03.503GPPTransmission planning aspects of the speech service in the GSM Public Land Mobile Network (PLMN) systemTS
B.3.1 Anechoic room
For the repeatability of the tests, the environment for the measurement of the office type handsfree shall be free field (anechoic) down to the lowest frequency of the 1/3 octave band centred on 200 Hz.
Satisfactory free field conditions exist where errors, due to the departure from ideal conditions, do not exceed ± 1 dB, inside a sphere centred on point B (see figure 3 of ITU‑T Recommendation P.34 ), with a 1 m radius, in the absence of the table (see note 3 as a provisional method for controlling these conditions).
The broadband noise level shall not exceed –70 dBPa(A). The octave band noise level shall not exceed the values specified in table A.1.
Table A.1: Noise level
Centre frequency (Hz)
Octave band pressure level (dBPa)
NOTE 1: For TCL tests and echo cancelling characteristics, it could be useful to define a standardized test room. For further study.
NOTE 2: The ambient noise in the test room for the adaptive gain control testing is under study.
NOTE 3: A room including the test arrangement fulfilling the following requirements probably meets the satisfactory conditions. Dimensions of the room: height > 2,2 m ; volume V > 30 m3.
The table should be placed horizontally in the centre of the test room and there should be an inclination of ~ 30° between the table and the ceiling.
The reverberation time T, measured at points B and C, should satisfy the following inequality:
T(s) < 0,0033 V (m3); which is based on a calculation with the radius of 50 centimetres.