DD ISO/TS 4869-5:2006

Foreword
Introduction
1 Scope
2 Normative references
3 Terms and definitions
4 Measurement of the noise reduction of hearing protectors
  4.1 Test signals
  4.2 Test site
      4.2.1 Conditions to be met for the test to be valid
      4.2.2 Reverberation time
      4.2.3 Background noise
  4.3 Test equipment
5 Test subjects
  5.1 Conditions for subject acceptance/dismissal
      5.1.1 General
      5.1.2 Age and sex
      5.1.3 Previous experience with hearing protectors
      5.1.4 Anatomical features
      5.1.5 Maximum hearing threshold levels
      5.1.6 Minimum hearing threshold levels
      5.1.7 Literacy
      5.1.8 Threshold variability
  5.2 Number of subjects
  5.3 Otoscopic inspection
  5.4 Spectacles and jewellery
  5.5 Maximum number of tests per subject
  5.6 Exceptions
6 Product samples
  6.1 General
  6.2 Custom-moulded ear-plugs
  6.3 Special requirements for product instruction
  6.4 Variable position headbands
  6.5 Variable band force
7 Test procedure
  7.1 Number of open-ear and occluded-ear threshold measurements
  7.2 Information to subjects
  7.3 Prior to entering the test room
  7.4 Inside the test room
      7.4.1 Positioning the subject
      7.4.2 Quiet period prior to first threshold determination
      7.4.3 Fitting the hearing protector for test
      7.4.4 Re-determination of thresholds
8 Computation of noise reduction values
  8.1 General
  8.2 Calculation of the individual noise reductions
  8.3 Calculation of group noise reduction
  8.4 Uncertainty of the noise reduction data
9 Reporting of data
Annex A (informative) Uncertainty of hearing protector noise
                      reduction measurements
Bibliography

Specifies a method for measuring noise reduction of passive hearing protectors at the threshold of hearing.

This Technical Specification specifies a method for measuring noise reduction of passive hearing protectors at the threshold of hearing. The method is designed to provide estimates of the noise reduction obtained by typical groups of users in real-world occupational settings, who may lack the training and motivation to wear hearing protectors in an optimum manner.

The principle of the test method is to measure the difference in hearing threshold with and without wearing a hearing protector. This difference between the thresholds constitutes the noise reduction. The measurement is done twice on a given number of test subjects.

NOTE 1 The principle of measuring the influence of a hearing protector on the hearing threshold is used in ISO 4869-1 and in this Technical Specification. The method described in ISO 4869-1 yields the sound attenuation of the hearing protector under test. The result of the measurement is a pure physical characteristic of the hearing protector. The method described in this Technical Specification yields the performance of the system as a whole, i.e. the influence of hearing protector, test subjects, fitting and instruction.

This test method yields data that are collected at low sound pressure levels (close to the threshold of hearing), but which are also representative of the noise reduction values of hearing protectors at higher sound pressure levels. This Technical Specification is inapplicable for level-dependent hearing protectors for sound pressure levels above the point at which their level-dependent characteristics become effective.

NOTE 2 At frequencies below 500 Hz, real-ear noise reduction data measured according to this Technical Specification may be spuriously high by a few decibels, with the error increasing as the frequency decreases. The error results from masking of the occluded-ear threshold by physiological noise during testing.