1. Wind noise in hearing aids
Harvey Dillon, Richard Katsch, Inge Roe,
National Acoustic Laboratories,
Australian Hearing,
With the support of GN Resound, Oticon, Phonak, & Widex

2. But why, and how, and how bad is the problem?
Wind + hearing aid = noise
But why, and how, and how bad is the problem?

3. Turbulence
f = US/L (Hz) L U
S = Strouhal number

4. Spectrum of noise behind wire

5. Laser Doppler Velocimeter

6. Velocity down the wind tunnel (CIC aid)

7. Velocity out of head (CIC aid)

8. Velocity upwards (CIC aid)

9. Turbulent velocity (CIC aid)

10. Turbulent velocity (ITE aid)

11. Turbulent velocity (BTE aid)

12. Effect on turbulence of distance from head

13. Solution 1: Extend the microphones

14. Wind velocity inside and outside the concha

15. Turbulence in the concha
Tragus

16. Sensitivity of ITC
Tragus

17. Smoothness of ITE
Tragus

18. Noise measurements: Specially designed wind-tunnel.

19. Noise measurements: Outlet of Wind Tunnel

20. Noise measurements: Outlet of Wind Tunnelz x y

21. Wind velocity 5 m/sec 18 km/hr 11 m.p.h.
Level 3 on 13 point Beaufort Scale
Flags unfurl but droop
Scattered whitecaps
Gentle Breeze
Exceeded 6% of time

22. Noise at BTE position

23. Aid comparison at 0 degrees

24. Aid comparison at 90 degrees

25. Aid comparison at -90 degrees

26. KEMAR at 0 degrees to wind

27. Aid comparison at 30 degrees

28. Aid comparison at 30 degrees

29. Solution 2:

30. Solution 2: Remove the pinnae

31. Solution 2: Remove the pinnae

32. ITE noise versus azimuth

33. KEMAR at -50 degrees to wind

34. Aid comparison at -50 degrees

35. Aid comparison at -50 degrees

36. Solution 3: Shed the vortices gracefully

37. ITE noise versus azimuth

38. KEMAR at -90 degrees to wind

39. Solution 4: Keep the aid towards the wind

40. ITE noise re CIC noise dB

41. ITE minus CIC

42. Factors affecting wind noise
Levels are very intense
Obstacles (head, pinna, tragus) act as:
Wind guards
Turbulence source
Turbulence shredder
Large obstacles create low-freq turbulence
head
Medium obstacles create mid-freq turbulence
pinna
Small obstacles create high-freq turbulence
tragus, inlet port

43. Other observations As wind speed increases:
noise levels increase
frequency spectrum extends upward
Two microphone ports produce:
correlated noise if a common source (e.g. head or pinna)
uncorrelated noise if separate sources (e.g. inlet port)

44. Potential solutions Wear one aid and orient the head Wear a scarf
Don’t fit a BTE
Don’t fit a fixed directional microphone
Low distortion input circuitry
up to at least 110 dB SPL
Low-cut filtering
especially over the vent-transmitted range
Smooth design
Electronic signal processing from multiple microphones

45. That’s all Folks

46. For a copy of this talk, send an Email to: