CROSS-REFERENCE To-RELATED APPLICATIONS  
       [0001]    This application claims priority to the provisional application identified by U.S. Serial No. 60/353,760, filed on Feb. 2, 2002, the entire content of which is hereby incorporated herein by reference. 
     
    
     
       STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT  
         [0002]    Not Applicable. 
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING  
       [0003]    [0003]FIG. 1 a  is a perspective view of an apparatus constructed in accordance with the present invention for attenuating sounds exceeding a predetermined level thereby protecting an individual&#39;s hearing.  
         [0004]    [0004]FIG. 1 b  is a side view of the apparatus depicted in FIG. 1 a.    
         [0005]    [0005]FIG. 1 c  is a perspective view of the apparatus depicted in FIG. 1 a , wherein an opposite side of the apparatus is shown  
         [0006]    [0006]FIG. 1 d  is a side view of the apparatus in a folded condition.  
         [0007]    [0007]FIG. 1 e  is a top plan view of the apparatus shown in FIG. 1 d.    
         [0008]    [0008]FIG. 2 is a block diagram of a circuit constructed in accordance with the present invention.  
         [0009]    [0009]FIG. 3 is a schematic diagram of the hearing protection circuit depicted in FIG. 2.  
         [0010]    [0010]FIG. 4 is a flow diagram of a main loop of a method developed in accordance with the present invention.  
         [0011]    [0011]FIG. 5 is a flow diagram of an Analog to Digital Interrupt Service Routine constructed in accordance with the present invention.  
         [0012]    [0012]FIG. 6 is a flow diagram of a Keypad Digital Interrupt Service Routine constructed in accordance with the present invention.  
         [0013]    [0013]FIG. 7 is a flow diagram of a set volume subroutine constructed in accordance with the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]    Referring now to the drawings and in particular to FIGS. 1 a - 1   e , shown therein and designated by a reference numeral  10  is an apparatus constructed in accordance with the present invention for attenuating or enhancing sounds exceeding a predetermined level thereby protecting an individual&#39;s hearing. In one preferred embodiment, the apparatus  10  permits the individual to set the volume of sounds passed through the apparatus  10  to the individual&#39;s ears and selectively attenuates the magnitude of the sounds, in real-time, based on the volume setting and a predetermined sound profile programmed into the apparatus  10 . The predetermined sound profile can be modified or tailored to certain environments so that the acoustical characteristics of the apparatus  10  can be customized without modifying the hardware of the apparatus  10  thereby reducing the manufacturing costs of apparatus  10 . The apparatus  10  shown in FIG. 1 is exemplified as a headset for use as a noise abatement headset, but could be exemplified as a single ear headset, an ear bud style device, or a hearing aid.  
         [0015]    The apparatus  10  is provided with a head piece  12  supporting two earpieces  14   a  and  14   b . Each of the earpieces  14   a  and  14   b  have a cushioned inner face  16   a  and  16   b , and an inner cup portion  18   a  and  18   b  retaining a speaker  20   a  and  20   b . The speakers  20   a  and  20   b  are each acoustically coupled to the ear canal when the apparatus  10  is being worn by an individual. Each of the ear pieces  14   a  and  14   b  also supports a microphone  22   a  and  22   b  configured to receive sound energy which occurs external to the earpieces  14   a  and  14   b  (hereinafter referred to as “external sound energy”) and to convert the external sound energy to electrical sound signals. The electrical sound signals are indicative of the sound energy received by the microphones  22   a  and  22   b . The microphones  22   a  and  22   b  can be any type of suitable microphones, such as condenser microphones.  
         [0016]    The apparatus  10  is also provided with a circuit  24 , and a sound control device  26 . The circuit  24  receives the electrical sound signals produced by the microphones  22   a  and  22   b  and drives the speakers  20   a  and  20   b  for selectively coupling the external sound energy to at least one of the individual&#39;s ear canals when the apparatus  10  is worn by the individual. The sound control device  26  has buttons or knobs which can be manipulated by the individual to control certain operations of the apparatus  10 . The control device  24  is implemented by way of example as a keypad. The control device  24  can be provided as a separate unit, attached to the head piece  12 , or attached to and supported by one of the earpieces  14   a  and  14   b . As will be discussed below, the control device  24  is preferably provided with an on/off button  30 , an up-volume button  32 , a down-volume button  34 , a left balance button  36 , and a right balance button  38 .  
         [0017]    A block diagram of one preferred implementation of the circuit  24  is shown in FIG. 2, and a schematic diagram of the circuit  24  is shown in FIG. 3. It should be understood that the present invention should not be limited to the implementation shown in FIG. 3. Changes can be made to the component values, arrangements of components as well as source of components so long as the circuit  24  functions in the manner set forth herein.  
         [0018]    The circuit  24  is provided with a pre-amplifier  44 , a digital potentiometer  46 , a microcontroller  48 , a speaker driver amplifier  50 , a power control  52 , a power supply  54  and a peak detector  56 .  
         [0019]    As will be understood by those skilled in the art, the electrical sound signals produced by the microphones  22   a  and  22   b  are low voltage signals. The pre-amplifier  44  amplifies the voltage of the electrical sound signals produced by the microphones  22   a  and  22   b . The gain of the pre-amplifier  44  can vary depending on a desired voltage level. It has been found that a suitable gain for the pre-amplifier  44  is about 40 V/V. The pre-amplifier  44  is also provided with a low-pass filter tuned to attenuate high frequency signals that 1) an individual&#39;s ear cannot detect, or 2) unnecessarily rob the circuit  24  of power. The low-pass filter of the pre-amplifier  44  can be tuned to any suitable frequency that provides a pleasing tone to the individual. It has been found that a suitable cutoff frequency for the low-pass filter is about 8 kHz. The pre-amplifier  44  can be implemented as an operational amplifier circuit having a feedback capacitor tuned to attenuate the high frequency signals. Although the pre-amplifier  44  is shown in FIG. 2 for purposes of clarity as one pre-amplifier, it should be understood that the pre-amplifier  44  is preferably implemented as two separate amplifiers with one amplifier for the microphone  22   a  (left microphone) and one amplifier for the microphone  22   b  (right microphone). The pre-amplifier  44  outputs amplified signals over signal paths  60   a  and  60   b.    
         [0020]    The amplified signals output by the pre-amplifier  44  are received by a first input of the digital potentiometer  46 . A second input of the digital potentiometer  46  is connected to a virtual ground  62 , and a “wiper” of the digital potentiometer  46  is connected to the microcontroller  48  via a signal path  64 . The “wiper” selects a percentage of the amplified signal output by the pre-amplifier  44  to be passed to the speaker driver amplifier  50  via signal paths  68   a  and  68   b . The percentage can range from 0% to 100%.  
         [0021]    In one preferred embodiment, the digital potentiometer  46  has 256 steps and the signal received from the microcontroller  48  via the signal path  64  is a serial data stream. For example, if the “wiper” of the digital potentiometer  46  is set at 128, then 50% of the amplified signal is output by the digital potentiometer  46  and passed to the speaker driver amplifier  50  via the signal paths  68   a  and  68   b . Although the digital potentiometer  46  is shown in FIG. 2 for purposes of clarity as one digital potentiometer, it should be understood that the digital potentiometer  46  is preferably implemented as a dual digital potentiometer with one digital potentiometer for the microphone  22   a  (left microphone) and one digital potentiometer for the microphone  22   b  (right microphone). Each of the digital potentiometers  46  are controlled independently by the microcontroller  48  so that the percentages of the amplified signals passed through the digital potentiometers  46  can be either the same or different. The digital potentiometer  46  for the right microphone  22   b  forms a right channel, and the digital potentiometer  46  for the left microphone  22   a  forms a left channel.  
         [0022]    The signals output by the digital potentiometer  46  via the signal paths  68   a  and  68   b  are received by the speaker driver amplifier  50 . The speaker driver amplifier  50  drives the speakers  20   a  and  20   b . The speaker driver amplifier  50  is typically implemented as an integrated circuit.  
