BS EN 62585-2012 pdf download.Electroacoustics Methods to determine corrections to obtain the free-field response of a sound level meter.
Clauses 9 to 14 give further information on determination of various corrections that may be required in order for a periodic test of a Sound level meter to be performed according to IEC 61672-3, or during testing to IEC 61672-2 to verify the data provided in the instruction manual, or by a manufacturer during the design process. Wherever possible the data for these corrections shall be provided separately.
NOTE If the conhlguraton of the sound level meter includes use of extension cables this can result in a different value for the correction to that obtained when the microphone is directly mounted on the sound level meter case
Care should be taken to ensure that ambient noise does not affect the measurement results, and this should be considered in the evaluation of the uncertainty components,
7 Submission and Inspection
In general for all the test methods described, as applicable, at least three sound calibrators of the same model, one electrostatic actuator, one comparison coupler. three microphones of the same model and one sound level meter shall be submitted, allowing for various combinations to be tested. If the typical frequency response of a microphone is to be measured, at least five microphones shall be submitted. Appropriate instruction manuals applicable to the model and version of the sound level meter. the sound calibrator, comparison coupler and electrostatic actuator shall be supplied.
At least three samples of all relevant accessories, such as adaptors for the sound calibrator. and at least five samples of windscreen as appropriate, shall also be supplied.
If possible the five samples of windscreen should be taken from different production batches.
Prior to any measurements the sound level meter, sound calibrators, comparison couplers and electrostatic actuators, as appropriate, shall be visually inspected for any damage. and all appropriate controls shall be operated to ensure that they are in working order. It shall also be ensured that any power supplies are functioning within the specified operating limits.
8 Determination of the adjustment value at the calibration check frequency
According to IEC 61672-1 at least one model of sound calibrator, conforming to the requirements of IEC 60942, shall be specified in the instruction manual of the sound level meter for checking and maintaining the required indication on the display of the sound level meter at the calibration check frequency. Annex A of this International Standard gives the method for obtaining a suitable adjustment value at the calibration check frequency when adjusting the sensitivity of the sound level meter by application of the recommended sound calibrator.
The expanded uncertainty of measurement for the corrections for the typical effects of reflections from the case of the sound level meter and diffraction of sound around the microphone shall not exceed 0.25 dB up to and including 4 kHz, and 0,35 dB at all frequencies above 4 kHz. The manufacturer or testing laboratory shall state the expanded uncertainty of the actual measurements performed, together with the associated coverage factor, in the documentation supplied,
10 Determination of corrections for the deviation of the microphone free-field frequency response from a uniform frequency response
IEC 61672-3 requires the use of corrections for the deviation of the typical microphone free- field response from a uniform frequency response. This shall be interpreted as the deviation of the actual microphone response from a uniform frequency response, unless it is not possible to measure this, in which case the deviation of the typical microphone response shall be used.
Methods of measuring the frequency response are given in IEC 61094 (all parts).
Where a sound calibrator, comparison coupler or electrostatic actuator is used to measure the actual microphone response, corrections shall be available to obtain the microphone free-field response over the required range of frequencies.
Measurements shall be made at octave intervals over the frequency range 63 Hz to 16 kHz for microphones used on class 1 sound level meters, and from 63 Hz to 8 kHz for microphones used on class 2 sound level meters. Exact frequencies shall be used for the measurements and in reporting the results.
NOTE I Exact frequencies are specified n Annex H.
For microphones where the reference direction is not along the principal axis e.g. some microphones used outdoors, the reference direction defines a range of directions. In this case at least four measurements at equally spaced rotational intervals shall be made, and the mean value and the maximum deviation from the mean value shall be calculated and reported for each microphone measured. If the variation in the results obtained is greater than the applicable tolerance limit, the correction shall not be used to demonstrate conformance of the sound level meter to IEC 61672-1.
NOTE 2 This method 5 being used whilst further experience is gained for microphones where the reference direction is not along the principal axis.
Where a typical free-field response is determined by the manufacturer for inclusion in the instruction manual, measurements shall be made on at least five samples of the model of microphone. The mean value shall be calculated at each frequency, and this is considered to be the typical response. The maximum deviation from the mean shall also be specified.BS EN 62585-2012 pdf download.