High-Resolution Technologies Stage IV Speaker/Amplifier System

REVIEW
by Robert E. Greene
Jan 21, 2020

The HRT Stage IV system arrived for review almost exactly, all but to the day, sixty years after the release of the first stereo LP. This coincidence could be thought of as deeply symbolic, because the Stage IV system constitutes an unusually effective way to present stereo information as it should be presented—at least in one theory. The explanation of this is going to involve a digression into the history and theory of stereo. But it will be, as I hope, well worth your while to follow this digression. How you decide to deal with the issues involved will determine how your system sounds far more than the choice of most equipment items.

Even before stereo began as a commercial reality, thoughtful people had realized that it would open up a new prospect for reproducing musical reality. Gone would be the interest in reproducing the sound of instruments and voices unto themselves, replaced by reproducing them within their natural acoustic context. This would be a fundamental improvement, because almost no music fits naturally into a domestic acoustic environment as such. One person singing quietly, an acoustic guitar played gently, a clavichord…one has almost exhausted the list. Even “chamber music”—string quartets, say—originally composed to be played in small rooms, has in modern times come to be performed primarily in concert halls, and its performance style has changed to accommodate the change of venue. And, of course, when one considers orchestras—in the words of At the Drop of a Hat [“A Song of Reproduction,” Flanders and Swann], “Personally I cannot think of anything I should like less than having an orchestra actually playing in my sitting room.” Stereo offered the chance to make reproduced music actually work in musical terms, by moving you, the listener, to the original venue, rather than pursuing the idea of bringing the performers to your domestic environment.

RCA, in particular, jumped on this prospect from the very start in its orchestral recording. In improvised but startlingly effective deployments of relatively few microphones, it produced a series of orchestral recordings in the late 1950s and early 1960s that captured not only the sound of the instruments and their positions but also the whole acoustic envelope of the real sound. The recordings, released as “Shaded Dogs” (for the design of the label on the records themselves), became legendary and remain high-water marks for recording of the real sound of orchestral music in a performance venue. Others pursued and reached the same goal later on, but RCA established once and, one supposed, for all that the thing could be done—that an orchestral recording could sound not like the painful and inappropriate idea of having the orchestral instruments in your own room, but rather like what you would have heard in the concert hall. It was a new era. And when high end and The Absolute Sound came along, Harry Pearson’s description of the idea—“the sound of real music in real space”—became the marching song, the veritable “Marseillaise,” of the stereo revolution.

What This All Has to Do With Playback
In one common view, audio recording and playback are treated separately. One sets up a “neutral” playback system and uses that to judge recordings, and “good” recordings are then supposed to sound good. But this picture is vastly oversimplified because what kind of playback will work ideally depends on how the recordings were made. Imagine recording one person singing. A close-up, quasi-anechoic mono recording played back on a single flat-response speaker with the same radiation pattern as the person singing would, in principle, sound like the person singing in your listening room—the person would be “there” for all audible intents and purposes. But, of course, nothing like this happens. Vocal recordings are often made in the way I’ve described, but when one plays them back on stereo speakers with radiation patterns that are not the same as a person singing, the whole attempt falls apart. The ear/brain is almost anxious to be fooled, to believe that what is being heard is real. And one can convince oneself that even such a recording is almost real. But, of course, it is, in fact, not the real sound at all. And even on the off-chance that the speaker’s radiation pattern worked out to get the over-all power response of a vocalist right, this would not be true for a musical instrument with a different radiation pattern than a vocalist—which is all of them. Instruments and voices into room is not only musically inappropriate in almost all cases, it is also bound to fail if one listens critically.

But what is possible, what does work, as Alan Blumlein pointed out in his original stereo patent in 1933[!], is to reproduce the whole sound of the original voice in the original venue, by recording the original soundfield in the original venue at a plausible listening position and reproducing this in the listening room by suppressing the acoustics of the listening room sufficiently. In effect, one can cut out a section of the listening room acoustics and replace it with the acoustics of the original venue. Actual realism becomes possible.

Enter the Stage IV
These ideas are far from new, and many speaker designs have pursued this general goal in various ways. And to some extent, speakers with wide uniform “dispersion” (a wide uniform radiation pattern) can synthesize an impression of large space using room reflections. The extreme form of this are omnis and the original Bose 901, which for all its controversial nature as a practical device, was based on a theory that made some sort of sense. Wide radiation pattern speakers can “sound good,” all right. I listen often to an (eq’d) pair of Acoustic Research 303s, which are wide in frontal pattern out to around 6kHz. The space heard may not be an exact replica of the original venue, but the tonal character is convincing on large orchestra works in particular.

