NHT Classic Four Loudspeakers

NHT Classic Four Loudspeakers Manufacturer: NHT, 6400 Goodyear Road, Benicia, CA 94510; 1-800-NHT-9993; www.nhthifi.com Price: $1,800/pair Source: Manufacturer loan Reviewer: Glenn Oliver Strauss While this is my first review of NHT products, their speakers are actually well-known to me. When Ken Kantor was chief engineer and before NHT experienced a series of buyouts/turnovers (NHT is now owned by Vinci Labs), I actually owned a pair of 2.5i loudspeakers, trading up to a pair of 2.9 s as soon as they were released. The 2.9 s offered much of the performance of NHT s legendary 3.3 speakers, but at a price this audio enthusiast could then afford. The NHT legend was built around striking gloss black finishes, outstanding bass performance, and innovations in overall design: NHT pioneered the use of extremely narrow front baffles angled towards the listener, side mounted woofers, and very deep cabinets to assure internal volumes which would both support deep bass and foster reasonable 87 db/1w/1m sensitivities. This narrow baffled, deep cabinet design with side mounted woofer(s) is now fairly common. Yet, Kantor s legendary design is supported to this day by his innovative use of the unusual depth of the sealed 2.9 and 3.3 systems; Ken optimized the designs to be mounted against the front wall, woofers facing each other. This not only helped buyers and sellers alike by eliminating several placement variables, but supported both bass quantity and quality by ensuring the front wall loading was precisely factored into the overall bass design. Although there were many other design elements with which to contend, KK s creative physical realization of the 3.3 (and later used in the 2.9 as well) helped produce some of the best bass ever produced by a full range loudspeaker with a single-driver woofer. So with this bit of audio history in mind, I looked forward to see what the intervening years and new engineering talent had produced in the Classic Four but I am getting a little ahead of myself. First things first; let s begin at the beginning. The Classic Four Loudspeaker The NHTs in the test system are part of the Classic line, which includes small mini-monitors and the top-of-line towers reviewed here, and a few more in between. I thought the name chosen rather put NHT in a put up or shut up posture since NHT has a reputation for making some of the best speakers of the 1990s, an NHT Classic has quite a legacy to live up to and as we will see, they did not disappoint! The Classic Four I received were finished in a unique color, called Special Dark. Imagine a giant dark chocolate bar and you will have a pretty good mental picture of the color. I had expected to receive traditional (Classic?) black NHTs, and when first unpacking these 65 pound towers, I thought I was seeing things. My wife assured me otherwise, and she grew rather fond of the color, if not yet another invasion of her home. Fit and finish were good, but not spectacularly so, as I have read elsewhere. NHT uses numerous iterations of sanding and color finishing to get an extremely shiny end result. Truly, I could find no fault in the coating it had no runs, drips, thin spots, or defects of any kind. At this price point, that is indeed an accomplishment. However, anyone who has restored cars (as I have) knows that surface preparation is as important as the painting itself, perhaps more so. The Classic Four, while very shiny, did still have some ripples in the base MDF, and no degree of painting can overcome that; this rippling was only visible when laboring to view it in the reflections from adjacent surfaces. There was some minor overspray in the rear port, visible only to picky, poking observation by this reviewer. But if you want absolutely ripple-free, be prepared to pay Wilsonesque prices laborious surface preparation takes man-hours, and does not figure into a high value product like the C4 s. And indeed, the Classic Fours are high value. At only $1800/pair, one gets an attractive, shiny, four-way loudspeaker with very high performance. The drivers are all aluminum, and made to NHT s specs in China. But let s give them a listen before we get into all that. The Classic Fours were auditioned in Room 2, which is of average size of approximately 2000 cubic feet, and where most of my speaker-review listening is performed. The speakers were teamed with NHT s the Controller and the Power2 amplifier in a stereo configuration. The speaker has a large rectangular port on the rear of the cabinet, and while this will somewhat limit how close the speaker can be placed to the front wall, any reasonable distance resulted in either very good, or simply outstanding bass no subwoofer was provided, and none was needed! NHTs have always

