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Equipment Review
December 1998

InnerSound Eros Speaker System

by Frank Alles

Reviewers' Choice Logo
A well-engineered
high-performance speaker
system at a price more
audiophiles can afford.

Review at a Glance
Sound Smooth, fast, transparent, delicate and dynamic. Narrow sweet spot and a touch light in the deepest bass, but oh what they do!
Features Must be biamped, but external active crossover unit with integral 200Wpc bass amplifier is included.
Use Wider-than-normal placement with pronounced toe-in recommended; sit too low and you’ll lose some high-frequency life.
Value Not as luxurious as some high-zoot models, but a very attractive package for the loot.

School daze

When I entered junior high at the tender age of 12, I was exposed to two things that would change my life. The first was my infatuation with the opposite gender, and the second was my ongoing love affair with music (my one true love). Until that time I had never (at least that I can recall) heard a full orchestra playing live music. One day, we were all assembled in the auditorium for some sort of holiday celebration, and I finally got to hear the sound of live instruments all playing together just like a real symphony orchestra, though perhaps not quite as well rehearsed. I mention this because although it was clearly an amateur production, the simple beauty of the music evoked a purely emotional response from me as I sat there enthralled in its powerful grip. Struck by the beauty of the moment, my eyes began to well up with tears that I quickly wiped away so that my peers wouldn’t know how affected I had become.

Over the years I’ve occasionally been moved to tears by my home music system. There have been many other times when I wanted to cry not for joy but because my system sounded poor. I’m happy to report to you that the InnerSound Eros is one of the few speaker systems I’ve encountered that has been able to bring tears to my eyes because of its sonic splendor.

Have you ever pondered why exactly so many speaker manufacturers claim that their conventional dynamic speaker systems possess "electrostatic speed and clarity," with some even claiming their product to be "superior to electrostatics?" Well, to put it simply, it’s because the better electrostatic designs achieve such low levels of distortion combined with superior reproduction of fast transient sounds that they are considered by many to be the benchmark for performance in those areas. Thus we have much misused and overworked catch-phrase "electrostatic purity." I must tell you that in my many years as an audiophile I’ve discovered that most manufacturer claims of conventional drivers surpassing electrostats in the areas of speed and low distortion have been little more than advertising hoopla invented to fool the all-too-gullible consumer. Many speakers that I have personally investigated had proved to be rather disappointing in actual listening tests.

May I present...

That said, I’d like to introduce you to the InnerSound Eros, an electrostatic hybrid speaker system developed by the man who wrote the book, The Electrostatic Loudspeaker Design Cookbook (published by Audio Amateur Publications), Roger Sanders. The Eros is a two-way hybrid design that employs a 10" woofer and an electrostatic cell with a diaphragm measuring approximately 40" x 12". The enclosure is a modern-looking structure similar in appearance to the Martin-Logan electrostatic hybrids. The standard finish is basic black, but wood-grain trim strips are available at extra cost.

There is no grille cloth and an epoxy-coated wire grid, matching the stators of the electrostat, covers the woofer and extends to the bottom of the enclosure. Rapping on the metal grille with my finger showed it to be somewhat resonant. It is held in place by about ten screws and the two removable adhesive trim strips that run the full height of the enclosure. This makes accessing the woofer-securing screws more of a nuisance than it should be. In listening to music I didn’t detect any anomalies related to grille resonance. Nonetheless, I see this as a possible area for improvement.

Included with the system is a 200Wpc stereo bass amplifier that contains an integral active crossover on the same chassis. The crossover frequency is 450Hz and the roll-off is at 24dB per octave. The advantages to using an active crossover are that it cannot be overloaded (in normal use) and that the amplifiers are used more efficiently and will have better control over their respective drivers. A convenient front-panel volume knob allows the user to match the level of the bass amp to his choice of midrange/treble amplifier.

