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Equipment Review

October 1999

NHTPro A-20 Speaker System

by John Potis

nht_a20_speaker.jpg (9908 bytes)

A-20 speaker

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A-20 control amp


Review Summary
Sound Potent bass along with "clean, detailed and smooth" midrange; "decidedly forward," but not harsh or fatiguing.
Features Speakers come with highly adjustable 250Wpc external control amplifier; impedance-matched cables also included.
Use Amplifier adjustments make setting the speaker system up in rooms of varying sizes and shapes an easier proposition.
Value Speakers, high-power amplifier and cables all for $2000; "I kept thinking that this system offered too much for the asking price."

Late in ‘97, upon completion of a review of NHT's 2.9 loudspeakers for another website, I learned that Ken Kantor, vice president of technology and co-founder of NHT, was leaving the company and the 2.9 was to be his swan song. This was not welcomed news because I had always found a lot to like in the NHT brand. But upon acceptance of the fact that all things must change, I became increasingly curious about what he would do next. I later learned that he had started a new company, Vergence Technology, and licensed the NHTPro moniker to produce active monitors intended primarily for the professional market. (Co-founders Ken Kantor and Chris Byrne had sold NHT to International Jensen, Inc. in 1990.) Considering Kantor’s success with NHT, I was more than curious about the direction he would pursue with his new company. Now that he was beginning a new project, what would he do differently? What would he do again?

Then I received the review pair of NHTPro’s A-20 speakers for review here at SoundStage!. Kantor’s new speakers bare a striking familial resemblance to his designs of the recent past. The new company's flagship, and subject of this review, employs the now-familiar "Focused Imaging Geometry" (NHTPro refers to it simply as FIG) and is manufactured using 3/4" MDF. I was delighted to find that the speakers are finished in the same Italian brushed laminate as that used on Kantor’s previous company's top-of-the line speaker, the 3.3. High-pressure laminate is used both inside and outside the A-20, and it is said to reduce warping and increase cabinet stiffness and strength.

As I own a pair of the NHT 3.3s, I found much that was familiar with the A-20. The 1" liquid-cooled dome tweeter used in the A-20 looked to be the same as the one used in the 3.3, but Mr. Kantor tells me, "The tweeter is a SEAS. [It] is very similar to that of the 3.3, but the voice-coil adhesive used is somewhat improved in terms of power handling and damping, since we run it lower." NHTPro explains that this aluminum dome avoids the typical ringing that most people ascribe to metal domes by using a "micro-fabric surround at the edge termination in conjunction with ferro-fluid in the voice coil for proper damping."

The 6 1/2" woofer did not look familiar, and I'm told that it is sourced from Vifa, composed of treated paper, and is a long-throw design in a cast frame. Both drivers are said to be magnetically shielded, but NHTPro warns that due to the large size of the magnet structure, a distance of 12" is recommended between the speaker and a computer monitor or TV. Crossover is set at 2.1kHz, and both filters have 12dB/octave slopes.

Getting back to the enclosure and the FIG configuration, NHTPro claims several benefits for this enclosure. First, standing waves within are said to be minimized due to fewer parallel walls. Second, that the canted baffle (at 21 degrees) reduces the effects of side-wall reflections on imaging due to the drivers’ toed-in positioning. A strip of acoustic foam is used along one side of the tweeter (on the outermost side) in an effort to minimize defraction and thus improve imaging. Each speaker's dimensions are 14"H x 7.5"W x 11.9"D, and they weigh in at 17 pounds each. NHTPro specifies a frequency response of 48Hz to 20kHz with a -6dB low-frequency cutoff of 40Hz.

Under control

As I mentioned in regard to the aims of NHTPro, the A-20 is an active speaker system. Usually this means that the speakers employ built-in power amplification and require only a source and possibly preamplification. As I see it, the principal advantage of an active speaker is that the speaker and amplifier can be designed as a true system, as all the guesswork about matching speaker impedance and efficiency with current capability and power is addressed by the designer. Output capability of the speaker is matched to that of the amplifier and, most importantly, the two can be designed to be a synergistic match, resulting in a product where the whole is greater than the sum of its parts. (Whoops! The cat's out of the bag now!)

