Abstract:
New and improved electroacoustic devices each including at least one transducer assembly having one or more microphones typically mounted on a baffle plate and disposed in substantially the same acoustic plane as a speaker or speakers. In the various embodiments, at least one microphone and at least one speaker face the same or opposite directions. Each microphone may be parallel to or oriented at an angle with respect to the speaker. In other embodiments, the speaker includes a central opening or cavity in which a microphone having one of various orientations is provided. The orientations of the microphone or microphones with respect to the speaker or speakers minimize adverse noise reduction effects associated with the differences in sensitivities, frequency responses and phase responses and acoustic time delays between the microphones and the speaker or speakers, as well as minimize sound reflections that are picked up by the microphone or microphones.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional application No. 60/528,528, filed Dec. 10, 2003. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to electroacoustic devices for translating electronic signals into acoustic signals perceived by the human ear. More particularly, the present invention relates to electroacoustic devices which include novel speaker and microphone configurations that are particularly effective in reducing noise perceived by a listener during use. 
     BACKGROUND OF THE INVENTION 
     Electroacoustic devices include headphones, headsets, helmets, speaker enclosures and other devices having electro-acoustic functions. Headphones typically include a pair of ear cups mounted on respective ends of an arcuate or C-shaped adjustable headband. Each of the ear cups contains a headphone speaker that converts electrical energy from a television, radio, compact disk (CD), cassette tape or the like into acoustic energy that is perceived by the ears of the wearer. Headsets additionally include a “boom” microphone that is positioned in proximity to the wearer&#39;s mouth to permit the wearer to engage in two-way communication with a second person. Most headphones and headsets include some type of noise reduction capability which reduces the quantity of unwanted acoustic energy that reaches the ears of the wearer. 
     There are two general types of noise-reducing or noise-canceling capability among headphones and headsets. The most basic of these capability types is passive noise attenuation, in which the physical structure of the headphone insulates the wearer&#39;s ears from extraneous and unwanted noise. Headphones and headsets characterized by passive noise attenuation may include an acoustically-absorbent material which lines the interior of the ear cups, as well as some form of an ear cushion that lines the edge of each ear cup and presses against the wearer&#39;s skin around the ear during use. The second type of noise-canceling capability is known as active noise attenuation and requires an electromechanical device and electronic circuitry. This type of noise-canceling capability results from a combination of active noise attenuation and passive noise attenuation. 
     Those headphones and headsets having active noise attenuation capability require a microphone or microphones to pick up the original sound and convert this original sound to electrical energy, electronic circuitry to control the electrical energy of the original sound and a speaker to convert the electrical signal back to an acoustic signal. The electronic circuitry inverts the phase of the original sound by 180 degrees and amplifies the signal to an acoustic level which is equal to the level that reaches the wearer&#39;s ear. The amplified signal, 180 degrees out of phase with respect to the original signal, cancels the original signal and results in a clearer sound perceived by the ear of the headphone or headset wearer. 
     One of the problems inherent in conventional active noise reduction designs for headphones is that the microphone or microphones and the speaker used in the headphone have sensitivities, frequency responses and phase responses which differ from each other. Furthermore, the acoustic time delay between the microphone and the speaker causes a phase shift between the original signal and the attenuated signal. Consequently, not all of the frequencies in the original signal will be canceled by the attenuated signal because not all frequencies of the attenuated signal will be 180 degrees out of phase with respect to all frequencies of the original signal. It has been found that placement of a microphone and a speaker in substantially the same acoustic plane minimizes the difference between the sound wave phase or time delay and the sound pressure that acts on the microphone diaphragm with respect to the signal from the speaker. 
     Another problem that exists in active noise reduction designs is that the microphone or microphones tend to pick up direct reflections of certain frequencies of the original signal. This distorts reproduction of the phase-inverted original signal as the amplified attenuated signal. Accordingly, new and improved electroacoustic devices are needed which are capable of minimizing adverse noise reduction effects associated with the differences in sensitivities, frequency responses and phase responses and acoustic time delays which exist between microphones and speakers, as well as minimizing direct sound reflections picked up by the microphone or microphones. 
     SUMMARY OF THE INVENTION 
     The present invention is generally directed to new and improved electroacoustic devices each including one or more microphones typically mounted on a baffle plate and disposed in substantially the same acoustic plane as a speaker or speakers. In the various embodiments, at least one microphone and at least one speaker face the same or opposite directions. In one embodiment, a microphone faces the same direction as the speaker or speakers and is oriented in the same plane as the baffle plate. In another embodiment, the microphone faces the same direction as the speaker or speakers and is oriented at an angle with respect to the plane of the baffle plate. In still another embodiment, the microphone and the speaker or speakers face opposite directions and the microphone is disposed in the same plane as the baffle plate. In yet another embodiment, the microphone and the speaker or speakers face opposite directions and the microphone is disposed at an angle with respect to the plane of the baffle plate. In other embodiments, one microphone faces the same or opposite direction as the speaker or speakers and is disposed in the same plane as the baffle plate or at an angle with respect to the plane of the baffle plate. Another microphone faces the same or different direction as the speaker or speakers and is disposed in the same plane as the baffle plate or at an angle with respect to the plane of the baffle plate. In other embodiments, the speaker includes a central opening or cavity in which a microphone having one of various orientations is provided. The orientations of the microphone or microphones with respect to the speaker or speakers minimize adverse noise reduction effects associated with the differences in sensitivities, frequency responses and phase responses and acoustic time delays between the microphones and the speaker or speakers, as well as minimize direct sound reflections that are picked up by the microphone or microphones. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1A  is a schematic view, partially in section, of an illustrative electroacoustic device of the present invention; 
         FIG. 1B  is a block diagram of an illustrative signal processing circuit for an electroacoustic device of the present invention; 
         FIG. 1C  is a block diagram of another illustrative signal processing circuit for an electroacoustic device of the present invention; 
         FIG. 1D  is a block diagram of still another illustrative signal processing circuit for an electroacoustic device of the present invention; 
         FIG. 2  is a side view of an illustrative microphone suitable for use with the electroacoustic devices of the present invention; 
         FIG. 3  is a side view of an illustrative speaker suitable for use with the electroacoustic devices of the present invention; 
         FIG. 4  is a front view of an illustrative baffle plate for mounting a microphone or microphones and a speaker in an electroacoustic device; 
         FIG. 5A  is a cross-sectional view of a parallel cavity flat baffle plate for mounting a speaker and a microphone or microphones in an electroacoustic device in accordance with the present invention; 
         FIG. 5B  is a cross-sectional view of an angled cavity flat baffle plate for mounting a speaker and a microphone or microphones in an electroacoustic device in accordance with the present invention; 
         FIG. 5C  is a cross-sectional view of a parallel cavity slant baffle plate for mounting a speaker and a microphone or microphones in an electroacoustic device in accordance with the present invention; 
         FIG. 5D  is a cross-sectional view of an angled cavity slant baffle plate for mounting a speaker and a microphone or microphones in an electroacoustic device in accordance with the present invention; 
         FIG. 6A  is a cross-sectional view of a flat baffle plate design for an transducer assembly in a first embodiment of the electroacoustic devices of the present invention; 
         FIG. 6B  is a cross-sectional view of a slant baffle plate design for an transducer assembly in a first embodiment of the electroacoustic devices of the present invention; 
         FIG. 7A  is a cross-sectional view of a flat baffle plate design for an transducer assembly in a second embodiment of the electroacoustic devices; 
         FIG. 7B  is a cross-sectional view of a slant baffle plate design for an transducer assembly in a second embodiment of the electroacoustic devices; 
         FIG. 8A  is a cross-sectional view of a slant baffle plate design for an transducer assembly in a third embodiment of the electroacoustic devices; 
         FIG. 8B  is a cross-sectional view of a flat baffle plate design for an transducer assembly in a third embodiment of the electroacoustic devices; 
         FIG. 9A  is a cross-sectional view of a flat baffle plate design for an transducer assembly in a fourth embodiment of the electroacoustic devices; 
         FIG. 9B  is a cross-sectional view of a slant baffle plate design for an transducer assembly in a fourth embodiment of the electroacoustic devices; 
         FIG. 10A  is a cross-sectional view of a flat baffle plate design for an transducer assembly in a fifth embodiment of the electroacoustic devices; 
         FIG. 10B  is a cross-sectional view of a slant baffle plate design for an transducer assembly in a fifth embodiment of the electroacoustic devices; 
         FIG. 11A  is a cross-sectional view of a flat baffle plate design for an transducer assembly in a sixth embodiment of the electroacoustic devices; 
         FIG. 11B  is a cross-sectional view of a slant baffle plate design for an transducer assembly in a sixth embodiment of the electroacoustic devices; 
         FIG. 12A  is a cross-sectional view of a flat baffle plate design for an transducer assembly in a seventh embodiment of the electroacoustic devices; 
         FIG. 12B  is a cross-sectional view of a slant baffle plate design for an transducer assembly in a seventh embodiment of the electroacoustic devices; 
         FIG. 13A  is a cross-sectional view of a flat baffle plate design for an transducer assembly in an eighth embodiment of the electroacoustic devices; 
         FIG. 13B  is a cross-sectional view of a slant baffle plate design for an transducer assembly in an eighth embodiment of the electroacoustic devices; 
         FIG. 14A  is a cross-sectional view of a flat baffle plate design for an transducer assembly in a ninth embodiment of the electroacoustic devices; 
         FIG. 14B  is a cross-sectional view of a slant baffle plate design for an transducer assembly in a ninth embodiment of the electroacoustic devices; 
         FIG. 15A  is a cross-sectional view of a flat baffle plate design for an transducer assembly in a tenth embodiment of the electroacoustic devices; 
         FIG. 15B  is a cross-sectional view of a slant baffle plate design for an transducer assembly in a tenth embodiment of the electroacoustic devices; 
         FIG. 16  is a cross-sectional view of an transducer assembly in an eleventh embodiment of the electroacoustic devices; 
         FIG. 17  is a cross-sectional view of an transducer assembly in a twelfth embodient of the electroacoustic devices; 
         FIG. 18  is a cross-sectional view of an transducer assembly in a thirteenth embodiment of the electroacoustic devices; and 
         FIG. 19  is a cross-sectional view of an transducer assembly in a fourteenth embodiment of the electroacoustic devices. 
     
    
    
     DESCRIPTION OF THE INVENTION 
     An illustrative embodiment of an electroacoustic device of the present invention is generally indicated by reference numeral  10  in  FIG. 1A  and includes a first embodiment of a pair of transducer assemblies  49  connected to a pair of attachment points  16  of an adjustable headband  20 , optionally including a pad  18 . A boom microphone  22  may also be attached to a transducer assembly  49  or to the adjustable headband  20 . One end of a cable  24  may be connected to the respective transducer assemblies  49 , in which case the opposite end of the cable  24  is adapted for connection to an external device or devices (not shown). Alternatively, the transducer assemblies  49  may have internal electronic circuitry. While the electroacoustic device  10  in  FIG. 1A  and throughout the drawings is shown in the configuration of a headset, it will be understood that the present invention is equally adaptable to use as a telephone handset, a helmet or other electroacoustic device. Furthermore, the electroacoustic device  10  can be used for headphones and headsets that perform functions such as amplification and monitoring while simultaneously feeding a recording device or that perform multiple functions at the same time. 
     The transducer assemblies  49  convert an acoustic source signal to an electrical signal and simultaneously convert a processed electrical signal to an acoustic signal. Each transducer assembly  49 , the structural details of will be hereinafter described in more detail, is typically encased in a cup-shaped housing and designed to fit directly and comfortably over the ear canal so as not to “plug” the ear and allow the original sound wave which emanates from the speaker to enter the ear canal. Each transducer assembly  49  typically includes an ear cushion  56  which cushions the transducer assembly  49  against the head of a wearer. The adjustable headband  20  can be designed in such a manner as to conceal wires (not shown) crossing from one transducer assembly  49  to the other, thus reducing the risk of damage and aiding in cosmetic appearance of the device  10 . The boom microphone  22  may optionally be included as part of the device  10  for communication needs of the wearer. The external device or devices to which the electroacoustic device  10  is connected through the cable  24  is configured to adjust the volume, balance and other characteristics of sound emanating from the apparatus  10 , according to the knowledge of those skilled in the art. 
     For active noise cancelling applications, the electroacoustic device  10  includes components which receive and convert an original acoustic signal to an electrical signal, process the electrical signal with a 180 degree phase shift, and convert it back to a modified wave signal in such a manner that the modified signal can add to and cancel the original acoustic signal in real time. Accordingly, because the modified acoustic signal is substantially 180 degrees out of phase with the original acoustic signal, the modified signal substantially cancels the original acoustic signal. The transducer assemblies  49  are typically the same in construction. 
     Referring next to  FIG. 2  of the drawings, a transmitter or microphone  30  which is suitable for use with the electroacoustic devices of the present invention typically includes a microphone housing  31  having a face  32  through which extends multiple openings (not shown) to enable sound to enter the microphone housing  31 . A charged, typically flat diaphragm  34  is provided in the microphone housing  31  and may be located adjacent to the face  32 , as shown, or alternatively may be located closer to the back  33  than to the face  32  or about midway between the face  32  and the back  33  of the microphone housing  31 . The microphone  30  may be a conventional, omni-directional electret condenser microphone known by those skilled in the art. Such a microphone includes a Field Effect Transistor (FET, not shown) which is positioned in the microphone housing  31 . As acoustic energy enters the microphone housing  31  through the openings in the face  32 , the charged diaphragm  34  moves proportional to the acoustic energy and the FET converts this change in capacitance into an electrical signal. 
     Referring next to  FIG. 3  of the drawings, a receiver or speaker  36  which is suitable for use with the electroacoustic devices of the present invention includes a housing  37  having a front  38  and a magnet  39  at the rear of the housing. A movable diaphragm is mounted in the housing  37  and is indicated at rest by the solid line  40 . The diaphragm moves in an acoustic plane  41  between a frontmost position  40   a  and a rearmost position  40   b . Accordingly, the frontmost position  40   a  of the diaphragm defines the frontmost limit of the acoustic plane  41 , and the rearmost position  40   b  of the diaphragm defines the rearmost limit of the acoustic plane  41 . The speaker  36  may be conventional and further includes a magnet  39  that is contained in the rear portion of the housing  37  and a voice coil (not shown) attached to the diaphragm. 
     Referring next to  FIG. 4  and to  FIGS. 5A-5D  of the drawings, a baffle plate  1  which is suitable for use with the present invention includes a speaker opening  2  through which the front  38  of the speaker  36  ( FIG. 3 ) is exposed. A microphone recess  3  is provided adjacent to the speaker opening  2  and may contain a microphone  30 . A rim  4  typically surrounds the speaker opening  2  and the microphone recess  3  and serves to mount the baffle plate  1  in the transducer assembly  49 . As shown in  FIGS. 5A-5D , the baffle plate  1  may have one of four basic cross-sectional configurations in each of the various embodiments of the invention as hereinafter described. 
     As shown in  FIG. 5A , a parallel cavity flat baffle plate  1   a  includes a speaker opening  2   a  and an adjacent microphone recess  3   a  surrounded by a rim  4   a . The microphone recess  3   a  may have a generally rectangular cross-sectional configuration and is generally parallel with respect to the plane of the rim  4   a . The parallel cavity flat baffle plate  1   a  is designed to impart a “straight” configuration to the transducer assembly such that the speaker  36  and the microphone or microphones  30  are held in a parallel position with respect to the ear of a person wearing the electroacoustic device, as hereinafter further described. 
     As shown in  FIG. 5B , an angled cavity flat: baffle plate  1   b  includes a speaker opening  2   b  and an adjacent microphone recess  3   b  surrounded by a rim  4   b . The microphone recess  3   b  has a cross-sectional configuration which is generally bi-angled with respect to the plane of the rim  4   b . Like the parallel cavity flat baffle plate  1   a  of  FIG. 5A , the angled cavity flat baffle plate  1   b  is designed to impart a “straight” configuration to the transducer assembly. 
     As shown in  FIG. 5C , a parallel cavity slant baffle plate  1   c  includes a speaker opening  2   c  and an adjacent microphone recess  3   c  surrounded by a rim  4   c . The microphone recess  3   c  may have a generally rectangular cross-sectional configuration and is generally parallel with respect to the plane of the rim  4   c . The parallel cavity slant baffle plate  1   c  is designed to impart a sloped configuration to the transducer assembly such that the speaker  36  and the microphone or microphones  30  are positioned at an angle with respect to the ear of a person wearing the electroacoustic device, as hereinafter further described. 
     As shown in  FIG. 5D , an angled cavity slant baffle plate  1   d  includes a speaker opening  2   d  and an adjacent microphone recess  3   d  surrounded by a rim  4   d . The microphone recess  3   d  has a cross-sectional configuration which is generally bi-angled with respect to the plane of the rim  4   d . Like the parallel cavity slant baffle plate  1   c  of  FIG. 5C , the angled cavity slant baffle plate  1   d  imparts a sloped configuration to the transducer assembly as hereinafter described. 
