The designers say they can also do quite a bit of frequency-response correction to make the speakers output far more linear as well. Because this is all done digitally, phase errors wont be introduced the way they are with passive crossovers. Basically, the designers dont have to choose their compromises; they can have their cake and eat it too.
Well, almost. The one thing working against the NHT design team is time -- time to do all this processing. If they were just concerned with producing audio, it wouldnt really matter how long it all takes. But when you need to synchronize with video, such as in a home-theater system, you cant hold up the audio portion too long or whats happening with the sound wont match whats happening on the screen. Therefore, because this system has been designed for use with audio and video systems, the designers had to put a limit on how long the XdA could take to do its thing. Their limit was about 9ms, which they say shouldnt be noticeable when synching with video.
The XdA has a few user-definable features. First, it can be set to be on all the time, "triggered" on by other components, or turned on automatically when it senses an incoming signal; this is set with a switch in the back. (The XdW has a power switch, but then only an auto-on option for its electronics, something Ill talk about below -- it created a bit of an issue for me.) The "Mode" switch on the front of the XdA alters the XdSs frequency response. Which setting you use depends on whether you have the speakers placed out in the room and away from boundaries (my preferred setup, and what I used for this review), close to one boundary, close to two boundaries, or on the TV acting as a center-channel. Each channel can be adjusted independently.
Quite a bit more can be said about all of the Xd system's technology, but the best resources are the NHT and DEQX websites, where there are technology papers that go into all the technical detail in far greater depth. Whats safe to say, though, is with the way things are going today -- digital, digital, and more digital -- digital crossovers like the one used in the Xd system represent the future of high-end audio, and were bound to see similar products in the years to come.
Unpacking and setup
Although I winced at the number of boxes that arrived to make up the Xd system -- six in total -- I was impressed with how fast and easy it all was to connect. The Xd system was set up and playing with a mere 20 minutes of assembly.
The XdS speakers are the trickiest part of the setup because of their integral stands, but even though this part required the most labor, its obvious that NHT put a lot of thought into the assembly. You simply flip each XdS speaker on its top and screw a threaded rod into the bottom of the cabinet. After that, you slide the pedestal portion of the stand over the rod and a base plate over that. Then, with just a wing nut and washer for the end inserted through the base, you tighten it all up. Done. Threaded spikes are also supplied for each base to make the stands sturdier on a carpeted floor.
Setting up the XdW sub and XdA processor/amp was even easier, although the XdW is a fairly heavy beast in comparison to the rest. Simply unbox and place the components where needed. In my case, the XdW went between the speakers, and the XdA was placed on my equipment rack. As I mentioned, NHT supplies the cabling, and quite a bit of it (about 20 feet of each), giving lots of placement freedom.
With such a quick setup, I was able to experiment with ancillary components, which proved vital to getting the most out of this speaker system. From the get-go, my Blue Circle BC3000 preamp and Theta Data Basic/Stello DA220 digital front-end produced a sound that was big, bold, and incisive with the Xd system. In fact, Ive never heard such a small speaker system sound so big. This setup could play at low levels with great detail, and it could play quite loud with good control. It sounded wonderful right off the bat, but there were some technical glitches right from the start too.
When the Xd system was simply on and idling, there was an easily detectable buzz from each XdSs midrange/woofer (a ground loop was my first thought), quite a bit of hiss from each tweeter (hiss from the tubes in my BC3000 preamp crossed my mind), and a high-frequency whine from the XdA itself (no idea of the cause there). I talked to NHTs Jack Hidley, and he also felt the buzz was a ground-loop problem, and that if I could switch to balanced connection (my BC3000 only has single-ended outs) that would help. He thought the high-frequency whine was likely a component in the XdA that NHT pots at the factory to eliminate the whine, but the review sample still exhibited some of the problem. We didnt really discuss the hiss.
So out went my regular source and in came the Aurum Acoustics all-in-one Integris CDP CD player/preamplifier, which has single-ended and balanced outputs. Its so quiet itself that youd swear its not even turned on. The Integris CDP cured the buzzing completely, but it wasnt necessarily a single-end/balanced thing. The buzz was gone regardless of the connections I used, which left me a tad puzzled.