Not a man content to follow blindly in the footsteps of others, Ken Kantor did not proceed exactly as others had. First, he took the amplifier out of the speaker and made it rack mountable. This allows the speaker enclosures to be smaller and lighter, and it spares the speaker components the rigors of the amplifier's heat. It also allows the amplifier to be placed in a better-ventilated location, spares the electronics the deleterious effects of speaker-borne vibration and puts all the speaker's controls within easier reach of the user. And behind the control panel lies a very substantial power amplifier. While the unit measures only 3.5"H x 19"W x 10.8"D, which makes it the size of the average preamplifier or CD player, at 42 pounds, this is one solid unit that will take you by surprise the first several times you attempt to move it. Under the hood is a dual-mono amp with discrete output devices and 250Wpc at your disposal.

Speaking of controls, there is another huge benefit to designing a system where the characteristics of speaker and amplifier are known quantities: system predictability. Most audiophiles shy away from using tone controls in their systems. They cite concerns about additional circuitry and its effects on the purity of the signal. Particularly in less expensive electronics, there is probably a lot of weight to this argument, but I've found that the use of tone controls is fraught with problems because while they may fix one problem, they are likely to create others. For example, you want to bump up the low-bass response in your room, so you nudge the bass control up a few notches. Unfortunately, the effect of the bass control is too broad, and you have just bumped up the midbass as well, resulting in sound that is bloated and slow. This is because the tone controls were created to fix largely unknown problems. The designer doesn't know your taste in sound, your room, your music, or your choice of speakers. How can he prepare a one-size-fits-all solution? He can't. But as the speakers were designed at the same time as the amplification, with a very specific purpose, the controls on the A-20's control amp do exactly as intended. So what was intended?

First is the Switchable Input Sensitivity control. This is a five-position switch with settings of +11dB, +4dB, -3dB, -10dB and mute. You use it to match the control amp to the voltage output on your source device, enabling full output of the amplifier as well as minimization of noise with just about any likely voltage input. I used the A-20 system with everything from a full-function preamplifier (Classé 5) to a passive line stage (Adcom SLC-505) to the output directly from a CD player (Yamaha CDC-735) with equally great results.

Then there is the Wall Boundary control. This is intended to compensate for different amounts of boundary reinforcement of the bass. Don't forget the A-20s were designed for the professional recording engineer who will likely be taking them into the field, where accommodations are uncertain. Will the speakers be placed up against a wall or will they be placed in the middle of a large room or field? Who knows? So designed into the system is a method of effective bass EQ to compensate for just about any circumstance. After using the system in three different rooms, and at varying distances to the walls in each, I can tell you that I was always able to dial in the right amount of bass with zero deleterious effects on the midrange. These controls worked for me with very predictable and repeatable results through the use of another five-position control.

Lastly there is the Listening Proximity control. This is intended to vary the high-frequency output of the system in accordance with the distance between you and the speakers. It is basically a treble control that "compensates for the higher ratio of reflected sound to direct sound when the listening position moves from the near-field to the far-field and in between, ultimately enabling the same high frequency response at all listening positions." While I didn't find this control's use as predictable as the boundary control (I didn’t find myself having to use it all that much beyond one or two settings), I did find it to behave exactly as I wished it to. It offered exactly the attenuation of the treble frequencies required to balance the speaker's output in a variety of rooms and distances. Like the Wall Boundary control, the Listening Proximity control didn't fix what wasn't broken. If all bass and treble controls worked as effectively as these did, they would be in far greater use.

