Emerald Physics CS2.3 Mk II Loudspeaker

Genuine Bargain

Equipment report
Emerald Physics CS2.3 Mk II
Emerald Physics CS2.3 Mk II Loudspeaker

In the Emerald Physics room of the Newport Audio Show the year before last I experienced some of the best sound I’ve heard at any show in over forty years as an audiophile, the speakers those under review here. This is what I wrote in my report: “The CS2.3 II offered simply the most precise imaging and best soundstaging I have ever heard anywhere; for once and without exaggeration I could use the word holographic. Dynamic range is extremely wide, bass response subterranean, midrange rich and open. Orchestral music is spectacular, while Sinatra on “Angel Eyes” is palpably present, three-dimensional, and spookily real—also rare at this show, unmistakably a true baritone (it took all of maybe twenty seconds before a smile appeared on my wife’s face). If this thing performs in most rooms the way it did here, and given the quality of these hotel rooms that should be practically anywhere else, it may be just about the best performance per dollar I know in high-end loudspeakers.”

Hyperbole is a liability of show reports because most of the sound at audio shows is so poor that when one hears something good one tends to overreact, not least because negativity, even when warranted, is so dispiriting. But as the review that follows will reveal, apart from the “subterranean bass” bass observation, which is overstated, I stand by that report.

The Design
The speaker is a descendent—sort of—of the original Emerald Physics CS2 that my colleague Robert E. Greene reviewed so enthusiastically in TAS. I say “sort of” because when the company was purchased by Walter Liederman a few years ago, the CS2 became the $5995-per-pair CS2.3 Mk II, which is claimed to share no parts with its forebear and its midrange/ tweeter configuration is markedly different. Nevertheless, the two models do share some basic design principles and philosophy: large stacked woofers vertically mounted on an open baffle, and the use of DSP to assist in crossover slopes and equalization. They differ in that the CS2 crossed over the dual 15" woofers to a compression-driver tweeter, with no midrange. The CS2.3’s point-source midrange/tweeter is said to improve the speaker’s imaging. The design is unusual enough to warrant describing in some detail its components parts and how they’re meant to go together.

The drivers, though not manufactured by Emerald, are proprietary. Per side they consist in a pair of imposing 15" woofers that operates below 100Hz and a 12" upper-bass/ midrange driver with a coaxially mounted, lens-loaded 1" tweeter (henceforth I shall refer to this as the midrange/tweeter module even though it handles part of the upper-bass). The speakers operate as dipoles up to the transition to the tweeter. Biamping is required and necessitates either four mono amps, two stereo amps, or one four-channel amp. Per side, one amplifier connects directly to the stacked woofers, the other to the midrange/ tweeter module through an outboard crossover box that crosses the midrange to the tweeter at 900Hz. Unlike the woofers and the midrange driver, the tweeter operates in monopole mode (more about the implications of this later).

Also supplied with the system is an outboard digital signal processor called the DSP2.4. (In the original version this was an outboard DSP and equalizer by Behringer, but the current owner and engineers felt that it was too unreliable to be retained and that it wasn’t “truly an audiophile product.”) Although physically very compact—about the size of a cellphone differently configured and thicker—the 2.4 is a powerful and sophisticated device. Connected between the preamplifier and the power amplifiers, it serves two functions: crossing over between the woofer and the rest of the frequency range, and judiciously equalizing to flatten and smooth the response throughout the upper bass and lower midrange, exactly the region where so many floorstanding speakers exhibit the unfortunate “floor bounce” effect that makes them sound too thin or lean. Note that the CS2.3 doesn’t offer full DSP room correction; instead it offers an array of fixed-equalization settings that help to flatten the bass response in a range of listening rooms.

Full DSP room correction is usually done with a microphone and several measurements taken in situ, but the current CS2.3 II went a different route. When Clayton Shaw owned the company, he undertook a program of extensive and detailed measurements of speakers in a wide variety of typical listening rooms so as to determine their bass-response characteristics at various distances from front and side walls. Using these he came up with algorithms to flatten the response curves. End users supply Emerald Physics or the dealer with the dimensions of their rooms (preferably with a diagram) and the desired location of the speakers, and the manufacturer programs the appropriate response algorithm into the DSP box. The owner must also supply the sensitivities of the amplifiers to be used. It is not necessary that the amplifiers be the same, but if they are not, the DSP2.4 must be programmed so that the amplifiers’ signal outputs are identical. I had on hand only two amplifiers of such different characteristics—a Quad 909 and a Zesto Zia—that the good people at Wyred 4 Sound generously lent me a pair of superb ST Series II amps (see sidebar), so the issue of identical sensitivities didn’t arise. Emerald specifies the sensitivity of these speakers as 97dB, so quality of wattage matters much more than quantity. Although the sensitivity is 97dB at 1kHz, the separately powered bass drivers’ sensitivity is 90dB. As for tubes versus solid-state, bear in mind that each speaker has two large woofers operating in free space, so logic suggests amplifiers with reasonably high damping factors, which most of the time means solid-state.

In addition to the DSP2.4 there is also, as noted, an outboard crossover for each speaker array. The outputs of the bass amplifier connect directly to the paralleled bass drivers, but those of the upper amplifier go through the crossover box, which has separate outputs for the upper-bass/midrange driver and the tweeter (the boxes, supplied with all necessary cabling, are each placed behind a speaker on the supporting platform).