Hearing damage limiting headphones

A device includes an input for receiving an audio signal, a speaker to convert the audio signal into an audible sound, and a memory for storing remediation instructions and detection instructions. The device further includes a processor coupled to the input, the speaker, and the memory. The processor is configured to process the audio signal according to the detection instructions and the remediation instructions to modulate amplitude of the audio signal based on the remediation instructions.

FIELD

This disclosure relates generally to headphones for listening to sounds, such as music. More particularly, this disclosure generally relates to headphones configured to automatically limit possible hearing damage by controlling characteristics of the sound output.

BACKGROUND

Exposure to audio signals at greater and greater amplitudes through the use of headphones and media devices, such as cell phones and MP3 players, has been increasing at an alarming rate. Exposure to audio signals at high decibel levels has been determined to be one of the primary causes of age-related permanent hearing impairment. However, hearing impairment is not only increasing in the general population, but is increasing at a significantly faster rate among young people, especially in among those who utilize media devices and wear headphones (or wireless earpieces) for significant amounts of time.

The extent of hearing damage sustained through exposure to sounds has been determined to be a function of both the amplitude and the duration of the audio signals, and particularly exposure to audio signals at amplitudes that exceed a safe acoustic threshold. Permanent hearing damage is a cumulative effect of exceeding the minimum thresholds or safe pressure levels for extended periods. Safe listening durations at various amplitudes can be calculated by averaging audio output levels over time to yield a time-weighted average. Various administrative bodies (such as the Occupational Safety and Health Administration (OSHA)) and health awareness agencies (such as the National Institute for Occupational Safety and Health (NIOSH)) have adopted guidelines for safe acoustic levels that are based on an eight hour work day. However, such guidelines were not necessarily designed to address the most common source of acoustic damage, namely headphones.

Unfortunately, most common media devices and their associated headphones encourage listening to music at volume levels well above the safe acoustic threshold set, for example, by OSHA. Such volume levels may have no immediate effect on hearing, but long-term exposure can nevertheless cause permanent hearing impairment.

To help prevent hearing damage, some devices have been developed to periodically measure sound levels of ambient audio signals. Such measurements can be used to estimate a cumulative effect of the ambient audio signals over time. However, such devices often simply notify the user when they have exceeded the OSHA or NIOSH guidelines for acoustic exposure. Unfortunately, these devices typically provide no preventative measures for the device user. Further, such devices are often worn in place of headphones, making the two devices incompatible. Some headphones utilize a predetermined maximum output level in an attempt to limit the output amplitude to prevent ear damage. This approach, however, is ineffective as it does not take into account listening duration and the calculation of risk for auditory injury over time.

Other devices have been developed to be placed as an accessory between the media player and the earphones increasing earphone impedance as the decibel level increases. This approach, however, is limited, in part, because such devices cannot be calibrated for the speakers in the headphones. As a result, these devices may either limit the audio output too much or not enough.

In the following description, the use of the same reference numerals in different drawings indicates similar or identical items.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

Sound (or noise) dosimeters are devices used to measure sound levels or sound pressure levels over time to estimate the noise exposure of a person. Studies indicate that sustained exposure to noise levels in excess of 85 dB and/or short and loud noises above a peak threshold can permanently damage hearing. To protect workers from acoustic exposure-based hearing impairment, the European Community, for example, adopted a rule that no worker, while on the job, should be exposed to an acoustic pressure of more than about 200 Pa, which equates to approximately 140 dB.

Dosimeters have been developed that can be worn on the user's belt and/or worn as a badge or pin on the user's clothing. Such devices can be configured to measure sound parameters and to warn the person when the decibel level exceeds a safe threshold level. Most sound pressure level dosimeters are meant to be worn all day and to monitor all audio signals to which the dosimeter is exposed. However, this is often impractical because such devices are not discrete and are not necessarily designed to measure the types of sounds that tend to cause the most damage. For many people, especially young people, the most damaging audio signals are delivered by media players configured to reproduce sounds at high decibel levels for short periods of time, often through headphones that deliver sound signals directly into the user's ear canal, which sound signals cannot be measured by such noise dosimeters.

Embodiments of a headphone system are disclosed below that are configured to monitor audio levels over time and to adjust the audio levels appropriately to prevent the headphone system from permanently damaging the hearing of the user. In a particular embodiment, the system includes a dosimeter to monitor acoustic exposure and logic to selectively adjust audio output levels over time based on the acoustic exposure. By providing a sound pressure level dosimeter in the headphones and by allowing automatic adjustment of the audio output levels, a large percentage of hearing damage caused by headphone usage can be prevented, even if the dosimeter is not designed to monitor ambient noise and other non-headphone produced noise to which the user may be exposed.

