IEC 61265:2018 pdf download

IEC 61265:2018 pdf download.Electroacoustics – Instruments for measurement of aircraft noise – Performance requirements for systems to measure sound pressure levels in noise certification of aircraft
1 Scope
This document specifies requirements for the electroacoustical performance of systems of instruments used to measure sound for the purposes of aircraft noise certification, and for other comparisons among aircraft models, and provides methods by which tests can be made periodically to verify that the performance continues to conform to the requirements within stated limits. In general, a sound measurement system for this purpose comprises a combination of instruments extending from a microphone, including its windscreen and other accessories, through data recording and processing devices to a suitable output. Different measurement systems, regardless of their composition, perform the necessary functions in different ways and operate on either analogue or digital principles.
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply. ISO and IEC maintain terminological databases for use in standardization at the following addresses: • IEC Electropedia: available at http://www.electropedia.org/ • ISO Online browsing platform: available at http://www.iso.org/obp 3.1 calibration record time-pressure history or recorded value obtained during a calibration procedure, consisting of a measurement system output while its acoustic input is provided by a sound calibrator 3.2 effective perceived noise level EPNL EPNdB single number evaluator of the subjective effects of aircraft noise on human beings, expressed in decibels (EPNdB) as described in ICAO Annex 1 6, Appendix I Note 1 to entry: This note applies to the French language only. 3.3 floating-range measurement system measurement system incorporating automatic level range switching 3.4 free-field microphone microphone having substantially uniform frequency response to plane progressive sound waves arriving at angles substantially normal to the plane of the microphone diaphragm 3.5 free-field sensitivity <microphone system> quotient of the root-mean-square voltage at the output of a microphone system by the root-mean-square sound pressure that would exist at the position of the microphone in the absence of the microphone, for a sinusoidal plane progressive sound wave of specified frequency, at a specified sound-incidence angle Note 1 to entry: The free-field sensitivity is expressed in volts per pascal. 3.6 free-field sensitivity level <microphone system> twenty times the logarithm to the base ten of the ratio of the free-field sensitivity to the reference sensitivity of one volt per pascal Note 1 to entry: The free-field sensitivity level is expressed in decibels. Note 2 to entry: The free-field sensitivity level can be determined by subtracting the sound pressure level (re 20 μPa expressed in dB) of the sound incident on the microphone from the voltage level (re 1 V expressed in dB) at the output of the microphone system, and adding 93,98 dB to the result. 3.7 grazing incidence condition where sound from the source of interest impinges on the microphone primarily at an incidence angle parallel to the plane of the microphone diaphragm 3.8 L ASmax maximum value obtained during a given time period or event of A-frequency-weighted, S-time- weighted sound pressure level3.1 0 level difference measured one-third-octave band output signal level on any level range, adjusted for the difference between the settings of the level range controls on the level range and the reference level range, minus the level of the corresponding electrical input signal Note 1 to entry: The level difference is expressed in decibels. 3.1 1 level non-linearity level difference on any level range, at a selected one-third-octave mid-band frequency, minus the reference level difference, all input and output signals being relative to the same reference quantity Note 1 to entry: The level non-linearity is expressed in decibels. 3.1 2 level range setting of the controls provided in a measurement system for the recording and level measurement or spectral analysis of a sound pressure input signal Note 1 to entry: The level range is expressed in decibels.