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Muraudio SP1 Hybrid Electrostatic Loudspeaker

Going on a century ago, in the early 1920s, C. W. Rice and E.W. Kellogg began work at General Electric on how to use electricity to generate sound for reproduction of music. They considered seriously two possibilities, the electro-magnetically driven cone and the electrostatically driven membrane. For practical reasons, they chose the cone driver. (A main problem of the electrostatic was that, this being before the days of plastic films, the membrane was made from what was known as goldbeater’s skin or cloth, which was, not to put too fine a point on it, hammered-out pig guts. It tended to rot, odiferously. Interestingly this material is still made, for other purposes; see the Wikipedia article online on goldbeater’s skin for more.) But Kellogg and Rice, and everyone else who heard the electrostatic prototype were entranced with the sound. People have been entranced with the sound of electrostatics ever since. And with the arrival on the scene of plastic film, practical electrostatics appeared starting in the 1950s, from Peter Walker’s Quad and from Arthur Janszen for KLH, and subsequently from many others. (Historically minded readers might be interested to recall that Janszen’s KLH Model 9 electrostatic played an important role in the founding of The Absolute Sound, its audible superiority to the highly reviewed Bose 901 of the time leading Harry Pearson and John Cooledge to feel that a new approach to reviewing was needed, and so they founded TAS.)

This all came to my mind when I first heard the new Muraudio SP1 loudspeaker because the electrostatic “magic” was so much in evidence. The SP1s are a hybrid design: each speaker contains four cone drivers, two above and two below the electrostatic assembly, with crossover at 750Hz. But in spite of this relatively high crossover point, the essential sound is very much that of electrostatic drivers: ultra-low in distortion, very pure, free of resonance and box effects—the whole electrostatic show as it were.

The Nature of the Speaker
Hybrid electrostatics abound, but the Muraudios are unique. All the other hybrids that operate the electrostatic part as a dipole have an electrostatic part that is essentially a line source. A box woofer surmounted by a narrow, tall electrostatic membrane flat or curved horizontally—that is the rule. (The admirable Janszen hybrids are left out of this discussion: They are enclosed speakers. See http://www.theabsolutesound.com/articles/janszen-za21-loudspeaker/). The Muraudios are unique in that the electrostatic elements are curved in both horizontal and vertical directions. The horizontal curvature involves multiple angled segments, each curved vertically. The effect acoustically is that the speaker presents something more akin to a point source than a line source. The point-source idea is not geometrically exact: The curvature of the electrostatic element is greater horizontally than it is vertically. But the resultant listening effect is of focus behind. And the symmetrically mounted woofers, four per channel— two above two below as noted, makes the point-source effect even more convincing. Muraudio, in its first offering, the PX1, used three of these doubly-curved electrostatic elements to give a horizontally omni pattern above the woofer crossover frequency, which also had considerable vertical coverage (see http://www.theabsolutesound.com/articles/muraudio-px1-omnidirectional-electrostatic-hybrid-loudspeaker/). Here the same element is used, one per channel, plus woofers to give a speaker with nominally 120-degree horizontal coverage. And indeed, the pattern is quite close to uniform up until plus-or-minus 45 degrees up to 5kHz or so, and with considerable energy still there at even larger angles and higher frequencies. And over the traditionally considered plus-or-minus 15 degrees, the pattern is very uniform indeed, almost perfectly so all the way up to the top octave, where there are only small variations. This is as wide and uniform a pattern as many “wide dispersion” box speakers have. Or more precisely, it is uniform over a wide range of angles in terms of upper envelope of response, which is primarily what one hears. Frequency by frequency beyond around 30 degrees there are some narrow dips arising from the segmented nature of the driver, but as is well known, such dips are not seriously disturbing audibly. In listening terms, the perceived overall balance is quite constant over a wide variety of listening positions horizontally. Vertically, there is a certain magic in being exactly in the middle of the electrostatic element, but variations away from there are not extreme over a reasonable range. In particular, the SP1s have a much wider and more uniform pattern than the MartinLogan quasi-line-source models, e.g., the Montis, which have horizontally curved panels but with a much smaller amount of curvature than found in the SP1’s segmented panels.

In short, what one has here is a wide-dispersion electrostatic which resembles a wide-pattern point source in a way no other electrostatic hybrid even aspires to, let alone equals. Now everyone knows that there are certain advantages to line sources in terms of not bouncing sound off the floor and ceiling. And speakers that are beamy horizontally can sometimes have a distinctive kind of image precision. But at the same time, wide-pattern speakers have their points, too, in terms of wider listening area, imaging that is stable with respect to listener position—a stability which is really impressive here, actually—and a certain naturalness that arises from resembling more nearly how real musical instruments tend to radiate into rooms. The comparative virtues of these two approaches to speaker design have been talked over, even argued over, for many years and will no doubt continue to be a topic of some controversy for as long as people listen to speakers. But both ways work well if done well, even if they work well in somewhat different fashions; I do not mean to waffle here but given that people are presumably familiar with the differences in listening terms between wide- and narrow-pattern speakers, the point seems not to need much further explication.

