Patent Publication Number: US-8992437-B2

Title: Ear input sound pressure level monitoring system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This Application is a Divisional of U.S. application Ser. No. 11/757,152, filed Jun. 1, 2007 and claims the priority benefit of Provisional Application No. 60/803,708 filed on Jun. 1, 2006 and Provisional Application No. 60/887,165 filed on Jan. 30, 2007, the disclosures of which are incorporated herein by reference in their entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention is directed to a system for monitoring the sound pressure levels at a listener&#39;s ear, and in particular, thought not exclusively, monitoring the sound pressure levels over time and to utilize that information to reduce hearing damage. 
     With the advent of an industrial society, people are exposed to noise pollution at greater and greater levels; both from background, such as street traffic, airplanes, construction sites and intentional exposure to high sound levels such as cell phones, MP3 players, and rock concerts. Studies show that ear damage, leading to permanent hearing impairment is not only increasing in the general population, but increasing at a significantly faster rate in younger populations. 
     The potential for hearing damage is a function of both the loudness and the duration of exposure to the sound stimulus. Safe listening durations at various loudness levels are known, and can be calculated by averaging audio output levels over time to yield a time-weighted average. Standard guidelines published by OSHA, NIOSH or other agencies are known. This calculation can be even further improved by accounting for aspects of the playback scenario, specifically the characteristics of the sound source and their proximity to the listener&#39;s ear. 
     Studies have also indicated that hearing damage is a cumulative phenomenon. Although hearing damage due to industrial or background noise exposure is more thoroughly understood, the risk of exposing one&#39;s self to excessive noise, especially with the use of headphones has also been recently studied. Protecting the ear from ambient noise is primarily done with the use of static earplugs that attempt to shield the inner ear from excessively high decibel noise. Background noise canceling earphones such as those produced by Bose and others, attempt to protect the ear form excessive ambient noise by producing a counter noise wave to cancel out the ambient noise at the ear. These prior art devices have been less than satisfactory because they do not completely prevent high decibel noise from reaching the ear, and do not account for the duration of exposure to harmful sounds at the ear. 
     It is also known from the prior art to provide active noise reduction at the ear to protect the ear from exposure to loud noises as disclosed in U.S. patent Application No. U.S. 2005/0254665. The art actively attenuating noise reaching the inner ear utilizing a control; a connection with an earpiece and attenuating the noise to the ear. However, there is no monitoring of the noise over time to account for the cumulative effect. Furthermore, there is no accounting for any restorative effects for sound pressure levels which are healing to the ear rather than destructive. 
     Dosimeters, such as that described in U.S. published Application No. U.S. 2005/0254667 are known. The device periodically measures prior sound level within the ear canal. However, the device does not take into account the cumulative effect of the noise or the effect of any restorative period. Furthermore, no remedial action is taken as a result of the readings. 
     It is also known from the prior art that headphones for consumer electronics have been provided with a predetermined maximum output level in an attempt to prevent ear damage. This approach is ineffective as it does not take into account listening duration and the calculation of risk for auditory injury. Other headphones are maximum-limited to produce levels that can still result in significant overexposure given enough time, or limit the user to levels, which may not be sufficient to achieve a short term listening level. In the latter case, consumer acceptance for the protective gear could be severely limited and a product would fail to survive in a competitive market and therefore be of no use. 
     Another alternative known in the art is to reduce the headphone output levels by increasing earphone impedance via an accessory placed between the media player and the earphones. The limitation of this approach is that it gives no consideration to the duration of exposure, and again either the user&#39;s chosen listening level cannot be achieved because the maximum level is too limited, or the level is sufficient to allow the user access to high enough sound levels, but risk overexposure due to potential duration of use. 
     Accordingly, a system that overcomes the shortcomings in the prior art would be useful. 
     BRIEF SUMMARY OF THE INVENTION 
     A system for monitoring sound pressure levels at the ear includes audio inputs for receiving ambient sounds and sounds received within the ear and outputting an audio input signal. An audio input level monitor receives the audio input signal and outputs a sound level signal corresponding to the strength of the audio input signal to a minimum threshold detector. The minimum threshold detector outputs a start signal if it has been determined that the sound level does not equal a minimum threshold level. 
     A digital timer receives the start signal and begins a clock until the minimum level threshold detector either receives a minimum level threshold sound level signal and discontinues output of the start signal or until the sound level pressure changes to another value, at which time a new start signal measuring a new time interval is output. The timer measures an amount of time during which the audio inputs have been exposed to a sound having a different level than the minimum threshold level. The elapsed time period is input to both a listening history database and to a listening fatigue calculator. The listening fatigue calculator receives an input from the digital timer and the input level detector and, as a function of the level of sound exposure and the time-period of exposure, determines a listening fatigue factor. When the listening fatigue factor corresponds to a state predictive of a damage level, the listening fatigue calculator outputs a warning to the system user of potential harm. 