     Referring next to  FIG. 6A , in a first embodiment each transducer assembly  49  of the electroacoustic device  10  includes a generally concave housing  50  which may be completely closed, partially closed or completely open with respect to the exterior of the transducer assembly  49 . A piece of acoustic foam  51 , herein after referred to in the various embodiments as outer acoustic foam, is typically provided on the interior surface of the housing  50  to attenuate sound wave reflections and resonance. A parallel cavity flat baffle plate  1   a , heretofore described with respect to  FIG. 5A , is mounted to the housing  50 . Accordingly, an outer cavity  52  is defined between the housing  50  and the rear surface of the parallel cavity flat baffle plate  1   a , with the outer acoustic foam  51  provided in the outer cavity  52 . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   a , with the front  38  of the speaker  36  disposed in communication with the speaker opening  2   a  ( FIG. 5A ) in the baffle plate  1   a . A generally flat piece of acoustic foam  53 , hereinafter referred to in the various embodiments as microphone acoustic foam, is typically provided in the microphone recess  3   a . A microphone  30  is mounted to the baffle plate  1   a , inside the microphone recess  3   a , and the face  32  of the microphone  30  faces the microphone acoustic foam  53 . The microphone acoustic foam  53  helps reduce resonance problems and attenuates some frequencies. The diaphragm  34  ( FIG. 2 ) of the microphone  30  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P” and the face  32  of the microphone  30  and the front  38  of the speaker  36  face substantially opposite directions. A sheet of acoustic foam  54 , hereinafter referred to in the various embodiments as inner acoustic foam, is provided on the interior surface of the baffle plate  1   a  and typically encloses the microphone  30  in the microphone recess  3   a  to provide a finished cosmetic appearance to the transducer assembly  49 . The inner acoustic foam  54  also protects the speaker  36  and the microphone  30  from dust and other particles that could damage the speaker  36  and/or microphone  30 , and maybe a water-resistant material to additionally protect the speaker  36  and the microphone  30  from moisture. An ear cushion  56  is provided on the exterior surface of the rim  4   a  of the baffle plate  4  to cushion the transducer assembly  49  against the head of a wearer. An inner cavity  55  is defined by the ear cushion  56  and between the inner acoustic foam  54  and the wearer&#39;s head (not shown). 
     Referring next to  FIG. 1C , an illustrative signal processing circuit  87  for the transducer assembly  49  includes an external audio input  81  which is connected to a summing circuit  83  through an audio preamplifier  82 . The summing circuit  83  is, in turn, connected to the speaker  36  through a speaker amplifier  84 . The microphone  30  is connected to the summing circuit  83  through a microphone preamplifier  85 . The face  32  of the microphone  30  and the front  38  of the speaker  36  face substantially opposite directions. In operation of the transducer assembly  49 , the external audio input  81  receives an input electrical signal from a source (not shown). The input electrical signal is amplified by the audio preamplifier  82  and then modified as desired and transmitted through the summing circuit  83  to the speaker amplifier  84 . The speaker amplifier  84  further amplifies the input electrical signal to suitable levels to drive the diaphragm  40  of the speaker  36 , which converts the input electrical signal to an original sound wave that is transmitted from the speaker  36  into the inner cavity  55  ( FIG. 6A ) of the transducer assembly  49 . For active noise cancellation, the microphone  30  simultaneously receives and converts the original sound wave into a converted electrical signal which is amplified by the microphone preamplifier  85  and transmitted to the summing circuit  83 . The summing circuit  83  then shifts the phase of the converted electrical signal 180 degrees, or the signal may be shifted elsewhere in the circuit, and the phase-shifted electrical signal is amplified by the speaker amplifier  84  to drive the diaphragm  40  of the speaker  36 . Accordingly, a phase-shifted sound wave combines with and cancels the original sound wave in the inner cavity  55 . Consequently, the phase-shifted sound wave omits extraneous acoustic distortions from the original sound wave as the phase-shifted sound wave impinges on the ear of the wearer. It will be understood that the signal processing circuit  87  shown in  FIG. 1C  includes the simplest configuration required to effect the external audio input signal processing, and that additional circuitry can be used to correct the effects of re-processing. 
     Referring next to  FIG. 6B , in an alternative first embodiment each transducer assembly  59  includes a generally concave housing  60  which includes a housing extension  60   a  in the upper portion thereof to facilitate positioning of the interior transducer assembly components away from the ear of a wearer. A piece of outer acoustic foam  61  is typically provided on the interior surface of the housing  60  to attenuate sound wave reflections and resonance. A parallel cavity slant baffle plate  1   c , heretofore described with respect to  FIG. 5C , is mounted to the housing  60 . An outer cavity  62  is defined between the housing  60  and the rear surface of the baffle plate  1   c , with the outer acoustic foam  61  provided in the outer cavity  62 . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   c , with the front  38  of the speaker  36  disposed in communication with the speaker opening  2   c  ( FIG. 5C ) in the baffle plate  1 C. A piece of microphone acoustic foam  63  is typically provided in the microphone recess  3   c , and the face  32  of a microphone  30  mounted to the baffle plate  1   c  inside the microphone recess  3   c  faces the microphone acoustic foam  63 . The diaphragm  34  ( FIG. 2 ) of the microphone  30  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”, and the face  32  of the microphone  30  and the front  38  of the speaker  36  face substantially opposite directions. A sheet of inner acoustic foam  64  is provided on the interior surface of the baffle plate  1   c  and typically encloses the microphone  30  in the microphone recess  3   c . An ear cushion  66  is provided on the exterior surface of the rim  4   c  of the baffle plate  1   c  to cushion the transducer assembly  59  against the head of a wearer. An inner cavity  65  is defined by the ear cushion  66  and between the inner acoustic foam  64  and the wearer&#39;s head (not shown). Due to the slanted configuration of the baffle plate  1   c  in combination with the housing extension  60   a  of the housing  60 , the microphone  30  and the speaker  36  are angled away from the ear (not shown) of a wearer, across the inner cavity  65 . 
     Referring next to  FIG. 7A , in a second embodiment each transducer assembly  69  includes a generally concave housing  70  and a piece of outer acoustic foam  71  typically provided on the interior surface of the housing  70 . A parallel cavity flat baffle plate  1   a , heretofore described with respect to  FIG. 5A , is mounted to the housing  70  to define an outer cavity  72  between the housing  70  and the rear surface of the parallel cavity flat baffle plate  1   a , with the outer acoustic foam  71  provided in the outer cavity  72 . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   a , with the front  38  of the speaker  36  disposed in communication with the speaker opening  2   a  ( FIG. 5A ) in the baffle plate  1   a . A piece of microphone acoustic foam  73  is typically provided on the rear surface of the rim  4   a  of the baffle plate  1   a , inside the outer cavity  72 . The face  32  of a microphone  30  mounted to the baffle plate  1   a  faces the microphone acoustic foam  73 . The diaphragm  34  ( FIG. 2 ) of the microphone  30  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”, and the face  32  of the microphone  30  and the front  38  of the speaker  36  face substantially the same direction. A sheet of inner acoustic foam  74  is provided on the interior surface of the baffle plate  1   a . An ear cushion  76  is provided on the exterior surface of the rim  4   a  of the baffle plate  4  to cushion the transducer assembly  69  against the head of a wearer. A front cavity  75  is defined by the ear cushion  76  between the inner acoustic foam  74  and the wearer&#39;s head (not shown). A simple signal processing circuit  80  which is suitable for the transducer assembly  69  is shown in  FIG. 1B  and includes an external audio input  81 , an audio preamplifer  82 , a summing circuit  83 , a speaker amplifier  84  and a microphone preamplifier  85 . The face  32  of the microphone  30  and the front  38  of the speaker  36  are oriented in substantially the same direction. 
     Referring next to  FIG. 7B , in an alternative second embodiment each transducer assembly  109  includes a generally concave housing  110  which includes a housing extension  110   a  in the upper portion thereof to facilitate positioning of the interior transducer assembly components away from the ear of a wearer. A piece of outer acoustic foam  111  is typically provided on the interior surface of the housing  110 . A parallel cavity slant baffle plate  1   c , heretofore described with respect to  FIG. 5C , is mounted to the housing  110 . An outer cavity  112  is defined between the housing  110  and the rear surface of the baffle plate  1   c , with the outer acoustic foam  111  provided in the outer cavity  112 . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   c , with the front  38  of the speaker  36  disposed in communication with the speaker opening  2   c  ( FIG. 5C ) in the baffle plate  1   c . A piece of microphone acoustic foam  113  is typically provided on the rear surface of the baffle plate  1   c , inside the outer cavity  112 , and the face  32  of a microphone  30  mounted to the baffle plate  1   c  faces the microphone acoustic foam  113 . The diaphragm  34  ( FIG. 2 ) of the microphone  30  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”, and the face  32  of the microphone  30  and the front  38  of the speaker  36  face substantially the same direction. A sheet of inner acoustic foam  114  is provided on the interior surface of the baffle plate  1   c . An ear cushion  116  is provided on the exterior surface of the rim  4   c  of the baffle plate  1   c  to cushion the transducer assembly  109  against the head of a wearer. An inner cavity  115  is defined by the ear cushion  116  between the inner acoustic foam  114  and the wearer&#39;s head (not shown). Due to the slanted configuration of the baffle plate  1   c  in combination with the housing extension  110   a  of the housing  110 , the microphone  30  and the speaker  36  are angled away from the ear (not shown) of a wearer, across the inner cavity  115 . 
