Electroacoustic Measurements

The audio hobby is an interesting one; it’s both a deeply personal experience, but simultaneously one rooted in scientific underpinnings. You can’t have one without the other.

The vast majority of audio websites (and even companies, to a certain degree) veer to one side or another; they either stress the personal, subjective experience as the end all be all, or unwaveringly cling to objective numbers.

Instead of clearly drawing lines in the sand, we believe in marrying the two.

We’re not the first site or blog to do so — excellent websites such as InnerFidelity do a great job both of educating the public on the scientific principles underlying the audio devices we love, and also of reminding us of the joy in the audio experience. Close-knit forums and communities such Changstar and SEEKO also encourage members to perform their own measurements.

That’s why we reached out to speakerphone ( @farbic ) in South Korea to bring us reliable measurements to enhance the content of our articles. You can find out more about his background on his biography page here.

All articles with accompanying measurements from him will be listed here, and tagged with ‘measurements‘ as well.

List of Available Measurements (as of June 2015)

  1. LH Labs Verb
  2. Dynamic Ear Company Inor DS-11 (a.k.a. ACS T15)
  3. Sony MDR-EX1000
  4. Etymotic Research MK5 Isolator
  5. DUNU DN-2000J

Articles with Legacy Measurements (not directly comparable to current ones)

  1. Astell&Kern ARK03 (a.k.a. JH Audio Roxanne) [Universal-Fit]

Apparatus

All posted measurements, unless otherwise noted, ​will comply with IEC 60318-4 (formerly IEC 60711), ITU-T Recommendation P.57, and ANSI S3.25 standards for artificial ears.​

Measurement Acquisition

Acquisition follows a modified IEC 60268-7 standard, with ~0 Ω output impedance (instead of 120 Ω) for the output amplifier (NwAvGuy’s O2 headphone amplifier). The modified standard is used to better suit low input impedance devices, such as the IEMs and other earphones being measured. For reference, both Knowles and Sonion also qualify their balanced armature receivers with output amplifiers possessing ~0 Ω output impedance.

For frequency response analysis, the source signal is pink periodic noise (smoothed 1/24th of an octave). For harmonic distortion analysis, the source signal is stepped sine (1/6 octave increments).

Unless otherwise noted, unprocessed data points obtained from frequency response analysis will further apply the following compensation models:

  • Diffuse Field Target, following the ISO 11904-2 standard (indicated only from 20 – 10,000 Hz), with a 10,000 – 20,000 Hz extension at -6 dB/octave
  • Olive-Welti In-Room Target (Olive, Sean; Welti, Todd; McMullin, Elisabeth, at AES), from acoustic research at Harman International.

References

  • IEC 60318-4 : Electroacoustics – Simulators of human head and ear – Part 4: Occluded-ear simulator for the measurement of earphones coupled to the ear by means of ear inserts [Link]
  • ITU-T Rec. P.57 : Series P: Telephone transmission quality, Objective measuring apparatus : artificial ears [Link]
  • IEC 60268-7 : Corrigendum 1- Sound system equipment – Part 7: Headphones and earphones [Link]
  • ISO 11904-2 : Determination of sound immission from sound sources placed close to the ear [Link]
  • ​Olive-Welti Target : Listener Preferences for In-Room Loudspeaker and Headphone Target Responses [Link]
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