     In at least one exemplary embodiment, this system includes an output acoustical transducer within the ear to reproduce the sound received at the ear. The system controls the level of noise produced in the ear as a function of the listening fatigue calculation. Additionally, ambient noise detection cancellation can be used to control the level of ambient noise. The warning of unsafe exposure to noise can include an audio warning at the ear, a visual warning in associated equipment, or one of attenuation or a complete noise cutoff at the output transducer. 
     In at least one exemplary embodiment, the audio input is disposed within an earpiece in situ in the ear for substantially occluding the ear. The system can also include an output transducer in the earpiece, which converts the input sound to a sound signal produced within the ear. The listening fatigue calculator attenuates the noise output by the output transducers upon receipt of the fatigue signal. 
     In at least one exemplary embodiment, the listening fatigue calculation is a function of the sound pressure level over time, the effective quiet level and exposure to the effective quiet level over time. 
     In still another exemplary embodiment, the listening fatigue calculation may also be a function of a noise reduction rate of the earpiece embodying the system as it processes the input audio signal to produce the output audio signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of the system for measuring and determining exposure to sound over time at the ear constructed in accordance with a first exemplary embodiment of the invention; 
         FIG. 2  is a block diagram of the system in accordance with at least one exemplary embodiment of the invention in situ in the ear; 
         FIG. 3  is a flow chart for calculating listening fatigue in accordance with at least one embodiment of the invention by measuring a quantity (e.g., the sound pressure level) over time as perceived at the ear; 
         FIG. 4  is a flow chart for determining a weighted ear canal sound pressure level in accordance with another exemplary embodiment of the invention; 
         FIG. 5  is a flow chart for determining a personalized recovery time constant in accordance with another exemplary embodiment of the invention; 
         FIG. 6  is a flow chart for determining an update epoch in accordance with at least one exemplary embodiment of the invention; and 
         FIG. 7  is a flow chart for determining an update epoch in accordance with yet another exemplary embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description of at least one exemplary embodiment is merely illustrative in nature and is in no way intended to limit the invention, its application, or uses. 
     Processes, techniques, apparatus, and materials as known by one of ordinary skill in the relevant art may not be discussed in detail but are intended to be part of the enabling description where appropriate, for example the fabrication and use of transducers. 
     In all of the examples illustrated and discussed herein, any specific values, for example the sound pressure level change, should be interpreted to be illustrative only and non-limiting. Thus, other examples of the exemplary embodiments could have different values. 
     Note that similar reference numerals and letters refer to similar items in the following figures, and thus once an item is defined in one figure, it may not be discussed for following figures. 
     Note that herein when referring to correcting or preventing an error or damage (e.g., hearing damage), a reduction of the damage or error and/or a correction of the damage or error are intended. 
     At least one exemplary embodiment of the invention is directed to measuring and determining the exposure to sound at the ear over time. Reference is made to  FIG. 1  in which a system, generally indicated as  100 , is constructed in accordance with at least one exemplary embodiment of the invention. System  100  includes an audio input device  113  for receiving sound at the ear. As will be discussed below, audio input device  113  can include an analog audio input device  11 ,  23  and a digital audio input  19 . In at least one exemplary embodiment, audio input  113  receives audio input from at least one of three sources, namely; ambient noise around the ear, direct input noise such as a MP3 player or other device which can produce a digital audio input at digital audio input  19 , and noise as detected within the ear canal  31  ( FIG. 2 ). The audio input device  113  outputs an audio signal corresponding to the received sound. Analog output signals from analog audio inputs  11 ,  23  are converted to a digital signal by an analog-to-digital (A/D) converter  118  so that digital sound signals are input into an input level detector  120 . 
     Input level detector  120  determines the sound pressure level of the sound received at audio input device  113 . Input level detector  120  outputs a sound pressure level (SPL) signal, which is input to a minimum-level threshold detector  122 . Minimum level threshold detector  122  determines whether or not the sound pressure level as detected by input level detector  120  exceeds a minimum level threshold. As will be discussed below, the minimum level threshold can be the effective quiet level of the individual, or some predetermined level substantially corresponding to a level which is ear damage neutral over time or a level of interest, such as, 80 dB, because of its effect on the ear. Therefore, if the minimum level threshold is detected as being exceeded, a loud signal is output to a start timer  124 , which triggers a digital timer system  126  to begin a clock. Conversely, if the minimum level threshold is detected as being below the minimum threshold, a quiet signal is output to a start timer  124 , which triggers a digital timer system  126  to begin a clock of a restorative period. If the sound pressure level is at the minimum threshold, no clock needs to be started because this is neutral to the desired effect. In a preferred embodiment, the clock signal is changed with every significant (more than 1 dB by way of example) change in sound pressure level to get an accurate profile of sound exposure over time. 
     Once the sound pressure level as detected at input level detector  120  is at the minimum level, a stop timer signal is output from stop timer  128  to digital timer system  126  to stop the clock corresponding to exposure to the loud level. Digital timer system  126  outputs a clock value corresponding to the time period at which the minimum level threshold was not met, or in the proffered embodiment, for each period corresponding to a discrete level change. 
