NHT Evolution T6 Tower surround speaker system
NHT speakers have never been conventional. Even their earliest, cheapest models had narrow, angled front baffles designed to provide a sharply toed-in radiation pattern, even with the cabinets pointed straight ahead. Dubbed Focused Image Geometry, this arrangement reduced side-wall reflections to produce a well-defined soundstage.
When NHT launched its first high-end flagship speaker in the early 1990s, the 3.3, it retained the narrow-front, sloped-baffle design but added an onboard 12-inch woofer. The 3.3, with its textured finish of black laminate, resembled a metallic slab. Its 3-foot-deep cabinet, even when positioned (as designed) with its back against the wall, protruded well out into the room. To say that a pair of these monoliths had a low Wife Acceptance Factor would be putting it mildly. But the 3.3 received almost unanimous rave reviews for its sound, and remained in NHT's line for nearly a decade. (The 3.3 was reviewed by Stereophile in December 1993, and in a Follow-Up in March 1994.)
The 3.3 and NHT's other high-end speakers have now been replaced by the Evolution series, which consists of four different subwoofers and two compact, full-range models. The full-range designs can be used either alone (unlikely in a home-theater setup due to their modest low-end extension) or with the subwoofers in a variety of combinations. In particular—and of primary interest for this review—the full-range M6 together with the B6 sub and associated electronics forms the T6 Tower System. (The M5 and B5 can also be used together as the less expensive T5 Tower System.)
Because the T6 comes as separate modules, you'll have to do a little assembly on your own—or talk your dealer into doing it. This consists of connecting each M6 to a B6 using supplied brackets and hardware. It isn't particularly straightforward, but if you can follow directions, the well-written owner's manual will get you there.
We're sure NHT would be happy to sell its customers five (or even seven) complete T6 Towers for use in a surround package, but most buyers will likely opt for T6s at the left and right front with M6s alone for the center and surround channels. The M6 is a ruggedly built 3-way design with a single set of input terminals—no biwiring option here. Two 6.5-inch drivers handle the bass. The 4-inch midrange is mounted in its own separate chamber. The magnet structure of the 1-inch, aluminum-dome tweeter is attached to a solid aluminum rod that extends to the back of the cabinet. This "Wonder" bar acts as a large heatsink to increase the tweeter's power handling and reduce its power compression. The M6 is magnetically shielded; the B6 is not.
The most interesting feature of the M6 (and the M5) is its driver configuration. When the M6 is used vertically—for example, as part of the T6 Tower System—the midrange and tweeter are positioned not vertically but side by side. Most woofer-tweeter-woofer center-channel speakers are designed this way. Readers who have followed our speaker measurements for any length of time know that such a driver arrangement can cause interference patterns that result in serious off-axis response dips.
NHT claims to have incorporated this fact into the M6's design. When the left and right speakers are set up with the midranges on the outside, the radiation pattern is focused toward the listening area. The driver interference pattern reduces radiation toward the outside. The effect is concentrated at 3kHz in the crossover region, where the ear is most sensitive. The claimed result: reduced side-wall reflections and a better-defined image. In homage to their roots, NHT calls this design concept Virtual Focused Image Geometry.
We don't generally recommend positioning so-called "bookshelf" speakers on bookshelves or in cabinets because such placement can introduce serious colorations. If you must use the M6 this way, however, the speaker has a two-position boundary-compensation switch; flat is "0," while the "1" setting reduces the response below about 500Hz. This setting may also be useful when the speaker is used for the center channel on top of a large television. Such response tailoring will never be perfect for all situations, but the switch will at least give you some useful control if you can't avoid such locations.
Each B6 subwoofer has two 12-inch drivers mounted on one side of a sealed cabinet. By itself, the narrow cabinet isn't particularly stable, so it comes with two outrigger feet that provide adequate protection against accidental tipping. The feet also have threaded holes into which the included spikes can be inserted.
The B6 is passive—that is, it must be driven with an external amplifier. NHT makes the compact A1 monoblock amp for this purpose. While one A1 amplifier can be used to drive both the left and right B5 subwoofers in the T5 system (the B5 has one 12-inch driver), with the T6 system you must use two A1s, one for each B6.
The X1 crossover can be used with either balanced or single-ended connections. Depending on how you set it up (there are several options; more on this below), it provides variable boundary compensation for the B6 subwoofers, a continuously adjustable lowpass filter, three highpass filter options (50, 80, and 110Hz), continuously adjustable phase control (0-270° relative to the highpass output), and separate adjustment of both the overall subwoofer level and the low-frequency effects (LFE) output.