Warwick Acoustics APERIO Electrostatic Headphone System

Equipment report
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 higher-performance 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.”