EP2453672B1

EP2453672B1 - Method and system for controlling a maximum signal level output to headphones coupled to a wireless device

Info

Publication number: EP2453672B1
Application number: EP11195765.0A
Authority: EP
Inventors: Cyril Martin
Original assignee: Research in Motion Ltd
Current assignee: BlackBerry Ltd
Priority date: 2009-02-27
Filing date: 2009-02-27
Publication date: 2013-05-01
Anticipated expiration: 2029-02-27
Also published as: EP2453672A1; CA2691308A1; CN101820697A; ATE531208T1; EP2387254A2; EP2224749A1; CN101820697B; EP2224749B1; CA2691308C; EP2387254A3; EP2387254B1

Abstract

A method for controlling a maximum signal level output to headphones of a wireless device is provided. The method includes: determining an impedance of the headphones; determining a carrier specific maximum signal level for headphones having the impedance; and, adjusting an audio amplifier of the wireless device coupled to the headphones to restrict the maximum signal level output to the headphones to the carrier specific maximum signal level.

Description

FIELD OF THE APPLICATION

This application relates to the field of wireless devices, and more specifically, to a method and system for controlling a maximum signal level output to headphones coupled to a wireless device.

BACKGROUND

Current wireless mobile communication devices include microprocessors, memory, soundcards, speakers, headphones, and run one or more software applications in addition to providing for voice communications. Examples of software applications used in these wireless devices include micro-browsers, address books, email clients, instant messaging ("IM") clients, and wavetable instruments. Additionally, wireless devices have access to a plurality of services via the Internet. A wireless device may, for example, be used to browse web sites on the Internet, to transmit and receive graphics, and to execute streaming audio and/or video applications. Such wireless devices may operate on a cellular network, on a wireless local area network ("WLAN"), or on both of these types of networks.
One problem with current wireless devices pertains to the adjustment of maximum output sound pressure levels for headphones coupled to such devices. Headphones are typically used to listen to voice calls, radio programs, audio programs (e.g., music), etc., stored on or accessed by the wireless device. In particular, the maximum output sound pressure level for headphones for wireless devices and handheld products is legally constrained in several jurisdictions in order to protect users from hearing loss. For example, European Standard EN 50332-1:2000, dated March 2000 and entitled "Sound System Equipment: Headphones And Earphones Associated With Portable Audio Equipment - Maximum Sound Pressure Level Measurement Methodology And Limit Considerations - Part 1: General Method For 'One Package Equipment"' restricts maximum sound pressure level at the headphones (i.e., for headphones provided with the portable audio equipment and from the same manufacturer) to 100 dB. In addition, European Standard EN 50332-2:2003, dated October 2003 and entitled "Sound System Equipment: Headphones And Earphones Associated With Portable Audio Equipment - Maximum Sound Pressure Level Measurement Methodology And Limit Considerations - Part 2: Matching Of Sets With Headphones If Either Or Both Are Offered Separately" restricts maximum sound pressure level at the headphones (i.e., for headphones provided separately from the portable audio equipment by a different manufacturer) to 94 dB. Measurement of maximum sound pressure levels according to these standards is specified with respect to headphones having an impedance of 32 Ohms. One problem relating to such standards is that in order to set the output signal level (e.g., in mV RMS) appropriately at the output jack of the wireless device in order to meet the maximum sound pressure level specified, the impedance of the headphones must be known. This is especially problematic if the headphones are not provided by the manufacturer as a package with the wireless device.
German Patent Specification No. DE 10 2007 032281 discloses a system which includes a sound transducer, an output terminal, an amplifying means and a controls means. The control means is operable to adjust a gain of the amplifying means in response to a sound level.
Published PCT Patent Application No. WO 2008/128563 discloses a hearing system which comprises a storage unit. The storage unit comprises location-related data relating to the hearing system's current location. The function of the hearing system changes in dependence of the location of the hearing system
European Patent Specification No. EP 1 720 375 relates to a system for enabling a hearing device wireless access to a communication network. The system comprises a first transceiver unit communicating according to a first communication protocol. The system further comprises a server device comprising an input/output unit, which is connected to the communication network and communicates according to a second communication protocol.
Published US Patent Application No. US 2006/182294 relates to a hearing aid which, with the aid of an integrated positioning unit or a positioning unit integrated in a mobile activation device automatically sets operating parameters of the hearing aid as a function of the location of the hearing aid or of the activation unit. Further related art is described in US 2006/0099967 and US 7 263 367 .
A need therefore exists for an improved method and system for controlling a maximum signal level output to headphones coupled to a wireless device. Accordingly, a solution that addresses, at least in part, the above and other shortcomings is desired.

