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 www.hearingcrc.or g creating sound value TM

2. 1 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. Noise Cochlear Insert Earphone Earmuff Bone conduction Ear canal

3. creating sound value TM 2 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. Noise Advice on which insert earphone to use Advice on which earmuff to use SLM Advice on the Maximum Permissible Ambient Noise Levels Advice on correction factors for bone conduction measurements

4. creating sound value TM 3 Worked performed Part 1 1.Background research Papers, Patents & Products 2.Objective testing of external noise attenuation using an acoustic mannequin in a diffuse noise environment for: 1.Single Protection – Earmuffs or Insert Earphones 2.Dual Protection – Combinations Earmuffs & Insert Earphones 3.Effect of insert earphone delivery signal wire / tube 3.Objective testing (10 subjects) of external 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 1.external noise attenuation using the Real Ear Attenuation at Threshold (REAT) technique in diffuse noise environment for single and dual protection 2.bone and air conduction thresholds for single and dual protection

5. creating sound value TM 4 Part 2 – Subjective testing Selected Earphone Selected Earmuff Subjective assessment of the selected devices (as determined by objective measurement in Part 1 )

6. creating sound value TM 5 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 Insert earphones and earmuffs fitted Attenuation = difference in thresholds with and without devices fitted

7. creating sound value TM 6 Limited by bone conduction 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.

8. creating sound value TM 7 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. creating sound value TM 8 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. Part 2 – Subjective testing results Mid frequency of one-third octave band Maximum permissible ambient noise levels (MPANL's) L max dB SPL Test tone frequency range Hz125 Hz to 8 kHz250 Hz to 8 kHz500 Hz to 8 kHz 31.57989101 40778798 50748495 63708092 80687889 100647486 125607183 160566380 20054 76 25054 72 31556 71 40058 64 50060 63056 80054 100052 125048 160045 200041 250045 315048 400053 500054 630054 800054 NOTE - Using the values given, the lowest hearing threshold level to be measured is 0 dB, with a maximum uncertainty of + 2 dB due to the ambient noise. If a maximum uncertainty of 5 dB due to ambient noise is permitted, the values may be increased by 8 dB.

10. creating sound value TM 9 Bone conduction correction factors Bone conduction thresholds will? > reduce when wearing insert earphone and earmuffs Correction of bone conduction thresholds is required … Insert Earphone Earmuff Bone conduction moves ear canal walls as well as cochlear membranes and middle ear ossicles etc Ear canal Bone Conductor (Centre of forehead) 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 Part 2 – Subjective testing

11. creating sound value TM 10 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. Part 2 – Subjective testing results Correction factors for bone conduction thresholds (for normal hearers with bone conductor on forehead) dB Test Tone Frequency Hz 2505001000200040008000 Nearest 1 dB22161031 Nearest 5 dB201510500 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. creating sound value TM 11 Conclusions Conclusions: 1.Double protection provides significantly better attenuation than single protection using achievable insertion depths 2.Leakage due to cable / tube under muff is relatively minor 3.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 4.Active earmuffs appear to offer little benefit over good passive earmuffs when used in combination with insert earphones. 5.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: L max 41 dB SPL) 6.The change in the bone conduction thresholds due to insert earphones and earmuffs being worn by normal hearers can be compensated for.

13. creating sound value TM 12 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 Summary & Acknowledgements Noise Advice on which insert earphone to use Advice on which earmuff to use SLM Advice on the Maximum Permissible Ambient Noise Levels A reminder of what it is all about Advice on correction factors for bone conduction measurements