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TESTED: Emerald Physics CS2 Controlled-Directivity Speaker System

TESTED: Emerald Physics CS2 Controlled-Directivity Speaker System

What an extraordinary act of creation from designer Clayton Shaw this speaker is! While this isn’t the first speaker to use digital signal processing for its crossover, the DSP is here used for something new. Most earlier DSP speakers have aimed at very wide dispersion using small drivers, e.g., the NHT I reviewed in Issue 163. But in the Emerald Physics CS2s, the DSP is used to craft a carefully controlled and comparatively narrow radiation pattern. This is very much to the CS2’s advantage in my view. This speaker really delivers what is on the recording.<o p=””></o>

Way back in Issue 64 (1990), I wrote these words: “Sound reflected off walls, floor, and ceiling cannot and does not provide information about what the absolute sound at the recording session was nor even about what is recorded on the record or CD.” And indeed I expressed similar ideas in almost my first equipment review for TAS, of the Spendor SP1, on why narrow radiation in the higher frequencies is desirable. On-going experience has made this almost an article of religion with me, and I have looked systematically for speakers that are ideally independent of the listening room via directionally controlled radiation of sound, especially in the higher frequencies. The CS2s come very close to this complete independence. They offer, in short, much of what I want in a speaker. I think they will be very much what you want, too. <o p=””></o>

The Emerald Physics design in effect puts radiation pattern first and fixes frequency response via DSP. In this situation, uniformity of driver frequency response, one of the things that makes expensive drivers expensive, is not critical: the response can be and is tailored to specification by the DSP. Just as an inexpensive car with electronic fuel-injection works better than the most expensive carburetor car could do in years gone by, the Emerald Physics does things that no analog speaker, and surely no inexpensive analog speaker, could imagine. For instance, there are settings provided to make driver integration ideal for various listening distances, compensating for the relatively different distances of bass units and treble unit to the listening position. Try that with an analog crossover!<o p=””></o>

Operationally, the speakers have the usual setup for electronic crossovers and bi-amplification (required here). The system comes with an outboard, powered crossover box, a programmed unit from Behringer, fitted with stereo analog inputs from your preamp, and two pairs of analog outputs, one left/right pair for the low-frequency units of the speaker, one pair for the tweeter units. These outputs go into four channels of analog amplification, which you have to supply. So where is the DSP? Inside the Behringer box, the signal is converted to 96/24 digital, processed, and then converted back. The point of this is that the processing can be far more detailed, intricate, and adjustable than would be possible with an analog electronic crossover. <o p=””></o>

The crossover point is at 1kHz, with very steep slopes, which are easy in DSP but difficult in the analog domain. Moreover, the DSP box is adjusted individually for each speaker for flat response, adjustments being made not only to compensate for the generic non-flat behavior of drivers but for their detailed individual characteristics, as noted earlier. Even the best drivers are not flat by nature. For example, a midrange driver has in its natural state rising response as frequency goes up. Again, this can be simply compensated for here, far more simply than with an analog crossover. As it happens, I had for review an early version of the speaker in which generic setting were used, but the version you buy will have been individually adjusted to exact driver behavior, involving small corrections that I accomplished for myself by doing a bit of extra EQ on my own, following the manufacturer’s suggestion. This included tweaking amplifier gain to pull down the treble a bit: I used four channels of a surround amp with gain controls on the inputs. The speaker you buy will be similarly EQed to flat via the crossover box. This really works—it worked with my pre-production samples with small corrections, and the manufacturer supplied me with measurements of a production sample for comparison. The power of DSP is evident here once again.<o p=””></o>

Acoustically, the speaker is a dipole up to its crossover point, the bottom unit being a pair of fifteen-inch drivers mounted in an open baffle (cloth-covered, though, so as not to look industrial). Everything above 1kHz is handled by a forward-radiating “waveguide” compression driver. The waveguide and the dipole match well in directivity at crossover, the big low-frequency drivers having become somewhat beamy by that frequency, thus matching the controlled radiation of the waveguide. This really works: The speaker is surprisingly coherent, especially considering that its top and bottom drivers are so different in operating principle. The DSP crossover is important here: The fifteen-inch drivers are crossed over with the steep slopes made possible by DSP so that the crossover occurs exactly where they match in directional behavior.<o p=””></o>

