Ear protector attenuation of impulse noise

Abstract

The attenuation provided by seven different circumaural hearing protectors on the newly-standarized aluminum artifical head was measured for parallel and perpendicular sound incidence. The impulse sound source was a 38-caliber handgun shooting blanks, which created a 150-dB re 20 μPa peak sound pressure level with an A-duration of 0.13 ms. The ear protector was 1 m from the gun. The incident noise impulse external to the ear protector was measured with a “1/8-in.” condenser microphone and the resultant noise inside the ear protector was measured with a “1/4-in.” condenser microphone. These two impulse signals were captured in a digital transient storage device from which both a pressure amplitude versus time plot and a magnetic tape recording were made. The tape recording was used to obtain a spectral analysis employing a time-compression real-time analyzer. The attenuation of the peak levels and the energy-density spectrum of the ear protector was found by suitable comparison of the external and internal signals. The energy density results show that most of the energy of the noise inside the ear protectors is at low frequencies.