By Larry Greenhill, Stereophile
July 2001

Electrostatic speakers are my passion. Why else have I put up with their high prices, unreliability, low power handling, tendency to arc, high-frequency beaming, limited bass response, and widely fluctuating impedances?

Take the Quad ESL-57. Configured as a gnarly, stubby panel, it was often mistaken for an oversized space heater. Left on, it sucked, up dust and grime as its panels filtered the air. Far worse, it arced-those flickering blue lights in the panel signaled diaphragm perforation and eventual destruction.

"Gayle Sanders, MartinLogan's president and chief
designer, has spent his career making his electrostatic
designs safe and reliable for audiophiles like me."

But the sound! When I sat in their tiny sweet spot, my ESL-57s had gobs of air, liquid transparency, neutrality, pinpoint imaging, lightning-fast transient response, wide and deep sound-staging, and low distortion, all with no listener fatigue. Their midrange far more liquid and transparent than that of Quad's 1981 ESL-63, in my opinion was the most natural I have heard from any loudspeaker, and justified the post-traumatic stress disorder my '57s caused me.

So I was both excited and uneasy when a review pair of MartinLogan's new hybrid Prodigys arrived in my listening room. I needn't have worried Gayle Sanders, MartinLogan's president and chief designer, has spent his career making his electrostatic designs safe and reliable for audiophiles like me.

The Prodigy is imposing: 5'7" tall, 16.5" wide, and more than 2' deep. Its two sections the electrostatic panel and the chunky, back-busting bass module couple to form a 133-lb unit. The Prodigy's technology trickled down trom the company's flagship, the $70,000/pair Statement Evolution2 includes a proprietary electrostatic transducer and a woofer array, called "ForceForward" by MartinLogan, that is intended to reduce bass room interactions and resonances. MartinLogan uses a proprietary manufacturing technique to curve the Prodigy's perforated, metal-framed panels into a "curvilinear line source" (CLS) transducer, This frees the loudspeaker from rhe narrow dispersion pattern common to most electrostatics.

MartinLogan's CLS screens are arc-proof. Sanders and his engineers determined that panel arcing was due to local buildup of charge from uneven coatings on the 0.0005"-thick polyester diaphragm. While other manufacturers hand-paint diaphragms with a conductive material, MartinLogan vapor-deposits the conductor as a 1-angstrom-thick (0.0000000001m) layer onto the diaphragm's surface. This process produces an optically transparent conducting layer with uniform characteristics of surface resistivity that prevent charge buildup and migration, and arcing. According to Sanders, this layer has the electrical surface conductivity of human skin, allowing it to hold a static charge of from 1500V to 3000V.

The Prodigy's diaphragm is sandwiched between perforated steel plates, called stators, that carry tile varying audio-signal voltage while providing insulation to protect tile user, A nylon-based powder insulation is deposited at very high temperatures on the perforated steel stators to provide a safety tolerance of 12kV. Fourteen evenly spaced ClearSpars, or horizontal Lexan insulators/spacers, subdivide the panel and create a unitorm gap between the stators and the diaphragm. When the amplifier's audio signals are stepped up to high voltages by a transformer and applied to the stators, an electrostatic field of opposing voltages produces forward and backward movement of the diaphragm, which in turn generates sound waves in air.

"The Prodigy's midrange was transparent, timbrally
accurate, and free of congestion and distortion. Vocal/clarinet/piano selections came alive as the
speakers created a wide, seamless soundstage that
gave no clue of their positions in the room."

One problem with electrostatic speakers has been the tendency of the charged membrane to collect dust. However, the Prodigy's diaphragm accumulates dust only slowly because it automatically shuts down its electrical field when no music is playing. When dust has accumulated, the manual advises the owner to leave the speaker unplugged for 12 hours, then vacuum the panels.

The Prodigy's second-order crossover switches the signal from the bass module to the electrostatic panel at 250Hz. It uses point-to-point wiring and physically separated high- and low-pass crossover circuits to reduce magnetic interaction. The panel driver's dual transformers are said to result in lower distortion and increased power handling.