         [0023]    The circuit  24  is provided with an external audio input having a left channel  70   a  and a right channel  70   b  so that an individual can connect an external audio device, such as a portable tape player or a Compact Disc player to the apparatus  10  and listen to audio while simultaneously receiving input from the left and right microphones  22   a  and  22   b  via the pre-amplifier  44  and the digital potentiometer  46 . The left channel  70   a  and the right channel  70   b  are connected to the speaker driver amplifier  50  via resistors and capacitors to provide a fixed amount of attenuation of the signals provided on the left and right channels  70   a  and  70   b . The volume of the audio provided through the left and right channels  70   a  and  70   b  can be controlled by varying the volume of the external audio device rather than by modifying the volume of the apparatus  10  with the control device  26 . The amount of attenuation of the external audio signal can be varied depending on the magnitude of the external audio signal, the gain of the speaker driver amplifier  50 , the characteristics of the speakers  20   a  and  20   b  as well as the desired maximum volume level. When the gain of the speaker driver amplifier  50  is about unity and a maximum volume level is about 82 db, it has been found that a suitable amount of attenuation of the audio signal provided by the external audio device is between about 99% and 90% (i.e., 1% to 10% of the audio signal is passed to the speaker driver amplifier  50 ).  
         [0024]    As will be discussed in more detail below, the microcontroller  48  samples the amplified signals output by the pre-amplifier  44  to determine whether the amplified signals exceed a predetermined threshold value. If the amplified signals exceed the predetermined threshold value, the microcontroller  48  immediately outputs signals to the digital potentiometer  46  to reduce the volume levels of the signals being passed through the digital potentiometer  46 . In this manner, sounds exceeding a predetermined threshold will be attenuated while sounds not reaching the predetermined threshold will not be attenuated. This permits the circuit  24  to reduce the overall amplification during loud sounds while permitting an amplification level selected by the volume control during lower level sounds.  
         [0025]    The microcontroller  48  is provided with an A/D converter  74  for sampling the amplified signals output by the pre-amplifier  44 . The A/D converter  74  samples at a pre-selected rate of about 62 kHz. To optionally ensure that a strong pulse in the amplified signal does not decay in between samples, the circuit  24  is provided with the peak detector  56 . That is, the amplified signals output by the pre-amplifier  44  are fed to the peak detector  56  where the left and right channels are mixed and the mixed signal is peak held for a predetermined time period. The sample period (1/frequency) of the A/D converter  74  is the maximum time that could occur between a peak and a sample. The droop during the sample period must be less than the acceptable error allowed. The peak holding function of the peak detector  56  may be eliminated due to the rapid sampling period of the A/D converter  74 . However, if a slower sampling period for the A/D converter  74  is implemented the peak holding function of the peak detector  56  can also be used.  
         [0026]    As will be discussed in more detail below, the balance, volume and attenuation levels of the apparatus  10  are set by storing values in the microcontroller  48  (or associated computer readable medium, such as a memory external to the microcontroller  48 , or the like) and selectively writing such values to the digital potentiometer  46 . A right volume level variable is maintained for the volume level of the right channel and a left volume level variable is maintained for the volume level of the left channel of the digital potentiometer  46  so that the volume levels of the right and left channels are independently controlled. The microcontroller  48  is programmed to provide a plurality of separate volume levels for the apparatus  10 . For example, the microcontroller  48  can be programmed to provide 10 volume levels, 20 volume levels or the like. A lookup table is stored in the microcontroller  48  (or associated computer readable medium) where 1) a volume level value and 2) an attenuation value is stored for each separate volume level. During normal conditions where the circuit  24  is not attenuating the electrical sound signals, the microcontroller  48  writes a volume level value to the digital potentiometers  46  for the right channel and the left channel.  
         [0027]    For example, if the right volume level variable is set to 3, and the left volume level variable is set to 5, the volume level value for a volume setting of 3 is output to the digital potentiometer  46  for the right channel, and the volume level value for a volume setting of 5 is output to the digital potentiometer  46  for the left channel. To attenuate the electrical sound signals, the attenuation value for a volume setting of 3 is output to the digital potentiometer  46  for the right channel, and the attenuation value for a volume setting of 5 is output to the digital potentiometer  46  for the left channel.  
         [0028]    For a volume level 1 (minimum volume), a volume level value of 0 may be stored, and for a volume level 20 (maximum volume) a volume level value of 255 may be stored for a 256 step digital potentiometer  46 . Volume level values for the remaining volume levels 2-19 are provided between the minimum volume level value and the maximum volume level value. The volume level values stored in the microcontroller  48  can be selected to provide any desired transfer function. The volume level values are preferably selected to approximate a 2 db-3 db logarithmic decay of the volume levels. However, the volume level values can be spaced linearly or randomly between the minimum and volume level and the maximum volume level to provide any desired transfer function.  