Also on the front panel is an LED display. Switchable for one of three display modes, it lights up when the amp is energized and defaults to a display of estimated output expressed in dBs. As the amp and speakers were designed as a system, by monitoring output voltage, the acoustic output can be determined for a given distance from the speakers. (This distance is not given and is not strictly important as the display is provided to aid in the determination of a consistent playback level when monitoring.) Until the output is calculated to be 68dB or greater, the display reads 00 and average output (as opposed to peak output) is recalculated every second or so after that.

At the push of a button, the display will change to show the AC line voltage. I can understand the professional implications, but in my home, this didn't have too much significance. But if you live in an area with poor power regulation or frequent brown-outs, you may find this quite handy. At yet another push of the button, the display indicates the temperature of the amp’s heat sinks in Celsius. As I found the amp to run warm while never approaching alarming temps, I found this too more interesting than useful. But if you are forced to locate the amp in a location where ventilation is difficult, this temperature readout will eliminate the guesswork. NHTPro prescribes that if the amp tends to run hotter than 80º C, you had better find a new location. If the temp reaches 100ºC, the amp will shut down until it cools.

Located next to the power switch and beneath the pilot light is a red LED that indicates if the amplifier is clipping. And as if that weren’t enough, there is also a built-in headphone amplifier accessed from the front panel too.

At the rear panel of the amp, connection to the system may give the home enthusiast initial reason for pause but only for a moment. The A-20 monitors are connected to the amplifier via supplied XLR connectors and impedance-matched cables. Connection between the source component/preamp is through either XLR connectors or TRS ones. If, like me, you have no idea what a TRS connector is, I direct you to your 1/4" headphone plug or your guitar's line cord plug. It's the same thing, but the TRS is a balanced variety. Mr. Kantor says that unbalanced works fine when driven from an RCA via an adapter (1/4 " to RCA) that will allow use of any preamp at an incremental cost of about $3. Adapters can be found at your local Radio Shack, and if you run your guitar through your stereo system on occasion (as I do), you may already have these in your possession. NHTPro was kind enough to send such adapters along for the purpose of this review, and I can tell you that the system worked flawlessly.

The sound

As previously stated, I used the A-20 system in three different rooms, each differing in size, geometry and layout. Sometimes the speakers were on the long wall, other times they were on the short wall. Sometimes they were close to the wall, other times they were considerably out into the room. Unlike some systems I've used that could not maintain their prowess when moved to larger and still larger rooms (and conversely, could not work in small and even smaller rooms), the A-20 system's performance remained consistently excellent, in large part due to the aforementioned ability to adjust certain performance parameters.

Out of the box I had mixed emotions on the bass performance of the A-20 system. With previous Kantor-designed small speakers, one of the things I'd admired was that the bass, while not visceral by any stretch, was completely natural and without lumps or bumps. This is what I was hearing from the A-20 system. As I say, I wasn't surprised, but I was rather hoping for more. Thankfully, after only an hour of playing (I have no idea whether or not these speakers saw any break-in time before I received them) the bass took on a completely different characteristic. It was still completely neutral, very detailed and solid, but now it was considerably more extended and powerful. While the speakers never became real ground shakers, from there on out, I was treated to excellent bass performance otherwise.

To my ears, the A-20 system’s midrange was always impeccable: clean, detailed and smooth with nary an obvious coloration. The upper midrange is where the A-20s became more a matter of taste. They have a decidedly forward quality, though not to the extent that they are bright, harsh or fatiguing. Treble was irreproachable to my ears.

Associated Equipment

Loudspeakers – ACI Sapphire III, B&W Nautilus 805.

Amplifiers – Classé CA-100.

Preamplifier – Adcom SLC-505, Classé 5.

Digital – Yamaha CDC-735 CD changer used as transport, Meridian 563 DAC.

Interconnects – DH Labs Silver Sonic BL-1.

Speaker cables – DH Labs Silver Sonic T-14.

Digital cable – DH Labs Silver Sonic D-75.

