ISO 11904-1-2002 pdf free download.Acoustics — Determination of sound immission from sound sources placed close to the ear — Part 1: Technique using a microphone in a real ear (MIRE technique).
The pressure response of the miniature or the probe microphone shall be without pronounced resonances, and it shall be known except for the situation described in 10.9. The response shall be checked by comparison with a calibrated pressure-type microphone which is in accordance with IEC 61094-1. In the area of the concha, the microphone (including supporting elements and electrical leads) shall occupy an area not exceeding 10 mm 2 in any plane.
5.2 Reference field microphone When individual free-field or diffuse-field frequency responses (∆L FF,H or ∆L DF,H ) are determined as described in clause 10, a reference field microphone is used to determine the sound pressure level in the reference sound field with the subject absent. This microphone and the connected equipment used shall fulfil the requirements of IEC 61672-1 for a class 1 instrument, and shall have a known free-field or diffuse-field frequency response.
5.3 Check of calibration The calibration of the microphones and the measuring equipment shall be suitably checked. For the reference field microphone, this shall be done using an acoustic calibrator complying with the requirements for class 1 of IEC 60942.
5.4 Filters Signals shall be analysed with one-third-octave band filters complying with the requirements for class 1 of IEC 61260. 6 Subjects Only persons free from inflammation and any other disease of the outer ear and the middle ear are suitable subjects. For measurements in the open ear canal, only persons whose ear canals are not too narrow, flat or severely bent, and who reveal no eardrum defects shall be chosen. If cerumen obstructs the ear canals, it shall be removed. All such required actions shall be carried out by a qualified person.
7 Use of ear canal microphone
7.1 Choice of ear canal measurement position The ear canal measurement point shall be between the entrance to the canal and the eardrum, or, in the case of a blocked ear canal, between the entrance and the blockage, in either case preferably close to the centre axis of the canal. If data from Table 1 are to be used for the free-field or diffuse-field frequency response, only three selected ear canal measurement positions are possible, as stated in clause 9. For each single subject the ear canal measurement position may be chosen independent of the choice for other subjects. NOTE For earphones and headphones which occupy the majority of the volume immediately outside the ear canal entrance, the choice of a blocked or partly blocked ear canal can reduce the accuracy if the sound under test has significant narrow band components above approximately 3 kHz.
Due to the risk of damaging the eardrum, ear canal measurement position close to the eardrum should only be used by qualified persons and only when using a probe microphone with a soft plastic probe.
Examples of convenient ear canal measurement positions are illustrated in Figure 1.ISO 11904-1 pdf download.