Electroacoustic Measurements from speakerphone

Editor’s Announcement: Ladies and gentlemen, we have great news to announce — CYMBACAVUM will now provide in-house acoustic measurements!

Our newest contributor is speakerphone; he has been running his own acoustic measurement blog, http://clarityfidelity.blogspot.kr/, but will be partnering with us to deliver measurement results on select items featured on this website. Occasionally, he will also be delivering commentary regarding measurement results and products. As a modest guy, speakerphone claims that his English isn’t that good and is reticent to provide opinion pieces, but Mr. T thinks otherwise and will be encouraging him to open up with thoughts!

We believe speakerphone is an invaluable addition to the CYMBACAVUM team and will help enrich readers’ experience by helping us correlate our perceptual experience with data sets comparable across products. His measurement methodology is finely tuned to comply all current international standards of information for the measurement of headphones and earphones, as well as recent developments and revelations in headphone acoustic research.

The following details protocol to be followed in all forthcoming electroacoustic measurements:

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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