James Horner's Braveheart [London 448-295-2] is a favorite disc of mine, and the A-20 system more than did the music justice. While deep subterranean tones were absent, down to 40Hz or so, the bass was full and detailed. Bass drums at the beginning of "Attack on Murron" were deep and foreboding. While the walls were not shaking, there was lots of bass to please the ear. On "Revenge" I was immersed in a wave of bass that is most impressive for a speaker this size, and I could actually sense the bass pulse toward me -- it was enough to send a shiver up my spine, literally. Frankly, not everybody wants to be physically assaulted by bass, and I personally know several people who would love the A-20s for this reason. Bass drums and lots of ‘em had the amp's clipping indicator flashing and the SPL meter registering 106dB on the opening of "Making Plans/Gathering The Clans," but I heard no signs of distress from either the speaker or the amplifier. NHTPro says that the A-20 system is capable of 117dB output for short periods and maintains a THD specification of less than 0.4% at 90dB.

With this same recording, the presentation was pleasingly transparent and the soundstaging was very wide. In fact, it was as good as I've ever heard it. The violin section was centered just to the outside of the left speaker and well beyond it on " Main Title" The string instrument (is that a lute?) at the beginning of "Murron's Burial" was outside to the right of the right speaker, slightly behind it and definitely above it. Notably, the forward nature of the upper midrange never called attention to itself on classical music.

"Take the A Train" from DMP Big Band's Carved In Stone [DMP CD 512] also surprised me because I expected this recording to jump out at me too, but it didn't. It was smooth, composed and contained just the right level of "alive." Soundstaging was not as dramatic as with Braveheart, but it was quite good. Instrumental specificity was excellent and the soundstage was wide and even. Keyboards on "Satin Doll" were behind the left speaker and to its rear. Trumpets on "Malaguena" were solidly to the right of the right speaker and suspended above it. This was a track that brought my Sonus Faber Concertos to life while I owned them, and what I was hearing with the A-20 system reminded me of them.

Joe Jackson's Body And Soul [A&M CD-5000] combined with the A-20s to bring back some more memories. Cymbals on "The Verdict" were reproduced with a realism and metallic splashhhhhh I had not heard since my Martin Logan Sequel IIs left my possession. If the Sequels did nothing else, they sure got cymbals right. Overall this disc was big, alive and balanced. The lowest bass was missing, but the piano from "Loisaida" was presented with exceptional evenness through the lower registers, which is a difficult task for many speakers.

Imaging was a mixed bag with the A-20s. As they really are intended for the professional market, they give you exactly what is on your disc without glossing over problems or homogenizing your discs. Soundstaging ranged from marvelously expansive to slightly constricted depending on the program material. In an effort to get a consistently wider soundstage, I experimented with moving my listening seat closer to the speakers. Largely due to the FIG configuration, I was able to get quite close to the speakers without suffering a degraded central image. But what I noticed was that as I did this, the solidity of off-center images started to blur, but never to the point where imaging was worse than what you experience with live music. NHTPro recommends a listening distance of 1.5 times the distance between the speakers. In general, I preferred to sit a little closer than that for what I found to be optimum performance in my room. Prudent advice to anybody with any system is to experiment. At closer to 1.25 times the distance between the speakers, on very good recordings, I was treated to a very wide and holographic soundstage with superbly delineated images and excellent detail -- when the recording called for it.

Soundstage depth, too, varied with the recording. Most often, what I got was a soundstage that started just behind the plane of the speakers and proceeded back from there. How far back depended on the recording and the type of music, but generally, "pancaking" of the sound was not a problem.

Compare and contrast

The A-20 system’s performance as a whole was somewhat stupefying. Honestly, they sounded so good that my initial impression was that this system was too good to be true or that I must be missing something. So I arranged the short-term loan of a pair of B&W's new Nautilus 805s from a local dealer. This dealer was kind enough to offer me whatever I wanted, and I chose the 805 based on its very solid reputation along with the fact that by themselves the 805s cost as much as the A-20 speakers and the control amp combined. I figure that if you are going to make comparisons, make them to the best, right?

