NHT Evolution T6 loudspeaker system Postscript from May 2005

Postscript from May 2005 (Vol.28 No.5):

When I reviewed NHT's Evolution T6 loudspeaker system in April, I ran out of time and space before I could explore the possibility of running the system "commando" style; ie, with the X1 electronic crossover bypassed for the M6 satellites. While the satellites would no longer benefit from the filter's high-pass function, thus reducing their ultimate dynamic-range capability, I wondered if the elimination of the filter, which is constructed to utilitarian rather than high-end electronic standards, would get the ultimate sound quality from these impressively engineered speakers.

I run my system balanced, so I constructed a passive adapter that took the left and right feeds from my Mark Levinson No.380S preamp and fed them to two pairs of output XLR jacks via short lengths of twisted solid-core wire. One pair fed my ML No.33H monoblocks, which drove the M6 satellites. The second pair fed the X1 crossover, the low-pass outputs of which were each connected to an NHT A1 monoblock driving an NHT B6 subwoofer.

As there is now no high-pass filter in the M6 feed, this necessary function is provided by the speaker's natural rolloff. Looking at fig.15 in my April review, the M6 extends down to 80Hz, with then a well-controlled second-order rolloff. And because the M6 uses a sealed-box alignment, its twin woofers will be less likely than a reflex design to run into excursion problems at high levels.

Even so, getting the optimal blend of satellites and subwoofers proved a lot more tricky than with the X1 providing the high-pass filtering. I kept ending up either with a discontinuity in the midbass, which left the low bass sounding behind the musical beat, or with too much midbass energy, which made the sound too muddy. Fortunately, the X1's versatile controls—you can change subwoofer low-pass frequency, level, and phase—allowed me eventually to dial in a balance that wasn't very different from what I'd achieved in my review (see fig.18 in April, blue trace).

But wow. If I thought the sound of the Evolution T6 system was pretty damn good with the X1 in the satellite feed, with the M6es fed direct there was now a superb sweep to the presentation. Perhaps more important, though the M6es without their grilles on were still slightly on the bright side, there was now a sense of high-frequency ease to the presentation that eliminated any feeling of strain. I had mentioned in my original review how I found myself playing more chamber and small-scale works, neglecting the big orchestral recordings. That was not the case with the "commando"-style T6es.

I reached for an old favorite, Bryden Thomson conducting the London Philharmonic in orchestral works by Ralph Vaughan Williams (CD, Chandos CHAN 8502). From the haunting opening of the first Norfolk Rhapsody, with high violins punctuated by harp, oboes, clarinet, then pizzicato basses, through to the cinematic climax of In the Fen Country, which echoes a theme from the composer's A Sea Symphony, this 1987 recording held my rapt attention. The low frequencies were rich and majestic, the midrange detailed and uncolored, the high frequencies clean without either reticence or sizzle.

Stereo imaging was also improved, in that a better sense of depth was developed behind the plane of the speakers. The solo instruments in the Vaughan Williams works, for example, were very well defined in space, their images stable and solid. The NHTs were also excellent at presenting the reverberant clues that, in a recording made with purist mike techniques, indicate the venue's size. While preparing this and the previous issue of Stereophile, I have also been editing a new CD from Canadian pianist Robert Silverman, to be released this spring (footnote 1). For the sessions, which took place last summer at Weber State University in Utah, I used Ray Kimber's IsoMike array, specifically a pair of Neumann M150 omnis spaced either side of a large, heart-shaped baffle. Whether I listened to the 88.2kHz session files decoded by my Mark Levinson No.30.6, the Musical Fidelity X-DACV3 I write about elsewhere in this issue, or by the Benchmark DAC 1, the NHT T6es presented an image of Bob's Steinway that was surprisingly stable (given my use of omni mikes), within a believable modern concert-hall acoustic. Nice. Very nice.

With its subwoofers rapidly rolling off below 30Hz (see fig.10 in my April review), NHT's Evolution T6 cannot achieve a Class A rating in Stereophile's "Recommended Components," for which true 20Hz extension is mandatory. But with the M6 satellites driven direct and the X1 reserved for driving the B6 subwoofers, I can confidently recommend the Evolution T6 for inclusion in our Class A (Limited Extreme LF) category. And at $4000 for the compete system, it is a true bargain.—John Atkinson



Footnote 1: Excepts from these sessions, captured by Ray Kimber in surround using four Neumann M150s and a DSD recording system from EMM Labs and Genex, can be heard on his latest IsoMike demonstration SACD. $20.00 from Kimber Kable; the fee goes to Weber State University music program.
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