An introduction to electrostatic headphones and Sonoma Acoustics
There are three types of headphone drivers/transducers. The first and the most common is the dynamic driver, where a metal coil is inserted into a magnetic field and fixed to a suspended driver cone. When a charge is applied to the coil, it reacts with the magnetic field, causing the driver cone to move and produce sound.
The second type of driver is called the planar magnetic driver and it has become increasingly popular lately. Here, a thin conductive film is typically positioned between two magnets. When an electrical charge is applied, the film reacts to the magnetic field of the magnets and moves to produce sound.
This a diagram is a rough approximation of how an electrostatic transducer looks like. The thickness of the stators and the diaphragm (electrostatic film) has been exaggerated for this illustration. They are much thinner in actuality. (Image source: Wikipedia)
Finally, there are electrostatic transducers which consist of a thin conductive film suspended between two or one metal plates called stators. A bias voltage is applied to the film to create an electrostatic field and music signals are sent to the stators, which attract and repel the film to produce sound.
There are a couple of theoretical advantages to the electrostatic design. Because they are no magnets involved, the driver can be made very light. And since the film is usually mere micrometers thick, the frequency response of electrostatic headphones easily exceed 20kHz - the upper limits of human hearing. In addition, the stators are perforated, allowing sound to pass through easily to the listener’s ears. These advantages are the reasons why electrostatic headphones have an unrivaled response and airiness in their sound.
But for all of electrostatic’s advantages, one of the problems associated with manufacturing electrostatic headphones is that they are expensive to make. Manufacturing inconsistencies such as volatile drivers and imbalances from one driver unit to the next drives up manufacturing costs, which in turn translates to a high product cost. This also explains why only a handful of brands are committed to making electrostatic headphones.
Warwick Audio Technologies has developed a new electrostatic transducer that can be manufactured with greater efficiency and consistency.
However, a company called Warwick Audio Technologies is attempting to change this. Based in the UK, the company has developed a new electrostatic driver called HPEL or High-Precision Electrostatic Laminate. The film is ultra-thin, measuring just 15 microns, but more crucially, the driver can be produced on a roll-to-roll process and with remarkable consistency, which means more efficient manufacturing and lower manufacturing costs. Along with the driver, Warwick Audio Technologies have also developed a drive system for their new HPEL driver. In short, its a complete electrostatic headphone solution.
This provided a company called Sonoma Acoustics with the perfect platform to realize their dream of a headphone system. But first, who is Sonoma Acoustics?
This is an example of a Sonoma Pure DSD multi-track recorder and editor that is used to create DSD recordings. (Image source: Super Audio Center)
Sonoma Acoustics was formed by a group of ex-Sony and Philips employees who worked on the Super Audio CD project (SACD). And the name Sonoma comes from the DSD recording and editing workstation that they helped to develop in the early days of the SACD. In short, these are the guys who helped pioneered high-resolution audio. Given their affiliation with SACD, it is easy to see why they wanted to build a headphone that would be optimized to play the type of music that they helped create. And the end result is the Sonoma Model One electrostatic headphone system that we have here.
Read on as we cover more about it in the following pages and how it performed.
The Sonoma Model One headphones
The design of the Sonoma Model One headphones remind me of Sennheiser's HD 650.
The Sonoma Model One headphone system consists of the headphones and its own dedicated energizer and DAC. Let’s talk about the headphones first.
The Sonoma Model One headphones have an open-back design and have large ear cups that remind me of Sennheiser’s legendary HD 650. A point to note is that they leak an awful lot of noise, both in and out. Everyone sitting around you will be able to hear what you are listening to. Likewise, you can hear what’s going on around you too, which means you need a private and quiet space to be able to really enjoy these headphones.
The ear cups are of an open design and leak a lot of sound, both in and out.
The headphones are finished in silver and the ear cups are actually made out of super light magnesium. Considering their size, the Sonoma Model One headphones are incredibly light, weighing just 303g. The ear cups are plush and soft and are covered with hand-stitched Cabretta sheepskin leather. The ear cups are also very large and deep, and should be able to accommodate most ears easily.
The ear pads are deep, plush, and soft.
Cabretta leather comes from sheep that grow hair instead of wool and the leather is valued for its softness and durability. The leather is sourced from Ethiopian sheep and then sent to the UK where they are tanned by leather specialists Pittard. Finally, the leather is sent to Germany where they are hand-stitched to create the ear pads used in the Sonoma Model One.
