Any fan of high-end headphones will be unlikely to require conversion to the joys of electrostatic headphones, which are an aspirational high for head-fi lovers everywhere. Renowned for speed and detail, electrostatic designs replace the usual cone speaker inside a headphone with a flat diaphragm held at a fixed charge, while a dedicated headphone amplifier biases and modulates the voltage across perforated metal grids (stators) on either side. (Not to be confused with planar magnetic designs, in which the signal is applied to the diaphragm itself, positioned between fixed magnets.)
At least, that’s how electrostatics have worked for the last 60 years. So who is this upstart Sonoma Acoustics, arriving with not only a luxurious-looking pairing of electrostatic headphones and amplifier, but a significant new take on electrostatic design itself?
Who is Sonoma Acoustics?
The company’s origins are strangely absent from its website, other than listing offices in Colorado, USA, and in Henley in Arden, deep in Shakespeare country between Redditch, Stratford and Leamington Spa in the UK. Such reticence often points to a China-based company, but not in this case. Indeed the Sonoma name is not entirely new — it was used for a professional workstation originally developed by Sony specifically to record using the digital DSD format which originated on SACD discs. That Sonoma professional workstation is currently under another Colorado-based company, Super Audio Center, which has SACD-related origins going back to 2004.
Meanwhile Sonoma Acoustics has been created by a team including several former Sony engineers, while the key electrostatic technology itself comes from Warwick Audio Technologies (WAT), also based in Henley in Arden, UK, with technical development in Ebbw Vale, South Wales, which perhaps explains which Sonoma specifically mentions Wales on its own website. Warwick Audio Technologies was a spin-off from Warwick University, and previously released a flatpanel directional speaker called ZonarSound, but here the key development is a transducer technology called HPEL (High Precision Electrostatic Laminate). The WAT team includes Sonoma Acoustics’ CEO Martin Roberts, plus Dan Anagnos as its Chief Technical Officer (also formerly of Sony, and of D&M Holdings and Turtle Beach), and also, rather impressively, Gary Waters, a former Vice President and General Manager of Bose Corporation. So it’s a team that brings together expertise in transducer technology, in high-res audio — and in headphone marketing. The Model One (M1) system is the result.
So the Sonoma M1 is the first ever headphone to use the HPEL electrostatic technology developed by the Warwick Audio Technologies team. What’s new about this? Well it does away with the grid between the diaphragm and your ears, instead using only a back grid of stainless steel mesh, to which the usual high bias voltage is applied, modulated by the audio signal. The supply of this bias voltage is why electrostatics require dedicated amplifiers and multicore cables. (The 1350V DC here is not a safety issue because the current is very low.)
Then the HPEL diaphragm itself sits where the front grid would normally be, tightened across a series of large open cells on a Formex spacer layer to create a series of small ‘drum skins’, as Sonoma calls them. Each cell’s skin is acoustically independent, but they are all driven in parallel from the rear grid, while the whole construction is lodged in a polycarbonate shell for rigidity. The sound from each cell’s drum skin combines with the others, but unwanted resonances should average out, avoiding the specific resonant peak of a larger single driver.
With the laminate a mere 15μm thick, its low mass is highly responsive to transients and details, and Sonoma claims its response is linear up to 60kHz. Together with a low-end quoted down to 10Hz, the technology is clearly a good match for high-res audio performance.
And that’s the other focus for Sonoma, and for the amplifier component here, which is a DAC as well as headphone amplifier, with a digital coaxial input and USB-B for your computer. (A high quality USB cable is supplied, co-developed with Straight Wire and using gold-plated connectors and a silver-plated data path.) This USB 2.0 input and the dual-mono 32-bit/384kHz ESS Reference Sabre DACs behind it will handle up to 32-bit/384kHz PCM, and DSD64/128 via DoP transmitted using the DoP protocol — it cannot decode raw DSD. The coaxial input is good to 24-bit/192kHz PCM.
There are also two analogue inputs — but these are digitally sampled by an AKM Premium analogue-to-digital converter, so allowing the Sonoma’s DSP to process them and implement the fully digital volume control. The ADC is 32-bit/384kHz capable, though we’re unsure at what rate the actual sampling takes place.
From there the DSP takes place at 64-bit double-precision fixed-point calculations, before handing off to the DAC and the output stage itself, which is pure single-ended, high-bias discrete-FET Class-A.
As the WAT man from Bose no doubt advised Sonoma, it’s no use cramming in such wonderous technology if the products themselves don’t impress on the outside. Perhaps that’s why the packaging is so wildly effusive, perhaps the most extravagant (some might say excessive) example of the art we’ve ever encountered in terms of hi-fi boxing, with the received cartons around 40 times the volume of the products within, unfolding like a pass-the-parcel game which ultimately yields a relatively small treasure. So extreme is the wrapping here that it potentially has the opposite of the desired effect.
Still, there’s no doubting the quality of the prize finally released. The design of amplifier and headphones is linked by curvy cuts to the outer headphone cap grilles and a similarly curvily-punched ventilation grille on the top of the DAC/amplifier’s CNC-machined aluminium casing, through which an orange glow can be seen within. It uses an external 24V switched-mode power supply.
As noted, the amplifier has coaxial and USB digital inputs, plus two analogue options. There are three lovely toggle switches — one on the front selecting between digital and analogue inputs, two on the back for power and to switch between the low-level minijack input (850mV maximum output) and the RCA inputs (up to 2.1V).
