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Warwick Acoustics APERIO Electrostatic Headphone System

Warwick Acoustics APERIO Electrostatic Headphone System

Time is passing much too rapidly. In my case, it seems as if it was just yesterday that I received a review sample of Warwick Acoustics’ first audiophile-oriented personal audio product, the $4995 Sonoma Model One (M1) electrostatic headphone system. My colleague Steven Stone praised the system when he reviewed it in The Absolute Sound, while I reviewed the system favorably in our sister publication, Hi-Fi+. Steven’s and my comments closely paralleled one another’s; we both appreciated the Sonoma system for its accurate, natural, and uncolored tonal balance, its uncommonly fast transient speed, its overall subtlety and nuance, its wide-range frequency response, and its versatility. The Sonoma M1 system came with a purpose-built electrostatic amplifier/DAC explicitly optimized for the Model One headphones, and with a flexible DAC section that ably decoded both high-resolution PCM and DSD files. The only drawbacks we noted were that, first, it was possible to overload the Sonoma M1 amp’s analog inputs with source components that delivered comparatively “hot” signal levels, and second, the system’s maximum output levels, though adequate for most general purpose listening, sometimes came up short on certain kinds of power music; e.g., rock crescendos, loud low-frequency passages, or large orchestral swells. Even so, we concluded that the Sonoma M1 was a desirable high-end headphone system—one whose limitations were outweighed by its strengths.

Given how good the Sonoma M1 system was and is, the last thing I expected was Warwick Acoustics’ decision to create an even higherperformance electrostatic headphone system—one whose capabilities promised to surpass those of the Sonoma M1 system in every way. That super-system is here and is called the Aperio electrostatic headphone system (Aperio, says Warwick Acoustics, derives from a Latin word that means to “uncover, open, or reveal”). Naturally, such an all-out attempt to redefine the state of the art in headphone performance does not come cheaply and, accordingly, Warwick Acoustics will be selling the Aperio system at $24,000. Realistically, some will think that figure falls on the far side of sanity, but once you grasp that the Aperio system aims to deliver sound quality rivaling (or surpassing) that of loudspeaker-based systems selling in the six- and even seven-figure range, the Aperio system’s price not only makes sense but starts to seem downright reasonable.

As a declaration of its intent, Warwick Acoustics states, “The Aperio is designed for the demanding professional audio market, as a reference studio monitor headphone system for high-resolution audio production, mastering, mixing, and recording applications,” but also for “ultra-high-end home consumer applications.” With these aims in mind, Warwick Acoustics has followed what it terms a “complete system design” approach, meaning that the system’s analog and digital front ends, its powerful electrostatic amplifier, and its intensely revealing headphones were designed from the ground up to complement one another in every way. 

The first indication of how different the Aperio system is the beefy, watertight, crushproof, and dustproof polypropylene travel case the Sonoma M1 system arrives in. The next comes when you first see the Aperio’s preamp/amp/DAC and realize that it is roughly three times wider than the Sonoma M1’s amp/DAC. The reason for the size increase is that the Aperio preamp/amp/DAC supports a much wider range of digital and analog inputs than the Sonoma M1 amp/DAC did, and features circuitry specifically optimized for each input type. Further, the Aperio amp also provides considerably more power output and a more elaborate and robust power supply than the Sonoma M1 amp/DAC did, and is fully capable of serving as a preamplifier in high-end audio systems.

In the analog domain the Aperio provides single-ended and balanced analog inputs and outputs, with high/low gain switches for both analog inputs. In the digital domain the Aperio offers a very flexible set of inputs, including USB, coaxial SPDIF, AES3, and a fully DLNA-compliant Ethernet interface. In turn, the Aperio DAC section, which is based on dual 32-bit, 8-channel DACs arranged in a dual-mono configuration, can decode PCM files with sample rates to 384kHz and DSD files (native or DoP) up to DSD256. One crucially important point, says Warwick Acoustics, is that “all audio signals are kept in their native domain and format: analog always remains analog; DSD stays DSD until its final conversion to analog; PCM samples are never converted.”

Warwick Acoustics uses the highest-quality parts throughout the Aperio, leading to some impressive performance specifications. The Aperio’s costly clocking circuitry, for example, provides very low jitter (82fSec RMS @ 100MHz) and an extremely low noise floor (-168dB/Hz). Warwick Acoustics notes that any DSP performed on PCM audio data is “double precision, 64-bit, fixed point, at native sample rates—equal to the best Digital Audio Workstations (DAWs).” The Aperio’s dual-DAC/dual-mono architecture yields a signal-to-noise ratio of 131dB. Separate EMI-shielded chambers enclose the DAC sections for each channel and are fed by quiet, noise-isolated power regulators.