GENERAL

The present teaching relates to a method as detailed in claim 1. The teaching also relates to a system as detailed in claim 13. Additionally, the teaching relates to a computer readable medium as detailed in claim 15. Advantageous features are provided in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Features and advantages of the embodiments of the present application will become apparent from the following detailed description, taken in combination with the appended drawings, in which:
FIG. 1 is a front view illustrating a wireless device coupled to headphones and adapted for implementing an embodiment of the application;
FIG. 2 is a block diagram illustrating the wireless device of FIG. 1 and a wireless network adapted for implementing an embodiment of the application;
FIG. 3 is a block diagram illustrating a memory of the wireless device of FIGS. 1 and 2;
FIG. 4 is a block diagram illustrating a headphones subsystem;
FIG. 5 is a block diagram illustrating an alternate headphones subsystem; and,
FIG. 6 is a flow chart illustrating operations of modules within the memory of a wireless device for controlling maximum signal level output to headphones of the wireless device, in accordance with an embodiment of the application.
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.

DETAILED DESCRIPTION

In the following description, details are set forth to provide an understanding of the application. In some instances, certain software, circuits, structures and techniques have not been described or shown in detail in order not to obscure the application. Embodiments of the present application may be implemented in any computer programming language provided that the operating system of the wireless device or data processing system provides the facilities that may support the requirements of the application. Any limitations presented would be a result of a particular type of operating system or computer programming language and would not be a limitation of the present application. Embodiments of the preset application may also be implemented in hardware or in a combination of hardware and software.
FIG. 1 is a front view illustrating a wireless device 100 coupled to headphones 105 (a.k.a., headphone set, headphone, headset, earphone, earphones, etc.) and adapted for implementing an embodiment of the application. The wireless device 100 includes a casing 150, a display screen 122, a graphical user interface ("GUI") 180 displayed on the display screen 122, a keyboard (or keypad) 132, a trackball (or thumbwheel) 110, various select buttons 120, various inputs/outputs (e.g., power connector jack, data interface ports, etc.) 160, and a headphones jack 106. Internally, the wireless device 100 includes one or more circuit boards (not shown), a CPU 138, memory 124, 126, 200, a battery 156, an antenna (not shown), etc., which are operatively coupled to the various inputs/outputs 160, the keyboard 132, the display screen 122, the headphones jack 106, etc., as will be described below.
The headphones 105 are coupled to the wireless device 100 by a headphones cable or lead 107 which is inserted into the headphones jack 106. The headphones 105 include a speaker assembly which is inserted into or placed over a user's ear. According to one embodiment, the headphones 105 include two speaker assemblies, one for each of the user's ears. Each speaker assembly includes a speaker having an impedance (referred to as the impedance of the headphones in the following). The headphones 105, headphones jack 106, and headphones cable 107 may be configured for stereo and/or mono operation. When the headphones cable 107 is inserted into the headphones jack 106, audio output signals may be switched from the internal speaker 134 (see FIG. 2) to the headphones 105. Control of audio signal level (e.g., in mV RMS) output to the headphones 105 is performed by a headphones subsystem 400 as described below. According to one embodiment, the headphones jack 106 is a 3.5 mm headset jack adapted to support both a stereo headphones output and a mono microphone input.
FIG. 2 is a block diagram illustrating the wireless device 100 of FIG. 1 and a wireless network 220 adapted for implementing an embodiment of the application. The wireless network 220 may include antenna, base stations, access points, transceivers, supporting radio equipment, etc., as known to those of ordinary skill in the art, for supporting wireless communications between the wireless device 100 and other devices (not shown).
The wireless device 100 may be a two-way communication device having at least voice and advanced data communication capabilities, including the capability to communicate with other devices. Depending on the functionality provided by the device 100, it may be referred to as a data messaging device, a two-way pager, a cellular telephone with data messaging capabilities, a wireless Internet appliance, a data communication device (with or without telephony capabilities), a Wi-Fi device, a WLAN device, a dual-mode (i.e., Wi-Fi and cellular) device, or a portable audio device.
The wireless device 100 has a communication subsystem 111, which includes a RF receiver, a RF transmitter, and associated components. As will be apparent to those skilled in the field of communications, the particular design of the communication subsystem 111 depends on the communication network 220 in which the device 100 is intended to operate.
The device 100 may be capable of cellular network access and hence the device 100 may have a subscriber identity module (or "SIM" card) 162 for inserting into a SIM interface ("IF") 164 in order to operate on the cellular network (e.g., a global system for mobile communication ("GSM") network).
The device 100 may be a battery-powered device and so it may also include a battery IF 154 for receiving one or more rechargeable batteries 156. The battery (or batteries) 156 provides electrical power to most if not all electrical circuitry in the device 100, and the battery IF 154 provides for a mechanical and electrical connection for it.
The wireless device 100 includes a microprocessor 138, also called a processor, which controls overall operation of the device 100. The microprocessor 138 interacts with device subsystems such as the display 122, a flash memory 124 or other persistent store, a random access memory ("RAM") 126, auxiliary input/output ("I/O") subsystems 128, a serial port (e.g., a universal serial bus ("USB") port) 131, the keyboard 132, the trackball or thumbwheel 110, the headphones 105, an internal speaker 134, a microphone 136, a short-range communications subsystem 141, and other device subsystems 142. The microprocessor 138, in addition to performing operating system functions, preferably enables execution of software applications on the device 100.