The headband, on the other hand, is made out of special nylon material called Nylon12, which was chosen for its strength and durability. The internal components are stainless steel and feature vapor-deposited titanium to provide smooth operation. Again, the headband pad is covered with soft Cabretta leather.
The headband features plush padding too.
I can attest to Nylon12’s strength because the headband feels stiff and tight. But I also found the clamping force to be excessive. Fortunately, this is somewhat mitigated by the super plush ear pads and headband. In my usage, I found the Sonoma Model One headphones to be comfortable enough for shorter listening sessions up to around an hour or so. But beyond that, my head starts to feel a little weary and numb from its tight vise. That said, I think the clamping force can be alleviated by slightly twisting the headband outwards.
Now, as I mentioned earlier, the Sonoma Model One uses an electrostatic transducer developed by Warwick Audio Technologies. Apart from ease of manufacturing, another advantage of the HPEL transducer is that it is single-ended in design, meaning it only uses a single stator. In this case, the stator is positioned behind the electrostatic film. A benefit of this is that sound produced by the film need not pass through a stator. This reduces distortion, which can be caused by sound being forced through a stator.
The cables are removable and snap easily into the ear cups.
To complete the headphones package, it comes with a specially designed low-capacitance cable that was designed from the ground-up by audio video cable specialists Straight Wire. The cable is made using fine strands of silver-plated oxygen free high conductivity pure copper, and a filler is used in the cable jacket to keep the conductors within apart and to reduce crosstalk and interference. It feels strong but isn’t overly stiff or heavy. A sense loop is also built into the cable, so if the cable is disconnected from the energizer or the individual ear cups, the energizer shuts itself down. And at 2 meters long, I feel that it is the right length for listening at a desk. It isn’t so short that it restricts your movements, but it isn’t too long either that it becomes cumbersome.
The Sonoma Model One Energizer/DAC
The Sonoma Model One headphones come with its special energizer because of its unique energy requirements.
Now let’s talk about the energizer and DAC combo. Because the headphones use Warwick Audio’s patented HPEL transducer, it requires a special energizer from Sonoma Acoustics and cannot be mixed and matched with third-party energizers. Mainly, the issue lies with the Sonoma Model One’s need for a very high 1350V DC bias voltage, which I believe is a consequence of its single stator design. Most other electrostatic headphones only require about 500V to 600V.
The energizer and DAC combo unit is made out of a solid billet of aluminum, weighs about 2.5kg, and looks handsome and minimalistic. It does take up quite a bit of desk space, but that’s par for the course when it comes to high-end desktop amplifier and DAC combos. On the front panel, there’s a chunky flip switch that lets users choose between analog and digital inputs, a large volume control knob, and the headphone outputs.
The energizer features USB and digital coaxial inputs, and also analog inputs via RCA and a 3.5mm audio jack.
Round the back, there’s two digital inputs in the form of USB and digital coaxial and two analog inputs in the form of your standard RCA jacks and a single 3.5mm audio jack. The power switch is located on the far end and there’s another switch that selects between the two analog inputs. There are no RCA outputs so you cannot use this as a standalone DAC or as pre-out to your powered speakers or your speaker amplifier.
The energizer uses a discrete single-ended Class-A design. Audiophiles typically prefer Class-A amplifier design because of their simpler design and inherent lack of distortion, since the output device is always conducting and drawing current at all times throughout the full 360-degree cycle of the waveform. This also means that the output stage is always active, regardless of whether there is a signal or not, which in turn means that the energizer gets fairly hot during operation.
Vents above help keep the energizer cool because of its Class-A output design. The special wave patterns are similar to the ones found on the ear cups.
The energizer also features an integrated digital-to-analog converter (DAC) that accepts digital inputs via USB or digital coaxial. It uses two ESS Sabre Reference DAC chips (one for each channel) that support PCM up to 32-bit and 384kHz as well as DSD up to DSD 128 (5.6MHz) via USB, and PCM up to 24-bit and 192kHz via digital coaxial.
So far so good, all pretty standard stuff for any high-end energizer/amplifier and DAC combo. But this is where things start getting interesting because the energizer and DAC unit also features a 32-bit/384kHz AKM analog-to-digital converter (ADC), which digitizes analog signals coming in from either the RCA analog input or 3.5mm analog input. Why the need for this? That’s because the Sonoma Model One also features a custom-designed 64-bit double precision fixed-point arithmetic digital signal processing running on a multi-core XMOS processor.