been great bass speakers, and the Classic Fours delivered on that legacy, although vented and using a single 10 driver (most previous NHT designs have been sealed bass systems). Bass extension was strong, and extended without sounding bloated or overblown. The Fours reproduced cleanly the lowest organ pipes, and only when driven extremely hard did I detect any port chuffing, and that could only be detected when close to the port itself it was a non-issue from the listening position. So for music and nearly any reasonable home theater use, a subwoofer indeed was not required the C4 had both the output capability and deep bass extension to handle anything I threw at it without complaining, and the Power2 was capable of driving the speakers to extremely high SPL s! Bass quality was very good, with the midbass particularly well defined, with excellent transient reproduction, something we do not always see in this price range in vented designs; upper bass reproduction was fine, with only an occasional thickening of the bass viol or kick drums harmonics. Midrange was handled by the ubiquitously-sized 6.5 driver, but because this is a four-way design, there was never a hint of the driver being overdriven, or beaming as it approached the upper linear dispersion limit many 3-way designs using a similarly sized midrange driver occasionally experience. (This midrange driver crosses over to a 2 dome well below the point where its size becomes significantly close to the wavelength it is reproducing). Midrange clarity was very high, and dispersion outstanding based on my moving around the room - pink noise showed no appreciable variations at any reasonable angle whether side to side, or while standing. String tone and human voice were very well reproduced, with no baritone chest boom, yet with a palpable sense of reality when handling difficult cello or piano passages. The sense of transparency was as good or better than anything else I have heard recently even remotely close to this price point.! Outstanding! The Fours have a rather unique treble system I say system because two drivers are mounted on the same inert molded plastic frame. The 2 low tweeter covered most of the presence range, and did so with superb dispersion and a very natural sense of timbre. They definitely were not reticent, having an up-front character but without any harshness, and the addition of the small.75 high tweeter only was icing an already tasty cake besides the ability to delineate brushed cymbals and violin harmonics with exemplary quality, the Classic Four could also play very loud on challenging rock Quadrophenia, one of the Who s best in my opinion, never sounded better than when played shatteringly loud on the Classic Fours; this of course means they similarly delivered the goods on challenging movie soundtracks, even played in 2-channel mode. Favorite and challenging classical selections such as those on John Eargle s Delos recording Engineer s Choice II revealed the Classic Four was similarly adept at rendering both accurate timbre and the micro and macro dynamics demanded by Eargle s wide choice of musical styles and orchestrations, made all the more demanding by the phenomenal recording itself. And the outstanding dispersion at any frequency means that no one in the room will be short changed when listening to music, or when a favorite film is being spun two of these combined with other Classic-series speakers would offer formidable home theater performance indeed! My only quibble with the treble system was that I occasionally heard what I can only call an electronic sheen in the mid-treble a sense that a bit of extra energy was being added to the mix that was not on the recording. I tried to confirm or disprove this perception by borrowing a pair of Sennheiser HD- 650 headphones, and indeed, the sheen was not found to be on the recording. Whether it was an amplitude issue or a resonance artifact I could not tell. So I hauled up the $2500/pair Paradigm Studio 100 v.3 s, and after matching the levels using my reference system, I found that I indeed very slightly preferred the mid-treble of the costlier Paradigms but this could be a room effect, or just a personal preference; yes, the Classic Fours performed so well that I could never be sure. On the other hand, the soundstage of the NHTs was superior to the Paradigms not only was it a bit more expansive vertically, but its off-axis performance

90 85 80 75 70 65 Fig. 1 NHT in-room horizontal amplitude response sweeps 25-20kHz @ 1meter On-axis 45 deg off-axis Fig. 2 NHT in-room vertical amplitude response sweeps 25-20kHz @ 1 meter 15 deg above axis 15 deg below axis 90 85 80 75 70 65 25 32 40 50 63 80 100 125 160 200 250 315 400 500 85 800 1k 1.25k 1.6k 2k 2.5k 3.15k 4k 5k 6.3k 8k 10k 12.5k 16k was even better than the Studio 100 s, which you may recall from my recent review I held very highly in that regard so this is a terrific outcome for the Classic Fours, especially factoring in their high value. Measurements A few comments on the measurements. First, note that I have used a tighter scale than the one that was displayed in my review of Paradigm s Studio 100/v.3 in a previous issue. This was a glitch in the handoff from the reviewer to the production staff, and resulted in an exaggerated sense of linearity, although both the Paradigm and the NHT s reviewed here were strikingly flat over a very wide range. Also, for both the horizontal and vertical measurements, the microphone was moved rather than the speaker, which will explain the discrepancy in the low bass measurements, where directivity should not be manifest. Finally, it is important to note that the measurements were done without any processing or equalization. Comments on the impedance analysis (not shown). The minimum impedance was a reasonable 3.9 ohms at 157 Hz, and the maximum was just 15.1 ohms at 940 Hz. These results are very smooth, especially for a four-way loudspeaker with its added crossover responsibilities for an additional driver NHT primarily uses 2 nd order slopes in the Classic Four, and seems to have that topology very well dialed-in. The phase angle is benign across the range, although sensitivity was only moderate at an estimated 86 db/1w/1m, somewhat surprising given that this is a bass reflex design, and NHT s previous air suspension designs had about the same sensitivity. Still when all is said and done, this is a speaker any good amplifier with at least 100 wpc can drive, whether tethered to a receiver or standing alone as a powerful monobloc. But recall that I found the Power2 is to capable of prodigious output, which was used to full effect on the demanding rock and classical selections so if you like to listen to your music or movies at high levels, be sure your amplification is up to the task. The saddle in the impedance is typical of a vented design, and in the C4 suggests a tuning of about 28 Hz; the port sweep was similarly balanced to the low- 30 s. The woofer minimum excursion point was 30 Hz. The combination of these measurements suggests classic NHT bass response very well engineered, and very extended. No wonder I found the bass extension to be outstanding unless you want to listen to 20 Hz at 95 db SPL, no subwoofer is needed here! This extends the value proposition, since an owner can do without a subwoofer; the PAF (partner acceptance factor) can only benefit as well. Figure One shows the horizontal in-room frequency response measured with the Classic Fours well away from the front and side wall boundaries. Normalized to about 77 db, the response is outstandingly smooth note how the bass holds up to below 30 Hz, as expected, showing a bit flatter than a semi-anechoic measurement might, which I attribute to real-world test conditions. The mid-bass elevation is primarily a room and measurement artifact, as most

