INNERSOUND EROS SPEAKERS Dr. Robert E. Greene, reviewer
Last Updated: 09 March 2014 09 March 2014
Created: 01 March 2009 01 March 2009
Fi Magazine, July 1998, Dr. Robert E. Greene, Reviewer
One of the perennial dreams of audio designers is to combine the dynamic punch and extension of box speakers with the purity and clarity of box-less electrostatics in the higher frequencies. Hybrid speakers with box woofer plus electrostatic mid-tweeter appear regularly and have for decades. (One of the popular audiophile do-it-yourself projects of the Fifties was to put together the Jantzen electrostatic tweeter with various box bottom ends; some of the resulting speakers were exceptional for their time and would have their points even today). But with rare exceptions, those designs past and present have not really jelled. Sooner or later the ear latches onto the discontinuity between the box woofer and the electrostatic, and it stays latched on. Once heard, the discontinuity becomes ever more annoying and that is the end of that speaker. Like college boys in the old song, hybrids come and go but mostly go.
The InnerSound Eros is yet another try. And by George, this one works! The Eros really does solve the integration problem. To my ears, it is as coherent as speakers with two dynamic drivers, and indeed more coherent than most of them. The result is a speaker with extraordinary virtues and few failings. It is smooth, sweet-sounding, clean, and pure, with superb stereo imaging performance. This is one hybrid that won't wear out its welcome.
Like a magic show, the Eros calls up the question: How's it done? Part of the answer is just the extreme care and careful experimentation that the design involved. Roger Sanders, the designer, is a well-known expert on electrostatics. (He literally wrote the book on the subject he is the author of a standard reference work about electrostatics). And he has been at work on this design for a long time. But there are two explicitly describable things in the design that separate the Eros from other, less successful hybrids. First the box woofer, which is a transmission line design, is very clean, precise, and nonresonant. I'll be darned if I'll call a woofer fast since that is not what a woofer can be, but if it weren't the wrong word, it would be the right word for this one. Second, the crossover from box to electrostat is higher than usual, at around 450 Hz, and has steep slopes (24 dB/octave).
Traditionally, people have tried to run their electrostatic elements down as low as possible, to try to make as much of the sound electrostatic as possible. The trouble is that down at say 150 Hz, a dipole electrostatic element is interacting with the room way differently from a more or less omni box-woofer. This discontinuity of radiation pattern is almost sure to be audible. In the Eros, the crossover point is high enough that the dipole's room interaction, and particularly its differentiation against room modes, is not so obviously different (room modes are really closely spaced by 500 Hz). Also, the electrostatic element does not have to operate so far down into the region where dipole cancellation becomes a big issue. So the woofer can be rolled off steeply, since it does not need to help out the electrostat above the crossover point. Anyway, those are my guesses as to why it works. But the real point is, it does.
You might say that if dipole operation is not so important above 500 Hz, then why bother with the electrostatic thing at all? Why not just use dynamic drivers on the top too? The electrostat has other advantages, however. First of all, it has really low distortion. It is hard to get anything like this clean a sound out of a box mid/tweeter.
The second point is a little more techno, but it counts for plenty. The electrostatic element in the Eros is forty inches high. This means that from say 1 kHz on up, the speaker is beamy in the vertical direction. There are no reflections off the floor or ceiling in the higher frequencies. And when it comes to that, because dipoles do not radiate sideways, you can get rid of the first sidewall reflection too, if you set the speakers up right. The first reflected highs you hear arrive about a week later than the direct sound. The result is that the Eros sounds so clear you almost can't believe it.
I listened first of course, but I couldn't resist a little impulse response test. Result: pulse in, first arrival, then nothing in the high frequencies for 15 milliseconds. Pretty amazing. No wonder the Eros sounds clear and also offers extraordinary insight into the acoustic environment of the recording. You aren't hearing your listening room for a long time, and not much of it then.
The Eros is a biamplified system. But the price includes a built-in amplifier for the woofer units, along with the necessary electronic crossover. You supply the amplifier for the electrostatic upper frequencies. The beauty of this arrangement is that not so much power is needed from 500 Hz on up. (It is bass that eats power). I wouldn't recommend a microwatt SET, but you can get big volume music from a medium power amplifier on the top here. You do need an amplifier though that does not mind the fact that the load is capacitive, and down to 2ê at 20 kHz. (Some amps will go into a tizzy, and give a rising, ringing top). If you must, you can also use another amplifier of your own for the bass the electronic crossover has outputs for that but I don't see why you would want to.