The Sonoma Model One relies on a multi-core XMOS processor for its DSP to attain its target frequency response. (Image source: Sonoma Acoustics)
The general consensus, at least amongst diehard audiophiles and purists, is that digital signal processing ruins the purity of the recording and is therefore frowned upon. However, Sonoma Acoustics say that digital signal processing is crucial to achieving their target frequency response of the headphones.
Unlike most high-end energizers and amplifiers which use an analog potentiometer to control the volume, the Sonoma Model One uses a completely digital volume control system.
In addition, because audio signals are now digitally processed, they were able to also implement a fully digital volume control system, which, Sonoma says, outperforms all pure analog implementations they tested. According to Sonoma, some advantages of this fully digital volume control system include no loss in fidelity and dynamic range, perfect left and right channel matching, no potentiometer irregularities, and no noise issues.
True enough, the volume control knob works well. Some amplifiers I have tried have exhibited channel imbalances at low volume levels, but not the Sonoma Model One.
In any case, it is the use of a DSP that makes the Sonoma Model One unique in the world of high-end audio. Where most high-end audio systems place great emphasis on analog purity, the Sonoma Model One is unashamedly digital in its approach to good sound. But does it succeed? I put on some music to find out and detailed my findings over the next page.
Audio Performance
The Sonoma Model One headphone system, with its fancy DSP, is one of the most unusual and advanced headphones I have ever listened to. I cannot claim to fully understand all of the tech behind it, but what I have are two ears to evaluate the way it sounds and after spending a good week and many hours listening to the Sonoma Model One headphone system using a variety of high-resolution audio files, MP3s, and even streaming from Apple Music, I think these words best describe its sound signature and performance: airy, clear, dynamic, effortless, resolving, spacious, and wide.
Like most electrostatic systems, the Sonoma Model One exudes a sense of airiness that is unmatched by any other headphones with dynamic drivers or planar magnetic drivers. The lack of mass in the electrostatic film means that the transducer of the Sonoma Model One reacts very quickly to signals, which in turns leads to a very dynamic and exciting listening experience.
This is most evident on classical and acoustic tracks such as Gymnopédie No. 1 as performed by the London Philharmonic Orchestra, and Manhattan by Sara Bareilles. In the former, the Sonoma Model One transitions breezily from quieter sections to more energetic sections of the track, and in the latter track, the headphones give great texture and emotion to Sara’s vocals and piano.
The Sonoma Model One was also extremely spacious and wide-sounding. I also have MrSpeakers’ flagship Ether Flow and Ether C Flow headphones with me for the past couple of weeks and I thought these two were quite expansive in their sound. However, the Sonoma Model One was on a completely different level. Putting on Yosi Horikawa’s Wandering, I was bowled away by how the tune seemed to engulf me. I suppose a large part of this is also due to the fact that the transducers themselves are quite a distance away from your ears.
But perhaps most of all, the Sonoma Model One is highly resolving. I think the best way to describe it is to use a TV analogy. Listening to music through the Sonoma Model One is like watching 4K HDR videos. Everything sounds super crisp, detailed, dynamic, and textured.
A common complaint leveled at electrostatic headphones is that they are light on bass and that they fail to provide that low-end rumble that bass heads love so much. I’m happy to report that the Sonoma Model One doesn’t suffer from this ailment. Putting on Mos Def’s Ms. Fat Booty, I couldn’t help but bop my head along to the thick and deep bass line.
More important than bit rate and sample rate is the quality of the recording. Poorly recorded music sounds flat and wonky on the Sonoma Model One, even if you have ripped them in a lossless format.
Electronica and trance sounds great too, but it also has the potential to sound harsh and overly bright at times. For example, Tritonal’s Murakami is a hard-hitting track and energetic trance track, and the Sonoma Model One had no problems keeping up even during the manic sections. Bass was delivered cleanly and with authority. But on Haywyre’s Doppelgánger, the headphones sounded too abrasive, especially during the drop which serves up a generous helping of drums, percussive sounds, and synthesizer tunes.
Apart from this shortcoming, I feel that, overall, the Sonoma Model One is an excellent sounding pair of headphones with high resolution, a lively and smooth mid-range, strong bass response, and an engaging and energetic sound. If you like a more dynamic and exciting listening experience, you are in the right place. But if you are looking for a more laid back and relaxed sound, you'd have to look elsewhere.