The bass module is a sealed dual-woofer design. The forward-facing 10" ScanSpeak aluminurn-cone woofer carries the bass audio signal. An independently enclosed, 10" fiber-cone woofer faces to the rear and is driven by a circuit that processes level, phase, and frequency range to create a partial cancellation of the front woofer's output in the lower frequencies. This ForceForward technology specifically reduces the cornmon 50Hz null and l00Hz peak found in many rooms. For those requiring more forward bass, the Prodigy has a rear-panel switch for increasing the below-50Hz response by 3dB.

The wing nuts on the Prodigy's speaker binding posts can be easily tightened without pliers or a wrench. Four binding posts are supplied on each speaker, allowing for biwiring. The excellent owner's manual gives instructions for horizontal passive biamplification (use a tube amplifier for the electrostatic panels, solid-state for the bass modules) and vertical passive amplification (use two identical stereo amplifiers, one dedicated to each speaker). Spiked feet called Energy Transfer Coupler (ETC) Spikes are supplied with jam nuts to allow for easy leveling.

Setup
I placed the Prodigys where the Revel Salon loudspeakers had sounded best: 63" from the rear wall and 36" from the side walls, sitting out in the room on a circular area rug. The speakers faced the long axis of my narrow listening room, which is 26' long, 13' wide, and 12' high, with a semi-cathedral ceiling. One long wall is covered with bookshelves, the other has a bay window. At the opposite end, the room opens into a 25' by 15' kitchen through an 8' by 4' doorway.

An electrostatic speaker needs to be plugged into an electrical outlet. When playing, the speaker displays a blue light in the shape of the MartinLogan logo through its electrostatic screen. Unlike the blue arcing in my old Quads, this light can he switched on and off from a pushbutton in the bass module.

Because the Prodigy's rated voltage sensitivity of 91dB/2.83V/m lies well above the average range of B-weighted speaker sensitivities reported in Sterophile, I found that I needed to set my Krell KBL preamplifier's volume control significantly lower than usual.

I first drove the Prodigys with the high-powered Bryston. 7B-ST monoblocks tested at 954W into 4 ohms because of the 7Bs' power reserves and easily visible front-panel clipping indicators. Configured in serial bridged mode, the Brystons' bass response was very tight, deep, and fast, their sound-stage huge the bass lines on Massive Attack's Unfinished Symphony (Circa WBRX2) were solid and full. However, I found the soundstage depth shallow and the transients harsh. I switched the 7B-ST into their parallel bridge mode tested at 595W into 2 ohms which enables the amplifier to drive low-impedance loads. Although the bass became less prominent, the soundstage assumed a more natural depth and width and the edginess disappeared. Even so, I preferred the less powerful Mark Levinson No.334 to the Bryston for its sweeter, more transparent sound.

"The Prodigy's treble spectrum was smooth
and beguiling, with no brightness, steeliness,
or metallic edge. Bells heard over this speaker
had a magical sheen..."

Final adjustments included comparative nearfield (8') and farficid (16') listening, low-frequency signal-generator sweeps, phase checks, pink noise, and fine-tuning of listening position for optimal soundstaging and imaging. The Prodigy's deep-bass output fell off smoothly between 41Hz and 35Hz in my listening room, with no doubling. Playing Stereophile's Test CD 3 for channel checks and phasing, I carefully positioned my chair in the Prodigys' nearfield until I could hear the in-phase pink-noise signal as a centrally focused sonic image. Sound-staging was optimized when speakers and chair described a 7' equilateral triangle (measured from the panels' approximate centers).

The Prodigy's electrostatic panel extends from 31.5" to 60" above the floor. This covers an area below my ear height (38") when I'm seated in my listening chair and extends above my ear height when I'm standing. This explained why the speaker's tonal balance didn't change when I stood while playing pink noise.