In a nutshell, the B&Ws really are fine speakers, but the A-20s gave them a rough row to hoe. To begin with, the 805s, driven by my Classé CA-100 amp, couldn't come near matching the bass performance of the NHTPros. In fact, it wasn't even close. The A-20s had much greater extension, detail and power. Midrange performance between the two speakers was very similar, but moving up into the upper midrange, these two speakers parted company in a major way. As forward as the NHTPros are, that's how laid-back the 805s are in the same region. Switching back and forth between them was not always fun because once you switched, the newly selected speaker would sound wrong at first. But after a matter of moments, as I adjusted, it would begin to sound right again.

I did a lot of switching back and forth, and I always found myself leaning toward the NHTPros. But did this mean that they were "right", or did I just want to like them better for the sake of this review? I was having a hard time deciding until I played Jennifer Warnes' Famous Blue Raincoat [Private Music 82092-2], specifically "Joan Of Arc" through the B&W 805s. Listening to the song most of the way through, I came to Warnes’ "la da da" chorus and realized that I had a very uneasy feeling about me. What I was hearing suddenly seemed wrong. I wasn't hearing the detail, the immediacy or the clarity that I was used to. Switching over to the NHTPros brought immediate relief.

After returning the B&Ws, I brought down my pair of Audio Concepts Sapphire IIIs and threw them into the ring with the A-20s. The $999-per-pair Sapphires are my reference for what a stand-mounted, 6 1/2" two-way for under $2K should be, and I love them dearly. The Sapphire IIIs were much more similar to the A-20s than they were different.

While I can’t say that the Sapphire's bass was as good as the A-20's, it came much closer than the B&W’s bass did. Both speakers had similar extension and detail, but the A-20s just edged them out where it came to power. Midrange was too close to call. Both are excellent and very similar up until they reach that fork in the road at the upper midrange. The Sapphires just about split the difference between the very laid-back B&Ws and the more forward NHTPros. Which is more right I'm not even going to speculate upon, but neither is wrong. Which the prospective buyer likes will come down purely to a matter of taste. Particularly on harsh recordings, I tend to favor the Sapphire IIIs. But on well-recorded rock, the NHTPros were more invigorating and up front. On drums, the forward nature of the NHTPros complimented the more powerful nature of the bass, keeping them perfectly in balance, which I liked.

Treble performance between the speakers was an interesting contrast. The A-20 had just a touch more subjective extension, but the Sapphire III sounded just a tad smoother to me. On ride cymbals the A-20 rendered a slightly more realistic metallic flavor in direct comparison, but the triangle seemed a touch smoother on the Sapphire III, if a touch less palpable.

On most music, differences were subtle at best, and I was unable to choose a clear winner in this battle royal. I liken it to different premium brands of vanilla ice cream: all are good, but different too.


I find the A-20 system's presentation lively, inviting and involving. It is an honest speaker that reflects back the quality of the recording fed to it, and I found it to serve all types of music well. The system as a whole is very well conceived and executed and it worked together superbly well. It is also very well built and offers a tremendous value for the asking price.

At $2k for both the speakers and the amp, among the first questions to enter my mind was whether NHTPro is selling through a retail distribution system (yes, they are) or are they selling factory-direct (no, they are not) and passing the resulting savings on to the consumer. I kept thinking that this system offered too much for the asking price. Frankly, I still do. Maybe it's just that audio professionals, NHTPro’s intended market, are a frugal bunch more impressed by performance and engineering than hype. From where I sit, NHTPro is offering you a pair of speakers fully competitive with the best $2k monitors out there and throwing in a free amplifier to boot. No matter what the reason or how you want to look at it, I highly recommend you check the A-20 system out for yourself.

...John Potis

NHTPro A-20 Speaker System
Price: $2000 USD per system.
Warranty: Three years parts and labor.

Vergence Technology, Inc.
3195 Park Road, Unit A
Benicia, CA 94510
Phone: (877) 464-8776
Fax: (707) 751-0271

E-mail: customerservice@nhtpro.com
Website: www.nhtpro.com

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