This part of ISO 8253 specifies relevant test signal characteristics, requirements for free, diffuse, andquasi-free sound fields, and procedures for sound field audiometry using pure tones, frequency-modulated tones or other narrow-band test signals presented by means of one or more loudspeakers. The primary purpose is the determination of hearing threshold levels in the frequency range 125 Hz to 8 000 Hz, but this range can be extended to 20 Hz to 16 000 Hz.This part of ISO 8253 does not include specifications for the use of hand-held loudspeakers. Speech as a test signal is not covered.The purpose of this part of ISO 8253 is to ensure that tests of hearin