Early last year, at the CanJam SoCal event, I met up with a spokesperson from Warwick Audio Technologies—a spin-off from the University of Warwick in Coventry. What Warwick Audio Technologies had created, the gentleman explained, was an entirely new way of making electrostatic headphone drive units. The technology was called HPEL, which stands for High-Precision Electrostatic Laminate. The benefits of HPEL, I was told, included the capability for producing light and highly responsive electrostatic drivers in large multi-layer sheets from which multiple drivers of virtually any desired size or shape could be cut and trimmed. Better still, the HPEL production methodology afforded exceptional driver-to-driver consistency and uniformity—something not easily achieved with conventional electrostatic driver manufacturing techniques.
Warwick Audio Technologies did not intend to manufacture electrostatic headphones, per se, but rather hoped to license its technology to someone who would appreciate the technical and sonic benefits of HPEL and who would be able to bring an HPEL-based headphone system to market in an effective way. That ‘someone’ turned out to be Sonoma Acoustics, a Colorado-based firm led by a group of the same technical visionaries who originally helped launch the high-resolution SACD disc format and its corresponding DSD digital audio file format. The leader and General Manager of Sonoma Acoustics is none other than David Kawakami—a man whose name is, in many high-end audio circles, almost synonymous with high-res audio. For now, Sonoma’s focus is on the successful launch of its newly released Model One electrostatic headphone system ($4,995 or £4,595), which is the subject of this review. But, don’t be surprised if you see the Sonoma Acoustics team launching other kinds of audio products in the future.
The Sonoma Acoustics’ Model One electrostatic headphone system is a turnkey high-resolution music playback system that includes not only an electrostatic headphone (based on Warwick’s HPEL technology), but also a matching, purpose-built electrostatic headphone energiser/DAC/ADC/DSP module. What are the ADC and DSP elements for, you ask? The answer is that the Sonoma team wanted to give the Model One headphones a very specific “modified pseudo-diffuse field” frequency response curve and needed to apply digital signal processing to make this possible. But, they also wanted to make sure that the Model One’s energiser module could accept both digital and analogue inputs. So, the purpose of having an analogue-to-digital converter on board is to allow incoming analogue signals to be digitised on arrival, facilitating downstream DSP processing later on. One point prospective Sonoma buyers should therefore bear in mind is that the Model One headphones work only with their companion energiser/DAC/ADC/DSP module and vice versa.
The Model One headphones use Warwick-developed, low mass, single-ended (as opposed to push-pull) HPEL electrostatic drivers. In essence, each driver consists of a three-layer ‘sandwich’ comprising a stainless steel mesh grid that faces the rear side of the ear cup, a centrally-positioned open-cell insulating spacer made of Formex™ (a type of polypropylene), and then a machine-tensioned, 15μm-thick, flexible film laminate diaphragm that faces the front (or ear) side of the ear cup. The diaphragm is made of bi-axially oriented propylene film (BOPP) with a vapour deposited aluminium surface sealed with a synthetic lacquer. This entire three-layer ‘sandwich’ is then clamped within a cassette-like two-piece protective frame made of 40% glass-filled polyphenylene sulphide (PPS) from which the driver is isolated by precision-made PORON™ microcellular urethane foam gaskets.