     A data memory or learning history databank  127  receives the clock value from digital timer system  126  as well as the actual input level detected at input level detector  120  and determines a listening history or sound pressure level exposure history. The sound pressure level exposure history is a record of the user&#39;s exposure to sound pressure levels over time. Because the effect of exposure is cumulative, it is important that the exposure history be maintained. The listening history, as will be discussed below, can include real ear level data, listening duration data, time between listening sessions, absolute time, sound pressure level dose data, including any restorative sound level, number of acoustic transients and crest factor and other data. 
     The sound pressure level exposure history or listening history includes both the listening habits history and the environmental or ambient noise exposure history. The environmental noise exposure history is the exposure of a user to environmental noise over time as a result of the auditory stimuli inherent to the environment where the user is present. This can be highway traffic, construction site, even the restorative effect of the quiet of a library whereas, the listening habits history is associated for the purposes for this disclosure with user-directed auditory stimuli such as music, words, other noises, which a user intentionally encounters for a purpose such as communication, learning, and enjoyment. Therefore, database  127 , as will be discussed below, stores the cumulative SPL exposure. 
     It should be noted that in at least one exemplary embodiment, minimum level threshold detector  122  also starts the timer  124  when the sound pressure level is below the predetermined level. In this way, the restorative effect of below effective quiet noise is accumulated for determining overall exposure damage potential. 
     In effect, the only time that digital timer system  126  is not running is when the detected sound pressure level signal is at the minimum threshold level. A listening fatigue calculator  130  receives the input level signal from input level detector  120  and data from the data memory listening history  127 , and determines whether or not listening fatigue or hearing damage is likely to occur as a result of further exposure. Hearing damage is the injury to the hearing mechanism including conductive and sensorineural decrement in hearing threshold levels. It can be either temporary or permanent so long as it is a result of the noise exposure above Effective Quiet. In other words, listening fatigue calculator  130  will output a signal when a threshold determined as a function of exposure time and sound pressure level, as will be discussed in greater detail below, is achieved. At that point, a listening fatigue signal is output. 
     It should be noted that in an alternative embodiment, system  100  can make use of an ambient noise detection/cancellation system  142  as known in the art. These systems produce signals, which negate noise pressure levels at certain frequencies and/or certain levels to reduce the effect of undesired noise, whether environmental noise or user directed noise. It will have some effect in elongating the exposure time by negating the sound pressure level detected by input level detector  120 . 
     In at least one exemplary embodiment, the listening fatigue signal is utilized to prevent damage and encourages some action by the user when exposure levels are near damaging levels. Therefore, in one non-limiting example, a listening fatigue display  140  is provided for receiving the listening fatigue signal and displaying to the user a prompt to discontinue exposure to the sound level from the damaging sound source or audio source. 
     In another non-limiting example, the listening fatigue signal is output to an audio warning source  132 , which outputs an output audio warning to the user notifying the user that exposure to the sound source has reached critical levels. 
     In at least one exemplary, but non-limiting, embodiment, as will be discussed below, system  100  includes an output acoustical transducer  25  to provide an audio signal to the ear. Output acoustical transducer  25  operates under the control of a digital signal processor (DSP)  134 . Digital signal processor  134  receives a digital audio signal from input level detector  120 , which acts as a pass through for the digitized signals from audio input device  113 . Digital signal processor  134  passes the sound signals through to a digital to analog (D/A) converter  136  to drive acoustical transducers  25  to recreate the sound received at audio input device  113  inside the ear canal  31  in at least one exemplary embodiment of the invention as shown in  FIG. 2 . With such an exemplary embodiment, audio warning source  132  provides an output to digital sound processor  134  causing output acoustical transducer  25  to output a warning sound inside the ear of the user. 
     Lastly, in at least one further exemplary embodiment, listening fatigue calculator  130  outputs a listening fatigue signal to digital processor  134  which causes digital signal processor  134  to attenuate the sound signal prior to output to acoustical transducer  25  to reduce the signal output level by any of the linear gain reduction, dynamic range reduction, a combination of both, or a complete shutdown of transducer  25 . Attenuation would be at least to the level, if not below, the effective quiet level to allow for ear recovery prior to damage. 
     It should be noted, that because personal hearing levels can change from person to person, and because both of the time intervals are a function of many variables, in a non-limiting example, to provide a dynamic ever-changing response, system  100  operates under software control. The configuration of the digital sound processor  134 , listening fatigue calculator  130 , the minimum level threshold detector  122 , and the input level detector  120  are operated under software control. 
     In an exemplary embodiment of the invention, the control programs are stored in a program memory  148  for operating the firmware/hardware identified above. Furthermore, the program stored within memory  148  can be personalized as a result of testing of the user&#39;s ear, or by other modeling methods, in which system  100  includes a software interface  144  for receiving online or remote source updates and configurations. The software interface  144  communicates with a data port interface  146  within system  100 , which allows the input of software updates to program memory  148 . The updates can be transmitted across a distributed communications network, such as the Internet, where the updates take the form of online updates and configurations  143 . 