I should remark that the SP1s are elegantly built and finished. And they offer a lot of design and technological expertise for a modest price. In a world where small two-way boxes can cost as much as cars, the SP1s are a clear bargain, priced in a way that makes one feel one is getting a lot for the money. And they look cool to my eyes, too—unusual but cool, and unusual for a reason. This is not novelty for its own sake, but inventive design.

 

Space
The big first impression upon listening to the SP1s, the thing that grabs your attention right off the bat, along with the general electrostatic clarity is the extraordinary presentation of space. The sound picture is expansive in all directions. Depth of image especially is quite startling—on the Telarc Ravel-Borodin-Bizet CD, which has been one of my go-to orchestral recordings lately, the off-stage trumpet (Track 13) sounded as if it were in the next county. And when the orchestra came in with the on-stage players, the whole picture had a spatial scope unusually reminiscent of a real orchestra, considerably more so than usual. No speaker in a domestic room will reproduce the literal size of an orchestra as heard at close range—orchestras are on the order of sixty feet wide. But some speakers get closer than others to reproducing the orchestra’s scale!

Furthermore, this convincing spatiality was remarkably stable over changes in listening position. It is inevitable that some spatial cues involving time-of-arrival of transient cues will change with unequal distances from speakers to listening position. But with the SP1s this theoretical inevitability seemed almost obviated. A spatially convincing soundfield was spread over a surprising portion of the room. Of course, people are always saying things like this—people like stereo and like how it works. But with the SP1s, it was working in a way quite different from usual. The combination of wide forward pattern and dipole radiation from 750Hz on up was somehow creating a really unusual and unusually convincing impression of being spatially elsewhere in large venues when a large venue was the site of the recording. 

I suppose everyone knows that I have a lot of admiration for speakers that place a big emphasis on direct sound, that beam the sound at you. But these are intrinsically for one listener alone and one who is not going to move. The SP1s managed to be very convincing not only in the one centered ideal position but over a wide area. How this works is not entirely clear to me in theory, but work it does. If you are after wide-open spaces, here you go.

The SP1s tend to remind one rather aggressively of how poorly a great many speakers with lots of drivers actually do stereo. Stereo perception is a robust thing and almost any pair of reasonably well-matched speakers will do stereo—after a fashion. But trying to put stereo together from a lot of drivers is a little bit like trying to make a photo by gluing together a lot of images from cameras at different angles. It sort of works but not really. Speakers that offer something very close to a real point source work for stereo in a way that the others do not. The details of this are not easy to put in words. But you will know it when you hear it. Single-driver speakers, whatever their other problems, illustrate this to an extreme. (I think back to the Ocellia Tillia, to which I gave a Golden Ear Award in 2002—once heard, never forgotten). And the SP1s really function very nearly as a single driver. They provide a quite different experience from floorstanders with umpteen drivers.

In short, through the SP1s the point-source nature of the imaging felt very natural. And compared to other hybrid electrostatics, well, when the chips are down, most instruments are not line sources. If you are willing to sit absolutely still in the vertical sense, the unusual imaging behavior of line sources, where the image moves up or down when you move up or down, will not be distracting. And, of course, line sources do have the advantage of bouncing little or no sound off the floor, in effect. But the SP1s, which are elevated above the floor a good bit, and which up to 750Hz have a symmetric driver arrangement that itself minimizes floor interaction, succeed in these ways in getting rid of the floor-reflection issue quite well on their own terms.

 

The Tone
The SP1s are quite neutrally balanced, though not entirely so. Within their essentially smooth response, there are some audible broadband trends, as there are with almost any speaker. The main issues are that the speaker is up a bit around 500Hz and down slightly just below 1kHz and then back up again. And there is a small depression around 200–300Hz that makes the sound slightly lightweight. These are small effects, but they are there. The -3dB point of the sealed-box bass is at 45Hz, with the expected slow (12dB/octave) roll-off. The bass is precise and well-defined in transient character. But on account, I think, of the lack of energy in the 100–300Hz region, the speaker does sound slightly light. EQing to sound as neutral as possible involved in this case bringing up 200-400Hz, pulling down 500Hz and upping 800Hz with some small adjustments at 2kHz and higher. This was an improvement to my ears but the change was not huge, though the lifting of the 100–300Hz region was fairly conspicuous. A lot of people would probably not bother with these adjustments. The nearly perfect consistency of response over a +/-15-degree window made this micro-adjustment of response especially rewarding, giving a close approach to neutrality over a considerable window. If you are involved in DSP adjustments, this speaker with its stable response over a variety of axes, its extremely low distortion, and its considerable dynamic range will really respond very well to such treatment.

