Electrical audio signal processing systems and devices – Hearing protectors – electrical
Patent
1995-02-15
1997-05-20
Kuntz, Curtis
Electrical audio signal processing systems and devices
Hearing protectors, electrical
381 74, A61F 1106
Patent
active
056319657
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hearing protector.
2. Description of the Prior Art
There are situations in military services, industry, sports involving the use of fire arms, aviation and the like, where persons are exposed to loud sounds at sound pressure levels in excess of those which are known to cause permanent hearing damage. To minimize the degree of heating damage incurred in these situations, hearing protectors in the form of earplugs, earmuffs, or a combination of earplugs and earmuffs can be worn. These hearing protectors can be classified as passive or active, and linear or nonlinear.
LINEAR-PASSIVE HEARING PROTECTORS: Linear protectors of the passive type in the form of earplugs or earmuffs are designed to attenuate incoming sound waves of different intensifies by approximately the same number of decibels before they reach the eardrum--that is, the mount of attenuation is independent of the sound pressure level of the incoming sound wave. The disadvantage of these linear hearing protectors of the passive type is that, although the wearer is protected from loud sounds, his/her ability to hear speech sounds and warning signals at sound pressure levels which normally produce low to medium loudness in the absence of the protector is impaired.
NONLINEAR-PASSIVE HEARING PROTECTOR: A nonlinear protector of the passive type may be in the form of an earplug with a small aperture. The attenuation characteristics of this type of earplugs are level-dependent and therefore nonlinear in that only incoming sound waves at levels greater than, say, 110 dB SPL are attenuated. These nonlinear earplugs therefore provide protection against intense impulse noises such as gunfire which produces peak sound pressure levels in excess of 110 dB SPL, but transmit sounds unattenuated at levels below 110 dB SPL. One disadvantage of these nonlinear earplugs of the passive type is that, at levels greater than 110 dB SPL, they provide less attenuation than the linear earplugs. Another disadvantage is that exposure to unattenuated loud sounds at levels greater than 90 dB SPL is known to cause permanent hearing damage. For a discussion of the attenuation characteristics of these nonlinear-passive hearing protectors, see for example E. A. G. Shaw, "Hearing Protector Design Concepts and Performance Limitations", Personal Hearing Protection in Industry, P. W. Alberti Editor, 1982, Raven Press, N.Y.
NONLINEAR-ACTIVE MUFF: U.S. Pat. No. 4,064,362 (Williams); U.S. Pat. No. 3,952,158 (Kyle et al.); and U.S. Pat. No. 3,394,226 (Andrews) describe non-linear protectors of the active type in the form of an muff, being designed to improve communication. A protector of this type contains, inside an earmuff enclosure, a microphone, an electronic circuit, a small loudspeaker and a battery. The microphone converts the incoming sound wave originating exteriorly of the earmuff enclosure to an electrical signal which is processed by the electronic circuit containing a nonlinear compression amplifier and other signal conditioning circuits. For incoming sound waves at sound pressure levels which normally produce low to medium loudness in the absence of the protector, the amplification characteristic of the compression amplifier is approximately linear with a fixed gain. For incoming sound waves at sound pressure levels which normally produce loud hearing sensations, the amplification characteristic of the compression amplifier is nonlinear in that its gain is inversely related to the sound pressure level of the incoming sound wave. The electrical output signal of the electronic circuit is delivered to the loudspeaker which converts the electrical signal back to sound inside the earmuff at the pinna. The electronic components of the electronic circuit arc chosen so that, for incoming sound waves which normally produce low to medium loudness, the sound pressure level at the pinna produced by the loudspeaker is approximately the same as that produced by the incoming sound wave in the absence of the ea
REFERENCES:
patent: 3952158 (1976-04-01), Kyle et al.
patent: 5002151 (1991-03-01), Oliveira et al.
Chang Joseph S.
Tong Yit C.
Chang Vivian W.
Kuntz Curtis
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