     Referring next to  FIG. 8A , in a third embodiment each transducer assembly  119  includes a generally concave housing  120  which includes a housing extension  120   a  in the upper portion thereof to facilitate positioning of the interior transducer assembly components away from the ear  127   a  of a wearer. A piece of outer acoustic foam  121  is typically provided on the interior surface of the housing  120 . A parallel cavity slant baffle plate  1   c  is mounted to the housing  120 . An outer cavity  122  is defined between the housing  120  and the rear surface of the baffle plate  1   c , with the outer acoustic foam  121  provided in the outer cavity  122 . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   c , with the front  38  of the speaker  36  disposed in communication with the speaker opening  2   c  ( FIG. 5C ) in the baffle plate  1   c . A generally flat piece of microphone acoustic foam  123   a  is provided in the microphone recess  3   c  of the baffle plate  1   c . The face  32  of a first microphone  30   a , mounted to the baffle plate  1   c  inside the microphone recess  3   c , faces the microphone acoustic foam  123   a . A second piece of microphone acoustic foam  123   b  is typically provided on the rear surface of the baffle plate  1   c , inside the outer cavity  122 , and the face  32  of a second microphone  30   b  mounted to the baffle plate  1   c  faces the microphone acoustic foam  123   b . The diaphragm  34  ( FIG. 2 ) of the first microphone  30   a  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the first microphone  30   a  and the front  38  of the speaker  36  face substantially opposite directions. The diaphragm  34  of the second microphone  30   b  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”, and the face  32  of the second microphone  30   b  and the front  38  of the speaker  36  face substantially the same direction. A sheet of inner acoustic foam  124  is provided on the interior surface of the baffle plate  1   c  and covers the first microphone  30   a  in the microphone recess  3   c . An ear cushion  126  is provided on the exterior surface of the rim  4   c  of the baffle plate  1   c  to cushion the transducer assembly  119  against the head  127  of a wearer. An inner cavity  125  is defined by the ear cushion  126  between the inner acoustic foam  124  and the wearer&#39;s head  127 . Due to the slanted configuration of the baffle plate  1   c  in combination with the housing extension  120   a  of the housing  120 , the first microphone  30   a , the second microphone  30   b  and the speaker  36  are angled away from the ear  127   a  of the wearer, across the inner cavity  125 . 
     Referring next to  FIG. 1D , an illustrative signal processing circuit  89  for the transducer assembly  119  includes an external audio input  81  connected to a summing circuit  83  through an audio preamplifier  82 , a speaker amplifier  84  of the speaker  36  connected to the summing circuit  83 , a first microphone amplifier  85   a  connected to the first microphone  30   a  and to the summing circuit  83 , and a second microphone amplifier  85   b  connected to the second microphone  30   b  and the summing circuit  83 . In operation of the transducer assembly  89 , the external audio input  81  receives an input electrical signal, which is amplified by the audio preamplifier  82  and then transmitted through the summing circuit  83  to the speaker amplifier  84  to ultimately drive the diaphragm  40  of the speaker  36 . The speaker  36  converts the input electrical signal to an original sound wave that is transmitted from the speaker  36  into the inner cavity  125  ( FIG. 6A ) of the transducer assembly  119 . Simultaneously, the first microphone  30   a  and the second microphone  30   b  receive and convert the original sound wave into respective electrical signals which are amplified by the respective first microphone preamplifiers  85   a  and second microphone preamplifier  85   b , and these electrical signals are transmitted to the summing circuit  83 . The summing circuit  83  then sums the electrical signals and shifts the phase of the electrical signals 180 degrees (or the phase of the signals may be shifted elsewhere in the circuit), and the phase-shifted electrical signal is amplified by the speaker amplifier  84  to drive the diaphragm  40  of the speaker  36  for active noise cancellation functions. The phase-shifted sound wave emanating from the speaker  36  combines with and cancels the original sound wave in the inner cavity  125 . Consequently, the phase-shifted sound wave omits extraneous acoustic distortions from the original sound wave as the phase-shifted sound wave impinges on the ear of the wearer. It will be understood that the signal processing circuit  89  shown in  FIG. 1D  includes the simplest configuration required to effect the external audio input signal processing, and that additional circuitry can be used to correct the effects of re-processing. 
     Referring next to  FIG. 8B , in an alternative third embodiment each transducer assembly  129  includes a generally concave housing  130  and a piece of outer acoustic foam  131  typically provided on the interior surface of the housing  130 . A parallel cavity flat baffle plate  1   a  is mounted to the housing  130  to define an outer cavity  132  between the housing  130  and the rear surface of the parallel cavity flat baffle plate  1   a , with the outer acoustic foam  131  provided in the outer cavity  132 . A speaker  36  is mounted to the baffle plate  1   a , with the front  38  of the speaker  36  disposed in communication with the speaker opening  2   a  ( FIG. 5A ) in the baffle plate  1   a . A generally flat piece of microphone acoustic foam  133   a  is provided in the microphone recess  3   a  of the baffle plate  1   a . The face  32  of a first speaker  30   a , mounted to the baffle plate  1   a  inside the microphone recess  3   a , faces the microphone acoustic foam  133   a . A second generally flat piece of microphone acoustic foam  133   b  is provided on the rear surface of the rim  4   a  of the baffle plate  1   a , and the face  32  of a second microphone  30   b  mounted to the baffle plate  1   a  faces the microphone acoustic foam  133   b . The diaphragm  34  ( FIG. 2 ) of the first microphone  30   a , the diaphragm  34  of the second microphone  30   b  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the first microphone  30   a  and the front  38  of the speaker  36  face substantially opposite directions, whereas the face  32  of the second microphone  30   b  and the front  38  of the speaker  36  face substantially the same direction. A sheet of inner acoustic foam  134  is provided on the interior surface of the baffle plate  1   a  and covers the first microphone  30   a  in the microphone recess  3   a . An ear cushion  136  is provided on the inner surface of the rim  4   a  of the baffle plate  4  to cushion the transducer assembly  129  against the head  137  of a wearer as the transducer assembly  129  fits over the wearer&#39;s ear  137   a . An inner cavity  135  is defined by the ear cushion  136  between the inner acoustic foam  134  and the wearer&#39;s head  137 . 
     Referring next to  FIG. 9A , in a fourth embodiment each transducer assembly  139  includes a generally concave housing  140  and a piece of outer acoustic foam  141  typically provided on the interior surface of the housing  140 . An angled cavity flat baffle plate  1   b  ( FIG. 5B ) is mounted to the housing  140  to define an outer cavity  142  between the housing  140  and the rear surface of the parallel baffle plate  1   b . A speaker  36  is mounted to the baffle plate  1   b . A flat piece of microphone acoustic foam  143   a  is provided on one of the angled surfaces of the bi-angled microphone recess  3   b  in the baffle plate  1   b . A first microphone  30   a  mounted to the baffle plate  1   b  has a face  32  which is angled toward the microphone acoustic foam  143   a . An angled piece of microphone acoustic foam  143   b  is provided on the rear surface of the rim  4   b  of the baffle plate  1   b , and the face  32  of a second microphone  30   b  mounted to the baffle plate  1   b  faces the microphone acoustic foam  143   b . The diaphragm  34  ( FIG. 2 ) of the first microphone  30   a , the diaphragm  34  of the second microphone  30   b  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the first microphone  30   a  and the front  38  of the speaker  36  face generally opposite directions, and the face  32  of the first microphone  30   a  is angled away from the speaker  36 . The face  32  of the second microphone  30   b  and the front  38  of the speaker  36  face generally the same direction, and the face  32  of the second microphone  30   b  is angled away from the speaker  36 . The faces  32  of both the first microphone  30   a  and the second microphone  30   b  are oriented at an angle of about 1-90 degrees with respect to the front  38  of the speaker  36 , and the first microphone  30   a  and the second microphone  30   b  face opposite directions. A sheet of inner acoustic foam  144  is provided on the interior surface of the baffle plate  1   b  and covers the first microphone  30   a  in the microphone recess  3   b . An ear cushion  146  is provided on the inner surface of the rim  4   b  of the baffle plate  1   b  to cushion the transducer assembly  139  against the head  147  of a wearer as the transducer assembly  139  fits over the wearer&#39;s ear  147   a . An inner cavity  145  is defined by the ear cushion  146  between the inner acoustic foam  144  and the wearer&#39;s head  147 . The transducer assembly  139  may be used in conjunction with the signal processing circuit  89  of  FIG. 1D , except with the face  32  of the first microphone  30   a  and the face  32  of the second microphone  30   b  each angled away from the speaker  36 . 