         [0029]    It should be noted that the input impedance of the speaker driver amplifier  50  is only about twice the output impedance of the digital potentiometer  46  thereby introducing a gain error. Thus, if the digital potentiometer  46  is set at 50% the output of the speaker driver amplifier  50  will not be set at 50%. The gain error can be eliminated by providing a buffer stage between the digital potentiometer  46  and the speaker driver amplifier  50 . However, adding a buffer stage increases the cost of the circuit  24 . Thus, the gain error is taken into account when determining the volume level values.  
         [0030]    The attenuation values are also selected to provide a desired amount of attenuation or enhancement for the apparatus  10 . It should be understood that the attenuation values can vary depending on the desired amount of attenuation of signals exceeding the predetermined threshold. Moreover, it should be understood that the attenuation values can exceed the volume level values. For example, the attenuation values can exceed the volume level values if it is desired to not let any sound come in unless the sound exceeded a certain level. This might be useful is an individual had to work next to a noisy machine and the individual wanted to block out this noise for comfort but if a loud sound such as a warning indicator was present, the signal would be allowed to pass through. In this case, the attenuation values would be selected so that no signal would go above about 82 db and the volume level values would be set to zero.  
         [0031]    When the on/off button  30  is pressed on the control device  26 , a signal is transmitted to the power control  52  via a signal path  76 . The power control  52  momentarily gates power to the microcontroller  48  via a signal path  78 . In response thereto, the microcontroller  48  toggles the power control  52  via a signal path  80  to maintain the power on. This provides the microcontroller  48  with the ability to automatically turn-off the apparatus  10  by again toggling the power control  52  via the signal path  80 .  
         [0032]    Referring now to FIG. 4, shown therein is a flow chart of a main loop of a software program executing on the microcontroller  48 . Upon receiving power from the power control  52 , the microcontroller  48  branches to a step  100  where the microcontroller  48  initializes the input output ports and miscellaneous variables and timers to specify the topology for the circuit  24 . The microcontroller  48  then branches to a step  102  where the microcontroller  48  enables power by writing a signal out to a port thereby toggling the power control  52 , as discussed above. The microcontroller  48  branches to a step  104  to initialize the interrupt service routines, and then branches to a step  106  to restore user settings, such as the volume and/or balance settings. The user settings are typically stored in on-board rewritable memory, although the user settings can be stored on a separate memory chip.  
         [0033]    The microcontroller  48  then checks to see if the on/off button  30  has been released at a step  108 . If not, the microcontroller  48  loops back to the step  108  to check again. If the on/off button  30  has been released, the microcontroller  48  branches to a step  110  to enable interrupts. The software program enables two interrupts: a keypad ISR (a block diagram of which is shown in FIG. 6, and an Analog-to Digital converter ISR (ADC ISR) (a block diagram of which is shown in FIG. 5).  
         [0034]    The microcontroller  48  then branches to a step  112  to decrement a shut off timer for automatically shutting off the apparatus  10  after a predetermined time period of for example, 20 minutes, 1 hour, 2 hours, 3 hours or 4 hours. Thus, if the individual forgets to shut off the apparatus  10 , the microcontroller  48  will automatically shut off the apparatus  10  after the predetermined time period has elapsed to help conserve the power supply  54 . The microcontroller  48  then branches to a step  114  where the microcontroller  48  determines whether the shutoff timer=0. If so, the microcontroller  48  branches to a step  116  to begin shutting off the apparatus  10 .  
         [0035]    If not, the microcontroller  48  branches to a step  118  to determine whether the on/off button  30  has been pressed. If the on/off button  30  has not been pressed, the microcontroller  48  branches to a step  120  where the microcontroller  48  sets an off delay timer to a maximum value and then branches to the step  112 . The off delay timer prevents the inadvertent shutting off of the apparatus  10  by making the individual hold the on/off button for a predetermined time period, for example. If the on/off button  30  has been pressed, the microcontroller  48  branches to a step  122  where the off delay timer is decremented. The microcontroller  48  then branches to a step  124  where the microcontroller  48  checks whether the off delay timer=0. If not, the microcontroller  48  branches to the step  112 , and if so, the microcontroller  48  branches to the step  116  to shut off the apparatus  10 .  