FIG. 3 is a block diagram illustrating a memory 200 of the wireless device 100 of FIGS. 1 and 2. The microprocessor 138 is coupled to the memory 200. The memory 200 has various hardware and software components for storing information (e.g., instructions, data, database tables, test parameters, etc.) for enabling operation of the device 100 and may include flash memory 124, RAM 126, ROM (not shown), disk drives (not shown), etc. In general, the memory 200 may include a variety of storage devices typically arranged in a hierarchy of storage as understood to those skilled in the art.
Operating system ("O/S") software modules 202 used by the microprocessor 138 may be stored in a persistent store such as the flash memory 124, which may alternatively be a read-only memory ("ROM") or similar storage element (not shown). Those skilled in the art will appreciate that the operating system, specific device applications, or parts thereof, may be temporarily loaded into a volatile store such as RAM 126.
To provide a user-friendly environment to control the operation of the device 100, operating system ("O/S") software modules 202 resident on the device 100 provide a basic set of operations for supporting various applications typically operable through the GUI 180 and supporting GUI software modules 204. For example, the O/S 202 provides basic input/output system features to obtain input from the auxiliary I/O 128, the keyboard 132, the trackball or thumbwheel 110, and the like, and for facilitating output to the user through the display 122, the speaker 134, the headphones 105, etc. The wireless device 100 is provided with hardware and/or software modules 206 for facilitating and implementing the method of the application as will be described below.
A user may interact with the wireless device 100 and its various software modules 202, 204, 206, using the GUI 180. GUIs are supported by common operating systems and provide a display format which enables a user to choose commands, execute application programs, manage computer files, and perform other functions by selecting pictorial representations known as icons, or items from a menu through use of an input or pointing device such as a trackball or thumbwheel 110 and keyboard 132. The GUI 180 may include a cursor 190, various selectable objects and icons 191, and various windows 192.
Thus, the wireless device 100 includes computer executable programmed instructions for directing the device 100 to implement the embodiments of the present application. The programmed instructions may be embodied in one or more hardware or software modules 206 which may be resident in the memory 200 of the wireless device 100. Alternatively, the programmed instructions may be embodied on a computer readable medium (such as a CD disk or floppy disk) which may be used for transporting the programmed instructions to the memory of the wireless device 100. Alternatively, the programmed instructions may be embedded in a computer-readable signal or signal-bearing medium that may be uploaded to a network 220 by a vendor or supplier of the programmed instructions, and this signal or signal-bearing medium may be downloaded through an interface 111, 131, 141 to the wireless device 100 from the network 220 by end users or potential buyers.
FIG. 4 is a block diagram illustrating a headphones subsystem 400. Components of the headphones subsystem 400 are generally contained in the wireless device 100 and are used to determine the impedance of the headphones 105 in order to adjust the maximum signal level (e.g., in mV RMS) output to the headphones 105 (and hence the maximum sound pressure level output by the headphones 105).
According to one embodiment, the headphones system 400 includes a signal generator 410, a digital to analog converter ("DAC") 440, and an audio amplifier 430 for generating an inaudible high frequency signal (e.g., 25 kHz). The signal generator 410, DAC 440, and audio amplifier 430 are controlled by the microprocessor 138. The audio amplifier 430 is coupled to the headphones 105 through a series resistor R. The series resistor R may have a low value (e.g., 5 Ohms). A voltage V produced across the resistor R when the high frequency signal is applied to the resistor R and headphones 105 is indicative of the impedance Z of the headphones 105. The signal may be applied to the resistor R and headphones 105 whenever the headphones 105 are connected to the headphones jack 106 via the headphones cable 107. The voltage V is amplified by a microphone pre-amplifier 450 which is coupled to an analog to digital converter ("ADC") 420. The ADC 420 monitors the voltage V and provides a digital signal indicative of the voltage V and hence the impedance Z of the headphones 105 to the microprocessor 138. The ADC 420 may also be used by the microphone 136 of the wireless device 100 in order to reduce component count. The microprocessor 138 receives the digital signal from the ADC 420 and determines the impedance Z of the headphones 105 from it (e.g., by voltage divider principles, etc.). The microprocessor 138 may do this by accessing a table that stores voltage values (or digital signal values) and corresponding headphones impedance values.
Having determined the impedance Z for the headphones 105, the microprocessor 138 controls the audio amplifier 430 to restrict the maximum signal level (e.g., in mV RMS) output to the headphones 105. In this way, the sound pressure level output by the headphones 105 may be restricted to a maximum sound pressure level for the determined impedance Z. The microprocessor 138 may do this by accessing a table (e.g., included in or associated with modules 206) that stores headphones impedance values, corresponding maximum signal level values for the audio amplifier 430, and/or corresponding maximum sound pressure values for the headphones 105. For example, for a headphones impedance value of approximately 32 Ohms, the table 406 may indicate that the maximum sound pressure level for the headphones 105 is 100 dB.
If a headphone impedance value corresponding to the determined headphone impedance Z is not listed in the table 406, no maximum signal level for the audio amplifier 430 and no maximum sound pressure level for the headphones 105 is prescribed and hence the maximum signal level of the audio amplifier 430 and the maximum sound pressure level for the headphones 105 are not restricted for that value of determined headphones impedance Z.