speakers usually show a slight dip in this region in this room but the Classic Four does have an unusually strong output in this region. Over most of the midrange, the response is very smooth, although I measured and heard a broad elevation of a few db in the presence range of 1-2 khz, which may explain my comment that I found the speaker a bit up-front, but quite transparent. The remainder of the treble range is quite smooth, save for a peak in the 8-kHz range it appears the combination of the 2 and.75 domes carefully balanced by the crossover really delivers the goods. Oh yes, and look how terrific the 45-degree off-axis response is in the horizontal plane only in the last half-octave at the top of the audible range does the off-axis tracking deviate significantly from the on-axis output. This results in a wonderfully wide listening window, and helps explain both the soundstage performance that was noted, as well as the precise placement of subtle movie soundtrack details. In Figure Two, we turn to the vertical performance, and it too is exemplary; note how closely it tracks the horizontal. This is seldom seen in a large tower loudspeaker, where the abundance of drivers often results in interference effects. NHT s close spacing of the drivers, as well as the four-way design, likely plays a hand here. Of special note is the lack of a significant suckout at the midrange and low treble crossover points above axis, although I did detect a drop in the 4-5 khz range 15 below axis, which could be a floor effect, but is of no real consequence regardless. Only when I raised the microphone well above any reasonable seated position did I see a significant variation in the vertical response this is again an outstanding result, and likely a contributor to the superb soundstage the Classic Four delivers. It is especially unusual since 2 nd order slopes often show a midrange suckout above and below axis, either due to the need to connect one of the drivers 180 out of phase with one another to preserve maximum on-axis linearity, radiation pattern interference, or both. The NHT engineering team, led by VP Jack Hidley, has clearly done its homework. I also did an RTA analysis in-room at the listening position, using continuous averaging and positional weighting my colleagues Howard Ferstler and David Moran would never forgive me if I did not perform this very important measurement! They believe that it is the paramount performance indicator, and to a large extent I share that opinion, although it occasionally can exaggerate a fine speaker s performance when the room and the speaker just do not want to get along. So where is it? Well, it costs money and takes up valuable real estate to show pretty graphs, so in my speaker reviews I try to focus on the measurements that best support the story I am trying to convey. In the case of the Classic Four, the in-room RTA at the listening position looked terrific, and other than an expected roll-off earlier in the high treble than we see in Figures One and Two, the RTA looked largely like what those graphs displayed. The bass actually looked a bit flatter overall, although it was down about 6 db at the 31.5 Hz octave, which is closer to what I estimate the speaker s intrinsic performance level would be when measured anechoically based on the impedance and port analyses I performed and discussed earlier. This is a very flat speaker with an exemplary radiation pattern (radpat), and it serves the listener extremely well where it counts where he or she listens. So taken overall, the Classic Fours measured performance is outstanding by any standard, and amazingly so for a speaker with an $1800/pair retail price. People like comparisons, and the speaker I had on hand which most closely matched the NHT was the forward-firing Paradigm Studio 100/v.3, at $2500/ pair. The NHT had better soundstaging than the Paradigm, which had impressed me enough when I reviewed it that I bought the review pair. The C4 s superior radpats produced a wider, more uniform, and more precise sonic image. The Studio 100 s have the edge in ultimate bass extension, with their three 7 woofers and lower bass tuning, and I slightly preferred the tonality of the Paradigm s midrange, as it was just a tad more palpable. The NHT had the edge in ultimate treble extension, but the slight peak in the high treble was not evident in the S100 so in the end it s a toss-up and a buyer s preference thing. Both speakers could play very loud and very cleanly, although I believe I squeezed out a few more db s from the 5 drivers in the Studio 100 s than I did from the NHT, using my reference 300 wpc Coda power amplifier. And as for looks well, the Paradigm had a slight edge in perceived quality of fit and finish, but

some may prefer the glossy finish of the NHTs to the realistic looking vinyl wrap of the Paradigms. In terms of bang for the buck, the edge has to go to the NHTs, with their $700 lower retail price. Conclusion The Classic Fours measured and perceived performance was a cut above. All the components are high-value and high-quality, and deserve serious consideration by our musically and electronically diverse $ensible Sound audience, especially with those floor standing value shoppers. Highly recommended indeed! T $ S -GOS Excerpted with permission from The Sensible Sound, Issue 115, May/June 08. Subscriptions to TSS can be purchased by calling 1-800-695-8439 or writing to: 403 Darwin Drive, Snyder NY 14226.