The amp/crossover unit, in addition to having RCA-type outputs for the midrange/treble amp, has a pair of RCA outputs to allow the owner to use a different bass amplifier if that is his preference. The level of the bass output jacks is also controlled by the front-panel volume knob. A female IEC connector is provided on the rear panel of the bass amp to facilitate the use of detachable AC power cords. Since the internal bias supplies of the Eros are designed to accept AC power, one IEC receptacle is installed at the bottom rear portion of each speaker cabinet and the necessary AC cords are included.

The Eros each measure 15"W x 18"D x 68"H and tip the scales at 74 pounds a piece. The amp/crossover measures 17.5"W x 15.5"D x 5"H and weighs 34 pounds. Both the speakers and the bass amplifier are fitted with the same type of heavy-duty gold-plated binding posts by Michell of England. This was a nice touch and made secure speaker hook-ups a breeze. The speakers came with adjustable spikes as well as regular foot pads for those of you who may not wish to mar your fine flooring.

InnerSound rates the speakers at 96dB/W/m. The impedance curve is a bit odd in that the maximum impedance of 113 ohms occurs at 450Hz and then tapers down to 2 ohms at 20kHz. There is a bit of capacitance for the amp to deal with also, approximately .6uF. These speakers can get by with amplifiers of modest power ratings just as long as the amplifier is stable into capacitive low-impedance loads. Because electrostatic speakers require voltage to play loudly as opposed to current, the more voltage the amplifier develops across its positive and negative rails, the louder the Eros will play. With the proper amplifier, the Eros is capable of playing at very high SPL levels.

In the case of tube amplifiers, it is probably best to use the lowest-rated output taps (usually 4 ohms), but you can try the Eros on the 8- or 16-ohm taps to compare the sound quality. I used the Eros with five different amplifiers, four solid-state units and one tube model, and didn’t encounter any problems. As it happened I achieved the best performance with the most powerful amp I had on hand, the Sonogy Black Knight (175Wpc at 8 ohms), which is also a very stable design. Don’t be shy to try your 500Wpc monster amp with Cupid’s little helpers -- they’ll sing just as sweetly, only LOUDER.

The woofer is rated at 4 ohms and presents a more conventional load to the bass amplifier. The back wave of the woofer is damped by an 8' folded transmission line covered internally with synthetic fibers. The transmission line extends and flattens the bass response while maintaining excellent transient speed and articulation. In my room, the bass began to roll off at about 40Hz, with useful output down to about 30Hz. Though the published specs claim response down to 24Hz, I think the Eros would require strong reinforcement from room boundaries to approach that mark. But you can set the woofer enclosures virtually right up against the front wall, so if the deepest possible bass reproduction is your bag, then that is the place to start. I did try using the Eros in conjunction with an Audio Pro B-250 powered subwoofer and was able to achieve a relatively seamless blend. This bolstered the bass just subtlety between 24Hz to 40Hz and added a degree of fullness and weight that was just what the doctor ordered for certain recordings. In my view, the addition of a high-quality subwoofer system to the Eros could go a long way toward turning this already outstanding speaker system into a devastating one.

At the other end of the spectrum, the electrostatic panel’s response is flat beyond 20kHz and is claimed to be 2dB down at 27kHz. In this particular design, Sanders, who had developed and experimented with curved electrostatic panels, opted for the flat-panel approach. His logic was that clearer, more focused and extended sound would result, though the horizontal dispersion would demonstrate pronounced beaming effects above 2kHz. The upside to this is that the "controlled dispersion" pattern of the Eros would launch more sound directly at the listener while at the same time diminishing high-frequency room reflections. While this did appear to work exactly as claimed, it also diminished the size of the sweet spot to an area about a foot wide. So unless you are listening very close together (as with a lover), your buddies will have to line up one behind the other to hear these speakers at their best.

Additionally, the best blending of the drivers, which resulted in the greatest image depth, was achieved at a point above the level of the woofer, but not too far from the bottom of the electrostatic panel. If you sit too low you will lose high frequencies because the electrostatic section will beam them right over your head. So if you align your ears just slightly above that point, where the high frequencies are evident and extended, that is right about where you want to be. To aid in this process, you can use the leveling feet to adjust the angle of the front baffle to correspond with your seated listening position.

