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Product Review - NHT SW3P Powered Subwoofer - September, 1998


Karl Suager

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NHT SW3P Subwoofer (5372 bytes)

SA-3 Subwoofer Amplifier/Crossover
Monaural Class G 250 Watts RMS into 6 Ohms
Frequency Response: 10 Hz-150 Hz ± 3 dB
Finish: Black
Size: 5 1/4" H x 17" W x 14 1/2" D
Weight: 24 Pounds
MSRP: $750 USA

SW3S Passive Subwoofer
Drivers: One 12" Long-Throw Polyproplyene with Butyl Surround
Manufacturer's In-Room Response: 23Hz - Selectable, ± 3 dB
Finish: Black Lacquer
Size: 19" H x 19" W x 19" D
Weight: 72 Pounds
MSRP: $600 USA

 

NHT (Now Hear This!), 535 Getty Court Benicia, California  94510; Phone 800-NHT-9993; Web http://www.nhthifi.com

NHT (Now Hear This!) has nurtured a reputation for delivering a high performance/cost ratio by designing products with intelligent, practical engineering, and a minimum of fluff. Loudspeaker performance can be very subjective, but few would argue with the notion that NHT, as a whole, produces solid loudspeakers for the asking price.

The SW-3P subwoofer system, comprised of the SA-3 subwoofer amplifier/crossover unit and the SW3S subwoofer, rests on that very foundation. Both the design and the appearance state an elegant simplicity. The SW3S, a passive unit by itself, houses a vented coil, cast aluminum frame, polypropylene long-throw driver (about 1" peak to peak linear excursion) in a lacquered 19" cube constructed from 1" MDF, via a sealed alignment.

The SA-3 subwoofer amplifier delivers 250 watts specified at less than .03% THD into the 6 Ohm rated impedance of the SW3S. The rear of the unit offers line level inputs as well as fixed high-pass (12 dB/octave) line level outputs selectable to 65, 80, 100, 125, or 150 Hz. The user can adjust the low-pass filter continuously from 35-150 Hz with a 24 dB/octave slope. Phase adjustment is possible from 0 to 270 degrees in 90 degree increments. The single pair of binding posts are the 5-way variety, which then feed the amplified and filtered signal to the subwoofer.

The amplifier itself is a class G variety, similar to the Class H amps which use multiple rail voltages to deliver high power output efficiently. The SA-3 doesn’t run all that hot, but it should still be well-ventilated. The front panel carries only a power switch, a volume control, and the NHT logo

That’s it. No servos, no EQ, no compression or limiter circuits, no clever driver and/or loading alignments. Just a crossover, amp, and a driver that pulls out the bottom without any encouragement. As plain and dry as that sounds, it makes the SW3P system pretty unique among higher performance subwoofers. As I said, a minimum of fluff.

NHT claims to design speakers using drivers that don’t need much correction to begin with. After measuring the T/S (Thiel-Small) parameters and running the calculations through the computer, I’d have to say that the NHT 1259 woofer driver put to use in both the SW3S and NHT’s flagship 3.3s crunched the nail on its flat shiny head. You DIY’ers probably know about the 1259. It can yield a true infinite baffle response (anechoic other than a single plane, such as the ground) down 3 dB at 28 Hz in the three cubic feet supplied by the SW3S cabinet. I calculated, by running software simulations, that in a 6 cubic foot box, a 26 Hz cutoff could be attained, with an even more gradual roll-off and slightly better transient response. But that wouldn’t be very practical, would it? I’d say that the three cubic foot cabinet (already on the largish side compared to the competition) works just fine, providing a slightly high system Q of 0.8, which merely imparts a few extra pounds of heft, something I think most people appreciate when listening to their favorite movie.

Now, one might think along the lines of, "28 Hz? So what? That’s not much deeper than my large floor-standing tower speakers." Well, that 28 Hz, for one thing, is deeper than most people realize. The rumbling on Enya’s "Watermark" CD, Track 10 -" The Longships", only dips down to the lower 30s. Secondly, that calculated infinite baffle 28 Hz cutoff only applies in the middle of a large parking lot. The sealed enclosure provides a gradual roll-off with lots of useable response below the –3dB cutoff point. With the assistance of room boundaries (most rooms have them), NHT's 23 Hz spec becomes entirely plausible. Coupled with proper placement in a suitable room, this makes flat response below 20 Hz a viable possibility.