     It should be noted that there is multiple functionality distributed across system  100 . In at least one exemplary embodiment, at least audio input device  113  and acoustical transducer  25  are formed as an earpiece, which extends into the outer ear canal so that the processing of signals pertains to sound received at the ear. However, it is well within the scope of at least one exemplary embodiment of the invention to provide substantially all of the functionality in an earpiece so that system  100  is a “smart device.” 
     Reference is now made to  FIG. 2  in which system  100  in which the transducer configuration, that portion of system  100  which converts sound pressure level variations into electronic voltages or vice versa is shown. In this embodiment, acoustic transducers include microphones as an input and loudspeakers as an acoustical output. 
       FIG. 2  depicts the electro acoustical assembly  13  (also referred to herein as an in-the-ear acoustic assembly  13  or earpiece  13 ), as it would typically be placed in the ear canal  31  of ear  17  of user  35 . The assembly is designed to be inserted into the user&#39;s ear canal  31 , and to form an acoustic seal with the walls  29  of the ear canal  31  at a location  27 , between the entrance  15  to the ear canal  31  and the tympanic membrane or eardrum  33 . Such a seal is typically achieved by means of a soft and compliant housing of assembly  13 . A seal is critical to the performance of the system in that it creates a closed cavity in ear canal  31  of approximately 0.5 cc in a non-limiting example between the in-ear assembly  13  and the ear&#39;s tympanic membrane  33 . 
     As a result of this seal, the output transducer (speaker)  25  is able to generate a full range bass response time when reproducing sounds for the system user. This seal also serves to significantly reduce the sound pressure level at the user&#39;s eardrum  33  resulting from the sound field at the entrance  15  to the ear canal  31 . This seal is also the basis for the sound isolating performance of the electroacoustic assembly  13 . Located adjacent to speaker  25 , is an ear canal microphone  23 , which is also acoustically coupled to closed cavity  31 . One of its functions is that of measuring the sound pressure level in cavity  31  as a part of testing the hearing acuity of the user as well as confirming the integrity of the acoustic seal and the working condition of itself and speaker  25 . Audio input  11  (also referred to herein as ambient sound microphone (ASM)  11 ) is housed in assembly  13  and monitors sound pressure at the entrance  15  to the occluded ear canal. All transducers receive or transmit audio signals to an ASIC  21  that undertakes at least a portion of the audio signal processing described above and provides a transceiver for audio via the wired or wireless communication path  119 . 
     In the above description the operation of system  100  is driven by sound pressure level, i.e. sound levels are monitored for time periods or epochs during which the sound pressure level does not equal the minimum threshold or is constant. However, as will be discussed in connection with the next exemplary embodiments of the invention, system  100  can also operate utilizing fixed or variable sampling epochs determined as a function of one or more of time and changes in sound pressure level, sound pressure dosage level, a weighted sound pressure level, and restorative properties of the ear. 
     Reference is now made to  FIG. 3  in which a flow chart for monitoring the sound pressure level dose at various sample times n is provided. The process is started in a step  302 . An input audio signal is generated in a step  304  at either the ear canal microphone (ECM)  23  or the ambient sound microphone (ASM)  11 . Exposure time is a function of the sound pressure level, therefore, the epoch or time period used to measure ear exposure or, more importantly, the time-period for sampling sound pressure level is determined in a step  305 . The update epoch is used in the SPL dose function determination as well as to effect the integration period for the sound pressure level calculation that, as will be discussed below, is used to calculate the weighted ear canal sound pressure level. 
     Reference is now made to  FIGS. 6 and 7 . In  FIG. 6 , a method is defined to change the update epoch as a function of the weighted ear canal sound pressure level, which will be discussed in greater detail below. System  100  is capable of determining when earpiece  13  is in a charger or communication cradle (i.e., not in use in the ear of the user). In a step  684 , a predetermined standard is provided for the update epoch, 60 seconds in this example. In step  688 , the update epoch is set as the in-cradle update epoch. The in-cradle state is detected in step  686 . If it is determined in a step  690  that earpiece  13  (also referred to herein as earphone device  13 ) is in a charger or cradle mode, then the update epoch is set as the in-cradle epoch; in the step  688 . 
     However, if in step  690  it is determined that the earphone device  13  is in use, in other words “not in the cradle”, then, by default, an audio signal is input to earpiece  13  in step  692 . In step  693 , an ear canal sound pressure level is estimated as a function of the audio input at step  692 . The current (n) ear canal sound pressure level estimate is stored as a delay level in a step  698 . An audio input is determined at a later time when step  692  is repeated so that a second in-time ear canal sound pressure level estimate is determined. 
     In a step  600 , the delayed (n−1) or previous sound pressure level is compared with the current (n) ear canal sound pressure level estimate to calculate a rate of change of the sound pressure level. The change level is calculated in units of dB per second. This process of step  692  through  600  is periodically repeated. 