But some designers have tried to make the speakers work as well as possible in terms of suppressing the listening room and giving one access acoustically to the original venue in the most literal sense. Indeed, in the early days of high end, this was a common goal. But in the contemporary world, this has become less common. Still, this quest continues on occasion. And Kevin Halverson’s HRT Stage IV’s do this exceptionally well. The base system comes with one amplifier and one pair of speakers, with each speaker containing three woofers and a tweeter. The speakers can be stacked horizontally atop one another on HRT-supplied stands to realize the four-speaker array (the “Stage IV”) reviewed here. Even if you are accustomed to speakers with some directional behavior by design, you will find it startling to walk up to the Stage IV’s from behind, and then sit down in a chair in front of them. The sense of walking into a sound world detached from the room around you is really surprising, almost uncanny. And, of course, on a well-made recording, this new sound world is the sound world of the venue where the recording was made.

This phenomenon is immediately and permanently entrancing. When Scot Markwell of Elite A/V Distribution, HRT’s U.S. distributor, mentioned to me that many of the customers for HRT speakers were replacing far more expensive designs, I could surely understand why. Indeed, upon my first listen, it crossed my mind that maybe this was a speaker which would justify getting rid of all fourteen pairs of large or medium-sized speakers I had accumulated over the years. (Later on, certain reservations occurred to me—more on those in a bit.)

This effect of literally suppressing one’s own room arises at bottom from the beaminess of the speaker. The twelve small mid/bass drivers in each speaker operate in effect as a unit so that with rising frequency one has what amounts to a driver that is large both horizontally and vertically compared to the wavelength of the sound. The four tweeter units (per side) form a vertical quasi-line source and have a lot of directivity vertically. Nothing much in the highs comes off floor or ceiling. I have written for years (as have other people) about the positive effects of beaming on image focus. Gradient, for example, has built its entire line of speakers around ideas of this sort. Acoustat, in the early days of TAS, used to argue compellingly for this in its “Manufacturer Comments,” for another example. The effects of various beamy patterns and minimization of floor reflections and so on is thus familiar in theory and in practice many times over the years. But the combined effect of the horizontal and vertical beaming in the Stage IV’s is very striking and will seize your imagination, I am confident.

Another aspect of using all those drivers is that no one of them is working very hard, resulting in low distortion. This is one clean-sounding speaker system, though some of that may come from minimization of early reflections. And the Stage IV’s will play loudly cleanly, too. The speakers sound really pure, quite startlingly so, even at high levels. The individual drivers were very carefully designed by Halverson, with a custom-designed cabinet and drivers from HRT—no off-the-shelf stuff here. Even one driver is low in distortion. Using so many that no single one is working hard pushes distortion down even further, down a long, long way to judge from listening. Really something.

The Limitations
In speaker design, no good deed goes unpunished, as it were. Almost all choices are compromises. In particular, directional behavior buys you differentiation against your own room, a desideratum for the reasons indicated, but it also puts upon you the need to sit in a particular spot. The Stage IV’s are sensitive to both the horizontal and the vertical position of the listener. I am undisturbed by such things, but you will want to experiment a bit to see if you are similarly complacent. This whole thing would probably work better in terms of consistency of pattern if the tweeter were in the center of symmetrically placed mid/bass drivers, as in the McIntosh XRT 28. On the other hand, putting the tweeter off to the side of a line source of mid/bass drivers seems to be common and commonly accepted—e.g., DALI Megalines, Scaenas—even though it creates a less than ideal horizontal pattern in principle. In practice, since I am inclined to listen without moving, having to sit where I belonged did not disturb me.

A second thing may seem a bit paradoxical. Although the speaker emphasizes direct arrival, which would suggest exceptional image focus, the Stages, in fact, make images a little unfocused, or if you prefer, larger than true point-source speakers when you get point-source speakers far from the walls. Again, Magneplanars, which are also physically wide in their bass and midrange drive units, exhibit to my ears a similar effect, though there are people who think of this as dimensionality rather than bloat. But a mono source ought to have a completely exact position on the vertical center line, and here, not quite.

None of this is devastating and all is easily forgiven in the context of the solution of the “second venue” problem. But there is one more difficulty, one that is somewhat serious to my mind, though negotiable. The Stage IV’s have a quite odd tonal character. The whole presence range is really shoved down, at least at the distance I was sitting. (The exact balance will be a function of distance because of the differing patterns of radiation at different frequencies.) This is not one of my OCD tonal tweaking items, calling up visions of my sitting up late at night frantically eq’ing to get pink noise to sound absolutely pink, as perhaps some readers imagine I do (and as I more or less do do sometimes). This is a quite big thing. The Stage IV’s sound a little muffled, actually. Further up in the treble, there is a partial return to level, so the muffled character is also very slightly edgy because the higher treble is up a bit compared to the lower treble.