FIG. 1is a block diagram of a headphone system100configured to automatically limit hearing damage. Headphone system100includes headphones102coupled to an audio source130. Headphones102include an audio input108for receiving an audio signal from audio source130. Headphones102may also include an analog-to-digital converter109including an input coupled to an output of audio input108and an output coupled to an input of a processor110. Processor110is coupled to memory112and to speaker104. Memory112includes instructions and data that can be executed or processed by processor110. Such instructions and data include damage calculating instructions120, damage threshold122, damage counter124, regeneration instructions126, remediation instructions127, regeneration threshold data128, and maximum (max) DB threshold data129, and optionally other thresholds and/or other instructions.

Damage calculating instructions120are executable by processor110to calculate the hearing damage per second caused by the audio signal's current decibel level. Damage threshold122includes a numerical representation of the amount of hearing damage a user's ear can absorb before the damage becomes permanent. Damage counter124includes instructions for accumulating an amount of damage attributable to the acoustic exposure of the user and a numerical value of the amount of damage the user has sustained from listening to audio signals reproduced by speaker104using headphone system100.

It should be appreciated that, in some instances, the ear can repair or regenerate itself through periods of low noise (i.e., noise levels below a safe hearing threshold) or no noise. Such regeneration takes time. Regeneration calculating instructions126are executable by processor110to calculate the amount of regeneration or repair that the user's ear has achieved over time. Remediation instructions127are executable by processor110to reduce the amplitude of or to otherwise modify the audio signal as the user listens to headphones102. As discussed below in greater detail, remediation instructions127may be programmed in a number of ways to provide a variety of listening options to the user. Regeneration threshold data128includes a numerical value representing the decibel level at which the damage caused by the audio signal is less than the regeneration rate of the user's ear. Max DB threshold data129is a numerical value representing a peak decibel level the ear can handle before instantaneous hearing loss occurs.

In one embodiment, the count of damage counter124is originally set to zero as if the user's ears are fully repaired (i.e., in a fully regenerated, no-hearing-impairment state). As, an audio signal is received from audio source130at audio input108, the audio signal is converted to a digital signal for processing by processor110. Processor110monitors the amplitude of the audio signal and executes damage calculating instructions120to determine the damage over time caused by the decibel level of the audio signal as it is reproduced for the user. Using the damage calculating instructions120, processor110converts the amplitude of the audio signal to a decibel level to obtain the damage per second at that decibel level. It is important to understand that the higher the amplitude of the audio signal, the higher the sound pressure level becomes and the more damage that is caused per second to a user's ear. Processor110uses damage calculating instructions120to determine the damage per second and to calculate the damage to the user's ear based on the amount of time the decibel level is maintained, and adds the resulting data to damage counter124to indicate the current state of the user's hearing.

Processor110also executes regeneration instructions126. Regeneration instructions126model the regeneration rate of the human ear, so after the user listens to audio signals, which can cause degeneration, the human ear is capable of repairing the damage at a determinable rate. Further, while the ear is exposed to sounds below the regeneration threshold128, the ear may repair itself. Regeneration instructions126model the regeneration rate of the human ear by subtracting the regeneration per second from damage counter124. It should be noted that the damage rate and the regeneration rate are both impacted by the amplitude of the audio signals, such that the rates will vary over time. Thus, as damage calculating instructions120add damage to damage counter124, regeneration instructions126may subtract damage. The addition and subtraction of damage may occur at different rates depending on the audio level. In this way, damage counter124models the total hearing damage that actually occurred to the ear at any time during the period in which the user listens to audio output from speaker104.

As previously discussed, prolonged exposure to noise levels above a safe acoustic threshold can cause permanent hearing impairment. Accordingly, as damage counter124approaches a permanent hearing threshold included within the damage threshold122, processor110selectively executes remediation instructions127to reduce the amplitude of the audio signal. Such remediation instructions127can include various steps or options, which may be executed at different stages as the damage counter124approaches the permanent hearing loss threshold.