     Referring next to  FIG. 9B , in an alternative fourth embodiment each transducer assembly  149  includes a generally concave housing  150  which includes a housing extension  150   a  in the upper portion thereof to facilitate positioning of the interior transducer assembly components away from the ear  157   a  of a wearer. A piece of outer acoustic foam  151  is typically provided on the interior surface of the housing  150 . An angled cavity slant baffle plate  1   d  is mounted to the housing  150 . An outer cavity  152  is defined between the housing  150  and the rear surface of the baffle plate  1   d . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   d . A flat piece of microphone acoustic foam  153   a  is provided on one of the angled surfaces of the bi-angled microphone recess  3   d  in the baffle plate  1   d . The face  32  of a first microphone  30   a  mounted to the baffle plate  1   d  faces the flat microphone acoustic foam  153   a . An angled piece of microphone acoustic foam  153   b  is provided on the rear surface of the rim  4   d  of the baffle plate  1   d , and the face  32  of a second microphone  30   b  mounted to the baffle plate  1   d  faces the angled microphone acoustic foam  153   b . The diaphragm  34  ( FIG. 2 ) of the first microphone  30   a , the diaphragm  34  of the second microphone  30   b  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the first microphone  30   a  and the face  32  of the second microphone  30   b  face opposite directions, with the first microphone  30   a  and the speaker  36  facing generally opposite directions. The faces  32  of both the first microphone  30   a  and the second microphone  30   b  are oriented at an angle of about 1-90 degrees with respect to the front  38  of the speaker  36 , and the face  32  of the first microphone  30   a  and the face  32  of the second microphone  30   b  are oriented away from the speaker  36 . A sheet of inner acoustic foam  154  is provided on the interior surface of the baffle plate  1   d  and covers the first microphone  30   a  in the microphone recess  3   d . An ear cushion  156  is provided on the exterior surface of the rim  4   d  of the baffle plate  1   d  to cushion the transducer assembly  149  against the head  157  of a wearer. An inner cavity  155  is defined by the ear cushion  156  between the inner acoustic foam  154  and the wearer&#39;s head  157 . Due to the slanted configuration of the baffle plate  1   d  in combination with the housing extension  150   a  of the housing  150 , the first microphone  30   a , the second microphone  30   b  and the speaker  36  are angled away from the ear  157   a  of the wearer, across the inner cavity  155 . 
     Referring next to  FIG. 10A , in a fifth embodiment each transducer assembly  159  includes a generally concave housing  160  and a piece of outer acoustic foam  161  typically provided on the interior surface of the housing  160 . An angled cavity flat baffle plate  1   b  ( FIG. 5B ) is mounted to the housing  160 , defining an outer cavity  162 . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   b . A flat piece of microphone acoustic foam  163  is provided on one of the angled surfaces of the bi-angled microphone recess  3   b , and the face  32  of a microphone  30  mounted to the baffle plate  1   b  faces the microphone acoustic foam  163 . The diaphragm  34  ( FIG. 2 ) of the microphone  30  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the microphone  30  is angled away from the speaker  36 , and the face  32  of the microphone  30  and the front  38  of the speaker  36  face generally opposite directions. The face  32  of the microphone  30  is disposed at an angle of typically about 1-90 degrees with respect to the front  38  of the speaker  36 . A sheet of inner acoustic foam  164  is provided on the interior surface of the baffle plate  1   b  and typically encloses the microphone  30  in the microphone recess  3   b . An ear cushion  166  is provided on the exterior surface of the rim  4   b  of the baffle plate  4 . An inner cavity  165  is defined by the ear cushion  166  and between the inner acoustic foam  174  and the wearer&#39;s head (not shown). The transducer assembly  159  may be used in conjunction with the signal processing circuit  87  of  FIG. 1C , except with the face  32  of the microphone  30  angled away from the speaker  36 . 
     Referring next to  FIG. 10B , in an alternative fifth embodiment each transducer assembly  169  includes a generally concave housing  170  which includes a housing extension  170   a . A piece of outer acoustic foam  171  is typically provided on the interior surface of the housing  170 . An angled cavity slant baffle plate  1   d  is mounted to the housing  170 . An outer cavity  172  is defined between the housing  170  and the rear surface of the baffle plate  1   d . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   d . A flat piece of microphone acoustic foam  173  is typically provided on one of the angled surfaces of the microphone recess  3   d , and the face  32  of a microphone  30  mounted to the baffle plate  1   d  faces the microphone acoustic foam  173 . The diaphragm  34  ( FIG. 2 ) of the microphone  30  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”, and the face  32  of the microphone  30  is angled away from the speaker  36 , with the face  32  of the microphone  30  disposed at an angle of about 1-90 degrees with respect to the front  38  of the speaker  36 . The face  32  of the microphone  30  and the front  38  of the speaker  36  face generally opposite directions. A sheet of inner acoustic foam  174  is provided on the interior surface of the baffle plate  1   d  and typically encloses the microphone  30  in the microphone recess  3   d . An ear cushion  176  is provided on the exterior surface of the rim  4   d  of the baffle plate  1   d . An inner cavity  175  is defined by the ear cushion  176  and between the inner acoustic foam  174  and the wearer&#39;s head (not shown). Due to the slanted configuration of the baffle plate  1   d  in combination with the housing extension  170   a  of the housing  170 , the microphone  30  and the speaker  36  are angled away from the ear (not shown) of a wearer, across the inner cavity  175 . A simple signal processing circuit  87  which is suitable for the transducer assembly  169  is shown in  FIG. 1C  and includes an external audio input  81 , an audio preamplifer  82 , a summing circuit  83 , a speaker amplifier  84  and a microphone preamplifier  85 . The face  32  of the microphone  30  and the front  38  of the speaker  36  are oriented in generally opposite directions. 
     Referring next to  FIG. 11A , in a sixth embodiment each transducer assembly  179  includes a generally concave housing  180  and a piece of outer acoustic foam  181  typically provided on the interior surface of the housing  180 . An angled cavity flat baffle plate  1   b  ( FIG. 5B ) is mounted to the housing  180 , defining an outer cavity  182 . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   b . An angled piece of microphone acoustic foam  183  is provided on the rear surface of the baffle plate  1   b , and the face  32  of a microphone  30  mounted to the baffle plate  1   d  faces the microphone acoustic foam  183 . The diaphragm  34  ( FIG. 2 ) of the microphone  30  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the microphone  30  is angled or tilted away from the speaker  36  at an angle of typically about 1-90 degrees with respect to the front  38  of the speaker  36 , with the face  32  of the microphone  32  and the front  38  of the speaker  36  facing generally the same direction. A sheet of inner acoustic foam  184  is provided on the interior surface of the baffle plate  1   b . An ear cushion  186  is provided on the exterior surface of the rim  4   b  of the baffle plate  1   b . An inner cavity  185  is defined by the ear cushion  186  and between the inner acoustic foam  184  and the wearer&#39;s head (not shown). A simple signal processing circuit  80  which is suitable for the transducer assembly  179  is shown in  FIG. 1B  and includes an external audio input  81 , an audio preamplifer  82 , a summing circuit  83 , a speaker amplifier  84  and a microphone preamplifier  85 . The face  32  of the microphone  30  and the front  38  of the speaker  36  are oriented in generally the same direction. 