Now, the maximum signal level (e.g., in mV RMS) and/or the maximum sound pressure level (e.g., in dB) for a given headphones impedance may be set by government regulation which may change depending on the carrier or the location in which the wireless device 100 is operating or is sold. As is known to those skilled in the art, the wireless device 100 has means for determining its carrier and/or location and hence the government regulations that may apply to set maximum signal levels and/or maximum sound pressure levels. Thus, the microprocessor 138 receives a signal indicative of the carrier and/or location of the wireless device 100 and determines whether a maximum signal level value and/or a maximum sound pressure level value has been prescribed for the carrier and/or location and for the determined headphones impedance Z. The microprocessor 138 may do this by accessing a table 406 that stores wireless device location, corresponding headphones impedance values, corresponding carrier (or location) specific maximum signal level values (if any) for the audio amplifier 430, and/or corresponding carrier (or location) specific maximum sound pressure level values (if any) for the headphones 105. For example, the table may indicate that if the wireless device 100 is associated with a carrier based in Great Britain and if the headphones impedance is 32 Ohms (i.e., +/- 20%), then the maximum sound pressure level should be restricted to 100 dB (i.e., if the headphones 105 and wireless device 100 are sold as a package). As another example, the table 406 may indicate that if the wireless device 100 is associated with a carrier based in Great Britain and if the headphones impedance is 32 Ohms (i.e., +/- 20%), then the maximum sound pressure level should be restricted to 94 dB (i.e., if the headphones 105 and wireless device 100 are not sold as a package).
Similarly, the maximum signal level (e.g., in mV RMS) and/or the maximum sound pressure level (e.g., in dB) may be set by government regulation which may change depending on the carrier or the location in which the wireless device 100 is operating or is sold (i.e., irrespective of the impendence of the headphones 105). Again, as is known to those skilled in the art, the wireless device 100 has means for determining its carrier and/or location and hence the government regulations that may apply to set maximum signal levels and/or maximum sound pressure levels. Thus, the microprocessor 138 receives a signal indicative of the carrier and/or location of the wireless device 100 and determines whether a maximum signal level value and/or a maximum sound pressure level value has been prescribed for the carrier and/or location. The microprocessor 138 may do this by accessing a table 406 that stores wireless device carrier (or location), corresponding headphones impedance values, corresponding carrier specific maximum signal level values (if any) for the audio amplifier 430, and/or corresponding carrier specific maximum sound pressure level values (if any) for the headphones 105. For example, the table 406 may indicate that if the wireless device 100 is associated with a carrier based in Great Britain, then the maximum sound pressure level should be restricted to 100 dB (i.e., if the headphones 105 and wireless device 100 are sold as a package). As another example, the table 406 may indicate that if the wireless device 100 is associated with a carrier based in Great Britain, then the maximum sound pressure level should be restricted to 94 dB (i.e., if the headphones 105 and wireless device 100 are not sold as a package).
Updates to the table 406 storing carrier (or wireless device location), corresponding headphones impedance values, corresponding carrier specific maximum signal level values (if any) for the audio amplifier 430, and corresponding carrier specific maximum sound pressure level values (if any) for the headphones 105 may be periodically downloaded to the wireless device 100 (e.g., over the network 220).
The carrier associated with the wireless device 100 may be determined from messages delivered to the wireless device 100 over the network 220. According to another embodiment, the carrier may be determined from information stored in the wireless device's SIM card 162.
The location of the wireless device 100 may be determined from messages delivered to the wireless device 100 over the network 220. According to another embodiment, the location of the wireless device 100 may be determined by a global positioning system ("GPS") receiver (not shown) optionally provided for the device 100. The location of the wireless device 100 may be determined from the location of antennae towers associated with the network 220 on which the wireless device 100 operates.
FIG. 5 is a block diagram illustrating an alternate headphones subsystem 400. In FIG. 5, a signal source 510 (e.g., microprocessor 138) generates a signal (e.g., an audio signal, an inaudible audio signal, etc.) that is applied to a digital to analog converter ("DAC") 540. The output of the DAC 540 is conditioned 530 (e.g., amplified 430, etc.) to allow for impendence measurement 520 (e.g., via a resistor R, etc.) of the headphones 105 connected to the headphones jack 506.
The application may provide several advantages. For example, the method of the present application allows wireless devices 100 to restrict maximum signal levels and maximum sound pressure levels to prescribed legal limits when necessary.
Aspects of the above described method may be illustrated with the aid of a flowchart. FIG. 6 is a flow chart illustrating operations 600 of modules 206 within the memory 200 of a wireless device 210 for controlling maximum signal level output to headphones 105 of the wireless device 100, in accordance with an embodiment of the application.
At step 601, the operations 600 start.
At step 602, an impedance Z of the headphones 105 is determined.
At step 603, a carrier specific maximum signal level for headphones having the impedance Z is determined.
At step 604, an audio amplifier 430 of the wireless device 100 coupled to the headphones 105 is adjusted to restrict the maximum signal level output to the headphones 105 to the carrier specific maximum signal level.
At step 605, the operations 600 end.
The above described method is generally performed by the wireless device 100. However, according to one embodiment, the method can be performed by, or in combination with, a data processing system (not shown) such a personal computer ("PC") or server, a stereo system, a television system, etc.
While embodiments of this application are primarily discussed as a method, a person of ordinary skill in the art will understand that the apparatus discussed above with reference to a wireless device 100 and a data processing system, may be programmed to enable the practice of the method of these embodiments. Moreover, an article of manufacture for use with a wireless device 100 or data processing system, such as a pre-recorded storage device or other similar computer readable medium including program instructions recorded thereon, may direct the wireless device 100 or data processing system to facilitate the practice of the method of these embodiments. It is understood that such apparatus and articles of manufacture also come within the scope of the application as defined in the appended claims.
Furthermore Aspects and features of this disclosure are set out in the flowing paragraphs provided as clauses, which correspond to the claims of the parent application as filed:

1. A method for controlling a maximum signal level output to headphones of a wireless device, comprising:
- determining an impedance of the headphones;
- determining a carrier specific maximum signal level for headphones having the impedance; and,
- adjusting an audio amplifier of the wireless device coupled to the headphones to restrict the maximum signal level output to the headphones to the carrier specific maximum signal level.
2. The method of clause 1 wherein the determining of the carrier specific maximum signal level further comprises searching a table stored in the wireless device using the impedance, the table listing impedances and corresponding carrier specific maximum signal levels.
3. The method of clause 1 or clause 2 wherein the determining of the impedance further comprises applying an audio signal to the headphones.
4. The method of clause 3 wherein the audio signal is an inaudible audio signal.
5. The method of clause 1 and further comprising determining a carrier for the wireless device and wherein the carrier specific maximum signal level for headphones having the impedance is determined for the carrier.
6. The method of clause 5 wherein the determining of the carrier specific maximum signal level further comprises searching a table stored in the wireless device using the impedance and the carrier, the table listing impedances, carriers, and corresponding carrier specific maximum signal levels.
7. The method of clause 5 or clause 6 wherein the carrier is determined from a signal received from a network in which the wireless device is operating.
8. The method of clause 1 and further comprising determining a location for the wireless device and wherein the carrier specific maximum signal level for headphones having the impedance is determined for the location.
9. The method of clause 8 wherein the determining of the carrier specific maximum signal level further comprises searching a table stored in the wireless device using the impedance and the location, the table listing impedances, locations, and corresponding carrier specific maximum signal levels.
10. The method of clause 8 or clause 9 wherein the location is determined from a signal received from a network in which the wireless device is operating.
11. A system within a wireless device for controlling a maximum signal level output to headphones coupled to the wireless device, comprising:
- a memory storing program instructions; and
- a processor coupled to said memory and configured to execute said program instructions to cause the system to implement the steps of the method of any one of clauses 1 to 10.
12. A wireless device having a system according to clause 11.
13. A computer readable medium containing program instructions executable by a processor of a wireless device for causing said wireless device to implement the steps of the method of any one of clauses 1 to 10.

