InnerSound Eros Mk.III electrostatic loudspeaker Page 2

Setup
The Eros system arrived in one of the longest trucks I've ever seen. InnerSound had shipped two 6' loudspeaker cartons and two heavy cartons for the electronics, all secured to a single pallet so large that the truck driver had to separate the four boxes before he could remove them from the van. Even so, the Eros speaker assembly was light enough for my wife and me to carry them into the house and up our narrow stairs to the living room.

My listening room is a lightly damped, rectangular, 5400ft3 area 26' long by 13' wide by 12' high, with a 12' semi-cathedral ceiling. The far end of the room opens into a 25' by 15' kitchen through an 8' by 4' doorway. I placed the speakers 3' from the front wall and 3' from the side walls.

Loudspeaker owner's manuals are some of the least-read publications in existence. Some who buy the Eros Mk.III might be able to skip reading InnerSound's spiral-bound instruction manual, but not I. The Ero loudspeaker system only produces sound if the crossover controls are set to "80" or higher. Both JA and I independently discovered this after much frustration. A quick guide card listing this instruction would prevent similar grief in new owners.

The instruction manual also suggests the optimal speaker setup. The speakers should be placed equidistant from the listener's position. With a carpenter's rule, I carefully measured 10' from each panel front to the bridge of my nose—supposedly equidistant from each ear—and put blue painter's tape on the floor to mark each speaker's exact location. I adjusted each speaker to point it directly at my chair. The manual suggested adjusting the speakers so that my visual reflection was centered in the middles of the Eroses' screens. For final adjustment, I held a small pencil flashlight above my head and made sure that the reflection of the beam was centered in both speakers, and was the same height.

I plugged the interconnects from my Krell KRC preamplifier into the Crossover-Bass Amplifier. The crossover's low-pass filter directed bass signals to its internal bass amplifier, which then drove the Eros's transmission-line woofers. The high-pass crossover outputs were connected to the input jacks of two Bryston 7B-SST monoblock amplifiers, which drove the ESL screens via my PSC ribbon loudspeaker cables. Again following the manual, I set the crossover's readouts for the overall system Level to "85," the Midrange to 85, and the Bass to "5."

I checked the speaker's low-frequency in-room response with 1/3-octave warble tones at -20dB, from Test CD 2 (Stereophile STPH002-2). I switched my RadioShack sound-level meter to its C-weighted, slow ballistics mode, and averaged several readings in a window 4' wide, 3' high, and centered on my listening position and ear height. I adjusted the crossover's overall level so that the 100Hz warble tone registered 0dB on the meter. At that setting, the Eros's bass response was within ±5dB from 200Hz to 50Hz, with a +5dB peak from 50 to 80Hz, which was a characteristic of the room. At 41.5Hz, the output was +4dB; at 31Hz, it was down by -4dB. By 25Hz, the signal had dropped to -10dB, with audible doubling. I repeated this procedure after setting the Crossover-Bass Amplifier's Bass control to "2," but this did not significantly change the response below 100Hz.

The Eros was designed to have a precise, small sweet spot in the nearfield. I substantiated this by playing pink noise and conducting the "sit down, stand up, walk around" test—I heard the Eroses' sweet spot only when I was sitting (ears 38" high), even though the electrostatic panels extend from 26" to 68" above the floor. If I leaned too far forward or too far back in my listening chair, the tonal balance dulled. It dulled even more when I stood up or moved around the room.

During the break-in period, the remote stopped working. Roger Sanders helped me find the culprit: a loose ribbon cable inside the crossover unit. A soft but pesky buzzing sound in the right electrostatic screen was loudest at 100Hz when swept with different frequencies. The buzz was mechanical—I could suppress it by pressing on the stator with my finger. I reduced this rattle somewhat by shoving a piece of paper between the stator and the speaker's wooden frame, and then blasting the screen with compressed air (footnote 1). I was reassured by InnerSound that, should a buyer suffer this type of problem, the company will replace the speaker at no charge.

Using CDs of my favorite vocalists, I varied the crossover settings from my listening chair via remote control. I was surprised that there was no set, standard anechoic-based reference point for these controls, either on the crossover faceplate or in the manual. Could I dial in the correct control settings? I heard the biggest changes in tonal balance when I decreased the Midrange setting from "88" to "78." This shifted female singing voices from smooth and extended to hollow and tunnel-like. For critical listening, I returned the Eros crossover settings to "88" for Level and Midrange, "5" for Bass.

Sound
The Eros Mk.IIIs' best quality was their first-rate imaging: They generated a seamless, wall-to-wall soundstage that did not seem to emanate from the speakers themselves. The first track on David Hudson's Didgeridoo Spirit (CD, Indigenous Australia IA2003 D) opens with sounds of a rainforest, complete with a soft rain falling, exotic birds chirping, and wind rustling through the leaves. I heard so much new information over the Eroses that I was startled.

I had the same stunned reaction when I played Fleetwood Mac's The Dance (CD, Reprise 46702-2). Sure, the mids and highs were fast, transparent, and rich, with a sheen and harmonic structure that were stunningly new and different. Sure, the speakers "disappeared" and engulfed me in sound. But there was more. Never had I heard such a large soundstage, such a distinctive layering of instruments and vocalists, or such realistic crowd noise. I could easily tell that lead singer Stevie Nicks was moving around, alternating between singing close to the microphone and then turning away. As she sang "Silver Springs," I wrote in my notes, "Nicks has never sounded as realistic, as emotionally moving, or as powerful. It's as if I've never heard this album before."



Footnote 1: According to Roger Sanders after he had examined the speaker, the cause of the buzzing was a grain of sand that had found its way into the electrostatic panel. "Fixing the problem was simple," he wrote. "Using a blow-gun, we shot some compressed air into the electrostatic panel. This simply blew the grain of sand away. A customer probably could probably remove the grain of sand using a vacuum cleaner with a soft brush. But the panel is very rugged. Blasting it with compressed air will not harm it."—Larry Greenhill
Company Info
InnerSound
7161 Valtec Court, Unit D
Boulder, CO 80301
(303) 440-3561
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