Set up

Because of the somewhat unconventional dispersion characteristics of the Eros, their placement in the listening room can be a bit tricky. But with a little help from the owner’s manual, I was able to get excellent results. I placed the speakers along the long wall of my listening room about 8.5' apart center to center, and about 30" from the front wall to the rear-middle of the woofer enclosures. I would’ve liked to have gotten them a bit closer to the wall to further reinforce their low-bass response, but there were complications in my particular installation that prevented me from accomplishing this.

Properly set up, the Eros throws a rock-stable multi-layered image with excellent center-fill. One helpful thing I discovered was if you can see the sides of the woofer enclosures, they're not toed-in enough. When viewing the speakers from the listening position, you should see the front panels and no more. The speaker’s high-frequency response will be truncated noticeably if the toe-in is inadequate. The Eros like to be farther apart than wide-dispersion speakers but still away from corners. Your listening seat can then be as close as the actual distance between the speakers, or slightly further back. My seat was about 10' back from the front plane of the speakers.

For my listening tests, the system was configured as follows. My analog source was a Townshend Audio Rock Mk III ‘table with a modified Rega RB-300 tonearm. The cartridge was a Transfiguration low-output moving-coil design, which fed a custom AHT/P phonostage. Nordost Red Dawn interconnects linked the phono preamp to an AHT tube linestage which in turn delivered the signal to the InnerSound active crossover/bass amp unit via Full Spectrum Exotic interconnects. The digital source consisted of a Parasound C/BD-2000 belt-drive transport linked to a Parasound D/AC-2000 Ultra converter with a WireWorld Gold Starlight III AES/EBU digital cable. Full Spectrum Signature interconnects conveyed the analog output from the DAC to the AHT linestage. Out of the InnerSound crossover, Full Spectrum Signature interconnects fed the mid/treble amplifier, a Sonogy Black Knight, which was connected to the Eros ‘stat panels with Sonoran Desert speaker cables. Finally, the InnerSound bass amplifier dumped its current to the Eros’ woofers through Luminous Audio Prestige speaker cables. A Full Spectrum Signature AC cord was used on the DAC and a Full Spectrum Exotic AC cord was employed on the Black Knight amp.

Falling in love

Although I was surely infatuated with the Eros right off the bat, we didn’t really fall in love until we’d dated several times and got to know one another a bit. Our courtship focused on the usual foreplay -- i.e., positioning the speakers in my room and mating the Eros with different speaker cables and amplifiers. Hey, what did you think I meant?

Initially the Eros’ disposition bordered on snobbery, and I say that for two reasons. Not only were they critical of minor positional adjustments (fractions of inches and scant degrees of toe-in), but they seemed fussy about the amplifier(s) to which they were mated as well. Though I got very good results with the excellent Clayton Audio M-70 monoblocks, the Music Reference RM-9 Special and my Sonogy Black Knight provided the best overall sound. The RM-9 had a somewhat softer treble presentation than did the Sonogy, but in other areas their sound was surprisingly similar. Perhaps not coincidentally, these were the highest-powered amplifiers that I used during my listening tests.

If you are a fan of classical music, especially large-scale symphonic works, the Eros will reward you with one of the most natural and lifelike presentations that you’re likely to hear outside of the concert hall. I have to admit that I was both mesmerized and transfixed by the beauty and the power the Eros provided. Playing Gershwin’s Rhapsody In Blue from Dayful Of Song [Delos DE 3216] was such a moving experience that it literally brought tears to my eyes. The grand piano was so precise in its sound that it truly was a joy to behold. Even when the fingering became rapid and intense, the Eros held it all together. From the initial attack to the natural decay of each and every note, it was all there clear as day. The massed-horn section was both distinct and layered to beautiful effect, and the timbre of the instruments seemed to be right on the money. Whether it was the burnished blat of the brass or the hollowish honk of the woodwinds, the instruments couldn’t have sounded much more natural even in a live venue. As sharp and clear as the transient edges were, the sweet and seductive smoothness of the instruments was also quite apparent.

