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.