Abstract:
An acoustic conditioning apparatus. The mechanism includes an attenuator to limit excessive noise levels. The attenuator includes a circuit for compressing an output sound pressure level below a desired level, such as 90 dBA over an eight-hour period. The mechanism also includes an amplifier for conditioning ambient sound level in accordance with the normal needs of a hearing impaired person using the conditioning apparatus. Additionally included is a switch in an electrical circuit to enable selection of attenuation of excessive noise levels or normal amplification. The switch can be controlled either manually by means of a toggle on a housing enclosing the various components, or automatically in response to the sensed noise level.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a division of U.S. patent application Ser. No. 08/795,545, filed on Feb. 6, 1997, which is incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present invention deals broadly with the field of sound conditioning for the purpose of restricting the maximum sound pressure delivered to a hearer without sacrificing intelligibility. More specifically, however, the present invention deals with an acoustic conditioning system that is operational in modes both to effect sound attenuation and to accomplish amplification, as necessary. The focus of the preferred embodiment is a hearing aid which can be selectively switched between operational modes wherein high level sounds can be attenuated in normal, industrial or recreational environments, or amplified, as conditions warrant. 
     BACKGROUND OF THE INVENTION 
     Noise protection is necessary in a multiplicity of circumstances. Absent some means for protecting against excessive noises, aggravated hearing problems could occur in a person of relatively unimpaired hearing. Various medical conditions exist, however, wherein a person&#39;s hearing is particularly sensitive. One of these conditions is known as hyperacusis. Hyperacusis is a condition wherein a person experiences a collapsed tolerance to normal environmental sounds. It is a hearing disorder wherein the individual becomes highly sensitive to ambient noise. A person who experiences a condition such as hyperacusis loses much of his normal dynamic hearing range. Further, however, common noise conditions can be perceived as being unbearably loud. In aggravated conditions, the situation can be extremely painful. 
     A further hearing disorder of this nature is recruitment. In the case of hyperacusis, an individual is highly sensitive to sound but frequently experiences little or no hearing loss. A person with recruitment, on the other hand, is also highly sensitive to sound, but also experiences hearing loss. Extreme recruitment is a condition which is often confused with hyperacusis. 
     Obviously, there are other situations which dictate a need for aural protection. Persons having relatively normal hearing could experience conditions in loud industrial environments that could, over a period of time of exposure thereto, cause hearing impairment. Such loud environments may cause an aggravation of an existing hearing loss if aural protection is not used. In recognition of this fact, the Occupational Safety and Health Administration (OSHA) has imposed noise exposure limits for industrial environments. The standard noise exposure limit imposed is 90 dBA over an eight-hour period. 
     Another circumstance in which noise attenuation can be necessary is in vocational situations such as airport operations. Again, because of excessive noise, severe hearing impairment can result after exposure to such noise over time. Limitations are, therefore, imposed by governmental agencies in order to protect the hearing of employees working in such an environment. 
     Day-to-day military operations can also create conditions under which personnel experience extremely high noise levels. Obviously, a common military environment is air operations. Air operations are performed in virtually every branch of the armed services. In some cases, military personnel are exposed to helicopter noise; in other circumstances the excessive noise can be created by fixed-wing military aircraft. In either case, however, the noise level is far above a level to which personnel should normally be exposed. 
     Also in the military, personnel are exposed to excessive noise levels as a result of weapons firing. The weapons might be missiles, large guns, or small arms. In the case of virtually any weapon, however, high noise levels are generated which can cause damage to the hearing of personnel exposed to such noise. 
     Even apart from vocational and military environments, people are, on a day-to-day basis, exposed to loud noises, such as, for example, in recreational environments. Certainly, hunting is one environment in which a person is exposed to high decibel levels. 
     The problems of high noise level environments are aggravated by the fact that, very commonly, high level noise periods are alternated with other periods of time during which ambient noise is at a normal level. One very common solution offered to eliminate, or at least minimize, high noise level dangers is a device such as a common passive aural protector. Such a device typically includes a pair of cup-like structures which are mated together by a band which is fitted over a wearer&#39;s head. The cup-like structures normally include some sort of padded material on an inwardly facing oval surface brought to bear against a side of the wearer&#39;s head so that a cup-like structure tightly encircles the ear area of the individual. In the military, this type of device is known as “Mickey Mouse Ears”, and it is a device which is totally passive in the way it functions. That is, it merely filters the noise in a passive sense. 