     Referring next to  FIG. 11B , in an alternative sixth embodiment each transducer assembly  189  includes a generally concave housing  190  which includes a housing extension  190   a . A piece of outer acoustic foam  191  is typically provided on the interior surface of the housing  190 . An angled cavity slant baffle plate  1   d  is mounted to the housing  190 . An outer cavity  192  is defined between the housing  190  and the rear surface of the baffle plate  1   d . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   d . An angled piece of microphone acoustic foam  193  is provided on the rear surface of the baffle plate  1   d , and the face  32  of a microphone  30  mounted to the baffle plate  1   d  faces the microphone acoustic foam  193 . The diaphragm  34  ( FIG. 2 ) of the microphone  30  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the microphone  30  is angled or tilted away from the speaker  36  at an angle of typically about 1-90 degrees with respect to the front  38  of the speaker  36 , with the face  32  of the microphone  32  and the front  38  of the speaker  36  facing generally the same direction. A sheet of inner acoustic foam  194  is provided on the interior surface of the baffle plate  1   d . An ear cushion  196  is provided on the exterior surface of the rim  4   d  of the baffle plate  1   d . An inner cavity  195  is defined by the ear cushion  196  and between the inner acoustic foam  194  and the wearer&#39;s head (not shown). Due to the slanted configuration of the baffle plate  1   d  in combination with the housing extension  190   a  of the housing  190 , the microphone  30  and the speaker  36  are angled away from the ear (not shown) of a wearer, across the inner cavity  195 . A simple signal processing circuit  80  which is suitable for the transducer assembly  189  is shown in  FIG. 1B . 
     Referring next to  FIG. 12A , in a seventh embodiment each transducer assembly  199  includes a generally concave housing  200  and a piece of outer acoustic foam  201  typically provided on the interior surface of the housing  200 . A parallel cavity flat baffle plate  1   a  is mounted to the housing  200  to define an outer cavity  202  between the housing  200  and the rear surface of the parallel cavity flat baffle plate  1   a , with the outer acoustic foam  201 ′ provided in the outer cavity  202 . A speaker  36  is mounted to the baffle plate  1   a . A flat piece of microphone acoustic foam  203   a  is provided in the microphone recess  3   a  of the baffle plate  1   a . The face  32  of a first speaker  30   a , mounted to the baffle plate  1   a  inside the microphone recess  3   a , faces the microphone acoustic foam  203   a . An angled piece of microphone acoustic foam  203   b  is provided on the rear surface of the rim  4   a  of the baffle plate  1   a , and the face  32  of a second microphone  30   b  mounted to the baffle plate  1   a  faces the microphone acoustic foam  203   b . The diaphragm  34  ( FIG. 2 ) of the first microphone  30   a , the diaphragm  34  of the second microphone  30   b  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the first microphone  30   a  and the front  38  of the speaker  36  face substantially opposite directions, whereas the face  32  of the second microphone  30   b  and the front  38  of the speaker  36  face generally the same direction with the microphone  30   b  angled or tilted away from the speaker  36  at an angle of typically about 1-90 degrees with respect to the front  38  of the speaker  36 . A sheet of inner acoustic foam  204  is provided on the interior surface of the baffle plate  1   a  and covers the first microphone  30   a  in the microphone recess  3   a . An ear cushion  206  is provided on the inner surface of the rim  4   a  of the baffle plate  4  to cushion the transducer assembly  199  against the head  207  of a wearer as the transducer assembly  199  fits over the wearer&#39;s ear  207   a . An inner cavity  205  is defined by the ear cushion  206  between the inner acoustic foam  204  and the wearer&#39;s head  207 . A simple signal processing circuit  89  which is suitable for the transducer assembly  189  is shown in  FIG. 1D  and includes an external audio input  81 , an audio preamplifer  82 , a summing circuit  83 , a speaker amplifier  84  and microphone preamplifiers  85   a ,  85   b . A speaker  36  is connected to the speaker amplifier  84 . First and second microphones  30   a ,  30   b  are connected to the respective preamplifiers  85   b ,  85   a , respectively. The face  32  of the microphone  30   a  and the front  38  of the speaker  36  are oriented in opposite directions, whereas the face  32  of the microphone  30   b  and the front  38  of the speaker  36  are oriented in substantially the same direction. As simple signal processing circuit  89  which is suitable for the transducer assembly  199  is shown in  FIG. 1D . 
     Referring next to  FIG. 12B , in an alternative seventh embodiment each transducer assembly  209  includes a generally concave housing  210  which includes a housing extension  210   a  in the upper portion thereof to facilitate positioning of the interior transducer assembly components away from the ear  127   a  of a wearer. A piece of outer acoustic foam  211  is typically provided on the interior surface of the housing  210 . A parallel cavity slant baffle plate  1   c  is mounted to the housing  210 . An outer cavity  212  is defined between the housing  210  and the rear surface of the baffle plate  1   c . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   c . A flat piece of microphone acoustic foam  213   a  is provided in the microphone recess  3   c  of the baffle plate  1   c . The face  32  of a first microphone  30   a , mounted to the baffle plate  1   c  inside the microphone recess  3   c , faces the microphone acoustic foam  213   a . An angled piece of microphone acoustic foam  213   b  is provided on the rear surface of the rim  4   a  of the baffle plate  1   c . The face  32  of a second microphone  30   b  mounted to the baffle plate  1   c  faces the microphone acoustic foam  213   b . The diaphragm  34  ( FIG. 2 ) of the first microphone  30   a , the diaphragm  34  of the second microphone  30   b  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the first microphone  30   a  and the front  38  of the speaker  36  face generally opposite directions, whereas the face  32  of the second microphone  30   b  is angled or tilted away from the speaker  36  at an angle of typically about 1-90 degrees with respect to the front  38  of the speaker  36  and faces generally the same direction as the front  38  of the speaker  36 . A sheet of inner acoustic foam  214  is provided on the interior surface of the baffle plate  1   c  and covers the first microphone  30   a  in the microphone recess  3   c . An ear cushion  216  is provided on the exterior surface of the rim  4   c  of the baffle plate  1   c  to cushion the transducer assembly  209  against the head  217  of a wearer. An inner cavity  215  is defined by the ear cushion  216  between the inner acoustic foam  214  and the wearer&#39;s head  217 . Due to the slanted configuration of the baffle plate  1   c  in combination with the housing extension  210   a  of the housing  2120 , the first microphone  30   a , the second microphone  30   b  and the speaker  36  are oriented away from the ear  217   a  of the wearer, across the inner cavity  215 . A simple signal processing circuit  89  which is suitable for the transducer assembly  209  is shown in  FIG. 1D . 
     Referring next to  FIG. 13A , in an eighth embodiment each transducer assembly  219  includes a generally concave housing  220  and a piece of outer acoustic foam  221  typically provided on the interior surface of the housing  220 . An angled cavity flat baffle plate  1   b  ( FIG. 5B ) is mounted to the housing  220  to define an outer cavity  222  between the housing  220  and the rear surface of the parallel baffle plate  1   b . A speaker  36  is mounted to the baffle plate  1   b . A flat piece of microphone acoustic foam  223   a  is provided on one of the angled surfaces of the bi-angled microphone recess  3   b  in the baffle plate  1   b . The face  32  of a first microphone  30   a , mounted to the baffle plate  1   b  inside the microphone recess  3   b , faces the microphone acoustic foam  223   a . A second flat piece of microphone acoustic foam  223   b  is provided on the rear surface of the rim  4   b  of the baffle plate  1   b , and the face  32  of a second microphone  30   b , mounted to the baffle plate  1   b , faces the microphone acoustic foam  223   b . The diaphragm  34  ( FIG. 2 ) of the first microphone  30   a , the diaphragm  34  of the second microphone  30   b  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the first microphone  30   a  and the front  38  of the speaker  36  face generally opposite directions, and the face  32  of the first microphone  30   a  is angled or oriented away from the speaker  36  at an angle of typically about 1-90 degrees with respect to the front  38  of the speaker  36 . The face  32  of the second microphone  30   b  and the front  38  of the speaker  36  face substantially the same direction. A sheet of inner acoustic foam  224  is provided on the interior surface of the baffle plate  1   b  and covers the first microphone  30   a  in the microphone recess  3   b . An ear cushion  226  is provided on the inner surface of the rim  4   b  of the baffle plate  1   b  to cushion the transducer assembly  219  against the head  227  of a wearer as the transducer assembly  219  fits over the wearer&#39;s ear  227   a . An inner cavity  225  is defined by the ear cushion  226  between the inner acoustic foam  224  and the wearer&#39;s head  227 . A simple signal processing circuit  89  which is suitable for the transducer assembly  219  is shown in  FIG. 1D . 
