Product Review

NHT Evolution T6 Tower Speakers with Powered Subwoofers

January, 2003

Yongki Go



M6 Specifications:
Description: 3-way, acoustic suspension design.
Drivers: (2) 6.5" woofers, 4" mid-range, 1" metal dome tweeter, all drivers magnetically shielded.
Frequency Response (± 3dB): 61Hz - 20kHz.
Nominal Impedance: 6 ohms.
Sensitivity: 87dB (2.83V @ 1m).
Dimensions/Weight: 8.25"H x 20"W x 10.25"D, 36 lbs.

B6 Specifications:
Description: acoustic suspension dual subwoofer.
Drivers: (2) 12" aluminum cone.
Frequency Response (± 3dB): 26Hz - 140Hz.
Nominal Impedance: 6 ohms.
Sensitivity: 94dB (2.83V @ 1m).
Dimensions/Weight: 27.1"H x 8.25"W x 23.65"D, 71 lbs.

A1 Specifications:
Description: Full range (20Hz - 20 kHz), class G monaural amplifier.
Power Rating (RMS): 200W into 8ohms, 250W into 6ohms, 300W into 4ohms.
THD: <.075% 10Hz - 20kHz.
Signal to Noise Ratio: 100 db (un-weighted).
Input impedance: >10K ohms.
Damping factor: >100 into 6 ohms.
Gain: 27dB (1.7V sensitivity) for full output.
Power consumption: 600W max
Dimensions/Weight: 1.5"H x 17"W x 11.5"D, 18 lbs.
Finish: matte black anodized front panel, black painted chassis.

X1 Specifications:
Description: Active crossover for use with Evolution U1, U2 subwoofers and T5, T6 tower systems.
Switchable High-Pass: 50Hz, 80Hz, 110Hz.
Variable Lo Pass: 50Hz-140Hz.
Frequency Response (± -3dB): 20Hz - 140Hz
THD: <.01% subwoofer output at 100Hz, 1V and <.001% hi pass output at 1KHz, 1V.
Signal to Noise Ratio: >100db at subwoofer output, >105dB at high-pass output.
Gain control: +10dB and 0dB input sensitivity.
Power consumption: 3W.
Dimensions/Weight: 1.5"H x 17"W x 11.5"D, 9l bs.
Finish: matte black anodized front panel, black painted chassis.


MSRP: $4,000 USA for the Package




The T6 tower speakers are part of NHT's new Evolution product series, which replaces the company's previous product lines, called the Music and Home Theater series. The Evolution line comprises two satellite models and four different configurations of powered subwoofers, including two that form the base of tower speakers when combined with the satellites.

The design concept of the speakers in this new line is to provide the end-users with enough flexibility to suit the configuration of their choice in a two-channel or multi-channel system, hence the modular approach. This departs from previous NHT designs, which separate the two applications into two separate product lines. According to NHT, this new concept is driven by the new surround formats such as DVD-A and SACD.

The T6 speakers are reviewed here mostly in the context of two-channel applications. However, I did also try them as the main left and right speakers in my home theater system to get an idea as to their capability in such setups.

The T6 is the larger of the two tower systems in the Evolution series (the other is T5). They differ only in their capability in producing a particular sound pressure level. The T6 is designed for medium to larger rooms, while the T5 is for small to medium sized rooms.

Although the T5 and T6 are designated as tower speakers, they are not conventional towers. They are essentially monitors matched with powered subwoofers. In fact, if your room cannot accommodate tower speakers, you can just match the monitors with the Evolution standalone subwoofers and get pretty much the same results.

System Description

The T6 tower systems arrived in ten separate boxes. That's right, ten boxes! I was surprised when I received so many cartons. Two boxes are for the M6 monitors, two for the B6 subwoofers, one for X1 bass management/active crossover, two for the A1 amplifiers, two for the tower kits, and one for the owner's kit.

Then, I remembered that these products are modular by design, so they need to be boxed separately to meet any desired configuration. But, ten boxes for two speakers is a lot of exercise. Hey, maybe that is actually another benefit. If I set up an NHT surround sound system, I can be Schwarzenegger's double in his next movie.