In a particular example, processor110executes remediation instructions127when damage counter124reaches or is about to exceed the damage threshold122. At this point, remediation instructions127cause the processor110to adjust the decibel level of the audio signal to a safe level that is below the regeneration threshold128and to limit the decibel level of the audio signal to that safe level until at least a portion of the hearing damage is repaired as modeled by the regeneration instructions126. In one example, remediation instructions127cause processor110to reduce the decibel level before damage counter124equals or exceeds damage threshold122. By reducing the decibel level before damage counter124reaches damage threshold122, system100may retain a hearing buffer to protect the user's hearing in case the user is exposed to other sound signals outside of the control of system100.

In a second example, remediation instructions127cause processor110to gradually decrease the amplitude of the audio signal over time in proportion to the distance between the damage counter124and the damage threshold122. The gradual decrease of the amplitude may be a substantially linear decrease or a non-linear adjustment that decreases the decibel level more rapidly as the damage counter124approaches the damage threshold122. By gradually decreasing the decibel level as the damage counter124approaches the damage threshold122, the user can listen to the audio signal longer at levels above safe hearing levels without causing permanent damage.

In another particular embodiment, processor110executes remediation instructions127to change the amplitude of the audio signal over time to fit a curve based on the original decibel level of the audio signal and a determined time period for listening. The curve is a pre-configured output curve designed to extend the amount of time the user can utilize system100at higher decibel and amplitude levels by lengthening the time it takes for the damage counter124to reach damage threshold122. The time period may be predetermined (such as the average listening time of a normal user), set by the user, determined from the user's normal listening behavior, or any combination thereof.

Remediation instructions127may be programmed or configured by a user to reduce the volume below regeneration threshold128before damage counter124reaches damage threshold122. In one particular example, processor110executes remediation instructions127to calculate a decibel adjustment curve, which processor110can use to adjust the audio output signal such that the decibel level of the audio signal drops below regeneration threshold128when damage counter124reaches a specified percentage of damage threshold122.

In yet another example, remediation instructions127cause processor110to use a stepped approach to limiting hearing damage. In this example, processor110executes remediation instructions127to determine a series of decibel levels based on the original decibel level of the audio signal, which step down incrementally from the original decibel level over time so that the audio level is reduced incrementally as damage counter124increases. After a first period of time, processor110executes remediation instructions127to reduce the audio signal by a first increment, and then allows the user to listen to the audio signal at that decibel level until damage counter124reaches a specified fraction of damage threshold122. After the specified fraction is reached or exceeded, processor110executes remediation instructions127to decrease the decibel level of the audio output by another incremental step. In a particular example, if there were four steps, processor110can decrement the decibel level by a step when damage counter124equals one fourth of damage threshold122, one-half of damage threshold122, three fourths of damage threshold122, and so on. When the damage counter124approaches the damage threshold122, processor110executes remediation instructions127to decrease the decibel level to a safe decibel level that is below regeneration threshold128.

In yet another example, remediation instructions127cause processor110to use scale the amplitude based on the rate of change of the damage counter124. This function may be linear, stepped, or exponential as described above but the rate at which the amplitude is adjusted down is based on the value of the damage counter124.

In all of the above examples, once the decibel level is reduced below the regeneration threshold128, processor110is configured to limit the audio signal to the safe decibel level until damage counter124indicates that regeneration has reached a predetermined fraction of damage threshold122. For example, system100may use remediation instructions127to increase the decibel level again once damage counter124falls to 50% of damage threshold122.

It should be understood that system100may also be designed to decrement the damage counter124. In this instance, damage counter124may be originally set at damage threshold122, and the damage counter124is reduced during operation based on damage calculating instructions120and is increased by regeneration instructions126. In this instance, other remediation instructions (such as incrementally adjusting or limiting the audio signal as the damage counter124approaches the damage threshold122) would be changed such that the remediation instructions127would cause the processor110to limit the decibel level of the audio signal as the damage counter124decreases.

WhileFIG. 1depicts a headphone system100that uses a processor110adapted to implement damage limiting instructions to selectively reduce an audio output of headphones102digitally, it is also possible to implement a headphone system that can limit the decibel level of the audio signal using analog circuitry. An example of such a headphone system is described below with respect toFIG. 2.

FIG. 2is a block diagram of an embodiment of an analog design of a headphone system200configured to limit hearing damage. System200is designed such that, when the user listens to an audio signal having a decibel level above the regeneration threshold, hearing damage is recorded and, when the audio signal's decibel level is below the regeneration threshold, hearing repair is recorded. System200includes headphones204coupled to an audio source202for receiving analog audio signals.