In fact, the gradual roll-off at 28 Hz provides a couple of advantages compared to subwoofer systems designed for a flat anechoic response to 20 Hz and below. First off, not many people listen in anechoic chambers. NHT could easily have provided an EQ circuit to make the driver deliver more output in the infrasonic range, but it might have resulted only in exagerated, less accurate reproduction in a typical listening room. Secondly, an anechoic flat response below 20 Hz would require substantially more excursion at the same output levels with musical and theatrical material, limiting dynamic range, and increasing distortion. To further their goal, NHT supplies optional passive filters to roll the bass off even more (6 dB/octave at 45 Hz) for those inclined to give up extension for output (such as might be desired with some movies). I didn’t find any need, so I left the filters somewhere on my mess of a desk. Besides, if you want more output capability, the SA-3 can power an additional SW3S subwoofer in parallel, giving 6 dB more output if the subwoofers are in close proximity due to the 3dB increase in efficiency and doubling of power handling. The amp won't provide quite half the power into a halved impedance, but close enough, since excursion limitations of the woofers, rather than power, are the issue to deal with at very low frequencies. That's not to say that the power supply in the amp doesn't have to be substantial to maintain sound quality, but only that it's not likely to be the weakest link in dynamic considerations when it comes to subwoofers being run as they should be, below 60 Hz. I fantasized more than once about running dual SA-3s to power two stacks of 4 SW3Ss wired in series/parallel, allowing 15 dB more output, and less distortion, with an intimidating stereo array. What a sight and sound that would be. Alas, back to the practical arena.

I will repeat that the subwoofer cabinet requires more space than most other 12" subwoofers on the market, so it’s not really geared toward small condos, apartments, or dorm rooms. Then again, some (not me) might say that subwoofers aren’t really suited for dinky spaces. Even if you’ve got the room, the sheer bulk may drag down the Spousal Acceptance Factor, despite the attractive black lacquer finish. So, keep it in mind if you’re wading through the subwoofer market with the constraints, uh, I mean mutual interests, of your significant other.

When I auditioned the SW3P, I noticed first that for a single 12" woofer, sans servo or porting, it pounds! It doesn’t slam and pummel like an M&K MX-5000, but this baby’s got some kick. It didn't keep going down and down and down like the servo-controlled Velodynes, but in my smaller listening room, that might be a good thing. In fact, it didn't go much deeper than the more modestly priced M&K V-75 mkII on hand from a prior review, if it did at all, but made use of the longer excursion to to allow greater dynamic range. The low-pass filter had to be kept below 60 Hz, or I could localize the subwoofer to the extent that it became distracting, even with the 4th order slope. I didn’t need to use the optional high-pass line-level filters, since the Denon AVR-3200 and the Yamaha RX-V992 have them on board, and my two-channel setup sounds better run full-range, but the outboard SA-3 comes in handy if that’s your goal. The separate chassis allows placement next to your other components which results in shorter interconnect runs, and hence better performance in the upper range, something one-piece powered subwoofers can’t offer.

I have heard slightly cleaner, slightly "faster" for lack of an appropriate word, and certainly deeper, from other legends in the deep bass game, but the SW3P did well through and through. The SW3P swings a solid, tight, punchy club deep and hard enough to rattle the bowels. Like a liberal arts education, it doesn’t specialize too much in any one area, but rather competes as a well-rounded package.

The rival price class contenders in subwoofer-land make the grading that much harder, but the SW3P system not only offers raw performance, but because of the modular nature of the sub/amp pairing, a great degree of flexibility that allows the user to achieve the most with his or her own environment. Performance in a single parameter doesn’t distinguish the SW3P, but the well-thought, pragmatic set of attributes does. The lacquer cabinet and minimalistic face of the amp give the combo a few pluses in the cosmetic department. If this sounds like something that might fit your own real-world circumstances, and you find the flexibility attractive, certainly add this to the audition list. I had a pretty good time with it.

Karl Suager

Associated Components used for the review:

Infinity Renaissance 90 Loudspeakers
Aragon 8008BB power amplifier
Passive controller w/50 k Nobel Pot
Denon AVR-3200 receiver
Yamaha RX-V992 receiver
DH Labs Silver Sonic interconnects & speaker cable
Monster Cable S-14 speaker cable (14 awg flexible zipcord)
Bybee/Curl prototype power purifiers and power cords
API Power Pack V AC line conditioner
JVC XL-Z1050 CD player


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