Ear Cup Selection for Feedforward Active Noise Reduction Hearing Protectors

Details

• Personal Author:
  Bernstein ER ; Brammer, A. J. ; Cherniack, Martin G. ; Peterson, D. R. ; Yu G
• Description:
  Performance of an active noise reduction (ANR) hearing protector device (HPD) is significantly affected by the mechanical design of the ear cup. Two characteristics are of critical importance when evaluating a passive HPD design for potential modification into an active feedforward HPD: passive noise reduction and predicted active noise reduction with active control. Several commercially available passive HPDs have been evaluated using these metrics in order to select the ear cup that would offer the best performance with a feedforward ANR system. Passive performance of the ear cup serves to augment the electronic control system in an active HPD. A well designed ear cup will compensate for the decreased attenuation provided by the active system at high frequencies as well as provide the maximum possible passive attenuation to improve the total attenuation of the complete system. Shaw and Thiessen (1965) detailed two important features that are necessary to maximize passive attenuation: the cushion must provide a high resistance to air leakage, and the volume underneath the ear cup should be as large as possible. Active noise reduction systems improve the performance of an active HPD by attenuating low frequency noises whose wavelength approaches or exceeds the size of the ear cup. Simple estimation of the active noise reduction (ANR(oe)) possible with an optimal feedforward controller can be determined from the coherence function (yre2(oe)) between a reference microphone placed outside the ear cup and an error microphone at the desired point of cancellation inside the ear cup (Nelson and Elliot, 1992), ANR(oe)=1-yre2(oe). This method of estimation of active control system performance is ideal for ear cup selection because it does not require the presence of a secondary source loudspeaker or electronic controller, only the reference and error microphones located where they would ideally be positioned in a final device. Caution should be exercised when using this equation in practice due to assumptions regarding the disturbance and the controller. First, this equation assumes a stationary disturbance, and thus controller performance could be better than predicted when using an adaptive controller with non-stationary signals. Second, the equation does not require the optimal controller to be causal and therefore may not be physically realizable. For a description of performance prediction with a causally constrained controller, see Elliott (2001). Description provided by NIOSH
• Subjects:
  • Communication
  • Ear
  • Hearing
  • Noise
  • Noise, Occupational
  • Occupational Health
  • Protective Clothing
  • Safety
  • Sense Organs
• Keywords:
  • Communication research
  • Noise control
  • Noise protection
  • Hearing protection
  • Equipment design
  • Ear protection
  • Mathematical models
• ISSN:
  0711-6659
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Journal Article
• Place as Subject:
  Connecticut ; OSHA Region 1
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  82-83
• Volume:
  38
• Issue:
  3
• NIOSHTIC Number:
  nn:20058843
• Citation:
  Can Acoust 2010 Sep; 38(3):82-83
• Federal Fiscal Year:
  2010
• NORA Priority Area:
  Construction ; Manufacturing
• Performing Organization:
  University of Connecticut School of Medicine and Denistry, Farmington, Connecticut
• Peer Reviewed:
  False
• Start Date:
  20060801
• Source Full Name:
  Canadian Acoustics
• End Date:
  20120731
• Download URL:
  https://stacks.cdc.gov/view/cdc/223228/cdc_223228_DS1.pdf
• File Type:
  [PDF - 186.61 KB]
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:7f0536a146b40334f52efafc9b730eb32130dc96bcbde24c0f618e934eaeec72f89a64dd391276d0b6eda415dae0060d8f217fa0277d30ff5ca1bdcaae5056ca