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Wind noise in hearing aids

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

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Wind noise in hearing aids

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

  3. U L f = US/L (Hz) Turbulence 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. Tragus Turbulence in the concha

  16. Tragus Sensitivity of ITC

  17. Tragus Smoothness of ITE

  18. Noise measurements: Specially designed wind-tunnel.

  19. Noise measurements: Outlet of Wind Tunnel

  20. Noise measurements: Outlet of Wind Tunnel z 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. KEMAR at 0 degrees to wind

  25. Aid comparison at 30 degrees

  26. Aid comparison at 30 degrees

  27. Solution 2:

  28. Solution 2: Remove the pinnae

  29. Solution 2: Remove the pinnae

  30. ITE noise versus azimuth

  31. KEMAR at -50 degrees to wind

  32. Aid comparison at -50 degrees

  33. Aid comparison at -50 degrees

  34. Solution 3: Shed the vortices gracefully

  35. ITE noise versus azimuth

  36. KEMAR at -90 degrees to wind

  37. Solution 4: Keep the aid towards the wind

  38. dB ITE noise re CIC noise

  39. 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

  40. 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)

  41. 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

  42. That’s all Folks

  43. For a copy of this talk, send an Email to: Research@NAL.GOV.AU

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