Reviewed on: SoundStage! Solo, January 2023

I measured the Akoustyx S-6 earphones using laboratory-grade equipment: a GRAS Model 43AG ear/cheek simulator/RA0402 ear simulator with KB5000/KB5001 simulated pinnae, and an Audiomatica Clio 12 audio analyzer. For isolation measurements, I used a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface. The earphones were amplified using a Musical Fidelity V-CAN amplifier. Except as noted, I used the supplied medium-sized silicone tips for all measurements. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed. If you’d like to learn more about what our measurements mean, click here.

Frequency response

This chart shows the S-6es’ frequency response. This is a very “smiley” response, with sharply boosted low bass and, especially, treble. I’d expect the midrange to sound recessed in comparison.

Frequency response

This chart shows how the S-6es’ tonal balance changes when they’re used with a high-impedance source, such as a cheap laptop, some tube amps, or some professional headphone amps. There’s just a small difference, a boost of about 1dB above 5kHz.

Frequency response

This chart shows the S-6es’ right-channel response compared with various earphones, including the AKG N5005s, which are said to be the passive earphones that come closest to the Harman curve. You can easily see how far outside the norm the S-6 earphones’ response is.


The S-6es’ spectral-decay plot looks mostly clean; there’s some bass resonance, but it’s well-damped and down by about 40dB after the first few milliseconds.


The S-6es’ harmonic distortion is mostly low; there’s a little bit of a rise between about 1 and 3kHz, but even at the crazy-loud level of 100dBA, it’s still below 2 percent.


In this chart, the external noise level is 85dB SPL, and numbers below that indicate the degree of attenuation of outside sounds. The lower the lines, the better the isolation. In the 43AG ear/cheek simulator, the S-6es offer a fairly modest amount of isolation with just the silicone tips, but if you add the silicone wings and use the foam tips, the isolation is truly outstanding.


The impedance curve of the S-6 earphones runs about 16 ohms up to about 2kHz, but above 5kHz, it starts to dive, ending up at 10 ohms at 20kHz; that’s why the response at these frequencies is down about 1dB with a high-impedance source. The phase takes a similar dive.

Sensitivity, measured in the right channel between 300Hz and 3kHz, using a 1mW signal calculated for 18 ohms rated impedance, is 102.9dB. That’s high enough that no portable device should have problems getting the S-6es to play as loud as you want.

Bottom line: The basic engineering of these earphones looks solid, but the frequency response shows extreme treble and low-bass boost, which I have to think will sound unnatural, even though decades of audio history suggests some listeners will probably enjoy it.

. . . Brent Butterworth