Headphones204includes variable gain amplifier (VGA)210with a first input coupled to audio source202for receiving audio signals, a gain control input, and an output coupled to a speaker212. VGA210is configured to scale the amplitude of the audio signals and to provide the scaled audio signals to speaker212, which generates an acoustic signal and provides it to the user. The output of VGA210is also optionally coupled to delay214, which is utilized in a feedback loop including an analog comparator224, a threshold indicator230, a transistor222, a pulse generator226, an energy storage element218(such as an integrator or capacitor), a switch220, and a power source216to provide stability for the system200. Delay214slows the rate at which volume adjustments happen.

Analog comparator224includes a first input coupled to an output of delay214, a second input coupled to the threshold indicator230, and an output coupled to a terminal of transistor222. Threshold indicator230is a signal that represents the regeneration threshold for use by analog comparator224to determine if the scaled audio signal is above or below the threshold. Analog comparator224is further coupled to transistor222to increase the resistance level of transistor222as the charge on energy storage element218increases. In this way, the rate of charge increase on energy storage element218is variable to correctly model the rate at which the user undergoes hearing damage at different acoustic amplitudes. When the scaled audio signal exceeds the threshold indicator230, analog comparator224provides an output signal to transistor222, which biases energy storage element218.

Energy storage element218operates as a damage counter by producing an output signal to adjust the gain of VGA210. Energy storage element218may be an integrator, capacitor, or other storage element. In the following discussion, energy storage element218is described as a capacitor. However, it should be understood that system200operates in a similar manner if energy storage element218is an integrator, where the integrator stores energy instead of charge. Energy storage element218is coupled to switch220which is turned on and off by pulse generator226to couple energy storage element218to power source216according to timing of the generated pulses. Energy storage element218receives its charge from power source216when switch220is closed. When transistor222is turned on, charge stored in energy storage element218flows to ground228through transistor222and the rate of current flow is dependent on the signal level/voltage applied to the gate of transistor222, which level is set by the output of analog comparator224. If the scaled audio signal has a decibel level that is above the threshold indicator230, analog comparator224turns on current flow through transistor222and current flows from energy storage element218through transistor222to ground. Energy storage element218is further coupled to VGA210, and based on the charge held within energy storage element218, controls the gain of VGA210to scale the audio signal.

In one example, an audio signal is received at the input of VGA210. VGA210scales the amplitude of the audio signal to produce a scaled audio signal at its output, which is then provided to speaker212for reproduction for the user. The scaled audio signal is also received by analog comparator224, which compares the adjusted signal to threshold indicator230. If the scaled audio signal is above threshold indicator230, analog comparator224generates a control signal to decrease the resistance of transistor222, allowing more current to flow from energy storage element218through transistor222to ground. If, however, the scaled audio signal is below threshold indicator230, analog comparator224controls transistor222to decrease or turn off current flow through transistor222, allowing less charge to escape from energy storage element218to ground228. Thus, the charge recorded by energy storage element218is consumed at varying rates dependent on the decibel level at which the scaled audio signal is received by analog comparator224and dependent on the level at which the threshold indicator230is set.

Energy storage element218models the human ear in a manner similar to the way damage counter124inFIG. 1. In particular, the charge held by energy storage element218can be used to model damage remaining before permanent damage is incurred. It is important to note that energy storage element218receives a charge from power source216when switch220is closed. Switch220is pulsed on and off by pulse generator226at a rate that provides a controlled charge/discharge rate for the capacitor that is selected to model the normal hearing repair rate of the human ear. Therefore, it should be understood that, by changing the pulse rate of pulse generator226, the rate at which energy storage element218stores charge and discharges it can be varied to provide additional adaptability of system200, such as to extend beyond a model of damage/repair profile of the human ear. Further the rate of the pluses may be programmed to provide additional functionality.

Thus, system200utilizes energy storage element218as an analog imitation of the regeneration and damage rate of the human ear, and system200can be configured to control the scaled analog signal based on damage sustained by the user's hearing over the period of time the user uses headphones204to prevent permanent hearing damage. Thus, the system200actively scales the amplitude or volume level of the audio signal as the user consumes the allowable dosage for the day as represented by the charge on energy storage element218.