     Referring next to  FIG. 13B , in an alternative eighth embodiment each transducer assembly  229  includes a generally concave housing  230  which includes a housing extension  230   a  in the upper portion thereof to facilitate positioning of the interior transducer assembly components away from the ear  237   a  of a wearer. A piece of outer acoustic foam  231  is typically provided on the interior surface of the housing  230 . An angled cavity slant baffle plate  1   d  is mounted to the housing  230 . An outer cavity  232  is defined between the housing  230  and the rear surface of the baffle plate  1   d . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   d . A flat piece of microphone acoustic foam  233   a  is provided on one of the angled surfaces of the bi-angled microphone recess  3   d  in the baffle plate  1   d . The face  32  of a first microphone  30   a , mounted to the baffle plate  1   d  inside the microphone recess  3   d , faces the microphone acoustic foam  233   a . A second flat piece of microphone acoustic foam  233   b  is provided on the rear surface of the rim  4   d  of the baffle plate  1   d . The face  32  of a second microphone  30   b  is mounted to the baffle plate  1   d  and faces the microphone acoustic foam  233   b . The diaphragm  34  ( FIG. 2 ) of the first microphone  30   a , the diaphragm  34  of the second microphone  30   b  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the first microphone  30   a  and the front  38  of the speaker  36  face generally opposite directions, and the face  32  of the first microphone  30   a  is angled or oriented away from the speaker  36  at an angle of typically about 1-90 degrees with respect to the front  38  of the speaker  36 . The face  32  of the second microphone  30   b  and the front  38  of the speaker  36  face substantially the same direction. A sheet of inner acoustic foam  234  is provided on the interior surface of the baffle plate  1   d  and covers the first microphone  30   a  in the microphone recess  3   d . An ear cushion  236  is provided on the exterior surface of the rim  4   d  of the baffle plate  1   d  to cushion the transducer assembly  229  against the head  237  of a wearer. An inner cavity  235  is defined by the ear cushion  236  between the inner acoustic foam  234  and the wearer&#39;s head  237 . Due to the slanted configuration of the baffle plate  1   d  in combination with the housing extension  230   a  of the housing  230 , the first microphone  30   a , the second microphone  30   b  and the speaker  36  are angled away from the ear  237   a  of the wearer, across the inner cavity  235 . A simple signal processing circuit  89  which is suitable for the transducer assembly  229  is shown in  FIG. 1D . 
     Referring next to  FIG. 14A , in a ninth embodiment each transducer assembly  239  includes a generally concave housing  240  and a piece of outer acoustic foam  241  typically provided on the interior surface of the housing  240 . A parallel cavity flat baffle plate  1   a  is mounted to the housing  240  to define an outer cavity  242  between the housing  240  and the rear surface of the parallel cavity flat baffle plate  1   a . A speaker  36  is mounted to the baffle plate  1   a . The back  33  of a first speaker  30   a  is mounted to the baffle plate  1   a  inside the microphone recess  3   a . An angled piece of microphone acoustic foam  243  is provided on the rear surface of the rim  4   a  of the baffle plate  1   a , and the face  32  of a second microphone  30   b  mounted to the baffle plate  1   a  faces the microphone acoustic foam  243 . The diaphragm  34  ( FIG. 2 ) of the first microphone  30   a , the diaphragm  34  of the second microphone  30   b  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the first microphone  30   a  and the front  38  of the speaker  36  face substantially the same direction, whereas the face  32  of the second microphone  30   b  and the front  38  of the speaker  36  face generally the same direction. The face  32  of the first microphone  30   a  is angled or tilted away from the speaker  36 , toward the microphone acoustic foam  243  at an angle of typically about 1-90 degrees with respect to the front  38  of the speaker  36 . A sheet of inner acoustic foam  244  is provided on the interior surface of the baffle plate  1   a  and covers the first microphone  30   a  in the microphone recess  3   a . An ear cushion  246  is provided on the inner surface of the rim  4   a  of the baffle plate  4  to cushion the transducer assembly  239  against the head  207  of a wearer as the transducer assembly  239  fits over the wearer&#39;s ear  247   a . An inner cavity  245  is defined by the ear cushion  246  between the inner acoustic foam  244  and the wearer&#39;s head  237 . A simple signal processing circuit  89  which is suitable for the transducer assembly  239  is shown in  FIG. 1D . 
     Referring next to  FIG. 14B , in an alternative ninth embodiment each transducer assembly  249  includes a generally concave housing  250  which includes a housing extension  250   a  in the upper portion thereof to facilitate positioning of the interior transducer assembly components away from the ear  257   a  of a wearer. A piece of outer acoustic foam  251  is typically provided on the interior surface of the housing  250 . A parallel cavity slant baffle plate  1   c  is mounted to the housing  250 . An outer cavity  252  is defined between the housing  250  and the rear surface of the baffle plate  1   c . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   c . The back  33  of a first microphone  30   a  is mounted to the baffle plate  1   c  inside the microphone recess  3   c . An angled piece of microphone acoustic foam  253  is provided on the rear surface of the rim  4   a  of the baffle plate  1   c , and the face  32  of a second microphone  30   b  mounted at an angle on the baffle plate  1   c  faces the microphone acoustic foam  253 . The diaphragm  34  ( FIG. 2 ) of the first microphone  30   a , the diaphragm  34  of the second microphone  30   b  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the first microphone  30   a  and the front  38  of the speaker  36  face substantially the same direction, whereas the face  32  of the second microphone  30   b  and the front  38  of the speaker  36  face generally the same direction. The face  32  of the first microphone  30   a  is angled or tilted away from the speaker  36 , toward the microphone acoustic foam  253  at an angle of typically about 1-90 degrees with respect to the front  38  of the speaker  36 . A sheet of inner acoustic foam  254  is provided on the interior surface of the baffle plate  1   c  and covers the first microphone  30   a  in the microphone recess  3   c . An ear cushion  256  is provided on the exterior surface of the rim  4   c  of the baffle plate  1   c  to cushion the transducer assembly  249  against the head  257  of a wearer. An inner cavity  255  is defined by the ear cushion  256  between the inner acoustic foam  254  and the wearer&#39;s head  257 . Due to the slanted configuration of the baffle plate  1   c  in combination with the housing extension  250   a  of the housing  250 , the first microphone  30   a , the second microphone  30   b  and the speaker  36  are oriented away from the ear  257   a  of the wearer, across the inner cavity  255 . 
     Referring next to  FIG. 15A , in a tenth embodiment each transducer assembly  259  includes a generally concave housing  260  and a piece of outer acoustic foam  261  typically provided on the interior surface of the housing  260 . An angled cavity flat baffle plate  1   b  ( FIG. 5B ) is mounted to the housing  260  to define an outer cavity  262  between the housing  260  and the rear surface of the parallel baffle plate  1   b . A speaker  36  is mounted to the baffle plate  1   b . The back  33  of a first microphone  30   a  is mounted on one of the angled surfaces of the bi-angled microphone recess  3   b  in the baffle plate  1   b . A piece of microphone acoustic foam  263  is provided on the rear surface of the rim  4   b  of the baffle plate  1   b , and the face  32  of a second microphone  30   b  mounted to the baffle plate  1   b  faces the microphone acoustic foam  263 . The diaphragm  34  ( FIG. 2 ) of the first microphone  30   a , the diaphragm  34  of the second microphone  30   b  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the first microphone  30   a  and the front  38  of the speaker  36  face generally the same direction, and the microphone face  32  is angled or oriented toward the speaker  36  at an angle of typically about 1-90 degrees with respect to the front  38  of the speaker  36 . The face  32  of the second microphone  30   b  and the front  38  of the speaker  36  face substantially the same direction. A sheet of inner acoustic foam  264  is provided on the interior surface of the baffle plate  1   b  and covers the first microphone  30   a  in the microphone recess  3   b . An ear cushion  266  is provided on the inner surface of the rim  4   b  of the baffle plate  1   b  to cushion the transducer assembly  259  against the head  267  of a wearer as the transducer assembly  259  fits over the wearer&#39;s ear  267   a . An inner cavity  265  is defined by the ear cushion  266  between the inner acoustic foam  264  and the wearer&#39;s head  267 . A simple signal processing circuit  89  which is suitable for the transducer assembly  259  is shown in  FIG. 1D , except the faces  32  of the first microphone  30   a  and the second microphone  30   b  are oriented in generally the same direction. 