     In a step  606 , it is determined whether or not the sound pressure level change is less than a predetermined amount (substantially 1 dB by way of non-limiting example) between iterations, i.e., since the last time the ear canal sound pressure level is calculated. If the change is less than the predetermined level, then in step  604  the update epoch is increased. It is then determined in a step  602  whether or not the epoch update is greater than a predefined amount D set in step  694  as a maximum update epoch such as 60 seconds in a non-limiting example. If in fact, the update epoch has a value greater than the maximum update epoch D then the update epoch is set at the higher value D in step  608 . 
     If it is determined in step  606  that the sound pressure level change is greater than −1 dB, but less than +1 dB as determined in step  612 , then the update epoch value is maintained in a step  610 . However, if it is determined that the sound pressure level change is greater than +1 dB, then the update epoch value is decreased in a step  618  to obtain more frequent couplings. A minimum predetermined update epoch value such as 250 microseconds is set in a step  614 . If the decreased update epoch determined in step  618  is less than, in other words an even smaller minimum time-period than the predetermined minimum update epoch E, then the new update epoch is set as the new minimum update epoch value in steps  616  and  622 . In this way, the sample period is continuously being adjusted as a function of the change in sound pressure level at the ear. As a result, if the noise is of a spike variety as opposed to a constant value, the sampling interval will be changed to detect such spikes and protect the ear. 
     Reference is now made to  FIG. 7  in which a method for changing the update epoch is illustrated as a function of the way that the ear canal sound pressure level estimate is provided. Again, in accordance with at least one exemplary embodiment of the invention, the update epoch is decreased when the ear canal sound pressure level is high or increasing. 
     The difference between the embodiment of  FIG. 7  and the embodiment of  FIG. 6  is that the update epoch is not continuously adjusted, but is more static. If the ear canal sound pressure level is less than effective quiet (a decibel level) which when exposed to the ear over time does not damage or restore the ear, then the update epoch is fixed at a predefined maximum epoch value and this is the value used by system  100  as will be discussed in connection with  FIG. 3  below. In this embodiment, if the ear canal sound pressure level is determined to be greater then effective quiet, then the update epoch is fixed at a shorter minimum value and this is returned as the update epoch to be utilized. 
     In  FIG. 7 , specifically, as with  FIG. 6 , an in-cradle update epoch of 5 seconds by way of non-limiting example, is stored in system  100  in a step  784 . In a step  788 , the initial update epoch is set as the in-cradle update epoch. A maximum update epoch time, such as 2 seconds by way of non-limiting example, is stored in a step  794 . In a step  714 , an initial minimum update epoch (250 microseconds in this non-limiting example) is stored. 
     In a step  786  and step  790  it is determined whether or not system  100  is in a non-use state, i.e., being charged or in a cradle. If so, then the update epoch is set at the in-cradle update epoch. If not, then a digital audio signal is input from ear canal microphone  23  in step  792 . A sound pressure level is estimated in step  795 . It is then determined whether or not the ear canal sound pressure level is less than effective quiet in a step  732 . If the sound pressure level is less than the effective quiet as determined in step  732 , then the update epoch is set at the maximum update epoch in a step  730 . If the sound pressure level is louder than the effective quiet, then in step  716 , the update epoch is set to the minimum update epoch. 
     Returning to  FIG. 3 , in a non-limiting exemplary embodiment, the update epoch is set at 10 seconds in a step  302  utilizing either a constant predetermined sample time, or either of the methodologies discussed above in connection with  FIGS. 6 and 7 . In a step  306 , the input audio signal is sampled, held, and integrated over the duration of the epoch as determined in step  308 . As a result, the update epoch affects the integration period utilized to calculate the sound pressure level dose as a function of the sound pressure level and/or as the weighted ear canal sound pressure level. 
     In a step  310 , an earplug noise reduction rate (NRR) is stored. The noise reduction rate corresponds to the attenuation effect of earpiece  13 , or system  100 , on sound as it is received at audio input  11  and output at the output transducer  25  or as it passes from the outer ear to the inner ear, if any exemplary embodiment has no ambient sound microphone  11 . In a step  311 , a weighting ear canal sound pressure level is determined, partially as a function of the earplug noise reduction rate value. 
     Reference is now made to  FIG. 4  where a method for determining the weighted ear canal sound pressure level in accordance with at least one exemplary embodiment of the invention is illustrated. Like numerals are utilized to indicate like structure for ease of discussion and understanding. Weighting is done to compensate for the manner in which sound is perceived by the ear as a function of frequency and pressure level. As sounds get louder, the ear hears lower frequencies more efficiently. By weighting, if the level of the sound of the field is low, the methodology and system utilized by at least one exemplary embodiment of the invention reduces the low frequency and high frequency sounds to better replicate the sound as perceived by the ear. 
     Specifically, a weighting curve lookup table, such as A-weighting, acts as a virtual band-pass filter for frequencies at sound pressure levels. In a step  304 , the audio signal is input. In step  410 , frequency-dependent earplug noise reduction ratings are stored. These values are frequency-dependent and in most cases, set as manufacturer-specific characteristics. 
     As discussed above, in a step  306 , the input audio signal is shaped, buffered and integrated over the duration of each epoch. The sound pressure level of the shaped signal is then determined in a step  436 . It is determined whether or not ambient sound microphone  11  was utilized to determine the sound pressure level in a step  444 . If microphone  11  was utilized, then the frequency-dependent earplug noise reduction rating of earpiece  13  must be accounted for to determine the sound level within the ear. Therefore, the noise reduction rating, as stored in step  310 , is utilized with the sound pressure level to determine a true sound pressure level (at step  446 ) as follows:
 