Most impressive was the fact that during ear-splitting orchestral crescendos the instrumental lines didn’t blur. They remained clear and intact, as they do in a good seat in a good concert hall. Playing Copland’s Fanfare for the Common Man and Billy The Kid from The Music of America [Telarc CD-80339], I was amazed at the weight and impact of the timpani and bass drums. Though the Eros lacks that last ounce of extension when compared to some full-range speaker systems (and ones with quality dedicated subwoofers), it acquitted itself admirably on this notably bombastic and torturous recording. In general, I found the bass reproduction of the Eros to be very adept in terms of its agility and delineation. The transmission-line enclosure seemed to work wonders with the big 10" woofer and did not sound at all boxy or bloated as lesser systems so often do.

If you want to have yourself a blast, put on The All Star Percussion Ensemble’s album of the same name [Golden String CD 005] and have a listen to Berlioz’s "March to the Scaffold," from Symphonie Fantastique. It contains some startling bursts of raw percussion. In the opening of the piece there is a high-frequency snap from the left channel that comes from out of nowhere with all the intensity of a gun shot -- believe me it will turn your head even if you know it’s coming. This is a gold CD and also contains the Ensemble’s rendition of Bizet’s "Carmen Suite," (i.e., Carmen Fantasy) as well as selected makeovers from Beethoven and Pachelbel. It’s all done with an incredible repertoire of unusual percussive instruments and throws an immense multi-tiered soundstage rife with delicate nuance as well as startlingly loud sonic assaults. I think it’s very well done, and it was certainly well conveyed through the Eros.

Don’t be concerned about any of the things you may have heard about electrostatics not being good at rendering dynamic contrasts. I can assure you that the Eros system is very capable of displaying a full range of dynamic gradients from the quietest pianissimo to thundering sforzandos -- and back again. Moreover, these speakers proved to be excellent reproducers of microdynamics. This added an extra dimension of expressiveness to musical compositions by exposing the subtle changes in loudness to an uncanny degree.

Because I’ve hinted at soundstaging performance, I will tell you that the Eros is capable of producing a stable and expansive image. When the speakers are set up as I’ve described, some instruments do appear to emanate from points outside and behind the left and right boundaries, which is what I’ve come to expect from top-quality speakers. They had an exceptional sense of layering and depth, and instruments/performers tended to be correct in size and precisely located within the expansive dimensions. That to me is very important when trying to re-create a musical event, and the Eros clearly delivers the right stuff. With symphonic works, the rows of the various instruments appear in their proper respective locations, just as they do in the concert hall, which is really the Litmus test for proper imaging.

At times, with certain recordings such as many tracks from Cassandra Wilson’s New Moon Daughter [Blue Note D 112088], the Eros gave the illusion of height to Ms. Wilson’s husky, haunting vocals. I’m not sure why the Eros would do this, but it was an intriguing effect. Of course, New Moon Daughter is a studio recording, so almost any sonic effect is possible, and somehow it seemed strangely appropriate that Cassandra Wilson was looming large above me.

I feel I’d be remiss here if I didn’t say a few words about the Eros’ reproduction of acoustic and electric guitars. Simply put, they provided the most accurate and soul-satisfying rendering of plucked and strummed guitar strings that I’ve heard from speakers, period. Try "Pipeline" from The California Guitar Trio’s Yamanashi Blues [Possible Productions DR 9301 2] and you’ll be utterly awed by the depth, dynamics and realism captured on this stirring classic piece. Actually, I ran across a good many recordings where I felt that the Eros’ reproduction of guitar work was second to none.

Rivals for my affections

For many years I have been using Acoustat 2 + 2s and Acoustat Monitor IIIs as my primary reference speakers. Full-range electrostatic panels are employed in these crossoverless designs to cover the entire audible bandwidth. Multiple panels are used in the various models (four in the 2 + 2 and three in the Monitor III) to increase the bass, the efficiency and the dynamic range of the system.

