IEC 61842 pdf download – Microphones and earphones for speech communications
4.2.9Rated impedance (Q)
Absolute value of the electrical impedance of a microphone or earphone for speechcommunications.
For an earphone with an electrodynamic transducer, it is recommended that the value ischosen so that the lowest value of the modulus of the actual impedance within the ratedfrequency range is not less than 80 % of the chosen value.Alternatively， it may be given asthe value at the reference frequency or the value at the frequency specified by themanufacturer.
4.2.10 Rated capacitance (nF)
The capacitance of an earphone for speech communications at the frequency specified by themanufacturer, or at 120 Hz.if not specified.
4.3Measuring conditions
4.3.1 Environmental interference
The level of disturbances due to environmental noise，reverberation，wind noise，electro-magnetically induced noise,vibration noise and other interference shall be at least 10 dBbelow the measured quantity.
4.3.2Reference sound pressure
The reference sound pressure for a microphone shall be 1 Pa and that for an earphone shallbe 20 uPa.
4.3.3Signal for measurement
A sinusoidal signal shall be used for measurement unless otherwise specified.
Results may also be gained from measurements using noise signals,quasi-random sequencesignals or impulsive signals， lf signals other than sinusoidal signals are used, it ‘is theresponsibility of the test house to show that the results are equivalent or have fewer artefactsthan those obtained with sinusoidal signals.
4.3.4Reference frequency and frequency range
The reference frequency shall be 1 kHz.The frequency range shall be from 150 Hz to 5 kHzunless otherwise specified. The frequency values for measurement at discrete frequencypoints shall be specified by the manufacturer.
4.3.5Apparatus for acoustic measurementThe following apparatus shall be used.
a) Microphone for measurement
A condenser microphone conforming to lEC 61094-1 or IEC 61094-4 shall be used.TypeLS2P or equivalent, or smaller than LS2P,is recommended. A pressure microphonewhose sensitivity was calibrated by using the standard condenser microphone isacceptable.
b)Artificial mouth
The artificial mouth defined by ITU-T Recommendation P.51 shall be used.c)Artificial ear
The artificial ear defined in lEC 60318-1 or lEC 60711 shall be used.Additional componentsshall be used. if necessary.
The type of artificial ear to be used，and conditions relating to shape，dimension or othercharacteristics of the additional components shall be specified by the manufacturer. Inparticular , the following items shall be specified clearly.
1)yPosition of the earcap reference plane,
2y Position of the earcap reference point, and,3) Direction of axis of the microphone part.
The artificial ear specified in IEC 60318-1,or an artificial ear with a construction as shown inFigure 1， is recommended for measurement of the supra-aural earphone，defined in theClause 1 of IEC 60268-7: with minimized leakage，mainly for measurements at less than3.4 kHz.
NOTE 1 The positions of the earcap reference plane and the earcap reference point may be different for adifferent handset, headset or earset to be measured , even if the same artificial ear is used,
NOTE 2 Only the P type microphone is suitable for use in the artificiall ear.
NOTE 3 Recent developments in lTU-Tdescribe the use of head and torso simulator (HATS) for the measurementof communication devices，The relevant Recommendations are ITU-TP.58,ITU-TP.57 and ITU-T P.64. A measurementequipment according to these recommendations can be used alternatively.The chosen test configuration shall bedescribed unambiguously in the test report as well as the exact positioning of the device under test.
4.3.6 Apparatus for electrical measurement
The following instruments shall be used.
a) Automatic frequency response recorder
lnterruption of the signal frequency trace at any instant during the measurement shallaffect the indicated response by less than 1 dB.
b) Sinusoidal signal generator and amplifier
The amplifier associated with the sinusoidal signal generator shall conform to the followingrequirements;
1)The total harmonic distortion of the signal applied to the artificial mouth for radiation of
the output sound pressure of 1 Pa under the calibration condition (see 4.3) shall beless than 0,1 %.
2) Earphone to be measured,or the earphone with the necessary additional resistance,
shall be less than 0.1 %.
3) The output level across the rated pure resistance load of the amplifier shall not differ
by more than 1 dB from the output level across a load of ten times the ratedresistance.
4.3.7cases for unit measurement
The acoustical performance of a microphone or earphone unit is often strongly dependent onthe mechanical and acoustical properties of the housing in which it is to be operated.Therefore,the microphone/earphone unit to be measured shall be installed in a case for unitmeasurement unless otherwise specified. An example of a case for microphone unitmeasurement is shown in Figure 2, and a case for earphone unit measurement in Figure 3.
NOTE The case for unit measurement should be speclfied for measurement with sufficient reproduciblity underconditions similar to actual use. The manufacturer is recommended to specify clearly the following conditionsrelating to the shape, dlmensions or other characteristics which may affect the measuring result:
ay mouthpiece holes or earcap holes.
by front cavity.
]front construction of the case,d) rear construction of the case,and ,e) rear cavity.
IEC 61842 pdf download – Microphones and earphones for speech communications
