Physical Address
304 North Cardinal St.
Dorchester Center, MA 02124
IEC 61842:2002 — Microphones and Earphones for Speech Communication
Performance Specifications and Test Methods for Communication Transducers
Key Insight
IEC 61842:2002 establishes performance requirements and standardized test methods for microphones and earphones used in speech communication systems, ensuring adequate speech intelligibility, consistent frequency response, and reliable electroacoustic performance across communication headsets and handsets.
IEC 61842:2002 establishes performance requirements and standardized test methods for microphones and earphones used in speech communication systems, ensuring adequate speech intelligibility, consistent frequency response, and reliable electroacoustic performance across communication headsets and handsets.
1. Scope and Application
IEC 61842:2002 specifies performance requirements and test methods for microphones and earphones intended for speech communication. It covers transducers used in telephone handsets, communication headsets, hands-free terminals, intercom systems, and two-way radio communication equipment. The standard addresses both the electroacoustic performance (frequency response, sensitivity, distortion) and the mechanical design (ear coupling, microphone positioning) aspects that affect speech communication quality. It does not cover high-fidelity audio reproduction (music) transducers or specialized hearing aid devices. The standard provides a comprehensive measurement framework using artificial ears, artificial mouths, and ear simulators meeting the specifications of IEC 60318 series, ensuring reproducible and comparable test results across different testing laboratories worldwide.
Scope Limitation
IEC 61842 addresses speech communication quality only. It does not cover wireless interface specifications (Bluetooth headsets), active noise cancellation performance, or safety aspects such as acoustic shock protection, which are covered by other relevant standards.
IEC 61842 addresses speech communication quality only. It does not cover wireless interface specifications (Bluetooth headsets), active noise cancellation performance, or safety aspects such as acoustic shock protection, which are covered by other relevant standards.
2. Microphone Performance Requirements
Microphones for speech communication must reproduce the transmitted speech signal with sufficient fidelity and level to ensure intelligibility at the receiving end. The standard specifies performance parameters including sensitivity, frequency response, distortion, and ambient noise rejection characteristics.
| Parameter | Requirement | Test Condition | Measurement Method |
|---|---|---|---|
| Sensitivity (transmit) | -47 to -30 dB V/Pa | 1 kHz, 1 Pa acoustic input | Artificial mouth per IEC 60318-4 |
| Frequency response range | 100-8000 Hz minimum | Constant volume velocity input | Artificial mouth, free-field corrected |
| Response flatness | ±3 dB over 300-3400 Hz (narrowband) ±5 dB over 100-8000 Hz (wideband) |
Reference at 1 kHz | Comparison to reference microphone |
| Total harmonic distortion | < 3 % at 1 kHz, 0.2 Pa input | Fundamental at 1 kHz, 0.2 Pa SPL | Notch filter or FFT analysis |
| Ambient noise rejection | ≥ 15 dB (directional types) | Diffuse field at 70 dB SPL | Comparison of on-axis vs. diffuse response |
| Output noise level | < -60 dBV (A-weighted) | Quiet room, 20 °C, rated supply | Precision sound level meter |
2.1 Frequency Response Shaping for Speech
The standard recognizes that microphone frequency response for speech communication should be optimized for speech intelligibility rather than flat response. For narrowband (telephone-band) systems, the response is specified over 300-3400 Hz, with a rising characteristic above 1 kHz to compensate for the typical speech spectrum roll-off and improve consonant intelligibility. For wideband systems, the response extends from 100 Hz to 8000 Hz, providing improved naturalness and fricative consonant distinction. The standard specifies preferred frequency response masks (templates) that define the allowable variation in response, ensuring consistent speech quality across different manufacturers’ products while allowing design flexibility in how the response shape is achieved. Microphone response below 100 Hz should be attenuated to reduce low-frequency ambient noise pickup, while response above 8 kHz contributes little to conventional speech intelligibility and may cause aliasing in digital communication systems.
2.2 Microphone Types and Positioning
The standard addresses different microphone types used in communication applications. Carbon microphones, historically used in telephone handsets, are covered but with acknowledgment of their higher distortion and limited frequency range compared to modern technologies. Electret condenser microphones are the primary focus, with their good sensitivity, wide frequency range, and small size making them ideal for most communication applications. MEMS microphones, emerging at the time of the standard, are covered by extension. For headsets, the mouth reference point (MRP) is defined at 25 mm from the lips, and the microphone positioning tolerance is specified at ±5 mm from the MRP to ensure consistent sensitivity. Noise-canceling microphones using differential (pressure-gradient) designs must achieve minimum front-to-rear discrimination of 15 dB at 1 kHz.
Engineering Best Practice
For maximum speech intelligibility in high-noise environments, select a noise-canceling microphone with a close-talking response that emphasizes the 2-4 kHz range by 3-6 dB relative to the 1 kHz reference. This pre-emphasis compensates for the masking effect of background noise on fricative consonants (s, sh, f, th) which carry most of the intelligibility information.
For maximum speech intelligibility in high-noise environments, select a noise-canceling microphone with a close-talking response that emphasizes the 2-4 kHz range by 3-6 dB relative to the 1 kHz reference. This pre-emphasis compensates for the masking effect of background noise on fricative consonants (s, sh, f, th) which carry most of the intelligibility information.