Another point to add is that you can enjoy the Sonoma Model One even if you are not playing high-resolution audio files. It sounds great playing lossy tracks from my collection of MP3 and through Apple Music too. The more important point to note is that as long as the music has been well recorded, the Sonoma Model One will make it sound great. But the flip side is also true, for poor recordings, the Sonoma Model will reveal all of its flaws in stunning detail.
A headphone system unlike any other (and some musings on DSP)
The Sonoma Model One headphones sound good, but could do with improved comfort. The headband is too stiff and clamps too tightly.
Insofar as performance is concerned, the Sonoma Model One has very little sonic faults, but if you are as treble sensitive as I am, it can sound a tad harsh at times. Otherwise, the Sonoma Model One is a fine sounding pair of headphones. In the end, it boils down really to personal preference - as is very often the case when it comes to high-end flagship headphones.
The overall characteristics of the Sonoma Model One can be best described as highly detailed, energetic, and spacious. If you are looking for a more relaxed sound this is not the headphones you’ll want.
On the whole, I like to think of the Sonoma Model One as the headphone equivalent of a modern day fighter jet. Fighter jets are highly maneuverable high-performance aircraft. But to get to that level of performance, it relies heavily on sophisticated computers and electronics. Without it, they won’t even fly. The Sonoma Model One is similar to fighter jets because in that it too relies on sophisticated electronics - its DAC, ADC, and DSP - to get to its level of performance. Take any one of them away, and you will likely end up with a pair of headphones that sound very different.
Now, the purists will probably balk at the fact that the Sonoma Model One relies on DSP. To purists, DSP or anything that digitally alters the sound is the work of the devil. These people worship at the altar of analog purity. But is DSP really a bad thing? Even the most accomplished pilots don’t get upset about having computer aids, so why should we remain antiquated in our pursuit of audio excellence especially when technology can be used to help us achieve better sound?
The crux of the matter is this: if you think the Sonoma Model One sounds good, then why should the fact that it has DSP matter? The focus here should be on the end product - the sound. And apart from the Sonoma Model One’s potential to sound sibilant and a tad harsh when playing electronic dance music (EDM), I can find no other real faults with the way it sounds.
Nevertheless, the Sonoma Model One is by no means the perfect pair of headphones. Here are some points of its shortcomings that should be considered before purchase.
To begin, comfort is not one of the headphone’s strong suits. The clamping force is excessive even if the pads are really soft and plush and the headphones themselves are really light. Fortunately, this problem can be alleviated somewhat by twisting the headband outwards to reduce the clamping force.
Another consideration is the amount of sound that it leaks. I know it is an open-back pair of headphones, but it leaks a lot of noise both in and out. Certainly more than other open-back headphones that I have tried. This means you’ll need your own quiet and private space if you want to enjoy all the subtleties and nuances of its sound, and also not to disturb people around you.
The Sonoma Model One headphone system might be pricey, but it delivers a very engaging, exciting, and clear sound.
The Sonoma Model One headphone system retails for US$5,000 and will likely cost around S$7,000 when it goes on sale here in Singapore later this year, which is a lot of money for a pair of headphones. But remember, the Sonoma Model One comes complete with its own energizer and DAC.
However, to offer even more perspective, consider the offerings from Stax, arguably the biggest name in electrostatic headphones. Stax’s flagship electrostatic headphones, the SR-009, goes for around S$5,200 - and that’s just for the headphones alone. Stax’s own flagship energizer/amplifier, the SRM-007, goes for around S$2,800. Combined, that’s S$8000. Oh, and you are still short of a suitably high-end DAC. In light of that then, the Sonoma Model One represents decent value for money, at least in the rarefied world of super high-end headphones. But more importantly, having heard the Stax SR-009 a couple of times, I’ll pick the former for its more engaging and dynamic sound.
In closing, the Sonoma Model One electrostatic headphone system is a fascinating and promising first attempt by Sonoma Acoustics. It might be pricey, but it is very well put together and features a lot of interesting tech which goes against the grain of what might be considered conventional hi-fi wisdom, but the results are quite outstanding. If you can overlook its minor shortcomings (and don't care much for EDM), I think you will be very pleased with what the Sonoma Model One can offer.
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