There are no outputs, which makes the M1’s incorporation into a larger system a bit awkward, with no way to send the results of its high-quality USB DAC onto your hi-fi system. You’d either have to replug your computer USB each time you use the headphones, or to run parallel USB outputs from your computer, setting the M1 as the default, so that when you power off the M1 the computer reverts to your main system (if it’s in a good mood). No problem, of course, if you’re spending your whole life on headphones only.
These are fully open headphones, spilling sound out as well as in, and given the advertised emphasis on comfort, we found the M1 just a tad imposing to wear, quite firm to the head, those earcups of top-grain Cabretta sheepskin leather (made from sheep that grow hair rather than wool) quite solid rather than soft and yielding. But this does ensure a clear fit (the instructions in the manual are excellent), and the injected magnesium earshell construction certainly keeps things fairly light — 300 grams all up, not counting the cable, which is another design made in cohoots with Straight Wire Inc., delivering ultra-low capacitance and impressive flexibility given its multicore nature. Note this is two metres long, rather than the more common three-metre length provided for home headphones, so plan your positioning.
Again the full manual gives excellent guidance on getting your Windows or Mac computer to provide true and proper output to the M1 via USB. We downloaded the firmware updater package for our Mac Mini (control-click the app if your Mac refuses to run it), and it informed us we were up to date and ready to play.
So, at the end of a long road of technology, what’s the result? Well unlike some electrostatics, the first impression is not one of open skies and scintillating top-end jangle — the M1 didn’t focus our attention on the frequencies, but rather on the speed; the timing of the M1’s performance is a revelation. Rhythm elements were so tight, vocals so trim, that it was like a photograph coming into focus. And the effect of such well-defined imaging is to clear a space where background information gets a fresh airing. We use Leonard Cohen’s O2 live version of Tower of Song as a tester for vocal tone — a test passed impeccably here, but what was that occasional rumbling off in the left channel? It sounds like wind noise on a mike, but it might be a passing underground train, or someone wheeling a flight case around backstage. Never noticed it before.
The Mr Sheen effect here similarly transformed the often stodgy delivery of Paul McCartney’s My Valentine into something relatively crisp (while making us aware that it might have been rather overcompressed in the mastering). It did not, however, fix the thin vocal on Dion’s I Read It (in the Rolling Stone), though it made the best possible of the instrumentation, a solid thump to kick drum and a nice realistic bass presentation.
Sometimes things felt as if they were missing some support down in the lower mids, so that male spoken word could sound less plummy than from conventional cone headphones, and acoustic bass could sound underplayed. But we eventually decided this was a side-effect of the clarity rather than a frequency anomaly, a re-acclimatisation to the deliberate upper bass bump engineered into so many headphones. Listening to the whole of the JVC K2-remastered ‘Songs For Distingué Lovers’ by Billie Holiday, the longer we sank into its ping-pong-panned instrumentation, the more that off-mike acoustic bass found its place in the mix. And a perceptual sweep confirmed Sonoma’s claim of impeccable linearity from top to bottom, and a very low bottom indeed — though not loud or in your face. The electrobass on Dhani Harrison’s #WarOnFalse from his 2017 debut album was far more fizz than fundamental compared with its arrival via a big pair of speakers, but we’re confident it’s the Sonoma that is most true to its nature. (Whether Dhani himself ever heard it replayed this way is another question, of course.)
The delightful presentation of jangliness served much of Sara Bareilles’ ‘What’s Inside: Songs From Waitress’ album very well, and again we were five tracks into the album before time and thought caught up with us, listening to the spaced multitrack vocals of Soft Place to Land, given a wide and spacious headspace in which to shine, every tiny cue to her vocal spread delivered to our eager ears.
Their timing and imaging will absolutely thrill classical fans — we opened up our high-res classical collection and revelled in the Duisburger Philharmoniker’s Mahler Symphony No. 5 (24/192) — it may not be Bernstein but the Acousence recording was impeccably rendered from the reverberation around the solo trumpet opening to the rollicking rondo closure.
A curiosity — the headshells themselves seem unusually sensitive: touch a finger to one of the outer grilles and when you remove it, the balance makes a little jump to the other side, as if you’ve momentarily earthed something. Moving your head can deliver a similar effect of instability to the balance.
As for downsides, we’d note only the amp’s fairly warm Class-A operation even when not actually playing, their inability to chain the DAC into an existing amp and speaker system, and that firm side pressure making them less comfortable than many (we didn’t like to try the ‘stretch’ thing on a review pair, lest their radical electrostatics took exception to this).
The level of performance from this combination of DAC-amp and new-concept electrostatic would be impressive from an established brand, so as a first delivery from a new company (in the consumer product space, at any rate) it is all the more remarkable. The studio heritage behind the brand may be the key to their neutrality — they would make a reliable reference headphone for recording and mixing, such is their lack of exaggeration in any regard, while their revelatory accuracy in the time domain makes them a thrill for listening to a full range of genres.
Sonoma Model One
+ New technology does the job
+ The joys of electrostatic sound
- Fit a bit firm
- No outputs to loop through into your main system
Type: Open-back, circumaural
Transducer: HPEL, single-ended electrostatic, effective diaphragm area 3570mm2
Quoted frequency response: 10Hz–60kHz
Cable: Two metres
Weight: 303g without cable
Inputs: 1 x USB 2.0 (32-bit/384kHz PCM, DSD64/128 via DoP), 1 x coaxial digital (24-bit/192kHz PCM), 1 x analogue minijack stereo, 1 x analogue RCA
DAC: ESS Reference Sabre
Amplifier/Energizer: Discrete FET, single-ended, high bias Class-A output
Quoted distortion + noise: <0.05%
Dimensions (whd): 57 x 190 x 290mm