     Obviously other passive noise attenuation devices have been devised and are used in various environments. Another very unsophisticated system is common ear plugs. 
     Some sophisticated systems have also been created. For example, electronic earmuffs have been devised which serve to electronically filter noise to a tolerable level. 
     Most of such systems discussed above, however, merely function to attenuate noise. No relief is given, in systems which merely function to attenuate noise, for an environment wherein conditions vary between excessive noise, at one time, and normal ambient conditions, at another. 
     In the case of a person already having a hearing disability, noise attenuation means are necessary so as not to worsen such a hearing impairment during high noise level periods, but amplification means are necessary during normal ambient noise periods. Options available to individuals having such impairments, utilizing prior art technology, include wearing a normal amplification hearing aid without any type of acoustic protection. Such an option, however, places the individual at further risk to noise-induced hearing loss because hearing aids are not designed to hold down, to a sufficient degree, the maximum sound pressure delivered. 
     Other options include wearing some sort of passive hearing protection and no hearing aid. In such a circumstance, however, the individual would be limited or possibly even fully unable to communicate. He might, therefore, become disabled from performing work duties. 
     Electronic earmuffs, as previously discussed, serve to afford hearing protection to the user. They are, however, relatively clumsy as hearing aids for hearing impaired persons requiring amplification. The employment of a hearing aid underneath electronic earmuffs can result in acoustic feedback and resultant inability to pick up desired sounds. 
     It is to these problems and the dictates of the prior art that the present invention is directed. It is an improved acoustic conditioner which enables these problems to be significantly surmounted. 
     SUMMARY OF THE INVENTION 
     The present invention is a device which functions to condition acoustical energy brought to bear upon the ear of a user of the device. The device includes circuitry for implementing a mode of electronically attenuating excessive noise levels in the vicinity of the wearer while still amplifying speech, music and other desired sounds. Such attenuating circuitry includes components by which an output sound pressure level is compressed below a desired level. 
     In one embodiment of the invention, the device can further include components which effect implementation of a normal hearing aid amplification of ambient sound level mode so that a hearing impaired user of the device can hear in accordance with his needs. Certain embodiments of the invention also include structure to enable selective actuation of either the attenuation or amplification modes. A switch interposed in circuitry within a housing enclosing the various components of the device can be employed for this purpose. 
     The switch, in turn, can be controlled in a number of fashions. A manual toggle can be mounted on the housing and operationally connected to the switch so that the wearer of the device can volitionally and positively select between amplification and attenuation modes. 
     Automatic control means are also envisioned. Such automatic controls would function in response to the noise level which is sensed at the device. A resistor in the circuitry is used to implement noise protection. An automatic noise switch is utilized to short out or place the resistor into the circuit in response to the background noise level. Since, in most cases, speech, music and other desired sounds generate a relatively short-term signal and excessive noise generates a long-term stationary signal relative to the signal representative of desired sounds, differentiation of the two signals can be made by averaging the received signal over a long period of time. The present invention employs a rectifier to sense the long-term average signal level. A field effect transistor is employed as an analog switch in order to change the impedance across the resistor which is used to implement the noise protection mode. 
     The present invention is thus an improved acoustic conditioning device which solves many of the problems of the prior art. More specific features and advantages obtained in view of those features will become apparent with reference to the DETAILED DESCRIPTION OF THE INVENTION, the appended claims, and the accompanying drawing figures. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an elevational view of an in-the-ear hearing aid in accordance with the present invention; 
     FIG. 2 is a general schematic circuit diagram illustrating the present invention; 
     FIG. 3 is a schematic drawing illustrating a first embodiment of an automatic attenuator mode operation; and 
     FIG. 4 is a schematic drawing illustrating a second embodiment of an automatic attenuator mode operation. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, wherein like reference numerals denote like elements throughout the several views, FIG. 1 illustrates an in-the-ear hearing aid  10  in accordance with the present invention. The hearing aid  10  includes a housing  12  having a face plate  14  and a molded shell  16 . The molded shell portion  16  is shown as being mated to the face plate  14  along a line of intersection  18 . 
