BS EN ISO 11904-1:2002 pdf – 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).
1 Scope This part of ISO 11904 specifies basic framework measurement methods for sound immission from sound sources placed close to the ear. These measurements are carried out with miniature or probe microphones inserted in the ear canals of human subjects. The measured values are subsequently converted into corresponding free-field or diffuse-field levels. The results are given as free-field related or diffuse-field related equivalent continuous A-weighted sound pressure levels. The technique is denoted the microphone-in-real-ear technique (MIRE technique). This part of ISO 11904 is applicable to exposure from sources close to the ear, for example during equipment tests or at the workplace by earphones or hearing protectors with audio communication facilities. This part of ISO 11904 is applicable in the frequency range from 20 Hz to 16 000 Hz. 2 Normative references The following normative documents contain provisions which, through reference in this text, constitute provisions of this part of ISO 11904. For dated references, subsequent amendments to, or revisions of, any of these publications do not apply. However, parties to agreements based on this part of ISO 11904 are encouraged to investigate the possibility of applying the most recent editions of the normative documents indicated below. For undated references, the latest edition of the normative document referred to applies. Members of ISO and IEC maintain registers of currently valid International Standards. ISO 8253-2:1992, Acoustics — Audiometric test methods — Part 2: Sound field audiometry with pure tone and narrow-band test signals IEC 60065, Audio, video and similar electronic apparatus — Safety requirements IEC 60268-7:1996, Sound system equipment — Part 7: Headphones and earphones IEC 60601-1, Medical electrical equipment — Part 1: General requirements for safety IEC 60942, Electroacoustics — Sound calibrators IEC 61094-1, Measurement microphones — Part 1: Specifications for laboratory standard microphones
4 Measurement principle Miniature microphones or probe microphones are placed to measure the sound pressure at a position in the ear canal, denoted as the ear canal measurement position. The subject is exposed to the sound source(s) in question, and the ear canal equivalent continuous sound pressure level is measured in one-third-octave frequency bands, L ear,exp,f . Each of the one-third-octave band levels is adjusted with the free-field or diffuse-field frequency response, ∆L FF,H,f or ∆L DF,H,f , to obtain corresponding free-field related or diffuse-field related one-third-octave band sound pressure levels. These one-third-octave band levels are adjusted using A-weighting constants, and subsequently combined to obtain the free-field related or diffuse-field related equivalent continuous A-weighted sound pressure level, L FF,H,Aeq or L DF,H,Aeq . The measurements may be carried out for one or both ears as appropriate. The free-field or diffuse-field frequency response is taken from clause 9, or determined for each individual subject and ear as described in clause 10. NOTE The accuracy of the final result depends on a number of parameters (e.g. ear canal measurement position, number of subjects, and whether clause 9 or 10 is used). 5 Instrumentation 5.1 Ear canal microphone The sound pressure in the ear canal shall be measured by a microphone, which is either a miniature microphone placed in the ear canal, or a probe microphone consisting of a microphone placed outside the ear and equipped with a probe tube placed in the ear canal; to prevent damage to the ear drum and the skin of the ear canal, the tube shall be made of a soft material.
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.