SPL ACT =SPL−NRR:
 
where sound pressure SPL ACT  is the actual sound pressure level perceived at the ear, SPL is the sound pressure level determined in step  436  and NRR is the noise rate reduction value stored in step  410 .
 
     If the ambient sound microphone  11  is not used to determine the sound pressure level then the sound pressure level determined in step  436  is the actual sound pressure level. So that:
 
SPL ACT =SPL
 
     It is well within the scope of at least one exemplary embodiment of the invention to utilize the actual sound pressure level as determined so far to determine the affect of the sound pressure level sensed at the ear on the health of the ear. However, in at least one exemplary embodiment, the sound pressure level is weighted to better emulate the sound as heard within the ear. Therefore, in a step  412 , a weighting curve lookup table is stored within system  100 . In a step  440 , the weighting curve is determined as a function of the actual sound pressure level as calculated or determined above in steps  436 ,  446  utilizing a weighting curve lookup table such as the A-weighting curve. The A-weighting curve is then applied as a filter in step  438  to the actual sound pressure level. A weighted sound pressure level for a sampled time period (SPL_W(n)) is obtained to be utilized in a step  414 . 
     The weighting curve can be determined in step  440  by applying a frequency domain multiplication of the sound pressure level vector and the weighting curve stored in step  412 . The weighting curves can be stored as a lookup table on computer memory, or can be calculated algorithmically. Alternatively, the input audio signal can be filtered with a time or frequency domain filter utilizing the weighting curve stored in step  412  and the sound pressure level as calculated. For low-level sound pressure levels, those less than 50 dB, by way of non-limiting example, a weighting curve, which attenuates low and high frequencies can be applied (similar to an A-weighting curve). For higher sound pressure levels, such as more than 80 dB, by way of non-limiting example, the weighting curve can be substantially flat or a C-weighting curve. The resulting weighted ear canal sound pressure level during any respective sampling epoch is returned as the system output SPL_W(n) in step  414 . 
     Returning to  FIG. 3 , a safe listening time is calculated by comparing the weighted sound pressure level with the effective quiet level in step  316 . Therefore, a value A corresponding to how far from safe listening the sound pressure level is, is determined by the equation:
 
 A =SPL_W( n )−EfQ
 
where EfQ is equal to the effective quiet time as stored at step  312 .
 