3. Earphone Performance Requirements
Earphones for speech communication must deliver received speech signals at adequate level with sufficient clarity. The standard defines earphone performance parameters measured using artificial ears and ear simulators specified in IEC 60318.
| Parameter | Requirement | Test Condition | Measurement Method |
|---|---|---|---|
| Sensitivity (receive) | 100-125 dB SPL at 1 Vrms input | 1 kHz, 1 Vrms drive | Artificial ear per IEC 60318-1 or -2 |
| Frequency response range | 100-8000 Hz minimum | Constant voltage drive | Artificial ear, comparison method |
| Acoustic output capability | ≥ 120 dB SPL peak | 1 kHz, maximum rated input | Artificial ear with peak hold measurement |
| Distortion | < 3 % THD at 110 dB SPL | 1 kHz, output at 110 dB SPL | FFT analysis via artificial ear |
| Leakage tolerance | < 6 dB variation with standard leakage | 2 mm diameter vent in coupler | Response with defined acoustic leak |
| Electrical impedance | 32, 150, or 600 Ω nominal | 1 kHz, 0.1 Vrms | Impedance bridge or VI measurement |
3.1 Ear Coupling and Acoustic Leakage
The standard addresses three ear coupling methods: supra-aural (on-ear) where the earphone rests against the pinna, circumaural (around-ear) where the earphone encloses the ear, and insert (in-ear) where the earphone is placed in the ear canal. Each coupling method has different acoustic characteristics that affect the frequency response at the eardrum. The standard defines acoustic leakage conditions for testing — representing real-world use where earphones are not perfectly sealed against the ear. A standard leakage of a 2 mm diameter hole or a defined slit leak is specified for test purposes. Earphone designs should minimize response variation with leakage, particularly at low frequencies where the response is most affected by leakage. Circumaural designs with soft foam-filled cushions generally provide the most consistent acoustic coupling across different users and use conditions.
3.2 Acoustic Safety Considerations
Although not a safety standard, IEC 61842 includes acoustic output limitations to protect users from hearing damage. The maximum acoustic output shall not exceed 120 dB SPL peak under any operating condition, including fault conditions. The standard references the acoustic shock protection requirements for headsets used in telecommunication systems. For headsets intended for continuous professional use (call centers, dispatch operators), the standard recommends limiting long-term exposure to time-averaged levels below 85 dB(A) over an 8-hour period, consistent with occupational noise exposure limits. Manufacturers are required to provide clear marking of the maximum output capability and any level-limiting features incorporated in the design.
Critical Design Consideration
Earphone frequency response compensation across different users is a significant challenge. The acoustic impedance at the eardrum varies between individuals by up to ±10 dB at frequencies above 3 kHz. Communication earphones should be designed with sufficient headroom (at least 6 dB) in the 3-6 kHz range to account for individual anatomical variations, ensuring that all users receive adequate high-frequency information for speech intelligibility.
Earphone frequency response compensation across different users is a significant challenge. The acoustic impedance at the eardrum varies between individuals by up to ±10 dB at frequencies above 3 kHz. Communication earphones should be designed with sufficient headroom (at least 6 dB) in the 3-6 kHz range to account for individual anatomical variations, ensuring that all users receive adequate high-frequency information for speech intelligibility.
4. Frequently Asked Questions
Q1: How does IEC 61842 relate to ITU-T P.57 and other telephony standards?
IEC 61842 complements the ITU-T P-series recommendations for telephone transmission quality. ITU-T P.57 specifies artificial ears, P.58 specifies head and torso simulators, and P.79 specifies the calculation of loudness ratings. IEC 61842 references these ITU standards for measurement methods while providing the specific performance requirements for the transducers themselves.
Q2: What is the difference between narrowband and wideband speech?
Narrowband speech (300-3400 Hz) is the traditional telephone-band audio used in PSTN and legacy cellular systems, providing adequate intelligibility but limited naturalness. Wideband speech (100-8000 Hz) extends the frequency range at both ends, improving the distinction of fricative consonants (s, f) through extended high frequencies and adding fullness and naturalness through extended low frequencies. Wideband is used in modern VoIP, HD Voice, and UC platforms.
Q3: Are the IEC 61842 test methods applicable to wireless Bluetooth headsets?
The electroacoustic test methods (frequency response, sensitivity, distortion) are applicable to the transducer portion of wireless headsets. However, testing wireless headsets requires additional considerations for the Bluetooth codec (SBC, AAC, aptX) used, which affects the end-to-end frequency response particularly at high frequencies. The standard does not specify wireless link test methods — these are covered by Bluetooth SIG specifications.
Q4: How is the speech intelligibility of a headset system evaluated?
While IEC 61842 specifies transducer-level measurements, overall system intelligibility is evaluated using the Speech Intelligibility Index or the Articulation Index, calculated from the combined transmit and receive frequency responses, noise levels, and distortion characteristics. For complete system evaluation, subjective listening tests using standardized word lists or the ITU-T P.800 conversational opinion tests provide the most direct intelligibility assessment.
