“I had not realized that music could be so beautiful.” Thus spake Bruno Walter after conducting in the Vienna Grosser Musikvereinsaal for the first time. His words came to mind listening to the Muraudio PX1 omnidirectional electrostatic speakers for the first time. I had perhaps not realized that music reproduced in the home could be quite like this: the purity, the smoothness, the roundness, the filling of the room, the effortlessness, the deep bass extension, the sense of speakers vanishing as sources, and the stability of the sound with respect to listener position, all combined to disarm my critical self and switch me over to the state of a listener hearing live music in a great concert hall, immersed in an ambient soundfield, albeit with the locations of instruments still clearly perceived. The experience is so different from ordinary stereo listening that it calls for some careful thought about what one wants from a stereo system. By intention, the PX1s present a unique experience—entrancing but different.
And the mechanism of this is truly something new. The PX1s are not just a slightly different version of something else, not just another variation on themes already stated and varied by others. Most of the speakers in our world would not really surprise Rice, Kellogg, Olson, Villchur, Walker, Hughes, and the other giants of the past. They would be impressed by the refinement of execution (and the prices!) but not startled by the designs, which would seem to them the natural extensions of their own work, using improved materials technology. The big floorstanding towers of today are the speakers Rice and Kellogg would have built if they could have. But I think it is safe to say that none of the masters of the past really envisioned as a practical possibility an electrostatic speaker with panels that curved in both directions with three of them fitting together to form not a pulsating sphere, but rather a sort of pulsating kiwi fruit with a radiation pattern that is horizontally omni. One can imagine Peter Walker saying, “Jolly clever work there.”
Reviewer comments from audio shows suggest that everyone had much the same experience as my own—of being swept away on first exposure to the PX1s. But it is, of course, part of review work to take such unified, more or less ecstatic experience and analyze it, slice it, and dice it to figure out how the speaker does what it does, and whether what it does is what one wants a speaker to do.
These sentences are not a preamble to finding fatal flaws in the PX1s later on. This won’t be like the Cheater: “He’s gonna build you up just to let you down.” But it will be necessary to describe the distinctive nature of the PX1s—not so much in terms of what the “right” transducer is (a question with no objective answer), but rather in terms of the differences among speaker types. Omnidirectional radiators are distinctive, without doubt, and this one is particularly so.
As it happens, I liked the PX1s just as much on the last note I heard from them (just a few minutes before they went back into their crates) as I did on first exposure. Maybe I even liked them better. But as with any speaker, the PX1 chooses a path, and one needs to understand what its path is and what its virtues and inevitable restrictions are. As I mentioned, it’s different from other speakers—not a little different, with this, that, or the other small variation of frequency response or whatever, but a lot different. And a potential purchaser has to decide whether the difference is what he wants.
How the PX1s Work
The frequencies below 450Hz are handled by a sealed-enclosure bass unit with three dynamic drivers, separated by 120 degrees, which have a total effective radiating area of 100 square inches. The enclosure is cast aluminum. On top of the bass enclosure is the electrostatic mid/tweeter unit made of three curved electrostatic pieces, each subtending 120 degrees, which fit together to give a continuous round unit. But the unit is not a cylinder—rather it is tapered at either end with maximum diameter in the middle and small diameters at either extreme. The effect is that the combined electrostatic units radiate in an omni pattern horizontally but, unlike what a cylinder would do, they spread their radiation vertically both up and down. The radiation is effectively uniform over a +/-8 degree window and thereby eliminates any sense of vertical beaming. The transition from woofer to mid/tweeter unit is effectively seamless, with the narrowing down of the vertical radiation to +/- 8 degrees happening much further up than the crossover frequency. However, at close-up positions there can be a hint of highs-up, bass-down.
In order to accomplish all this, it is clear that the electrostatic panels have to be curved in both horizontal and vertical directions. They have to have what mathematicians call “positive Gauss curvature”—curvature in all directions. This presents a challenge for metal-forming because thin metal parts are usually made by rolling flat sheets with the results curving only in one direction at each point. Here, the stators of the electrostatic elements are made by hydraulic pressure-forming with heat annealing at an intermediate point in the process to prevent excessive internal stress accumulation from resulting in fracture. This is not the typical electrostatic panel we are used to, not even of the curved sort; those curve only in one direction.
The whole speaker thus has a horizontally omni pattern. Vertically, it goes from omni in the bass (as usual for enclosed woofers) to a narrowed pattern in the top end as the vertical pattern gradually narrows with increasing frequency into the +/- 8 degree directionality mentioned.