Reviewed on: SoundStage! Solo, November 2018

I measured the TH909s using a G.R.A.S. Model 43AG ear/cheek simulator/RA0402 ear simulator, a Clio 10 FW audio analyzer, a laptop computer running TrueRTA software with an M-Audio MobilePre USB audio interface, and a Musical Fidelity V-CAN amp, with an Audio-gd NFB-1AMP used for distortion measurements. On the Model 43AG, I used the new KB5000 anthropomorphic simulated pinna for most measurements, and the original KB0065 pinna for certain other measurements as noted. These are “flat” measurements; no diffuse-field or free-field compensation curve was employed.

Frequency response

The above chart shows the TH909s’ frequency response measured with the new KB5000 and KB5001 anthropomorphic simulated pinnae. This is a fairly typical measurement for headphones in general, although most audiophile-oriented headphones are more or less flat up to about 2kHz. The TH909 has relatively more bass and less midrange.

Frequency response

This chart shows the TH909s’ right-channel frequency response measured with the old KB0065 pinna (which I’ve used for years) and G.R.A.S.’s new KB5000 pinna, which I recently switched to because it more accurately reflects the structure and pliability of the human ear. This is just for sake of comparison with older measurements of mine.

Frequency response

This chart shows how the TH909s’ tonal balance changes when they’re used with a high-impedance source, such as a cheap laptop or some cheap professional headphone amps. There’s just a slight bass boost with the high-impedance (75-ohm) source.

Frequency response

This chart shows the TH909s’ right-channel response compared with two other high-end open-back headphones (the Audeze LCD-Xes and the Sennheiser HD 800 Ses), as well as the Sony MDR-7506es, a standard fixture in audio production work that generally conforms to the “Harman curve,” shown in research by Harman International to be the preferred over-ear headphone response for most listeners. These measurements use the older KB0065 pinna, because that’s the only measurement I have for the HD 800 Ses. You can see that the TH909s have substantially more bass and a little less midrange energy than the competitors shown here.


The TH909s’ spectral decay (waterfall) chart shows no resonances worth commenting on.


Measured total harmonic distortion (THD) of the TH909s is trivial. Even at the extremely loud level of 100dBA, it’s only 2% at 20Hz.


In this chart, the external noise level is 85dB SPL, and numbers below that indicate the degree of attenuation of outside sounds. The TH909s’ isolation is above average for an open-back model, although it’s still much less than what you get from closed-back headphones such as the NAD Viso HP50s (also shown).


The TH909s’ impedance response is fairly typical for high-end dynamic-driver headphones, with a fairly flat response except for a resonant peak in the bass, at 36Hz. It’s pretty much in accord with Fostex’s rating of 25 ohms. The phase is also generally flat.

Sensitivity of the TH909s, measured between 300Hz and 3kHz using a 1mW signal calculated for 25 ohms impedance, is 100.4dB. That’s pretty high for audiophile-oriented headphones, and it means that the TH909s can be reasonably well driven from a smartphone or laptop computer.

. . . Brent Butterworth