I would not have stayed with the Acoustats for so long if it hadn’t been for the inspired design work of then-unknown Dan Fanny of American Hybrid Technology. Fanny was very familiar with Joe Curcio’s modifications to Acoustat’s original servo-charge direct-drive tube amplifiers and devoted considerable time and energy to improving this output-transformerless design to the point where its performance was truly prodigious. When the opportunity arose for me to buy one of his more advanced prototypes, I jumped at the chance and never looked back.

With the AHT servo-charge amps powering the Acoustats I was able to achieve levels of control, transparency and dynamics that were (and still are) virtually unattainable with ANY other amplifiers through even the most modified interfaces. The performance level of such a direct-driven Acoustat system will still surpass many contemporary high-end designs, other highly regarded electrostatics included. The reason I tell you this is to give you a frame of reference for the comparison I’m about to make -- the Eros System using conventional amplifiers to the AHT modified direct-driven Acoustat system.

When I first set up the Eros, my feeling was that I was hearing exceptional midrange reproduction that was superior to the Acoustat’s, mainly in its ability to achieve a sharper focus. The bass performance of the Eros, as fast as it was, could not keep pace with that of the Acoustats and certainly was not as punchy or powerful. After the Eros’ woofers broke-in, the Eros system had a fuller and more powerful bass that was certainly very respectable by high-end standards, but was still not as fast or full as the Acoustat system’s.

Also the Eros’ high-frequency response was a bit ill-defined at first and this was the area where I had expected it to excel. Once I’d found a suitable amplifier to drive the Eros (the Sonogy) the treble began to shape up. It clearly demonstrated a more extended, detailed and focused high-frequency spectrum. This in conjunction with its superlative midrange performance and its superb tracking of macrodynamics gave it the overall edge over the Acoustats in my book. Though the bass reproduction of the Acoustat system is a bit faster and plumper, I feel that the bass capability of the Eros is quite good and actually a little more dynamic-sounding in the low bass.

This contest proved to be an exercise of contrasting styles, with the Acoustat system being the more euphonic and forgiving of the two. In the final analysis the Eros system elicited more of the subtle nuances and fine details from my recordings that allowed me to move a bit closer to the original performance.


I have to express my most heartfelt congratulations to Roger Sanders, designer of the Eros system. In my view this is a very well-thought-out product that expounds upon previous electrostatic hybrid systems with some clever and noteworthy innovations. These speakers do present a narrow listening window because of Sanders’ flat-panel stratagem. But because of their precision of focus and their almost surgical incisiveness of fast musical transients, I felt this was a justifiable trade-off. The tuned transmission-line woofer enclosure worked like magic to eliminate boxy colorations and to deliver dynamic well-controlled bass. Add to this the fact that you are getting a quality high-powered bass amplifier and an active crossover in addition to the speakers, which offer near state-of-the-art performance, and the Eros system must be considered quite an attractive bargain.

Some reviewers have tagged the Eros a romantic-sounding speaker. To be honest, I am at a loss to understand that assertion because to me the term romantic implies a warm, lush or glamorous presentation. In my listening, I never thought of the Eros as having any major bumps in its frequency response that would support that position. If anything, it seemed to be a touch on the lean side. Frankly, I thought it sounded less colored than many other highly rated loudspeaker systems.

Yet I can agree that the InnerSound Eros are romantic speakers in one way. So beautiful is their sonic presentation that they made me fall in love with the music they played. In that respect, Roger Sanders has named this product with the utmost accuracy.

...Frank Alles

InnerSound Eros Speaker System
$4495 USD
Warranty: Three years parts and labor

InnerSound, Inc.
1700 Hwy 16
Whitesburg, GA 30185
Phone: (770) 838-1400
Fax: (770) 838-0111

E-mail: innersound@mindspring.com

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