The owner's kit box was marked “Open This First”, so that was where I started. Inside, I found the owner's manual together with the tools necessary to assemble the T6 system (Phillips screwdriver and binding post wrench). The binding post wrench can also function as a bottle opener (nice little bonus). And that's not all. A pair of black cotton gloves is also provided so that you won't leave your hand or finger marks on the speaker cabinets.

The owner's manual explains and illustrates quite clearly the step-by-step procedure to assemble and set up the system. Obviously, this is a speaker system where the manual is essential for proper system assembly. Unlike many other speaker systems, where the manual is merely an icing on the cake, for this system, you can easily get lost without it.

The M6 monitor is a three-way acoustic suspension speaker, which is magnetically shielded and employs a 1” aluminum dome tweeter, a 4” midrange driver, and a pair of 6.5” woofers. The M6 monitors can be placed horizontally (using it as a center channel for example) or vertically. In the T6 system, however, they are oriented vertically to sit on top of the B6 subwoofers. In such orientation, the tweeters should be positioned inward.

The terminal plate on the rear of the monitor sports a pair of gold-plated five-way binding posts and is defaulted for horizontal placement (see photo below). For vertical placement, this terminal plate should be rotated 900 so that the speaker wire can hang straight down nicely. A screwdriver is needed for this terminal rotation. There is also a boundary switch on the terminal plate to adjust the speaker response based on its placement, whether far or near boundaries such as wall or shelf (“0” and “1” position). This switch actually adjusts the monitor's response in the midbass range (80 Hz to 500 Hz). When the switch is in the “1” position (near boundary), the midbass energy is reduced to compensate for the boundary reinforcement.

The B6 subwoofer module (photo below) contains two 12” aluminum cone woofers in an acoustic suspension design. The two woofers are located on the same side of the enclosure. The two B6 modules in the T6 package are a mirror image of each other. The room geometry, speaker placement, as well as other furniture arrangement in the room determine the B6 modules orientation, that is whether the woofers facing inwards or outwards. The modules should be oriented such that the woofers are as far away from large objects or room boundaries as possible.

Also note that while the M6 is magnetically shielded, the B6 is not. And I can tell you that the magnetic field around the B6 is quite strong. As I moved the modules to their desired position, passing in front of my television at about 2 feet away, I noticed discoloration of its picture. NHT recommends that the modules be placed at least 18” from the sides of the television. I personally wouldn't feel comfortable in placing them any closer than about 24” from the television sides.

Kits are provided to place the M6 monitors on top of the B6 subwoofer modules. As you can see from the photo below, there is a pair of connectors on top of the B6 module, which is to be connected to the M6 binding posts (wire provided). Once connected, the M6 and B6 essentially become one (T6). The signal delivery to this speaker is given through two pairs of terminals (five-way binding posts) on the rear of the B6 module.

The top terminals are for the M6 monitor, and the bottom terminals are for the B6 subwoofer module. To add stability to the slim and tall T6 towers, there are two sets of stabilizer bars to be attached on the bottom of the B6 modules (two bars for each module). Metal spikes are also supplied to further decouple the speakers from the floor, which could improve their performance. NHT is thoughtful enough to provide four small metal cups to be placed underneath the spikes so that the spikes won't damage your wood or tile floors.

The T6 speakers are meant to be bi-amped with a pair of A1 mono power amplifier and X1 active crossover that are part of the T6 system package. The X1 crossover has the necessary features and controls to achieve the best response from the subwoofers. It can operate as a mono or stereo unit through the mono/stereo switch on the back. In the T6 system, the X1 should be switched to stereo.

All the usual subwoofer controls such as a low pass filter, phase control, and gain control can be found on the front panel. In addition, there are controls for boundary equalization (front panel), high pass filter (rear panel) and LFE (Low Frequency Effects) gain. The X1 can be set to be always on or put in standby. In the standby mode, the X1 automatically turns on when it detects an audio signal and turn off after 20 minutes of no signal. Alternatively, it can also be triggered remotely using a 5-24 volt DC signal. Both balanced (XLR) and unbalanced (RCA) inputs are provided. It should be noted that the X1 contains special equalization circuitry that is specifically designed for the Evolution subwoofers only.

