Sonoma Acoustics M1 headphones Lab Report

This is only the second electrostatic headphone we've measured in recent years, the first being the Stax SRS-4170 Signature [HFN Nov '13]. Sonoma's M1 performs very differently, particularly in the bass. Whereas the Stax had a pronounced bass peak at about 80Hz, with a rapid roll-off in output below that, the M1's bass extension reaches comfortably below 20Hz (–6dB re. 200Hz), making it the equal in this department of the best planar magnetic designs [see Graph 1]. Just how much of this – and the rest of the frequency response – is due to DSP equalisation would be interesting to know. Whatever, the M1 performs well in the bass, although the fact that the maximum SPL it is specified to deliver is 110dB means that it might overload on bass-heavy material played loud.


Unequalised responses (L/R, grey/red; ave. 3rd-octave, black) show an extended bass but reduced presence band output [see responses, below]


Third-octave freq. resp. (red = Harman corrected; cyan = FF corrected; green = DF corrected)

Our impedance test is inappropriate given that the M1 has its own drive electronics but I played pink noise over one channel only while wearing the headphones, mimicking the impedance test, to see if I could detect any vibrational misbehaviour in the headband. I could, just, hear some carry-over of sound to the inactive channel at low frequencies, which makes me wonder if the twin blips at around 65Hz and 80Hz in both capsule's responses are related to headband resonances. Higher in frequency there is less peaking of output around 2-3kHz than is classically considered necessary for a neutral tonal balance. One related effect was that small differences in capsule positioning on the ear can have quite a large influence on response, beginning around 1kHz and worsening above 5kHz.

At low frequency the M1's large, efficient earpads effectively banished the variability I so often see caused by poor earpad sealing. The 3rd-octave corrected frequency responses confirm Sonoma's claim to have taken note of Harman's research on the optimum headphone target response, albeit not entirely [red trace, Graph 2]. Shelving-up of the bass response isn't sufficient to flatten the Harman-corrected response, and the M1's output is also a little shy in the presence band between 2kHz and 8kHz – although that's a feature commonly seen in headphones which nonetheless sound well-balanced. KH

Capsule matching (40Hz-10kHz): ±3.9dB
LF extension (–6dB ref. 200Hz): <20Hz
Distortion 100Hz/1kHz (for 90dB SPL): 0.2% / <0.1%
Weight (inc cable): 424g
Price: £4995

Sonoma Acoustics Ltd
Boulder, Colorado, USA
Supplied by: Sonoma Acoustics Ltd, Henley In Arden, UK
07720 555754