NHT SuperZero loudspeaker & SW2 subwoofer Measurements
Fig.3 shows the manner in which the SuperZero's impedance changes with frequency. The peak centered just above 2kHz is due to the crossover; that in the upper bass is due to the sealed-box woofer tuning. Reaching a maximum of 19.2 ohms at 120Hz, it indicates a complete absence of mid- and low bass in the speaker's output. Overall, the SuperZero is a super-easy load for an amplifier to drive, which, coupled with a calculated B-weighted sensitivity of 85dB/W/m—highish for the size—means that it can be used even with inexpensive receivers (footnote 1).
Fig.3 NHT SuperZero, electrical impedance (solid) and phase (dashed) (2 ohms/vertical div.).
The NHT's quasi-anechoic response, averaged over a ±15 degrees window on its tweeter axis, is shown in fig.4. The treble is commendably flat for such an inexpensive design, though the upper midrange appears to be a little forward-balanced, there being a 2-4dB energy excess between 1300Hz and 2300Hz. As expected from fig.3, the SuperZero starts rolling out above the bass region proper. The nearfield response in fig.4 reaches its -6dB point at 88Hz, just above the lowest note of the electric guitar.
Fig.4 NHT SuperZero, anechoic response on tweeter axis at 45" averaged across 30 degrees horizontal window and corrected for microphone response, with nearfield woofer response below 200Hz.
In my listening room, the spatially averaged 1/3-octave curve (fig.5), calculated by averaging 20 individual measurements taken for left and right speakers separately over a 72"-wide by 36"-high window centered on the listening position, confirmed both the SuperZero's rather forward balance and catastrophically lightweight bass. Overall, however, this curve is much smoother than I would have expected from a pair of speakers in this price region, particularly in the treble.
Fig.5 NHT SuperZero, spatially averaged 1/3-octave response in JA's listening room.
This could readily be heard. Apart from a slightly "sniffy" quality in the high treble (this is almost a Ken Kantor trademark) which added some wiriness to the sound of violin and emphasized the crackle that accompanies trumpet tone, the SuperZero's high frequencies sounded clean. The midrange, too, was remarkably free from coloration for a speaker this inexpensive. (Remember that if the SuperZero sells for $230/pair, NHT's total parts cost for a pair can't be more than $45 if they are to make a profit and stay in business.)
Unlike CG, however, I had a harder time getting past the speaker's almost complete lack of low frequencies. It was very dependent on what kind of music I played. A lot of rock and small-scale classical music—string quartets, for example—emerged from the bass-truncation experience relatively unscathed, leaving me free to enjoy the NHT's excellent sense of recorded space, good sense of pace, and clean midrange (as long as I didn't play these tiny speakers too loud). But on large-scale orchestral music and power-rock with high-level low-bass lines, like Stanley Clarke's new East River Drive album (Epic EK 47489), it all fell apart, leaving me marveling that I hadn't noticed the emasculation of the music before. If choosing a minimonitor, and music with appreciable mid- and low bass contents is an important part of your life, you'd be better to choose the LS3/5A or (better) the Harbeth HL-P3 over the SuperZero. Or experiment with the NHT SW2 subwoofer, of course.
The SuperZero offers good dispersion in both lateral and vertical planes (figs.6 & 7, respectively, measured using DRA Labs' MLSSA system with the Italian Outline speaker stand/turntable). Laterally, its top octaves do roll off more than 15 degrees off-axis, and a suckout at the top of the woofer range and a complementary peak at the bottom of the tweeter range appear at extreme off-axis angles. As long as you sit with ears somewhere in the vertical vicinity of the front baffle, you should receive pretty much the same tonal balance. Fig.6 does show, however, that sitting below the speaker tends to compensate for the on-axis forwardness in the upper midrange/low treble. Putting the speakers upside-down on shorter-than-usual stands would accomplish the same thing, which would also bring the two drive-units into a degree of time alignment, if that's important to you. (The step response, fig.8, reveals that, on the tweeter axis, the tweeter's output slightly leads the woofer's.) The SuperZero's waterfall plot (fig.9) reveals an impressively clean initial decay. Though a number of resonant modes can be seen as ridges parallel to the time axis, these are all at a low level.
Fig.6 NHT SuperZero, horizontal response family at 45", normalized to response on tweeter axis, from back to front: reference response; differences 15 degrees off-axis, 30 degrees off-axis, 45 degrees off-axis, 60 degrees off-axis, 75 degrees off-axis, and 90 degrees off-axis.
Fig.7 NHT SuperZero, vertical response family at 45", normalized to response on tweeter axis, from back to front: difference in response 15 degrees above tweeter axis; difference 10 degrees above tweeter axis; difference 5 degrees above tweeter axis; reference response; difference in response 5 degrees below tweeter axis; difference 10 degrees below tweeter axis; difference 15 degrees below tweeter axis.
Fig.8 NHT SuperZero, step response on tweeter axis at 45" (5ms time window, 30kHz bandwidth).
Fig.9 NHT SuperZero, cumulative spectral-decay plot at 45".
Footnote 1: I find it interesting that, with the appearance of inexpensive multi-channel receivers for Home Theater use, Consumer Reports appears to have abandoned the testing of receivers into the more revealing 4 ohm loads. One could be cynical and say that if CR continued to test receivers into taxing loads, they would be forced to point out to their subscribers that they just can't get high continuous powers into loads below 8 ohms with a six-channel receiver without expecting to pay a lot more than they used to for a good two-channel receiver. And that, given their parsimonious philosophy, I am sure they would never do.—John Atkinson