Speakerphone: [Introduction] Measurement Procedures

[1. APPARATUS ]

IEMs(Earphones) and CIEMs are measured with:

Occluded Ear Simulator(a.k.a. IEC711 Coupler) complying with IEC 60318-4 (formerly IEC 60711), ITU-T Rec. P.57 type 2, and ANSI S3.25. Unless otherwise noted, Custom In-Ear Monitors (a.k.a. CIEMs) will be measured at the reference plane according to IEC 60711.

Headphones and opened earphones(earbuds) are measured with:

Ear and Cheek Simulator; Pinna Simulator(small size ear, 35 shore-OO) complying with IEC 60268-7 Annex A, and Cheek Simulator dimensionally complying with ITU-T Rec. P.58 and IEC 60318-7 (formerly IEC 60959).

※ Small Pinna Simulator (Revised IEC 60268-7)

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• ITU-T Rec. P.57 Type 3.3 (ITU-T準拠)

• IEC 60959 (IEC 60318-7) (IEC60959準拠)

• IEC 60268-7 annex A (日本提案耳介モデル)

Large pinna simulator is not adequate for the headphone measurement due to several reasons. As the frequency responses show below, the reproducibility of large pinna simulator is quite poor, compared to IEC 60268-7 Annex A compatible pinna simulator. Also, IEC 60318-7 is standard for the hearing aid measurement basically.

Frequency responses, which show the reproducibility of large pinna simulator (ITU-T Rec. P.57 Type 3.3) and small pinna simulator (IEC 60268-7 Annex A)

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Data by MIT Media Lab

Frequency Response (Uncompensated)

• Magenta: Large pinna simulator

• Navy Blue: Small pinna simulator

[2. MEASUREMENT ACQUISITION ]

The acquisition follows a modified IEC 60268-7 standard, with ~0 ohm 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.

Also we measure the over-ear and on-ear headphones at 5 different positions. (forward, back, up, down, and centered) After then, obtained frequency responses will be averaged.

According to IEC 60268-7, all of the data will be obtained under the condition of 94 dB SPL at 500 Hz.

For frequency response analysis, the source signal is pink periodic noise (smoothed 1/24th of an octave).

For harmonic distortion(THD, 1st, 2nd, 3rd, 4th, 5th, 6th+) 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 Target (Olive, Sean; Welti, Todd; McMullin, Elisabeth - AES paper 8994), from acoustic research at Harman International.
Harman Target (Olive, Sean; Welti, Todd - AES paper 9382), from acoustic research at Harman International.