     The molded shell portion  16  is typically custom molded to fit the individual person having a hearing impairment intending to use the hearing aid  10 . The shell portion  16  typically has a soft ear tip (not shown) for comfort and a better acoustic seal during mandibular movement. Molding is accomplished in accordance with processes known in the prior art. The face plate  14  is electronically in cooperation with a circuit board (not shown) located within the hearing aid housing  12 . The circuit board embodies the circuitry for the hearing aid device  10 . 
     The face plate  14  is shown as including a battery door  20  which can be opened to accept initial installation or replacement of a battery (not shown). The face plate  14  also mounts a volume control dial  22 , a manual toggle  24 , which controls a circuitry switch  26 , and a microphone  28 . The volume control dial  22  and microphone  28  function as do similar components known in the prior art. The manual toggle  24  and the switch  26  it controls will be discussed hereinafter. 
     FIG. 2 illustrates the basic operation of the invention, regardless of whether switching between attenuation and amplification modes of operation is accomplished manually or automatically. Sound is sensed by the microphone  28 , converted into an electrical signal, and conditioned in a manner consistent with the needs of the hearing impaired person for whom the hearing aid  10  is constructed. The compression amp  30  illustrated in FIG. 2 is used in this regard in a manner as known in the prior art. 
     FIG. 2 also illustrates a resistor  32  which is interposed in the circuit  34 . The specific resistance of this component  32  may vary from application to application, but a 1.2 Megohms resistance has been found to be acceptable for functioning to limit noise exposure of a wearer of the hearing aid  10  to 90 dBA over an eight-hour period. 
     The circuit  34  includes a bypass leg  36  which contains switch  26 . A MICROTRONIC No. 531 500MA rated switch has been found acceptable to function for this purpose. The switch  26 , when closed, shorts out the noise protection resistor  32  in the circuit  34  and enables normal amplification in accordance with the wearer&#39;s specific need. When the switch  26  is open, however, the circuit path is through the noise protection resistor  32  and the signal is significantly reduced. Sound pressure compression results to an extent so that the OSHA maximum requirements are not exceeded. 
     FIG. 2 also shows a volume control potentiometer  40 , controlled by volume control dial  22 , a coupling capacitor  42 , and a receiver  44 . These components function in a manner in accordance with the prior art. Typically, the volume control potentiometer is of a 10 Kohms value. 
     Operation of the noise protection resistor bypass switch  26  can occur in a number of manners. The switch  26  can be manually operated. Manual operation of the switch  26  entails utilization of the toggle  24  on the face plate  14  of the hearing aid housing  12 . In one position of the toggle  24 , the switch  26  will be in an open configuration, while, in the other position of the toggle  24 , the switch  26  will be closed. 
     Operation of the switch  26  can also be automatic in response to the level of noise sensed by the hearing aid  10 . More detailed discussion of automatic operation will be given with respect to FIGS. 3 and 4 hereinafter. 
     As previously discussed, there can be a manual toggle  24  for effecting operation of the switch  26  in the bypass leg  36  of the circuit  34 . There are, however, a number of disadvantages to employment of a manual toggle  24 . First, space is at a premium on the face plate  14  of the hearing aid  10 . By implementing automatic operation of the switch  26 , the toggle  24  can be eliminated. Further, when a toggle  24  is employed, the wearer of the hearing aid  10  is required to volitionally effect movement of the toggle  24  in order to flip the switch  26 . Consequently, automatic switching is a distinct advantage. 
     FIG. 3 shows a first embodiment for implementing automatic switching. It will be borne in mind, when considering the embodiments of both FIGS. 3 and 4, that speech or other desired sounds are typically characterized as a short-term average signal level, and noise is characterized as a long-term stationary signal, relative to speech signals. The average time period of a high-energy speech pulse can be less than several hundred milliseconds; background noise typically has a time period greater than that. Normal speech and other normal sounds, on the one hand, and noise, on the other hand, can thereby be differentiated. This can be accomplished by averaging the received signal over a long period of time. 
     The microphone  28  picks up ambient sound including both normal speech sound and noise. A preamplifier/rectifier  46  functions to represent the noise level signal and voltage. After being amplified, the measured noise level signal from the preamplifier/rectifier  46  is compared with a preset threshold voltage level inputted from a voltage divider  48 . A comparator  50  generates logic voltage signals which control the gate voltage of a P-channel field effect transistor (FET)  52 . The FET  52  is connected in parallel with the noise protection resistor  32 . When the background conditions are normal and there is not excessive noise, the noise level is lower than a preset threshold. Consequently, the P-channel FET  52  is on and the noise protection resistor  32  is shorted out. When the noise level exceeds the threshold, the FET  52  is turned off and the resistor  32  is placed into the circuit. 