The level of the woofer is adjustable so you can accommodate amplifiers of various gains with no problem. You should not use the control as a bass level adjuster as such, however. There will be only a narrow range of levels at which the woofer and electrostat blend to give an integrated and uncolored midrange. Find that level and leave the control there. (If you want to boom your bass occasionally, buy a tone control).
So how does the Eros really sound? The bass is clean, precise, and reasonably extended. It won't go down to earthquake or 32' organ stop territory, but there is ample extension for orchestral music to have its foundation. And the bass is very smooth and non-resonant. The midrange is also smooth, largely uncolored, and well-integrated. There is a little height sensitivity from the interaction between the woofer and the electrostatic element, but at usual seating heights and usual distances, all is well. In my room, when the bass level was set to make the smoothest transition from woofer to electrostat and to give the lowest coloration of the mids, the midbass and bass were slightly down in level. There is also a little relaxation in the presence region, so that the overall sound was slightly midrangy. (In the high treble, the level comes back up some). This balance flatters a lot of material (e.g., the human voice), and it also seems to be the kind of balance that recording engineers anticipate. Monitor flat (which is seldom delivered by monitors!) seems to make most material sound too aggressive. In any case, it is hard to imagine anyone finding the Eros balance anything but attractive. And as noted, the sound has an almost magical clarity, and a clarity not at all purchased at the price of exaggerated presence just the opposite in terms of tonal balance. The speaker is just clear by nature, intrinsically clear.
Now we come to a special feature of the Eros. It isn't a problem exactly, In fact, I consider it an advantage. But you do need to know about it. The thing is, the Eros speakers are beamy in the high frequencies, not just vertically as I already mentioned, but horizontally, too. When you sit down to listen, you had better be able to see yourself reflected in the electrostatic diaphragms speakers pointed right at you or say so long to the high frequencies. This beaminess actually gives a kind of precision and solidity of stereo image that you won't get if your speakers are flipping high frequencies all over the room. And you can play with it a little to get some of the time/intensity tradeoff stability of the Ohm 300s I talked about a few issues back. (Some but not all of it the Ohms are essentially unique there). But the beaminess may be different from what you are used to and it may take a little getting accustomed to it. The beaminess does mean that only one listener will hear the best possible imaging and tonal balance, although the rolled-off highs off to the sides are not disagreeable. One could of course set up the Eros audiophile style in the negative sense of pointing them straight down the room with lots of backwall reflection, more sidewall reflection, blurry spacious soundstage, etc. But I wouldn't, and yo certainly won't get much top end if you do. This is a subject on which there seems to be some confusion. The truth is that stereo is predicated on the first arrival dominating the picture. Reflections, later arrivals, just blur the imaging and don't really contribute genuine stereo information, although one might in some way enjoy the resulting spaciousness. The Eros is one of the best imaging speakers around, but it presents the purist picture, direct arrivals emphasized. It doesn't generate space when a recording hasn't got any; it lets you hear the phasiness of spaced microphone sound when the microphones are spaced, and so on. What is there is what you get.
Will, with one exception: Depending on the material, certain sounds can seem to come from the electrostatic panel itself a little more than really ought to happen. With images between the speakers and of course, theoretically that is where the images ought to be this does not happen. But when one listens to those spacey recordings that fling images outside the speakers, the images can pop forward to the panels a bit. It is hard to blame the speaker for that exactly, since such recordings are problematical by nature. But in your own auditioning, you might want to listen for this in terms of whether the Eros with their theoretically almost perfect imaging present your favorite recordings in a way too different from what you are accustomed to.
I both like and admire these speakers. They are very smooth tonally and have a most attractive, relaxed clarity. Moreover, they seem to me to represent an intelligent and effective approach to the difficult problem of minimizing the interaction of the speaker and the room around it. This approach of deliberately introducing directionality in the speaker to avoid bouncing sound around the room in unpredictable ways is not unique to InnerSound (Gradient comes to mind as another company that has pursued this systematically, as has Quad, also). But it is very well done here in any case, and the result is a speaker that produces extraordinary sound quality. Finally I want to point out that Eros is a real bargain. You get a lot for the money. The Eros gets far up the ranks of speaker sound at a reasonable price. I would call InnerSound a truly promising newcomer among speaker companies, except that the promise has already been greatly fulfilled in the Eros.