The high-frequency whine from the XdA remained, however; nothing was done about that. Admittedly, it was very slight and completely drowned out when the music began, even at low levels. Still, it was there. And the tweeter hiss -- well, it remained too. It wasnt diminished a bit, so the tubes in the BC3000 weren't causing it, as I first suspected. I turned off the CDP, left only the XdA running, and heard the same level of hiss through my speakers.
My conclusion is that the XdA -- at least the XdA I received -- is just a noisy fella, something that does happen with digital-switching amplification. The hiss gets drowned out when listening, mind you, but if youre just in the room and the system is on, theres a steady sssshhhh thats hard to miss.
Other than these anomalies, the Xd system sounded very good -- and even moved up a notch in overall sound quality when I inserted the Aurum Acoustics Integris CDP, because its as near-perfect a CD player and preamp as Ive had at my place. In fact, it might be one of the best components of any kind out there.
Playing Johnny Cashs American IV: The Man Comes Around [Universal 063339], for example, produced a sound that was so big, bold, and ballsy that anyone who listened couldnt believe it was all coming from a speaker system the Xd's size. I was surprised too. Id never before heard a subwoofer-satellite system this small produce a sound so big and with so much guts. And as much to my surprise, and pleasure, I didnt have to do a thing to make the XdS satellites and XdW sub sound "as one." I simply fiddled with the XdWs back-panel level control a bit, finally settling at the mid position that NHT calls "Just Right," and it was perfect. In my very large room, it's hard to say whether I was getting truly full-range sound (i.e., down to 20Hz) or not, but it was close enough. In short, the "scale" of the presentation impressed me given the speaker systems size and price.
The Xds systems sound was also highly focused and precise. In fact, Ive never heard a speaker system big or small that had this level of immediacy. When the music plays, its just there in a way that you cant miss. Voices, instruments, and what have you pop into space with starkness thats spooky. Frankly, some may find the presentation a tad Technicolor-ish, bordering on being a little "too there," but few will deny that its impressive. Theres also good clarity and "evenness" across the system's bandwidth that indicate the Xd system has been voiced to sound relatively neutral.
I chose the word "relatively" on purpose. Although the Xd is pretty flat, I could hear that the lower midrange sounded a touch "up" in comparison to the top end, which, obviously, came across as a touch "down." This made things like Cashs voice sound a little more forward than normal -- not much, just a wee bit.
As for the bass level, well, thats a different story because it can be adjusted with the XdWs level control. But regardless of where I set that control, the XdA satellites seemed to emphasize the lower mids and nothing with the Mode switch changed it. (Mode seems to affect response lower than the region Im talking about.) However, "up" or "down" just a touch is not necessarily a good or bad thing; its just the way the Xd sounds -- likely the way the system has been voiced -- and many people do like a speaker with a bit of added presence, which the NHT Xd system certainly has.
The soundstage was as big as Ive heard in my room -- an illusion free of the speakers, left to right and front to back -- and the imaging was razor-sharp. The opening track of Blue Rodeos classic Five Days in July [Discovery 77013], "5 Days in May," was projected with an enormous soundfield and imaging so precise that the musicians seemed almost holographic -- almost real.
Finally, as I've mentioned, this rather small speaker system could play impressively loud or quiet, but I did run into limitations both ways. The Xd system can certainly crank out, and I didnt hesitate to throw any type of music at it. The Xd played it all with ease, even hard rock, but there were limits as to how loud it could ultimately go. At ear-splitting levels playing hard rock or even Cashs The Man Comes Around, the lower mids start to turn hard and gritty. Obviously, the little 5 1/4" driver is being taxed to its limits at this point. On the other end of the spectrum -- i.e., playing quietly -- the XdSes sounded as good as they do at normal listening levels -- something that good-quality speakers should do, but dont always. But I hit an unexpected snag here too.
I have a habit of listening to "light" music in the mornings while Im working, with the music often getting progressively louder and more raucous as the day wears on. My "light" choice these days is Bruce Cockburns all-acoustic Speechless [Rounder 3250]. The album is not only light on my ears, but light in the bass as well -- there just isnt much of it. But its also not bass-devoid; there is some. The XdW simply didnt seem to like this low-level, bass-light music. Although it has an on-off switch, the XdW puts it into standby mode when it has idled too long. The low listening levels and the absence of consistent bass made the XdW turn on and off throughout listening, which was irritating. The turn-on is heard as a very light "thump," but its enough of a "thump" to be distracting -- to the point where I stopped using the speakers for background listening.