As the user listens to the audio signal at a level above the regeneration threshold, the amount of charge being drained from energy storage element218is increased above the level at which the charge is replenished, causing the overall charge on energy storage element218to decrease. As the charge decreases, energy storage element218will control VGA210to decrease the amplitude of the audio signal, such that the scaled audio signal will have a lower volume and thus a lower sound pressure level than the original audio signal, and the scaled audio signal will be delivered to the user through speaker212. The gain of VGA210is directly related to the amount of charge remaining in energy storage element218. By altering the relationship between charge on energy storage element218and the gain of VGA210, different correction curves can be generated by system200.

VGA210may eventually lower the audio signal's amplitude to a decibel level below that of threshold indicator230. This can happen if either the charge on energy storage element218reaches zero or the charge reaches a predetermined amount. For example, system200may reserve part of the repairable hearing damage that the user's ear can sustain for consumption by the user while not using system200. Therefore the charge level at which VGA210reduces the audio signal's amplitude to a decibel level below that of threshold indicator230could be at a charge level representing an acoustic dosage of approximately 90% of the allowable daily allotment, leaving 10% of the repairable hearing damage.

It should be understood that the above-described system is only one possible analog embodiment, and that it is contemplated that other systems could be devised using additional analog comparators and/or resistors. For example by adding a second comparator between transistor222and analog comparator224, system200could accommodate an acceptable safe level indicator and threshold indicator230, where the acceptable safe level indicator is a sound pressure level where the user could listen to audio signals for a 24 hour period and only consume 1% of the allowable dosage (where the allowable dosage is the amount of exposure to acoustic signals that a user can experience before permanent hearing impairment occurs). Thus setting the minimum volume level to a higher decibel value than that of threshold indicator230. In another example, multiple resistors or transistors could be utilized to provide a stepped function as described in the description ofFIG. 1. In still another embodiment, the pulse generator226can be configured to operate with other circuitry to produce a ramp or step function and/or an analog-to-digital converter to control the gain of VGA210incrementally.

FIG. 3is a flow diagram of an embodiment of a method300of limiting the hearing damage caused by headphone, which can be implemented to control headphones102or204inFIGS. 1 and 2. At302, an audio input is received from a media device. Proceeding to304, headphones (such as headphones102or204) determine the audio's sound pressure level. Advancing to306, if the sound pressure level is below a threshold, method300advances to308and the change in the hearing damage is recorded. In this case, the hearing damage is increased. After the hearing damage change is recorded, method300returns to302and continues to receive the audio input from the media device.

If, however, at306the sound pressure level exceeds the threshold, method300advances to310and, if the hearing damage is less than usable hearing dosage, the method advances to312and the amplitude level of the output signal is adjusted based on remediation instructions. The usable hearing dosage is the amount of hearing damage that the user has sustained by using the headphone system. Thus the usable hearing dosage is a percentage of the damage threshold122ofFIG. 1that method300may consume.

At310, if the hearing damage is greater than the usable hearing dosage, method300proceeds to314and the amplitude of the audio signal is adjusted to a level that is below the threshold. If, however, the hearing damage is less than the usable hearing dosage, the method300advances to312and adjusts the amplitude level based on the remediation instructions. The amplitude could be adjusted by the remediation instructions in a variety of ways and, in particular, in the manners described above with respect toFIGS. 1 and 2.

Once method300adjusts the amplitude either according to the remediation instructions or below the threshold, method300advances to308and records the change in the hearing damage. If the sound pressure level was above the threshold then the hearing damage sustained is decreased, but if the sound pressure level was above the threshold, the hearing damage is increased. After the change in hearing damage is recorded, method300returns to302and the cycle begins again with another audio signal.

It should be appreciated that, while the above-discussion has focused on amplitude of the audio signals, the techniques and systems described above may also be used to adjust other audio parameters, such as tone, pitch, bass, and other parameters. To the extent that certain parameters are determined to increase the rate of damage to the hearing, it may be useful to selectively adjust one or more acoustic parameters, including amplitude, pitch, tone, frequency, and other parameters, without substantially altering the content of the audio signal, thereby reducing the effects of prolonged exposure and (preferably) preventing permanent damage to the hearing of the user.

FIGS. 1-3depict several embodiments of a headphone system that monitors and protects the user from permanent hearing damage.FIGS. 4-6are illustrative embodiments of various sound adjustment curves that the systems inFIGS. 1-3could utilize to adjust the amplitude of the headphones in order to protect the user's hearing.