         [0036]    At the step  116 , the volume of the apparatus  10  is set to 0 in both the right channel and the left channel by writing a data stream representing a 0 value to the digital potentiometer  46 . The microcontroller  48  then branches to a step  126  where the interrupts are disabled followed by a step  128  where the microcontroller  48  determines whether user settings have changed. If the user settings have changed, the microcontroller  48  branches to a step  130  where current settings are written into the rewritable or flash memory. If not, the microcontroller  48  branches to a step  132  where power is disabled by toggling the signal path  80 . The microcontroller  48  then branches to a step  134  where the microcontroller  48  loops until all of the power is discharged from the power control  52 .  
         [0037]    Shown in FIG. 5 is a flow chart of the ADC ISR subroutine. The microcontroller  48  first reads a conversion value from the A/D converter  74  at a step  140 . The microcontroller  48  then branches to a step  142  where the microcontroller  48  determines whether the conversion value is greater than a predetermined threshold value. If not, the microcontroller  48  branches to a step  144  and the attenuation of the digital potentiometer  46  is not changed. If the conversion value is greater than the predetermined threshold value, the microcontroller  48  branches to a step  146  where an offset number is added to the volume level of the right channel to provide a modified right channel index variable, and the offset number is also added to the volume level of the left channel to provide a modified left channel index variable.  
         [0038]    The microcontroller  48  then branches to a step  148  where the modified right channel index variable is passed to a right set volume routine, and the modified left channel index variable is passed to a left set volume routine. The left and right set volume routines are similar in construction and function. Thus, only one of the left and right set volume routines will be discussed herein for purposes of clarity.  
         [0039]    The left set volume routine is shown in FIG. 7. Once the microcontroller  48  branches into the set volume routine, the microcontroller  48  branches to a step  152  where the modified left channel index variable is used as an index to retrieve an attenuation value for the left channel. The microcontroller  48  then branches to a step  154  where the attenuation value for the left channel is written to the digital potentiometer  46 . The microcontroller  48  then branches to a step  156  where the microcontroller  48  exits the set volume routine. The left and right set volume routines could be combined into a single routine.  
         [0040]    The microcontroller  48  then branches to a step  160  where the microcontroller  48  sets an attenuation delay timer which sets a time period in which the output of the digital potentiometer  46  will be attenuated. The time period of the attenuation delay timer can vary widely, but it has been found by Applicant&#39;s that a suitable time period is in the range from about 300 ms to about 500 ms. Desirably, the time period of the attenuation delay timer is set for about a 400 ms delay.  
         [0041]    The microcontroller  48  then branches to the step  144  where the attenuation delay timer is decremented. The microcontroller  48  then branches to a step  162  where the microcontroller  48  determines whether the attenuation delay timer is completed. If not, the microcontroller  48  branches to a step  164  and thereby returns from the ADC ISR. If the attenuation delay timer is completed, then the microcontroller  48  branches to a step  166  to reset the normal volume levels. More specifically, at the step  166 , the microcontroller  48  retrieves the volume level for the right channel and the volume level for the left channel.  
         [0042]    The microcontroller  48  then branches to a step  168  where the volume level for the right channel is passed to the right channel set volume routine and the volume level for the left channel is passed to the left channel set volume routine. Only one of the left and right set volume routines will be discussed herein for purposes of clarity. Once the microcontroller  48  branches into the set volume routine, the microcontroller  48  branches to the step  152  where the volume level for the right channel is used to retrieve a volume level value for the right channel. The microcontroller  48  then branches to the step  154  where the volume level values for the right channel is written to the digital potentiometer  46 . The microcontroller  48  then branches to the step  156  where the microcontroller  48  exits the set volume routine. The microcontroller  48  then branches to the step  164  to return from the ADC ISR.  