The embodiments of the application described above are intended to be exemplary only. Those skilled in this art will understand that various modifications of detail may be made to these embodiments, all of which come within the scope of the application as defined by the appended claims.

Claims

A method for determining a maximum signal level for output to headphones (105) of a wireless device (100), comprising:
determining an impedance of the headphones (105);

characterised in that the method further includes:
storing in memory (200) of the wireless device (100) impedances, cellular network carriers, and corresponding carrier specific maximum signal levels; and,

accessing from the memory (200) a carrier specific maximum signal level for headphones (105) having the impedance;

wherein the carrier specific maximum signal level is a maximum signal level prescribed for a cellular network carrier associated with the wireless device (100) and for headphones (105) having the impedance; and,

wherein the maximum signal level for output to the headphones (105) is restricted to the carrier specific maximum signal level.
The method of claim 1 wherein the impedances, cellular network carriers, and corresponding carrier specific maximum signal levels are stored in a searchable table in the memory (200).
The method of claim 1 or claim 2 wherein the determining of the impedance further comprises applying an audio signal to the headphones (105).
The method of claim 3 wherein the audio signal is an inaudible audio signal.
The method of any one of claims 1 to 4 wherein the cellular network carrier is associated with a location and further comprising determining the location.
The method of claim 5 wherein the memory (200) further stores locations associated with cellular network carriers and wherein the carrier specific maximum signal level is a maximum signal level prescribed for the cellular network carrier or for the location associated with the cellular network carrier, and for headphones (105) having the impedance.
The method of claim 6 wherein the locations are stored in the searchable table in the memory (200).
The method of any one or claims 5 to 7 wherein the location is determined from one or more of: a signal received from a network (220) in which the wireless device (100) is operating; a global positioning system ("GPS") receiver of the wireless device (100); and, a location of antennae towers associated with a network (220) in which the wireless device (100) is operating.
The method of any one of claims 1 to 8 wherein an audio amplifier (430) of the wireless device (100) coupled to the headphones (105) is adjusted to restrict the maximum signal level output to the headphones (105) to the carrier specific maximum signal level.
The method of claim 9 wherein the audio amplifier (430) is adjusted if the carrier specific maximum signal level can be determined for the impedance.
The method of any one of claims 1 to 10 and further comprising determining the cellular network carrier.
The method of claim 11 wherein the cellular network carrier is determined from one or more of: a signal received from a network (220) in which the wireless device (100) is operating; and, information stored in a subscriber identity module ("SIM") (162) of the wireless device (100).
A system for a wireless device (100) for determining a maximum signal level for output to headphones (105) coupled to the wireless device (100), comprising:
a memory (200) storing program instructions; and

a processor (138) coupled to the memory (200) and configured to execute the program instructions to cause the system to implement the steps of the method of any one of claims 1 to 12.
A wireless device (100) having the system according to claim 13.
A computer readable medium containing program instructions executable by a processor of a wireless device (100) for causing the wireless device (100) to implement the steps of the method of any one of claims 1 to 12.