FIG. 4is a graph400illustrating an embodiment of a possible representative amplitude adjustment curve, which can be generated to protect the user's hearing. Graph400depicts adjustment curve402and threshold404. Threshold404can be set to various sound pressure levels. In this embodiment, threshold404is set to 40 decibels. In a particular example, threshold404is selected as a safe acoustic level at or below which the user's hearing may regenerate or recover from temporary hearing impairment caused by exposure to hearing damaging acoustic signals.

Adjustment curve402is generated when processor110executes remediation instructions127. Adjustment curve402is determined by a number of pre-programmed or user adjustable variables including, but not limited to, listening time, starting amplitude, and the current state of damage counter124. In this example, processor110executes remediation instructions127upon activation of headphones102and calculates a continuous curve that would allow the user to listen to headphones102for 20 hours continuously without damaging the user's hearing. In this embodiment, processor110, in conjunction with remediation instructions127, takes an active role in determining the amplitude of the sound generated by headphones102over time, and adjustment curve402depicts a continuous and gradual reduction of the amplitude of the acoustic signals over time. While the adjustment curve402represents one possible adjustment, by altering the variables, many different continues curves can be provided.

WhileFIG. 4illustrates a continuous sound amplitude adjustment curve, other types of curves or signal shapes may be used to achieve the desired effect, such as the interval step function shown inFIG. 5.

FIG. 5is a graph500illustrating an embodiment of a second possible representative sound adjustment curve, which can be generated to protect the user's hearing using the systems discussed with respect toFIGS. 1-4. Graph500depicts an adjustment curve502with multiple steps for adjusting the audio signal amplitude and depicts a threshold504. Threshold504can be set to various decibel levels as discussed inFIG. 4. As inFIG. 4, in the illustrated embodiment ofFIG. 5, threshold504is set to 40 decibels.

However, unlike inFIG. 5, the adjustment curve502is configured to include multiple steps or intervals through which the acoustic signals can be adjusted incrementally over time. Thus, adjustment curve502is generated to have any number of desired steps. Further, the number of steps can be based, in part, on the amplitude of the sound for each step, total listening time, and the starting amplitude. Based on the number of steps desired, the user may listen to each step for a specific period of time. For example,FIG. 5shows adjustment curve502with four steps. In this instance, processor110adjusts the volume incrementally according to the adjustment curve when damage counter124is equal to a percentage (⅕th, ⅖ths, ⅗ths, ⅘ths and 5/5ths) of damage threshold122by incrementally reducing the decibel level of the output toward safe decibel level. By altering the number of steps, the granularity of the adjustment can be made finer or more course. Further, the number of transitions determines the period of time over which the user may listen to the acoustic signal at the particular output level before the next step reduction is implemented. By incrementally adjusting the acoustic signal, the overall amount of time that the user can listen to the audio signal without incurring hearing damage can be extended.

FIG. 6is a graph600illustrating an embodiment of a third possible representative sound adjustment curve, which can be generated to protect the user's hearing by the systems discussed inFIGS. 1-4. Graph600depicts adjustment curve602and threshold604. Threshold604can be set to various decibel levels as discussed inFIGS. 4 and 5. As inFIGS. 4 and 5in this embodiment, threshold504is set to 40 decibels.

Adjustment curve602depicts a step function, which allows the user to listen to sound at any level they desire until damage counter124is approximately equal to damage threshold122. When the damage threshold122is reached, the adjustment curve602, in conjunction with remediation instructions127executed by processor110, causes the processor110to decrease amplitude of the audio signal abruptly to a decibel level that is below threshold604.

It should be appreciated that other adjustment curves may also be used. For example, an adjustment curve could be a sloped line that decreases linearly over time. In another example, the adjustment curve may be an exponential decay curve. In still another example, the adjustment curve may include components of each of the above types of curves, forming a composite curve that takes different types of remediation actions at different times during the period over which the user is listening to the audio signal. Such different actions may be based on the amount of time, the current audio level, the amount of damage, or any combination thereof.

In conjunction with the systems and methods described above with respect toFIGS. 1-6, a headphone system is disclosed that is configured to monitor sound levels produced by the speaker of the headphones system and to selectively scale the audio signal over time, incrementally, or abruptly to safe audio levels to prevent permanent damage to the user's hearing. In an example, the amount of time that a user has listened to audio signals that exceed a safe or regeneration threshold level is counted and the hearing damage is calculated to determine a current state of the user's hearing. When the hearing damage approaches or exceeds one or more pre-determined thresholds, the audio signal can be automatically scaled to a lower decibel level to slow the rate of damage or to prevent any further damage to the user's hearing.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the scope of the invention.