         [0043]    The microcontroller  48  also executes a keypad ISR, which is shown in FIG. 6, for setting the volume and the balance of the apparatus  10 . When one of the up-volume button  32 , down-volume button  32 , left balance button  36 , and right balance button  38  is pressed a signal internal to the microcontroller  48  for the duration of the up-volume button  32 , down-volume button  32 , left balance button  36 , or right balance button  38  being pressed is generated. The keypad ISR is executed on a level of the signal, rather than on an edge of the signal thereby re-interrupting the microcontroller  48  when the up-volume button  32 , down-volume button  32 , left balance button  36 , or right balance button  38  are held down. Once the keypad ISR is executed, the microcontroller  48  branches to a step  180  where the shutoff timer is reset to a predetermined value.  
         [0044]    The microcontroller  48  then sequentially branches to the steps  182 ,  184 ,  186  and  188  where the microcontroller  48  determines whether the up-volume button  32 , down-volume button  32 , left balance button  36 , or right balance button  38  are being pressed.  
         [0045]    To set the volume of the left and right channels, as well as the balance the microcontroller  48  is programmed with a desired right volume level variable, and a desired left volume level variable. The desired right volume level variable and the desired left volume level variable are permitted to become negative so that the microcontroller  48  can keep track of the balance.  
         [0046]    If the up-volume button  32  is being pressed, the microcontroller  48  branches to a step  190  where the microcontroller  48  checks the values of the desired right volume level variable and the desired left volume variable. If neither of the desired right volume level variable for the right channel and the desired left volume level variable for the left channel are above the maximum volume level, such as 20, the microcontroller  48  increments the desired right volume level variable for the right channel and the desired left volume level variable for the left channel. The microcontroller  48  then branches to a step  192  where the microcontroller  48  calculates a balance for the apparatus  10 , and then branches to a step  194  where the microcontroller  48  calls the set volume routine for setting the volume level for the right channel and the left channel as discussed above. The step  192  will be discussed in more detail below.  
         [0047]    If the down-volume button  34  is being pressed, the microcontroller  48  branches to a step  196  where the microcontroller  48  checks the values of the desired right volume level variable and the desired left volume variable. If either of the desired right volume level variable for the right channel and the desired left volume level variable for the left channel are above the minimum volume level, such as 0, the microcontroller  48  decrements the desired right volume level variable for the right channel and the desired left volume level variable for the left channel.  
         [0048]    If the left balance button  36  is being pressed, the microcontroller  48  branches to a step  198  where the microcontroller  48  checks the values of the desired right volume level variable and the desired left volume variable. The desired right volume level variable for the right channel is decremented if the desired right volume variable is not already at the minimum volume level, such as 0. The desired left volume level is incremented if the desired left volume level is not already at the maximum volume level, such as 20.  
         [0049]    If the right balance button  38  is being pressed, the microcontroller  48  branches to a step  200  where the microcontroller  48  checks the values of the desired right volume level variable and the desired left volume variable. The desired right volume level variable for the right channel is incremented if the desired right volume level variable is not already at the maximum level. The desired left volume level variable for the left channel is decremented if the desired left volume level variable is not already at the minimum level.  
         [0050]    At the step  192 , the microcontroller  48  checks the value of the desired right volume level variable. If the desired right volume level variable is equal to or greater than zero, the right volume level variable is set to be equal to the desired right volume level variable. If the desired right volume level variable is less than zero, the right volume level variable is set to zero. The microcontroller  48  also checks the value of the desired left volume level variable. If the desired left volume level variable is equal to or greater than zero, the left volume level variable is set to be equal to the desired left volume level variable. If the desired left volume level variable is less than zero, the left volume level variable is set to zero.  
         [0051]    The volume level of the apparatus  10  is then set at the step  194  by passing the left and right volume level variables to the set volume subroutine, as discussed above.  
         [0052]    As will be recognized by those skilled in the art, the apparatus  10  has many advantages over the prior art. For example, the apparatus  10  utilizes low cost and low power components thereby decreasing the cost of the apparatus  10  while increasing the time periods in between battery changes. Moreover, the lookup tables stored in the microcontroller  48  can be selectively customized for customers without modification of the hardware.  
         [0053]    Changes may be made in the embodiments of the invention described herein, or in the parts or the elements of the embodiments described herein, or in the steps or sequence of steps of the methods described herein, without departing from the spirit and/or the scope of the invention as defined in the following claims.
An earmuff comprising a headpiece and a circuit. The headpiece supports the earmuff on the head of an individual. The circuit has an input device for receiving external sound energy and converting the external sound energy to electrical sound signals.