I broke the Prodigys in by playing music from an FM tuner for 12 hours, followed by 12 hours of the "Special Burn-In Noise" from Stereophile's Test CD 3.

Sound
I first put on some warmup music-David Hudson's Didgeridoo Spirit (Indigenous Australia IA2003 D), Fleetwood Mac's The Dance (Reprise 46702-2), and David Bowie singing "Putting Out Fire," from the Cat People soundtrack (MCA MCAD-1498). The Prodigys' transparency and deep, wide soundstage quickly involved me in the music. But at first, the bass response seemed understated, shy, and reticent.

After a month of listening, things had changed. The louder I played the Prodigy, the better it sounded. Its bass blossomed when driven hard. At a level where my usually unflappable Mark Levinson No.334 began to show signs of compression, the Prodigy's opened up. The bass became forceful and taut, and the instruments separated and became more distinct.

At these levels, the Prodigy's bass response sounded detailed and taut, and showed the advantages of the Force-Forward design. Solid, clean bass extended down to 31.5Hz in my room when playing a 1/3-octave warble tone at -20dB (Test CD, Stereophile STPH 002-2). The bass drum in Owen Reed's La Fiesta Mexicana was tuneful, solid, and powerful (Fiesta, Reference Recordings RR-38CD). The final organ chords of Part I of Elgar's The Dream of Gerontius (Test CD 2, Stereophile STPH 004-2) and the repetitive bass-drum beat in "Cosmos Old Friend," from the Sneakers soundtrack (Columbia CK 53146), were clean, but I had to listen carefully because their reproduction via the Prodigys was subtle. Similarly, Michael Arnopol's plucked double bass on Patricia Barber's "Use Me," from Companion (Premonition/Blue Note 5-22963-2), pulsed, throbbed, and burned with no sign of bloat.

The Prodigy's bass had excellent pitch definition. The woofer's sonic characteristics meshed well with those of the electrostatic panels.
It captured the pounding tom-toms on Richard Thompson's "I Misunderstood," from Rumor and Sigh (Capitol CDP 7 95713 2); and the 32Hz bass notes from the beginning of Strauss's Also sprach Zarathustra, from "Ascent" on Time Warp (Telarc CD-80106), were clean and tight.

The Prodigy's midrange was transparent, timbrally accurate, and free of congestion and distortion. Vocal/clarinet/piano selections came alive as the speakers created a wide, seamless soundstage that gave no clue of their positions in the room. Vocals were reproduced with a transparency I'd missed ever since I'd let the Quad ESL-57s escape from my listening room. Suzanne Vega's startling a cappella vocal on "Tom's Diner" (Solitude Standing, A&M CD 5136) floated in the room with a lifelike fullness. The tonality of the saxophone and guitar were startling on the title track of the L.A. Four's Going Home (Ai Music Co. 3 2JD-10043). The same rich but totally natural timbre was heard in Buddy Miller's mando-guitar accompaniment to Emmylou Harris's "Prayer in Open D" on Spyboy (Eminent EM-25001-2). The guitar work on that track was crystalline and airy, with silken tonality.

The female voice was rendered faithfully, with natural timbre and low distortion. Patti Austin's rendition of Armando Manzanero's "Only You" (Hothouse, N2K 10023) was etched and holographic. Kim Cattrall reading "Little Dog's Day" sounded see-through clear and bell-like on Mark Levinson's Live Recordings at Red Rose Music, Volume 1 (Red Rose Music RRM 1). And I was transfixed by the a cappella choral blend on "Calling My Children Home," from Spyboy. Emmylou Harris's voice was effortless, ethereal, clear, and translucent.

"I heard a transparent, multilayered aural
portrait: a wall-to-wall tapestry of voices, synthesizer,
drums, guitar, and crowd noise..."

Male vocalists fared just as well, with no midrange anomalies, suckouts, or other colorations. Willie Nelson sounded clear, clean, and totally free of honk or hollowness on "Getting Over You" and "Don't Give Up," from Across the Borderline (Columbia CK 52752). Harry Connick, Jr.'s tenor on "Don't Get Around Much Anymore," from the When Harry Met Sally... soundtrack (Columbia CK 45319), bad none of the darkness and over-richness I routinely hear from dynamic speaker systems.