Interestingly, the dipole-below/forward-radiation-above is what Jon Dahlquist advocated in his theoretical article for TAS in Issue 3, one of my all-time favorite TAS articles. Why is this pattern good? Because it takes the listening room away far better than most speaker radiation patterns do. These speakers, along with the Gradients and a very few others, give you the sound of the recording as it actually is, unaltered by the room. The speakers interact predictably with the room in the bottom end as dipole woofers close to the floor tend to do, and they eliminate room effects further up by controlled radiation pattern in the higher frequencies. <o p=””></o>

Because the bottom of the bass-driver vertical-pair is close to the floor, its floor reflection becomes part of the direct sound while the high-frequency driver is too directional to bounce much off the floor. So what you hear at the listening position is essentially the direct sound followed by nothing else for quite some time. This is very seldom accomplished as well as it is here. It is quite startling to look at an “impulse” through the speaker, or listen to a transient, including bass transients. What arrives at the listening position is an impulse—a pure transient—followed by nothing, except general room reverberation, with no substantial discrete early reflections being in evidence at all. <o p=””></o>

The virtual elimination of the room’s early reflections makes for an extraordinary sense of focus and precision. Speakers that bounce sound off side walls, floor, and ceiling sound mushy and confused and unfocused by comparison, not to mention colored by floor bounce. This speaker is vastly informative about the music in the most positive sense. Top to bottom you can hear everything that is going on in complex music in a way that is truly unusual, almost uncanny, and surely addictive. I was hearing inner voices of the orchestra, and bass and lower midrange detail, that are very seldom available in reproduction by speakers, <o p=””></o>

These radiation pattern matters are not the usual subject of most audio reviews, which instead tend to talk about what amounts to frequency-response considerations, albeit in poetic terms sometimes. But in the DSP world—the world we live in now if we have moved with the times, where frequency response is adjustable at the pressing of a button—radiation pattern is the main issue. All the usual paraphernalia of audio reviewing—is it bright, is it dull, is it bass heavy or bass light, is it mid-forward or mid-recessed?—is swept away by DSP EQ. One can simply make it right, or adjust it at one’s pleasure. But what is left is how the speaker radiates into the room. And the Emerald Physics does that right to an extraordinary extent.<o p=””></o>

The results are startling. My wife Paige, who is not an audiophile but has listened to a lot of speakers (how could she avoid it?), commented upon her first listen: “Oh, so that is what this stereo imaging stuff is about.” And indeed the stereo imaging behavior of the Emerald Physics is surprisingly precise—with the blurring arising from room sound largely removed, this is strictly “X marks the spot” precision.<o p=””></o>

But along with this, spatial scale is unveiled, too. This imaging precision is not the precision of miniaturization—anything but. A good but not explicitly audiophile recording like the Sony/Mehta/New York Philharmonic Bartók Concerto for Orchestra sounds large and unfettered, like a real orchestra. Put the speakers far enough apart and close your eyes and you could almost be there, within the intrinsic limitations of stereo. And the limitations of stereo turn out not to be nearly as extreme as one would have thought if one had listened only to speakers that interact strongly with the room around.  The sense of being in a large space and of hearing actual instruments in it with the timbre they actually have was remarkable with ordinary recordings and with a masterwork of spatial recording like Reference Recordings’ Das Lied von der Erde, it was even more compelling. This is the real “soundstage,” not some artifact generated by reflections off the walls of your listening room. The speakers sound as if they were in no room at all, nearly, and the original acoustics are nearly all you hear. The large radiating area in the lower frequencies and the dynamically unfettered upper-frequency driver made the whole sound effortless. The orchestral gestalt, as HP likes to call it, is extraordinarily well-presented. The high end de facto began with speakers with narrow radiation pattern, namely large planar radiators and speakers like the Infinity IRS, with very wide baffles. Somehow high-end audio wandered off into narrow-front wide-dispersion room-fillers. But controlled radiation never really went away, and here it is once again, and more power to it.<o p=””></o>

