R3.6.4 Improved Hearing Assessment in Noisy Environments – Parts 1 & 2 Project Leader: Michael Fisher Principal Re

1. R3.6.4 Improved Hearing Assessment in Noisy Environments – Parts 1 & 2 Project Leader: Michael Fisher Principal Researcher (Part 1): the late Ben Rudzyn creatingsoundvalueTM www.hearingcrc.org

2. Aim • Aim of the project – • Investigate methods of improving audiometric hearing assessment accuracy when background noise is present. • In particular the investigation is focused on evaluating combinations of insert earphones and earmuffs. Bone conduction Noise Insert Earphone Earmuff Cochlear Ear canal

3. Noise Advice on which insert earphone to use Advice on which earmuff to use Advice on the Maximum Permissible Ambient Noise Levels Advice on correction factors for bone conduction measurements SLM • Objective • Objective / Application – • Publish advice on how one can improve audiometric hearing assessment accuracy in noisy environments. • The intended end users of this advice are people performing hearing assessment such as audiologists.

4. Worked performed • Part 1 • Background research • Papers, Patents & Products • Objective testing ofexternal noise attenuation using an acoustic mannequin in a diffuse noise environment for: • Single Protection – Earmuffs or Insert Earphones • Dual Protection – Combinations Earmuffs & Insert Earphones • Effect of insert earphone delivery signal wire / tube • Objective testing (10 subjects) ofexternal noise attenuation using the Microphone in Real Ear (MIRE) technique in a diffuse noise environment for single and dual protection • Part 2 • Subjective testing (24 subjects) of the selected devices in terms of • external noise attenuation using the Real Ear Attenuation at Threshold (REAT) technique in diffuse noise environment for single and dual protection • bone and air conduction thresholds for single and dual protection

5. Part 2 – Subjective testing Subjective assessment of the selected devices (as determined by objective measurement in Part 1) Selected Earmuff SelectedEarphone

6. Part 2 – Subjective testing Subjective testing – Attenuation of background noise 24 subjects tested Testing Noise: 1/3 octave narrow band at audiometric frequencies Narrow band testing noise in a diffuse field Open Ear Insert earphones fitted Attenuation = difference in thresholds with and without devices fitted Insert earphones and earmuffs fitted

7. Part 2 – Subjective testing results Attenuation of background noise for an EAR-3A or ER-3A insert earphone with/without a MSA 766 243 left/RIGHT “High” (yellow) headband earmuff. Limited by bone conduction

8. Part 2 – Subjective testing results Maximum Permissible Ambient Noise Levels – for an EAR-3A or ER-3A insert earphone covered by a MSA 766 243 left/RIGHT “High” (yellow) headband earmuff.

9. Part 2 – Subjective testing results Maximum Permissible Ambient Noise Levels – for an EAR-3A or ER-3A insert earphone covered by a MSA 766 243 left/RIGHT “High” (yellow) headband earmuff.

10. Part 2 – Subjective testing Bone conduction correction factors Bone conduction thresholds will? > reduce when wearing insert earphone and earmuffs Correction of bone conduction thresholds is required … Bone Conductor (Centre of forehead) Bone conduction moves ear canal walls as well as cochlear membranes and middle ear ossicles etc Insert Earphone Earmuff Extra vibration of tympanic membrane resulting from increased sound pressure in the ear canal. This extra sound pressure is due to occlusion of the ear canal by insert earphone and earmuff Ear canal

11. Part 2 – Subjective testing results Correction factors for bone conduction thresholds with EAR 3A or ER 3A insert earphones inserted with/without wearing a MSA 766 243 left/RIGHT “High” (yellow) headband earmuff. NB The above correction factors correct for the effect of the insert earphones and earmuffs and are appropriate if the bone conductor is calibrated for placement on the forehead. If the bone conductor is calibrated for placement on the mastoid then difference between forehead and mastoid presentation also needs to be corrected for in addition to correction for the effect of the insert earphones and earmuffs.

12. Conclusions • Conclusions: • Double protection provides significantly better attenuation than single protection using achievable insertion depths • Leakage due to cable / tube under muff is relatively minor • The commonly used ER-3A insert earphones perform as well if not better than any other insert earphone when used in combination with good earmuffs • Active earmuffs appear to offer little benefit over good passive earmuffs when used in combination with insert earphones. • The combination of the ER-3A insert earphone and a MSA left/RIGHT “High” earmuff enables threshold testing to 0 dB HL in high background noise levels, MPANL’s (minimum one-third octave noise level: Lmax 41 dB SPL) • The change in the bone conduction thresholds due to insert earphones and earmuffs being worn by normal hearers can be compensated for.

13. Summary & Acknowledgements A reminder of what it is all about Noise Advice on which insert earphone to use Advice on which earmuff to use Advice on the Maximum Permissible Ambient Noise Levels SLM Advice on correction factors for bone conduction measurements National Acoustic Laboratories This research was financially supported by the HEARing CRC Ltd established and supported under the Australian Government’s Cooperative Research Centres Program the late Ben Rudzyn