The Prodigy's treble spectrum was smooth and beguiling, with no brightness, steeliness, or metallic edge. Bells heard over this speaker had a magical sheen as on Dvorak's Carnival, from Nature's Realm (Water Lily Acoustics WLA-WS-66-CD). The Japanese and Korean temple bells that back up Shane Cattrall's reading of Psalm 23 on Live Recordings at Red Rose Music were reproduced with stunning realism, transparency, and detail.

The Prodigys were able to maintain image stability at high volumes. On Going Home, the L.A. Four was precisely positioned on a wide soundstage, playing duets and solos on guitar, double bass, drums, flute, and saxophone. Images snapped into focus on the Prodigys' wide, well-defined sweet spot, whether Jose Carreras' holographic tenor singing the opening Kyrie of the Misa Criolla (Philips 420 955-2), or Richard Thompson's guitar as heard just outside the right speaker in the instrumental close of "Why Must I Plead," from Rumor and Sigh.

The sharpest and most precise imaging was heard from Sacred Feast, Sony's multichannel Super Audio CD recording of the choral group Gaudeamus (Sony SACD-9). Using a new Sony SCD-C555ES carousel SACD player, I selected a multichannel playback mode that fed full-range signals to the two front loudspeakers with no center channel. The result was a pure, airy, well-defined chorus rich in natural timbres.

Of all the Prodigy's sonic characteristics, the most impressive was its dynamic range. In my large listening room, it was one of the few loudspeakers that did not limit and crunch on the choral peaks of Elgar's Dream of Gerontius. Playing Spyboy's apocalyptic "Deeper Well" at top volume, I could still follow Emmylou Harris's birdlike voice and hear her lyrics clearly, despite the throbbing, churning bass synthesizer and distorted electric guitar.

The Prodigy handled both ends of the dynamic range beautifully, but just to be sure, I decided to push it hard. I reconnected the Bryston 7B-STs and cranked up the volume until the amps' clipping lights flashed when playing snare-drum rimshots. In this configuration, the Prodigy bettered all loudspeakers heard in my living room. Not only did it reproduce the powerful wall of synthesizer and electric guitar and the explosive rimshots in the drum solo on "The Maker," the showstopper from Emmylou Harris's Spyboy, out it conveyed inner detail that most speakers miss. I heard a transparent, multilayered aural portrait: a wall-to-wall tapestry of voices, synthesizer, drums, guitar, and crowd noise; the distorted out musical electric guitar solo; Harris's delicate but strained voice; the layered effect of the male backup singers; and those explosive rimshots.

Another revelation came when I played my favorite jazz selection, "The Mooche" from the Jerome Harris Quintet's Rendezvous (Stereophile STPH013-2). The Prodigy reproduced better than I'd ever heard them the honky timbre of the saxophone, the blattiness of the trombone, and the luminous, shimmering, see-through clarity of Steve Nelson's vibraphone.

Conclusions
The MartinLogan Prodigy reaffirmed my passion for electrostatic loudspeakers. Sure, I was swayed by the usual electrostatic attributes low distortion, timbral accuracy, and deep, wide soundstaging that took my breath away but there was more.

The epiphany came after I'd been living with the Prodigys for two months. I don't know why it took that long perhaps the woofers needed the time to fully break in and reveal their full dynamic range and power-handling capabilities but music I'd always loved then came alive in a brand-new way. Instrumental timbres and colors became much more vivid, intense, and startlingly realistic. The speakers' dynamic range expanded, allowing them to play louder, with greater depth, three-dimensionalicy, and detail.

For these reasons, I strongly recommend you audition a pair of well-broken-in Prodigys with your favorite source material. Crank up the volume and listen. I promise you the MartinLogan Prodigy will be a revelation, and the best cure for electrostatophobia.