Human voices are focused and present, and sound natural in timbre, as do individual instruments. The speakers do very well on intimate music. But it is in large-scaled music—or in smaller-scaled music played in large spaces—that they really distinguish themselves from almost all others. It has long been my belief (and that of many other people) that it is the room that makes reproduced music sound unreal, closed in, constricted, colored, and mushy when the music is complex. All you have to do is listen outdoors to an ordinary speaker to hear how well stereo works when room sound is not interfering with it. And here you get very nearly the same magical clarity and lack of sonic clutter, and the total precision of imaging. Something like the DaCapo recording of the Nielsen Fifth Symphony, with its multilayered textures, is superbly unraveled even at the loud moments where, with many other speakers, it can turn into confusion.<o p=””></o>

The Emerald Physics is the not only speaker that can do things very like this. The dipole Jamo R909 (Issue 167) accomplished similar things by analog means. And the various Quad electrostatic models also have good discrimination against the room with a similar resultant clarity, though the Emerald Physics deals better with the 100–200Hz region, where the Quads interact with the floor. And both Quads and Jamos are three to five times the price of the Emerald Physics. <o p=””></o>

The Emerald Physics CS2 does have some limitations. The dipole bottom end is superb and goes all the way down with very fine definition, but it will not plumb those deepest depths at the largest volumes. People who want earthquakes—or large pipe organs at full bore—may want a subwoofer, or additional bass units as offered by Emerald Physics. Also, if you are not careful with listening position, the waveguide driver can sound a little bit like a waveguide as such on some material, with a trace of coloration at the bottom of its operating range and a slight roughening of texture that I think of as “throat noise.” Also, a crossover at 1kHz, even a superbly done crossover, is a tricky matter compared to running a good driver straight across that region. There is a slight sense here, not of separate drivers, but of shift in sonic character as one goes from the large woofers to the waveguide mid/treble. The top of the lower drivers’ range can seem a bit obscured compared to the crystal clarity of the waveguide driver above. But these are definitely very minor matters compared to what the speaker does so well, and even more minor when one thinks of the price point here. Indeed, they are really evident only in the context of massed string choirs or other complex material with a wide tonal compass, and then only subtly so. <o p=””></o>

I think of how little the Emerald Physics CS2s cost for what they do. This is the world of DSP as it should be. By comparison, the little boxes that people are sometimes paying the Emerald Physics’ price for—or even many times that price—seem like toys, unable to offer the power and scale, the dynamics, the top to bottom transparency and the sheer quantity of musical information that the Emerald Physics speakers produce, always with a feeling of complete ease and without demanding much amplifier power. After this, I would find it really hard to go back to little boxes, no matter how good the little box might be nominally. So will you, I think, if you have a vivid memory of concert sound. No speaker is perfect, and perhaps with price-no-object drivers and so on, designer Clayton Shaw could produce even more remarkable sound, albeit at a higher cost. But the Emerald Physics CS2 comes remarkably close to putting at your ears the literal sound of the recordings you play on it, via the all-important minimized interaction with your listening room. Good by any standard, at its price it is quite amazing. A wonderful achievement in speaker design.

Specs & Pricing

Type: Bi-amplified stereo speaker system with electronic crossover (amplifiers not included, bi-amplification required)

Drivers: Two 15″ woofers in open baffle, dipole operation; 1″ compression driver forward radiator, conical waveguide

Crossover: 1000Hz, 48dB/octave slopes (digital signal processing crossover)

Frequencyresponse: 20Hz–22kHz, -3 dB down points

Sensitivity: 100dB/2.83 v

Dimensions: 48″ x 18.5″ x 6″ (baffle on metal base)

Weight: 62 lbs.

Price: $2995/pair; additional bass units(not tested), $1795/pair

By Robert E. Greene

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