The A1 is a full range mono power amplifier which can accept XLR or RCA inputs. This amp is a class G design and capable of delivering 200 W rms into 8 ohms and 300 W rms into 4 ohms at 0.075% THD. Like the X1, it can be triggered using audio signals or using 5-24 volt external DC signals, or be turned on all the time. The selector for the trigger mode is located in the rear panel, as are the main power switch and the five-way binding post speaker outputs. On the front panel, there are three different-color LEDs to indicate the status of the A1 amplifier, whether it is on (green), in standby mode (amber), or in fault/protection mode (red).

A1 Front Panel

A1 Rear Panel

X1 Front Panel

X1 Rear Panel

Both the X1 and A1 have a slim appearance and can easily be rack-mounted using optional hardware. They have the same outer dimensions and can be stacked neatly. If you stack them, the X1 should be placed underneath one of the A1 amplifiers, the reason being that the A1 is equipped with courtesy lamps under the front edge, which illuminate the X1 controls. It could be handy if you need to make adjustments to the X1 controls in the dark.

Although not wide, the T6 speakers are relatively tall and have a contemporary look. The build-qualities of all the components of the T6 system are excellent. The speaker cabinets are very rigid and heavily damped, as indicated by raping on their sides. As for the finish, the only choice is the anthracite matte lacquer finish that NHT currently offers. I did not dislike the finish, but I just wish that NHT made the high gloss black version as in its other product line (SuperAudio series).


As you can probably tell from my description of the T6 components above, a little bit of effort is required to assemble and set up this system properly. I would recommend browsing through the entire user's manual before initiating the installation, because I think that would help in smoothing out the step-by-step installation and setup procedure. About an hour or two is needed to read the manual and install the T6 system until it produces some sound (not necessarily the “proper” sound though). Then, ongoing adjustments on the controls of the X1 crossover will be needed during the search for the right and best integration of the bass modules for the overall sound. Just consider of all these efforts as the price you have to pay for the flexibility you get. And trust me, the rewards that you are going to have with this system make all these efforts worthwhile!

In the manual, NHT provides suggested settings for the X1 controls to use as a starting point. But of course, you need to do more to get the best result. The manual provides a guide for adjusting the bass using familiar music and your subjective judgment. But I would strongly suggest seeking help from an SPL meter and good test tones too for this process. That's what I did for this review. A combination of SPL meter readings and good music will ease the effort a great deal in adjusting the bass. I really admire the control flexibility that the T6 system offers for integration of the bass sound to the overall sound. I was able to get remarkably seamless bass integration and flat response down to about 25 Hz. In fact, the bass response is the flattest I've been able to achieve in my listening room with any speaker systems I've tried.

The T6 speakers are not designed to be toed-in. This is because the M6 monitors employ the so-called Focus Image Geometry (FIG) design principle. However, unlike in the company's previous generation line where the FIG principle is manifested physically in the angled front-baffles (classical FIG), in the Evolution line, it is manifested virtually, using the output of the tweeter to cancel that of the midrange at the appropriate angles. The goal is still the same, that is, to reduce the sidewall reflections, which can reduce the quality of the sound. This is done by careful matching of the phase relationship between the tweeter and midrange so as to obtain optimized response at specific range of angles.

Jack Hidley, the Director of Engineering at NHT, pointed out that the biggest advantage of virtual FIG over classical FIG is that most customers find squared corner boxes more acceptable. Also, the angled baffles in the classical FIG design made the speakers difficult to place on shelves. Furthermore, the virtual FIG has an advantage to the manufacturer, as the necessity to craft different left and right cabinets is eliminated.

Another thing to note is that the T6 speakers are supposed to be used with the front cloth grilles on. The manual specifically mentioned this very point, and that the speakers may sound slightly bright without the grilles.


In life, sometimes you meet people who seem to have everything they want: a terrific spouse, fine home, plenty of money, etc. Those lucky people are a good analogy to my impression of the T6 speakers. They seem to have all the desired attributes of an ideal speaker. Whether it is tonal balance, pace, rhythm, dynamics, image, focus, or you name it, these speakers are excellent. They may not possess the best of each aspect of the performance, but they excel everywhere, and in some cases, can be considered as one of the best.

