Electrical audio signal processing systems and devices – Hearing protectors – electrical
Reexamination Certificate
2000-12-22
2004-10-05
Ramakrishnaiah, Melur (Department: 2643)
Electrical audio signal processing systems and devices
Hearing protectors, electrical
C381S094100, C381S094300
Reexamination Certificate
active
06801629
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to protective hearing devices and, more particularly, to protective hearing devices with active sound attenuation and control.
2. Background
Environmental sounds typically comprise a mixture of various sound wave frequencies having varying intensities. It is well documented that repeated or prolonged exposure to sound waves of certain frequencies and intensities can damage the auditory organ and cause serious hearing problems, including deafness. Injurious noises, such as those caused by explosions or bursts, are often comprised of a mixture of sound wave frequencies of varying intensity. These dangerous sound waves are in both the high and low frequency bands and have an intensity sufficient to cause hearing damage. Individuals who are frequently exposed to sound waves at dangerous frequencies and/or intensities run the risk of incurring permanent injuries, such as hearing loss or even deafness. Such individuals include workers at demolition or construction sites, operators of heavy, noisy equipment and those in active military service. These individuals need hearing protection to prevent losses in hearing acuity and/or gradual increases in hearing thresholds resulting from extended exposures to loud noises.
Passive sound attenuation devices which specifically address this problem are well known. These include conventional earplugs, earmuffs and the like, which function to reduce the negative effects of exposure to dangerous sound frequencies and intensities by limiting the entry of all sound waves into the auditory organ. These conventional devices suffer from a significant disadvantage, however; namely, that auditory access to environmental sounds of relatively risk free frequencies and intensities is also limited. In particular, these devices typically provide much greater attenuation at high frequencies than at low frequencies, as well as excessive attenuation at high frequencies. The result is that wearers of these devices who want or need to hear non-dangerous sounds are prevented from doing so. Therefore, while these devices may be protective against the effects of overexposure to sound having dangerous frequencies and intensities, they create a new danger in that they shut out all environmental sounds, including non-dangerous speech and warning sounds.
Active noise cancellation has been another approach to noise reduction. Active noise cancellation systems eliminate unwanted sound using destructive interference. Cancellation is achieved by propagating “anti-noise,” identical to the unwanted sound waves, but inverted. The anti-noise waves interact with the unwanted noise wave resulting in cancellation. A feedback active cancellation headset typically includes a sound generator in each earpiece for producing anti-noise, and a residual microphone, also located in each earpiece, to provide feedback signals to a controller that generates the anti-noise signals. Each microphone detects the unwanted noise within each earpiece and provides corresponding signals to the controller. The controller supplies anti-noise signals to the sound generator corresponding to the noise detected in the earpieces, but inverted, with respect to the unwanted waveform. When the anti-noise interacts with the noise within each earpiece, destructive interference between the noise and the anti-noise cancels the unwanted sound.
For example, U.S. Pat. No. 5,600,729 to Darlington et al. discloses a device comprising a microphone located upstream of a loudspeaker relative to the approaching direction of unwanted noise waves, in an assembly adapted to be mounted at a site of entry of the noise into the ear chamber. The output of the microphone is amplified and fed to the downstream loudspeaker to produce noise that tends to cancel the unwanted intrusive noise. The device is attached by means of a headband.
U.S. Pat. No. 3,890,474 to Glicksberg discusses the incorporation of sound amplitude limiting into a device that is self-contained in the ear canal of the wearer. The sound amplitude limiter is designed so that most un-transduced sound is blocked out from reaching the middle ear by a highly effective sound absorbing material which is located within the ear piece. The earpiece has a thin-walled outer casing sized to provide an airtight fit inside the ear canal. Proper fit is achieved either by custom shaping each device for a particular wearer, or by providing an array of various shaped devices for a wearer to choose from.
U.S. Pat. No. 5,355,418 to Kelsey et al. discusses a frequency selective hearing protection device. When worn in the manner shown, this device performs a natural sound blocking function. It utilizes adaptive filtering to hinder the transmission of frequency components in ambient sound above a predetermined threshold. The device is encompassed in an ear unit fitting in the concha (outer ear) and having a plug portion partially inserted into the ear canal. The device must be appropriately sized for each wearer.
U.S. Pat. No. 5,305,387 to Sapiejewski discusses an earphone for use in an active noise reduction system. This earphone includes a shell accommodating a microphone closely adjacent to a driver shaped and sized to fit in the concha of an ear. A cushion is made of silicon gel covered by polyurethane film and is custom shaped for each wearer to provide comfort and a seal without moving the microphone away from the ear canal.
Embodiments are described in certain of the above references that employ earmuffs. However, the bulky size of earmuffs renders them inappropriate for many applications. For instance, earmuffs must seal the entire ear. Thick or long hairstyles can compromise the seal. Earmuffs can also interfere with the use of safety glasses or prescription glasses, protective gear, shields, gas masks, helmets, and cold weather clothing. Therefore, active noise reduction systems that mount within the wearer's ear are often preferable to earmuffs. However, inserting an audio device inside the ear canal raises safety and comfort issues analogous to those addressed by hearing aid designers. In that regard U.S. patent application Ser. No. 09/161,344, which is fully incorporated herein by reference, discloses a hearing device having a soft conformal tip that can be securely seated within the deep bony region of the ear canal, without causing appreciable pain or discomfort to the wearer.
Though active noise reduction systems mounted in the ear canal typically perform better than, for instance, systems mounted in earmuffs, a disadvantage of mounting such systems within the wearers ear is that conventional devices must each be custom fit to the individual wearer, increasing system cost.
For instance, U.S. Pat. No. 5,740,258 to Goodwin-Johansson discusses an active noise suppressor that fits in an ear canal without blocking the ear canal. The acoustically unobstructed passage allows the active reduction of undesired noise portions, while allowing the desired portions of the sound pressure waves to reach the eardrum. An integral housing is disclosed for securing the device inside the ear canal. The housing consists of elastic ribs attached to the circuit board, the ribs lodging the device in the ear canal.
U.S. Pat. No. 4,985,925 to Langberg et al. discloses an electronic earplug seated in the concha fossa (outer ear), which combines active and passive noise reduction in the quiet zone at the ear. The electronic earplug maintains an acoustical seal with a concha fossa and/or the external auditory meatus (ear canal). Noise that penetrates this passive barrier and reaches the quiet zone formed around the occluded ear canal volume adjacent the eardrum is further reduced by active means. However, neither Langberg et al. or Goodwin-Johansson address the problems of using “universal fit” devices for an in-the-ear-canal, active noise reduction system.
In particular, existing active noise reduction technology has several disadvantages. For instance, all the active noise reduction systems described above e
Brimhall Owen D.
Collotzi Craig M.
Koskowich Gregory N.
Ramakrishnaiah Melur
Ritchie David B.
Sonic Innovations, Inc.
Thelen Reid & Priest LLP
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