Once again, it was the electronics portion of the Xd system that seemed to be the Achilles heel of this otherwise outstanding product. Having an always-on switch on the XdW would fix this problem.
Comparing the Xd system to any speaker system is difficult, mostly because the Xd is active and there just arent many of these on the market. Although active speakers are a mainstay in the world of pro audio, theyre few and far between in home audio.
For example, the last active speaker system I reviewed was Paradigms Reference Active/40 -- that was in July of 2001. I loved that speaker system, finding its sound quality comparable to speakers two or three times its price. I still own a pair. The problem, though, is that the Active/40 is a five-year-old design and has been discontinued. Furthermore, although the NHT Xd system does better the Active/40 in terms of overall sound quality and styling, it's priced a whole lot higher. Even factoring in five years of inflation to the Active/40's 2001 price of $2000 per pair still doesnt even bring the price close.
Then theres the Aurum Acoustics Integris 300B active speaker system ($30,000) that I also have for review. The Integris 300B is a whole lot larger than the NHT Xd and sounds better across the board. The NHT Xd sounds great for the price, but the Integris 300B is truly state of the art. However, its five times the price of the Xd system!
So, with comparisons few and far between, the most logical thing to do is figure out what you can buy for $6000, speakers and amplifier included. When you think that way, the doors wide open. One of the best small speakers on the market is PSBs Platinum M2, which is $2000 per pair ($2500 with dedicated stands) and is about twice the size of the XdS. Ive used a pair of M2s for well over a year, and it just so happens that the M2s sound quite similar to the Xd system in terms of providing a rather even-keeled presentation, although I find the M2s to be closer to the "flat" ideal. However, the M2s alone dont have the bass that the XdS/XdW combination can provide. But even without a sub, they can still play louder and cleaner than the entire Xd system.
And once you add a sub, the M2s and Xd are even more competitive. The SubSonic 10 ($2500), PSBs best subwoofer, is self-powered and matches the M2s visually. It is at least twice the size of the XdW and almost double the weight. It is said to have a -10dB point at 24Hz. The M2/SubSonic 10 together, dressed with stands, will set you back $5000. The two can be considered a full-range speaker system that delivers reference-grade sound. However, to equal the Xd, you'd still need an amp to drive the M2s, and cables as well.
So, depending on the amplifier you use -- a reasonably good solid-state amp can be had for a grand, although, of course, you can spend a whole lot more if you want to -- the final sonic result may vary. Ive heard the M2/SubSonic 10 system in my room and driven by a variety of amps -- the cheapest one being the DK Design VS.1 Reference Mk II, an integrated amps that sold in its day for $3000. While I cant say that the PSB system betters the NHT system, or vice versa, I can say that theyre comparable in terms of the overall quality of their sound. Still, there are differences. The PSB system, on the one hand, is physically larger and sounds like it, despite what the NHT system can do at a fraction of the size. It can also play louder, go lower in the bass thanks to the SubSonic 10, and has comparable refinement and detail. The NHT Xd system comes close to the scale of presentation but in a much smaller package, which is darn impressive. Its sounds more immediate and precise, it looks even better, and it is easier to set up, partially due to its size and partially due to the fact that the XdS and XdW work perfectly together.
The point of all this is that for $6000, the NHT Xd system certainly has strengths, but it doesnt clearly better the best of the current "traditional" competition. If youre going to shop around, youll want to look at the NHT system, perhaps the PSB system, and similar systems from a variety of competitors. What the Xd system can claim, however, is that it can stand up with the best of like-priced products, and when you factor in the Xd's size, styling, and ease of use, you can understand why the people at NHT are justifiably proud of what they have created.
The NHT Xd speaker system reaches for greatness, and achieves it in some specific ways. Its big, bold, large-as-life sound comes from a gorgeous compact speaker system. In fact, its probably the best-sounding and best-looking small speaker system that Ive had in my listening room. But the audible hiss through the XdSes, the mechanical whine from the XdA, and the auto-sensing glitch of the XdW mean that, despite greatness in some areas, there are bugs in the electronics that preclude it from being the breakthrough product that it purports to be -- and potentially will be if these bugs are fixed in the future. Please address these issues, NHT!
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