The Aperio amp/DAC uses separate, domain-specific volume level controls. A fully differential analog attenuator, based on parallel, laser-trimmed, resistance-ladder networks, is used for analog and DSD signals. In turn, a DSP-based digital attenuator is used for PCM digital signals. Warwick Acoustics claims the attenuators are “calibrated and closely matched.” 


The Aperio’s amplifier section uses eight discrete 1000V MOSFET devices per channel in a fully balanced configuration using “a proprietary topology based on single-ended Class A operation.” The upshot is an amplifier that delivers a noise-free 1800V DC bias-voltage for “charging the (Aperio’s) BD-HPEL transducers” and serves up 15Wpc of power output with very low distortion and noise. Can you say, “exceptional dynamic headroom?” 

Finally, Warwick Acoustics has gone to great lengths to maximize the performance of the Aperio’s power supply and power regulation sections, its PCB layout and construction, the design and construction of its noise-isolating chassis, and its heat management system, which features four very-low-noise cooling fans. In short, Warwick Acoustics has explored virtually every design and construction detail—no matter how small or seemingly insignificant—in a quest to give the system state-of-the-art performance.

At the same time, the Aperio electrostatic headphone offers plenty of innovations of its own. The original Sonoma M1 headphone used a proprietary, single-ended electrostatic driver featuring the firm’s patented HPEL (High-Precision Electrostatic Laminate) technology. In contrast, Warwick Acoustics has used Multi-Physics Finite Element Analysis modeling to create all-new BD-HPEL (Balanced Drive High-Precision Electrostatic Laminate) drivers for the Aperio headphone. The BD-HPEL drivers are in essence a symmetrically driven (not single-ended) variation on the drivers used in the original Sonoma headphone. 

Much has changed, though, in the course of driver development. First, the Aperio diaphragm now uses a complex multilayer film, consisting of outer layers of 7µm-thick BOPP (bi-axially-oriented polypropylene) that enclose and protect a thin 24-karat gold inner layer held in place by an acrylic adhesive. Next, the new double-sided driver uses a fascinating sandwich-like structure featuring extremely rigid glass-filled polypropylene sulfide outer frames. Working from the outside in, the next layers in the “sandwich” include outer gaskets, followed by gold-plated OFHC stators, polypropylene spacers, and—at the center of the structure—the multilayer gold diaphragm. Warwick Acoustics has even come up with an automated, high-precision diaphragm-tensioning system that ensures tensioning consistency to “within a fraction of a Newton” and that, says Warwick Acoustics, ensures diaphragm tension is “differentially equalized in all axes across the film surface.” 

The Aperio headphone earcups are, as in the Sonoma M1, made of light, rigid, injection-molded magnesium, while ear cushions feature a combination of open- and closed-cell foam interiors with smooth Cabretta leather outer surfaces, perforated Cabretta leather touch surfaces, and an open-weave fabric on the inner ring surrounding the ear. The headphone’s weight is a very reasonable 405 grams, and Warwick Acoustics has lavished great care on its overall fit, finish, electrical integrity, and, especially, ergonomics (most notably, on clamping pressures). Attention to detail shows everywhere, and in particular in the construction of the Aperio’s signal cables. As with the Aperio preamp/amp/DAC, Warwick Acoustics has explored and fine-tuned virtually every aspect of system performance.

What does all this design and development effort buy for the listener in sound quality? To find out, I ran the Aperio system with an Auralic Aries wireless bridge linked to a music library containing a mix of CD-quality, and hi-res PCM, DSD, and DXD music material. The simple result was one of the most breathtaking headphone listening experiences I have ever enjoyed—one that in some respects was like listening to a Sonoma M1 system that had been working out in a gym, taken martial art classes, and worked to earn advanced degrees in particle physics and music philosophy. In other words, the Aperio can do everything the Sonoma M1 system could do and more, and do it better with overarching competence, sonic athleticism, depth, and refinement.

The system’s voicing comes as close to the ideal of neutrality as anything I have ever heard (including some exceedingly fine and very expensive speaker-based systems). Extension at high and low frequencies is exemplary, with the Aperio showing much stronger capabilities than the Sonoma M1 system on loud low-frequency passages and on fast-rising bass transient sounds. For example, I noted that the Aperio handled the mysterious, evocative, and high-amplitude low-frequency sections of Nils Frahm’s “Chant” [Solo, Erased Tapes, 16/44.1] with equal parts power, clarity, and grace.