     Referring next to  FIG. 15B , in an alternative tenth embodiment each transducer assembly  269  includes a generally concave housing  270  which includes a housing extension  270   a  in the upper portion thereof to facilitate positioning of the interior transducer assembly components away from the ear  277   a  of a wearer. A piece of outer acoustic foam  271  is typically provided on the interior surface of the housing  270 . An angled cavity slant baffle plate  1   d  is mounted to the housing  270 . An outer cavity  272  is defined between the housing  270  and the rear surface of the baffle plate  1   d . A speaker  36  is typically mounted to the rear surface of the baffle plate  1   d . The back  33  of a first microphone  30   a  is provided on one of the angled surfaces of the bi-angled microphone recess  3   d  in the baffle plate  1   d . A flat piece of microphone acoustic foam  273  is provided on the rear surface of the rim  4   d  of the baffle plate  1   d , and the face  32  of a second microphone  30   b  mounted to the baffle plate  1   d  faces the microphone acoustic foam  273 . The diaphragm  34  ( FIG. 2 ) of the first microphone  30   a , the diaphragm  34  of the second microphone  30   b  and the diaphragm  40  of the speaker  36  are disposed in substantially the same acoustic plane “P”. The face  32  of the first microphone  30   a  and the front  38  of the speaker  36  face generally the same direction, and the microphone face  32  is angled or oriented toward the speaker  36  at an angle of typically about 1-90 degrees with respect to the front  38  of the speaker  36 . The face  32  of the second microphone  30   b  and the front  38  of the speaker  36  face substantially the same direction. A sheet of inner acoustic foam  274  is provided on the interior surface of the baffle plate  1   d  and covers the first microphone  30   a  in the microphone recess  3   d . An ear cushion  276  is provided on the exterior surface of the rim  4   d  of the baffle plate  1   d  to cushion the transducer assembly  269  against the head  277  of a wearer. An inner cavity  275  is defined by the ear cushion  276  between the inner acoustic foam  274  and the wearer&#39;s head  277 . Due to the slanted configuration of the baffle plate  1   d  in combination with the housing extension  270   a  of the housing  270 , the first microphone  30   a , the second microphone  30   b  and the speaker  36  are angled away from the ear  277   a  of the wearer, across the inner cavity  275 . 
     Referring next to  FIG. 16 , in an eleventh embodiment each transducer assembly  279  of the electroacoustic device  10  includes a generally concave housing  280 . A piece of outer acoustic foam  281  is typically provided on the interior surface of the housing  280 . A standard or conventional, generally planar baffle plate  340  is mounted to the housing  280 . Accordingly, an outer cavity  282  is defined between the housing  280  and the rear surface of the baffle plate  340 , with the outer acoustic foam  281  provided in the outer cavity  282 . A speaker  287  is typically mounted to the rear surface of the baffle plate  340 . The speaker  287  includes a speaker housing  288  having a front  289  disposed in communication with a speaker opening (not shown) provided in the baffle plate  340 . A speaker diaphragm  291  is provided in the speaker housing  288 , and a central opening  292  extends through the speaker housing  288  and through the diaphragm  291 . A microphone  30  is mounted to the speaker housing  288 , inside the central opening  292 . The face  32  of the microphone  30  faces substantially the same direction as the front  289  of the speaker housing  288 , and the diaphragm  34  of the microphone  30  and the diaphragm  291  of the speaker  287  are disposed in substantially the same acoustic plane “P”. A sheet of inner acoustic foam  284  is provided on the interior surface of the baffle plate  340 . An ear cushion  286  is provided on the exterior surface of the baffle plate  340  to cushion the transducer assembly  279  against the head of a wearer. An inner cavity  285  is defined by the ear cushion  286  and between the inner acoustic foam  284  and the wearer&#39;s head (not shown). The transducer assembly  279  may be used in conjunction with the signal processing circuit  80  heretofore described with respect to  FIG. 1B . 
     Referring next to  FIG. 17 , in a twelfth embodiment each transducer assembly  299  of the electroacoustic device  10  includes a generally concave housing  300  having a piece of outer acoustic foam  301  typically provided on the interior surface of the housing  300 . A standard or conventional, generally planar baffle plate  340  is mounted to the housing  300 . An outer cavity  302  is defined between the housing  300  and the rear surface of the baffle plate  340 , with the outer acoustic foam  301  provided in the outer cavity  302 . A speaker  307  is typically mounted to the rear surface of the baffle plate  340 . The speaker  307  includes a speaker housing  308  having a front  309  disposed in communication with a speaker opening (not shown) provided in the baffle plate  340 . A speaker diaphragm  311  is provided in the speaker housing  308 , and a central opening  312  extends through the speaker housing  308  and through the diaphragm  311 . A microphone  30  is mounted to the speaker housing  308 , inside the central opening  312 . The face  32  of the microphone  30  and the front  309  of the speaker housing  308  face substantially opposite directions, and the diaphragm  34  of the microphone  30  and the diaphragm  311  of the speaker  307  are disposed in substantially the same acoustic plane “P”. A sheet of inner acoustic foam  304  is provided on the interior surface of the baffle plate  340 . An ear cushion  306  is provided on the exterior surface of the baffle plate  340  to cushion the transducer assembly  299  against the head of a wearer. An inner cavity  305  is defined by the ear cushion  306  and between the inner acoustic foam  304  and the wearer&#39;s head (not shown). The transducer assembly  299  may be used in conjunction with the signal processing circuit  87  heretofore described with respect to  FIG. 1B . 
     Referring next to  FIG. 18 , in a thirteenth embodiment each transducer assembly  319  of the electroacoustic device  10  includes a generally concave housing  320  having a piece of outer acoustic foam  321  typically provided on the interior surface of the housing  320 . A standard or conventional, generally planar baffle plate  340  is mounted to the housing  320 . An outer cavity  322  is defined between the housing  320  and the rear surface of the baffle plate  340 , with the outer acoustic foam  321  provided in the outer cavity  322 . A speaker  307 , such as that heretofore described with respect to  FIG. 17 , is typically mounted to the rear surface of the baffle plate  340 . The speaker  307  includes a speaker housing  308  having a front  309  disposed in communication with a speaker opening (not shown) provided in the baffle plate  340 . A speaker diaphragm  311  is provided in the speaker housing  308 , and a central opening  312  extends through the speaker housing  308  and through the diaphragm  311 . A microphone  30  is mounted to the speaker housing  308 , inside the central opening  312 . The face  32  of the microphone  30  and the front  309  of the speaker housing  308  face generally opposite directions, and the diaphragm  34  of the microphone  30  and the diaphragm  311  of the speaker  307  are disposed in substantially the same acoustic plane “P”. The diaphragm  34  of the microphone  30  is disposed at an angle of typically about 0-90 degrees with respect to the diaphragm  311  of the speaker  307 , and the face  32  of the microphone  30  faces the diaphragm  311 . A sheet of inner acoustic foam  324  is provided on the interior surface of the baffle plate  340 . An ear cushion  326  is provided on the exterior surface of the baffle plate  340  to cushion the transducer assembly  319  against the head of a wearer. An inner cavity  325  is defined by the ear cushion  326  and between the inner acoustic foam  324  and the wearer&#39;s head (not shown). The transducer assembly  319  may be used in conjunction with the signal processing circuit  87  heretofore described with respect to  FIG. 1C , except with the face  32  of the speaker  30  disposed at an angle with respect to the diaphragm  311  of the speaker  307  ( FIG. 18 ). 
     Referring next to  FIG. 19 , in a fourteenth embodiment each transducer assembly  329  of the electroacoustic device  10  includes a generally concave housing  330  having a piece of outer acoustic foam  331  typically provided on the interior surface of the housing  330 . A standard or conventional, generally planar baffle plate  340  is mounted to the housing  330 . An outer cavity  332  is defined between the housing  330  and the rear surface of the baffle plate  340 , with the outer acoustic foam  331  provided in the outer cavity  332 . A speaker  307 , such as that heretofore described with respect to  FIG. 17 , is typically mounted to the rear surface of the baffle plate  340 . The speaker  307  includes a speaker housing  308  having a front  309  disposed in communication with a speaker opening (not shown) provided in the baffle plate  340 . A speaker diaphragm  311  is provided in the speaker housing  308 , and a central opening  312  extends through the speaker housing  308  and through the diaphragm  311 . A microphone  30  is mounted to the speaker housing  308 , inside the central opening  312 . The face  32  of the microphone  30  and the front  309  of the speaker housing  308  face generally the same direction, and the diaphragm  34  of the microphone  30  and the diaphragm  311  of the speaker  307  are disposed in substantially the same acoustic plane “P”. The diaphragm  34  of the microphone  30  is disposed at an angle of typically about 1-90 degrees with respect to the diaphragm  311  of the speaker  307 . A sheet of inner acoustic foam  334  is provided on the interior surface of the baffle plate  340 . An ear cushion  336  is provided on the exterior surface of the baffle plate  340  to cushion the transducer assembly  329  against the head of a wearer. An inner cavity  335  is defined by the ear cushion  336  and between the inner acoustic foam  334  and the wearer&#39;s head (not shown). The transducer assembly  329  may be used in conjunction with the signal processing circuit  80  heretofore described with respect to  FIG. 1B , except with the face  32  of the speaker  30  disposed at an angle with respect to the diaphragm  311  ( FIG. 19 ) of the speaker  307 . 
     While the preferred embodiments of the invention have been described above, it will be recognized and understood that various modifications can be made in the invention and the appended claims are intended to cover all such modifications which may fall within the spirit and scope of the invention.