First of all, the T6 speakers have a wonderful tonal balance. Sound in any frequency spectrum (except in the very low end) is presented evenly with high accuracy. I found that, with a good recording, every musical instrument sound was reproduced with proper attack and note decay that created uncanny realism. As such, they induce a high degree of believability, as if the musician is playing the instrument right there in front of me. The combination of an excellent tonal balance with the realistic attack and decay is what I think leads to a beautiful presentation of rhythm and pace. Often, in doing a critical evaluation of these speakers, I was pulled into the music, did some foot-tapping, forgot what I was evaluating, and just enjoyed the music. These speakers often seduced me away from my evaluation of the boxes, with the music they played. Hmm . . . maybe they were just afraid of getting a bad criticism from me. But hey, if the speakers were able to sway me from evaluating, and just dazzled me with their sound, then they had to be good anyway. In fact, not just good, they had to be great in order to do so. In reviewing a product, I usually change the music often and listen just to the parts of the song that I thought would be discriminating, rarely listening to the entire track. But with the T6, often I found myself listening to the whole song instead of just parts of it. That's a testament of how seducing the NHT T6 sound is.

The T6 speakers reproduce vocals very naturally and full-bodied. To me, full-body sound characteristics of human vocals are what often differentiate extraordinary speakers and the merely good ones. It adds realism to the overall speaker presentation. Listen for example to Bill Morrissey in the title song from his album "You'll Never Get to Heaven". His voice could sound thin or have too much nasality in the wrong system, but it came out so full and lifelike through the T6 speakers. Also, vocal sibilance produced by the speakers seemed always to be correct and was never edgy.

The overall presentation of the T6 speakers is not forward, but is not laid back either. In my system with the T6, the lead singer was just a tad back for most songs, maybe a foot or two behind the plane of the speakers. The portrayal of the soundstage through the T6 speakers is in general deep and wide. The image is steady and could easily extend beyond the left and right speakers. In my notes, I wrote, “These speakers image like crazy”. What I really meant was these speakers create an image effortlessly. Also, the sense of space created by the speakers is tremendous. On music with a lot of instruments playing at once, the sense of separation among instruments is excellent. They never sounded as if they crowded the same space in the soundstage.

The T6s are also very dynamic. On loud vs. soft passages, they were able to maintain their resolution and never sounded recessed. They definitely can play very loud without strain. The sound of the cannon blasts in Tschaikovsky's 1812 Overture fromthe  Delos test CD was glorious played loudly through the T6. The bass produced by these speakers is deep and tuneful. It's no surprise here, because the T6 system is essentially a set of monitors aided by powered subwoofers. The key is to integrate the monitors with the subwoofer modules correctly, as is the case with any bi-amped system.

I didn't specifically do this review for home theater applications of the T6, but nevertheless, I tried them that way as an aside. I didn't use them in a matched system obviously, since I only had the one pair, but from what I heard, I have no doubt that the T6 would also be great as main speakers in a home theater setup. The nice thing is that you don't need an additional standalone subwoofer with the T6, because they already have two powered subwoofers in a pair of T6 speakers! Also, the X1 crossover provides the capability to mix the LFE output from your surround processor with the front left and right bass.


To say that the NHT Evolution T6 speaker system represents excellence is an understatement. The performance and flexibility offered by these speakers have impressed me, big time. The $4,000 price tag of the T6 system is very reasonable, considering that you get a pair of monitors, two powered subwoofers, and the active crossover that integrates it all. While "best" is relative to one's personal opinion, the combination of its brilliant performance, its flexibility, and its high value could easily put the T6 system on someone's short list. Kudos to NHT, who have came up once again with a very impressive speaker package.


- Yongki Go -

Associated Equipment for This Review

CD playback: Shanling CD-S100, Yamaha CDC-755, MSB Link DAC II
Preamplifier: Adcom GFP-750
Amplifier: ATI AT1505
Other speakers: NHT AC-1, NHT SB-2, KEF AV1, NHT 2.9
Cables: MIT Terminator 4 interconnects, MIT Terminator 2 speaker cables, Cardas Crosslink speaker cables.

Related to the article above, we recommend the following:

Speaker Primer

Misunderstood 0.1 LFE Channel

Nature of Equipment Reviews

A Big Dig into Bass Reflex

What we Hear

Big Bass in Small Places

High Fidelity


Accuracy, Distortion, and the Audiophile

© Copyright 2002 Secrets of Home Theater & High Fidelity
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