Resolution, transient accuracy, and almost blinding tonal purity are three of the Aperio’s strengths. On Hilary Hahn’s performance of the first movement from the Meyer Violin Concerto [DGG, 16/44.1] the Aperio beautifully revealed Hahn’s amazing dexterous fingering and bowing technique along with her distinctive string tone, which combines elements of sweetness, incisiveness, and—above all—clarity of musical intent. And there it is: The Aperio is about more than sound quality per se; it is about uncovering the very human emotions and communicative intentions underlying the sound.

Dynamic swagger and agility? Most definitely. Put on “Tom Sawyer” from Rush’s Moving Pictures [Mercury, 16/44.1] and note how the Aperio renders the ultra-crisp and super-punchy attack of Neil Peart’s drums, the aggressive yet well-controlled and richly textured snarl of Geddy Lee’s bass, or the live-wire intensity of Alex Lifeson’s guitar lines. There is vigor and energy everywhere, but also subtlety and—after a fashion—delicacy shown in the masterful way the musicians modulate dynamics to create dramatic mini-crescendos and decrescendos throughout the song. The Aperio can handle high-energy rock music and other forms of power music with an exuberant dynamic athleticism that the Sonoma M1 system could never have matched. Quite honestly, the Aperio system can play (much) louder than I personally can bear to listen—meaning one will never complain of the Aperio “running out of steam.”

Spaciousness and soundstaging? Oh my, yes. I got a glimpse of what the Aperio could do when I put on an old and well-loved audio chestnut, the title track from Andreas Vollenweider’s Caverna Magica [Savoy, 16/44.1]. “Caverna Magica” has long been famous for the way it produces enchanting 3D soundstages through most audio systems, but through the Aperio system I found there was suddenly not just a little but a lot more magic in the “Magica.” In fact, the Aperio took the song’s 3D presentation to a whole new level, creating a huge, resonant, cave-like environment, which Vollenwieder’s sumptuous-sounding harp filled beautifully. My point is that whenever there are useful spatial cues in music, the Aperio will find them and put them to great use.

I like to try to offer critical commentary where appropriate, but there really is nothing I can fault in the Aperio’s sonic performance. The only drawback I encountered—and it is one common to most electrostatic headphone systems I have heard—is that if I moved my head suddenly while listening, pressure levels within the earcups would change momentarily, causing a soft “clicking sound” from the diaphragms. Apart from that, the Aperio listening experience was an unalloyed joy.

The Aperio is the finest headphone system I have ever had in my home, and also the finest I have ever heard (including some that cost far more than the Aperio). If you seek a highly capable and profoundly revealing music exploration tool, the Aperio is the system for you.

Specs & Pricing

Aperio Headphone
Type: Circumaural, open-back, electrostatic headphone
Drivers: Full-range, low-mass, balanced-drive, high-precision, electrostatic-laminate (BD-HPEL) electrostatic drivers
Effective driver area: 3570mm²
Frequency response: 10Hz–60kHz
Weight: 405 grams (excluding cables)

Aperio Preamp/Amp/DAC Module
Type: Class A, solid-state, balanced-output electrostatic headphone amplifier, preamplifier, and DAC
Analog inputs: One balanced stereo input (via XLR jacks), one single-ended stereo input (via RCA jack), with high/low gain switches for both inputs
Analog outputs: One balanced stereo output (via XLR jacks), one single-ended stereo output (via RCA jacks)
Digital inputs: USB digital input, one coaxial SPDIF digital input, one AES3 input (via XLR jack), and one network/Ethernet input (via RJ45 jack) 
Outputs: One electrostatic headphone/bias voltage output jack
DAC: Dual mono, 32-bit/384kHz DACs with balanced outputs for PCM and DSD
DSP: For PCM only, 64-bit (double-precision) fixed-point processing at native sample rates
Digital audio formats supported: USB: all PCM inputs up to 32-bit/384kHz and DSD native or DoP inputs up to DSD256; coaxial SPDIF: all PCM inputs up to 24-bit/192kHz; AES3: all PCM inputs up to 24-bit/192kHz; network/Ethernet: all PCM inputs up to 32-bit/384kHz and DSD native or DoP inputs up to DSD256
Frequency response: Bandwidth >65kHz
Distortion + noise: <0.001%
Dimensions: 413mm x 68mm x 351mm
Weight: 7.4 kg (not including power supply)
System price: $24,000 

Mira Technology Park
Suite 1.02, NW05, Watling Street
Nuneaton, CV10 0TU 

United Kingdom
+44 (0) 24 7722 0377

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