In spite of these small deviations, the speaker’s absence of resonant coloration makes its tonal presentation uncolored-sounding. And as noted the sound has a startling purity. This is a speaker capable of producing truly beautiful sound in the strongest sense. The Carmen Intermezzo from the Telarc CD already mentioned was exquisite. And piano music was superb in its freedom from any grunge whatever and its resolution of the fine structure of piano tone. Janne Mertanen’s piano performance on his Chopin CD [Gradient] sounded superbly like the real thing. (This is one of the best piano recordings ever, and it sounded like that here!) And vocal reproduction was also excellent: Jane Monheit’s “I’ll Be Around” was even more heartbreakingly beautiful than usual, with impressive naturalness to the voice (close-up recording though it is).

The Competition
The SP1s are unique among dipole electrostatics in their essentially point-source character. Only the Quad 63s and their descendants have attempted a point source, done in the Quads via wave synthesis (concentric rings with time delays). But a physically accomplished point source, or close to it, from a dipole electrostatic has never been tried before. And comparison to the Quads shows that the literal physical construction of a doubly curved electrostatic element offers some advantage over wave-synthesis with delay lines. Admirable though the Quads were and are, the SP1s seem to me to offer a more convincing version of point-source imaging. Of course, there are other speakers that also function as point sources, both single-driver speakers and those with concentric drivers. The Devialet Phantom models and their Cabasse ancestors come to mind. These image superbly well and really do sound like point sources, but they are not electrostatic. And the obvious hybrid electrostatic competition include line-source speakers as far as the electrostatic part goes, namely the Sanders 10e and the various MartinLogan models.

The Sanders is not to my mind competition as such but rather a different kind of speaker altogether. It is intended to provide—and does provide—a nearly perfect replica of its input in its direct sound to the listening position. But it is not intended as a “room filler.” With its DSP built in, the Sanders does a quite startlingly good job of being flat and neutral when one is listening in its preferred “sweet-spot” position. But the nature of its sound is quite different from that heard with the Muraudio approach. To each his own.

When both the Sanders and the Muraudio Omni appeared at the same show (T.H.E. Show in Newport Beach several years ago), I ended up splitting my “Best Sound in Show” between the two. Both were doing a superb job of what they were trying to do. The Muraudio SP1s are in the same way doing an excellent, indeed uniquely excellent, job of what they are trying to do. Whether you want the room filler with stability of imaging over a larger area, or the all-but-perfect one-point experience with minimized room contribution is up to you.

The MartinLogan approach of using a slightly curved panel line source has never really jelled for me. (This applies only to the relatively narrow-panel versions, the Montis for example, which, while balanced nicely, does not really sound completely convincing to me in comparison to actual music. I have not heard under meaningful conditions the larger-panel MartinLogan Neolith that RH reviewed in Issue 259.) If you are going to curve, it seems to me that one ought to curve a lot and use a wider panel to get meaningful dispersion over a considerable angle, as Muraudio’s doubly curved panel does.

 

Listening for Yourself
I would strongly urge you to find the Muraudio SP1s at a show or a dealer and spend some time listening to them carefully. This is a landmark speaker design. There has never been anything else like it. It is unique and sounds like real music in a way that escapes most speakers entirely. I think many people are going to find it matchlessly satisfying, if they can get a serious listen to it. If the audio world were working as it should, dealers would be queuing up to take on the SP1s. But high-end audio dealers are not as numerous as they used to be, and opportunities to hear things at dealers are thus reduced. This is an unfortunate situation. Progress in audio and interest in it, too, depend on new things being available for consideration. Older speaker design ideas can be wonderful. Still, new ideas give new life, and new life is what high-end audio can very much use. And the SP1s are a new and very good idea indeed. 

In our world of internet rumor and gossip and overabundant if not always well-informed reviewing, we need more than ever to pursue independence of mind. To borrow from the Bible (Luke 14:34). “He[or she] that hath ears to hear, let him hear.”

Remarkable things are appearing in audio, and the Muruadio SP1s are among the most remarkable speaker designs to appear in recent years. But when a new and revolutionary product appears, you have to have faith in your own judgment, to listen and not to worry whether the product is something all your friends know about or the Internet is full of comments on. And you may have to go to some effort to find the product to listen to. The Muraudio SP1s will definitely be worth the effort. They are, to borrow the highest recommendation in the Michelin Tour Guides that I used to travel around Europe with, “worth a journey.” Seek them out. You will be glad you did.

Specs & Pricing

Type: Hybrid electrostatic loudspeaker
Driver complement: Four 6″ aluminum cone woofers per channel, mounted two above, two below a segmented doubly curved electrostatic element—woofers in a sealed-box enclosure, electrostatic element in open-backed mounting
Electrostatic element: 1650 square centimeters; 3.8 micron thickness
Max SPL: 103dB, 1m on axis
Crossover: 750Hz, second-order Linkwitz-Riley
Sensitivity: 86dB (2.83v/1 m)
Dimensions: 147 cm x 42.3 cm x 36.8 cm
Weight: 45 kg
Price: $14,700/pr. (special color finishes additional)

MURAUDIO
11 Tristan Court
Ottawa, Ontario 
Canada K2E 8B9
(855) 955-0630 (toll free)
[email protected]

By Robert E. Greene

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