     By utilizing this simple comparative function, fewer machinations and processes are needed. System  100  takes advantage of the fact that because the effective quiet time is neutral to the ear, sound pressure levels significantly above the effective quiet level are generally damaging and noise levels below the effective quiet are generally restorative. 
     In a step  318 , the remaining safe listening time at the beginning of any current sampling epoch (Time — 100%) is calculated. The remaining safe listening time is calculated as follows:
 
Time 100%=24/2*((SPL —   W ( n )−EfQ/3).
 
     In this embodiment, rather than make use of the Sound Level (L), the period is a function of the loudness and quietness of the weighted sound pressure level. It should be noted that effective quiet is used in the above example, but any level of interest, such as 80 dB, or no sound level, i.e., SPL_W(n)−0, may be used. The weighted sound pressure level and effective quiet can be expressed as a frequency-dependent numerical array or a value scalar. 
     It is next determined whether or not the difference between the current weighted sound pressure level and the effective quiet is above a tolerable threshold or not, i.e., whether the weighted SPL in the eardrum is considered loud or not. A sound pressure level dose is calculated depending upon whether the sound level is loud or not. The sound pressure level dose is the measurement, which indicates an individual&#39;s cumulative exposure to sound pressure levels over time. It accounts for exposure to direct inputs such as MP3 players, phones, radios and other acoustic electronic devices, as well as exposure to environmental or background noise, also referred to as ambient noise. The SPL dose is expressed as a percentage of some maximum time-weighted average for sound pressure level exposure. 
     Because the sound pressure level dose is cumulative, there is no fixed time-period for ear fatigue or damage. At effective quiet, the sound pressure level exposure time would theoretically be infinite. While the time period for the sound pressure level dose becomes smaller and smaller with longer exposure to loud noise. A tolerable level change threshold corresponding to the amount of noise above or below the effective quiet which has no great effect on the ear as compared to effective quiet is determined and stored in memory  127  in a step  320 . In a step  322 , the differential between the weighted sound pressure level and the effective quiet is compared to the level change threshold. 
     A differential value A, corresponding to the level change, is calculated as follows:
 
 A =SPL_W( n )−EfQ
 
If A is greater than the level change threshold, the noise is considered loud and the sound pressure level is calculated in a step  324  as follows:
 
SPL Dose=SPL Dose( n− 1)+(Update_Epoch/Time — 100%)
 
where SPL Dose(n−1) is the SPL Dose calculated during the last epoch; Update_Epoch is the time (in hours) since the last SPL Dose was calculated. As described above, Update_Epoch can be adaptive, e.g., shortened when the sound pressure level is louder; and Time — 100%, the time period remaining for safe exposure is determined by the equation:
 
Time — 100%=24 hours/2*(( L −EfQ)/3)
 
where L=sound level (in dB) of the combination of environmental noise and audio playback. It should be noted that sound level (L) can be substituted for SPL_W(n).
 
     It should be noted, as can be seen from the equation, that the time value becomes more important than the sound pressure level as updates are spread apart. However, this is to protect overexposure to harmful sounds because a less accurate sample size must account for the unknown. The wider the periodicity, the less accurate determination of actual exposure. Infrequent updates of the dose assume a relatively constant sound level, ignoring spikes and intervening restorative periods. Accordingly, sound pressure level and epoch periodicity are weighed against each other to protect the ear. 
     If in step  322  it is determined that the differential is not greater than the level change threshold, including negative values for A (which are restorative values), then in step  326  it is determined whether or not the differential, as determined in step  316 , is less than the level change threshold in a step  322 . If it is determined that the differential is not less than the level change threshold, then the received noise was the effective quiet level, i.e., the level change threshold equals zero and in a step  330 , the current SPL Dose is maintained at the same level. There is no change to the dose level. However, if the differential A is less than the level change threshold then this is a restorative quiet as determined in step  326 , so the SPL dose is determined in a Step  328  as follows:
 
SPL Dose=SPL Dose( n− 1)* e ^(−Update_epoch/τ)
 
Where: τ (referred to as “tau” in the following diagrams) is equal to approximately 7 hours. In some embodiments, tau is adaptive for different users. In at least one exemplary embodiment, the level change threshold is set at substantially 0.9-1.0 dB.
 