     The preamplifier circuit, comprising the preamplifier/rectifier  46 , is an off-the-shelf component such as the Gennum  581 . As will be understood, the preamplifier circuit has two primary functions. These are, first, to amplify the sensed signal from the microphone  28  and, second, to adjust the threshold of the rectifier in the Gennum  581 . The values of a resistor  54  and capacitor  56  in the circuit in series with the preamplifier/rectifier  46  should be selected so that the signal from the microphone  28  to the amplification circuit is not significantly reduced. The resistor  54  would, typically, be a variable resistor and, by adjusting this resistor&#39;s value, the gain of the preamplifier circuit and the threshold of the rectifier can be varied. 
     An additional capacitor  58  is connected to the rectifier output of the Gennum  581 . The value selected for this second capacitor  58  determines the time constant of the rectifier output signal. Consequently, by adjusting the value of this capacitor  58 , the switch response time and release time, responsive to the measured noise signal levels, can be varied. 
     The voltage across capacitor  58  functions to provide the noise level signal. This signal, in turn, is amplified by an inverting voltage amplifier circuit which includes a resistor  60  in series with an amplifier  62  and another resistor  64  in parallel with the amplifier  62 . The voltage divider  48 , which includes another variable resistor  66  and an additional non-variable resistor  68 , provides the threshold voltage for the voltage comparator  50 . The overall sensitivity of the switch  26  is determined by the threshold of the rectifier and the threshold of the comparator. This is accomplished by adjusting the value of the resistor  54  and the threshold of the comparator  50  by adjusting the resistor  66 . 
     FIG. 4 illustrates a second embodiment for effecting automatic operation of the switch  26 . In this alternative embodiment, noise is detected by obtaining the minima of the envelope of the noise signal. During pauses between speech intervals, the envelope of this speech. signal depends upon the noise floor. The higher the noise level, the greater the envelope minima. In view of this fact, the output of the noise detector can be used as a logic signal to control an analog switch. 
     FIG. 4 illustrates a noise detector which includes a preamplifier  70 , a rectifier  72 , a low-pass filter  74 , envelope minima detector  76 , and a voltage comparator  78 . The signal sensed by the microphone  28  is fed to the preamplifier  70  to raise the signal to a proper level. The rectifier  72  and low-pass filter  74 , together, form an envelope demodulator  80 . The envelope minima detector  76  measures the minima of the envelope, and the minima, so measured, are compared with a predetermined threshold voltage in the comparator  78 . In environments wherein there is not excess noise, the measured noise level is lower than a reference voltage, the preset threshold voltage, and the output of the comparator  78  is logic low. When the noise level exceeds the preset threshold, the output of the comparator  78  goes high to turn the FET off. 
     The signal sensed from the microphone  28  is ac coupled through a capacitor  82  to the preamplifier  70 . After amplification is accomplished, the signal is fed to the rectifier  72 . This rectifier  72  can be a full wave or half wave rectifier, as conditions dictate. The envelope is obtained by filtering the rectified signal through the low-pass filter  74 . The cut-off frequency of the low-pass filter  74  should be equal to or less than 30 Hertz. A voltage follower  84 , diode  86 , capacitor  88 , and resistor  90  form the envelope minima detector circuit. The resistor  90  and capacitor  88  in the minima detector circuit are connected to a positive power supply. When the voltage at an intersection  92  is lower than the voltage at  94  minus the diode voltage drop, the voltage at  94  follows the voltage at intersection  92 ; when the voltage at  92  increases from a minimum value, the diode  86  is reverse biased, and voltage at  94  depends on the time constant which is a product of the resistance of  90  and the capacitance of  88 . The minima of the envelope are, thereby, detected in view of these factors. The detected envelope minimum value is then fed to the circuit of comparator  78  to compare with a preset threshold voltage, the reference voltage. The reference voltage represents the threshold of the noise level. The desired value of the voltage reference can be determined through experimentation. It is desirable that this reference voltage be variable. 
     It will be understood that this disclosure, in many respects, is only illustrative. Changes may be made in details, particularly in matters of shape, size, material, and arrangement of parts without exceeding the scope of the invention. Accordingly, the scope of the invention is as defined in the language of the appended claims.