Now this suppression of presence range energy is not exactly anti-musical, perhaps—and most surely not in the same way that a really exaggerated presence would be. But it is definitely there. Pleasant it can be—lots of recordings are over-present compared to concert sound. Indeed, most of them are. But not to this extent. Can you fix this with eq—so easy to do in the DSP world? Of course you can in principle—you can fix any response error as far as on-axis response is concerned—but because of the speaker’s complex pattern, it is not easy to know, even with measurements, what the eq is that will make the speaker sound tonally neutral in the sense of sounding like an ordinary speaker with flat response combined with power response that slopes smoothly down with frequency. I did get some balance eventually that made recordings sound tonally more or less as I was accustomed to. The final result was gratifying, with the balance essentially natural and the suppression of the room around you still startling good and the sense of being immersed in the original venue still superb. But the change from the un-eq’d balance was quite large.

To return to the purely positive, let me give a specific but typical example of the remarkable reproduction of recorded acoustics. Track 13 of Telarc’s Ravel-Borodin-Bizet CD (Kunzel conducting the Cincinnati Symphony Orchestra) begins with an off-stage trumpet call followed by an on-stage answering trumpet. One can hear the sound bouncing around the hall, not just general reverberation but specific wall reflections. The Stages reproduced this most convincingly. One really felt one was hearing the sound of the original venue in a detailed way. The effect was almost uncanny. Of course, to some extent one hears hall sound on any system. One can tell when sports announcing changes from the studio to the stadium on a mono table radio. Such things are, however, a matter of degree, and the Stages are top performers in the revelation of the acoustics of the original venue. You not only hear the stadium, as it were; you can count the seats (exaggeration for effect, of course, but one does get unusual insight).

I am not sure how the speakers (un-eq’d) balance was arrived at. I did not check an individual unit, but it is perhaps worth noting that stacking flat individual drivers is no guarantee of flat total response (the lower frequencies load adjacent drivers in a way that higher frequencies do not). The individual drivers are in separate enclosures, and the combined bass does not have the level one might otherwise expect. One needs a subwoofer. (HRT supplied a REL, which worked superbly, as RELs typically do in my experience.)

Functionality
The Stage IV system includes an amplifier. It is not “active” in the sense of the crossover being done at line level and the system having separate amplifiers for mid/bass and tweeter drivers. But the amplifier module does include some equalization so that, while in principle one could power the system with a different amplifier, this is probably not a good idea. The amplifier is small physically, but it powers the system to more than convincing dynamic levels. The amplifier has USB inputs (which I did not use) but also a line-level input, which remains analog throughout. The amplifier unit has a volume control (and a remote control, too). Curiously, the amplifier needs power on the USB input to work at all. So, if you are not connecting a computer, you need to pick up a USB wall-wart power cube and plug it into the USB input even though no audio signal will be coming from it. Not a big deal, but you have to do it. The unit resets to minimum output when disconnected. The amplifier works fine. Don’t expect a lot of carrying on about exactly how good it is—it is doing the job it needs to do very well. The distinctive features of this system come from elsewhere.

Overall Picture
To say that the Stage IV is unusual would be to understate the case. While speakers with controlled radiation pattern have been around for a very long time, few have carried the idea of a forward-radiating design of narrow pattern as far as the Stage IV. You have to be prepared for something different here. But different, in fact, means extraordinarily good in some important directions. In the workaday audio world, one pattern (I hesitate to call it an ideal) of speaker design has more or less solidified—the floorstanding box speaker with omni bass behavior, wide pattern persisting on up into the mids, with some dealing with the “baffle step” at around 500Hz or so, then gradually narrowing with increasing frequency. This is what one might call the Toole school, who pushed for this with a gradual increase in directivity of about 10dB from bottom to top. Speakers of this type have, perhaps, gone about as far as they can go. But there are surely other roads to travel, and the Stage IV is one of them. And it has a distinctive sonic character associated to its distinctive radiation pattern.

More and more exotic cabinet and driver materials arise. But, to borrow the words of Barry McGuire, “You may leave here for four days in space/But when you return it’s the same old place.” Not that much is really going on with most conventional floorstanders. And most of them still have, among other things, the “usual floor dip” between 100 and 300Hz, a serious problem which relatively few usual floorstanders address.

The Stage IV’s are definitely something different, and something exciting, too. Whether you are happy with the unusual balance as it is or you feel the need to eq it to be more like usual, you will be the beneficiary of a truly unusual insight into the recordings you hear and especially into the recorded acoustics. This is not the sound I am accustomed to. But I have to admit, I miss the things now that they are gone. I have not got an excuse in the world to acquire more speakers. But lurking around in my mind is some temptation to latch onto this sound for good.

Specs & Pricing

Driver complement: 1x 28mm tweeter and 3x 70mm mid/woofer per speaker (four speakers per side)
Frequency response: 45Hz–20kHz +/-2dB
Sensitivity: 84.5dB/1m/2.83V
Impedance: 7 ohms (minimum)
Dimensions: 6.25″ x 15″ x 7.25″
Weight: 9.4 lbs. per speaker
Price: $1300 per speaker
Amplifier: Class AB
Power output: 70Wpc
Dimensions: 6.25″ x 8.5″ x 8″
Weight: 8.5 lbs.