     In step  332 , the recovery time constant tau is determined. It is not a function of exposure, but rather of recovery. It can be a default number or be determined as will be discussed below. As the SPL Dose is calculated by system  100 , it is also monitored. Once the SPL Dose reaches a certain level, as it is a cumulative calculation, ear fatigue calculator  130  determines whether or not the SPL Dose corresponds to a fatigued ear, and if so, it outputs warnings as discussed in connection with  FIG. 1 . 
     Reference is now made to  FIG. 5  which depicts an optional methodology for not only updating the recovery time constant (tau) for individual users, but to provide additional methods for acting upon detected damaging exposure. The process is started at a step  548 . In a step  550 , it is determined whether or not the user wishes to make use of a registration process, for example online, for setting a personalized update epoch through communication with a remote registration system. If the user declines the registration, then the default tau is set at 7 hours in a step  552 . In a step  554 , this default value is transmitted to system  100  via a wired or wireless data communication network. 
     Alternatively, if the user registers in step  550 , a questionnaire is presented in a step  556  in which the user informs system  100  regarding a user sound exposure history, age, work habits and other personal details that could affect the user&#39;s personal recovery function time, i.e., the time constant tau. The individual characteristics can be input to a formula or utilized as part of a look up table to determine the tau for the individual user. The estimate of tau determined in step  556  is transmitted to system  100  via a wireless or wired data communication system in a step  558 . In step  560 , the initial estimate of tau is set from the value determined in step  556  (or step  552 ). 
     An initial hearing test is performed in a step  561 , which acquires data indicative of the user&#39;s hearing sensitivity. The test may be an otoacoustic emission (OAE) test or audiogram administered utilizing the ear canal receiver or speaker  25 . However, the test can also be administered over the Internet, telephone or other communication device capable of outputting sounds sent across a distributed network and enabling responsive communication. The data is stored in a computer memory as an initial test value in a step  570  and is used in further processing to detect a change in the user hearing response. 
     In a step  564 , it is determined whether the user has been recently exposed to loud sound pressure levels. This can be done utilizing the sound pressure level dose as stored or permanently calculated by system  100 . If it is decided in step  564  that the user&#39;s ear canal sound pressure level is low, then in a step  559  it is determined whether the time since the last test is greater than a maximum test epoch. At the outset, the maximum test epoch is a set number determined in a step  562 . In this non-limiting example, the maximum test epoch is set at 20 hours. 
     If it is determined that the time since the last test is greater than the maximum test epoch or, that there has been recent exposure to loud sound pressure level, then another test is administered in a step  566 . The resulting test metrics are stored in steps  568 ,  570 . In a step  571 , the newly determined test metrics are compared to the initial test metrics to calculate any change in the metrics. In step  572 , it is determined whether the change is predictive of hearing damage. If not, then in a step  582 , the tau is modified according the obtained metric. 
     If it is determined that the hearing damage is predicted, then in a step  578  the user is recommended to remove themselves from the noise as discussed above with the operation of listening fatigue calculator  130  and furthermore, the user can be recommended to seek professional audiological evaluation in a step  578 . This could be done by an in situ auditory or visual warning in step  580  by system  100 . On the other hand, if system  100  is used in connection with a communications device such as a telephone or a personal digital assistant, an e-mail can be created in steps  574 ,  576 ; not only warning the user of potential damage, but notifying a health professional so that a follow up examination can be performed. 
     It should be noted that a change in the hearing metric (e.g., a hearing sensitivity curve) is measured by system  100 . In response to the user&#39;s hearing metric, the recovery time constant tau is updated. For example, tau is shortened if the change in the user&#39;s hearing metric indicates the user has “sensitive ears”, i.e., if, following loud sound exposure, the user&#39;s hearing sensitivity takes longer than seven hours to return to the individual&#39;s normal. This modified tau can be used to calculate the sound pressure level dose, in particular in a restorative phase, to determine better overall sound pressure level exposure. 
     By providing a monitoring and protective system which, in at least one mode, continuously monitors sound pressure level at the ear until a potentially harmful exposure has occurred, rather than only monitoring for a predetermined time as with noise dose monitors which monitor for work shifts, a more accurate predictor of harm to the ear is provided. By utilizing a method, which determines exposure in part as a function of effective quiet exposure as well as loud noise exposure, an enhanced model of potential risk is achieved. By providing a series of warning mechanisms and preventive measures as a function of the determined potentially harmful dosage levels ear damage is more likely to be prevented. By providing the system in an earpiece which substantially occludes the ear and making use of audio inputs at the external and internal ear, a more accurate reading of noise level is provided and more control through a real time warning system is achievable. 
     It should be known that values for level change threshold, effective quiet time, and epoch were used above as examples. However, it should be noted that any values which when input and utilized in accordance with the methodologies above prevent permanent damage to the ear are within the scope of the invention and the invention should not be so limited to the specific examples above. 
     While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all modifications, equivalent structures and functions of the relevant exemplary embodiments. For example, although specific numbers may be quoted in the claims, it is intended that a number close to the one stated is also within the intended scope, i.e., any stated number (e.g., 80 dB) should be interpreted to be “about” the value of the stated number (e.g., about 80 dB). 
     Thus, the description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the exemplary embodiments of the present invention. Such variations are not to be regarded as a departure from the spirit and scope of the present invention.