WO2009007322A2

WO2009007322A2 - Sound reproduction device and method for the calibration of a sound reproduction device

Info

Publication number: WO2009007322A2
Application number: PCT/EP2008/058693
Authority: WO
Inventors: John Heugle; Mario Manninger; Helmut Theiler; Peter Kammerlander
Original assignee: Austriamicrosystems Ag
Priority date: 2007-07-11
Filing date: 2008-07-04
Publication date: 2009-01-15
Also published as: WO2009007322A3; DE102007032281A1

Abstract

In a sound reproduction device (1), an output terminal (2) to which a sound transducer (3) is attachable, an amplification device (200), and a control device (100) are provided. The amplification device (200) has an output point (210) which is coupled to the output terminal (2). A sound level can be provided by a sound transducer (3) connected to the output terminal (2) in accordance with a specific voltage at the input opening (30, 31, 32) of the sound transducer (3) when the sound reproduction device (1) is in operation. The control device (100) can calibrate an amplification of the amplification device (200) as a function of the dependence of the sound level on the voltage at the input point (30, 31, 32) of the sound transducer (3). For this purpose, the control device (100) has a measuring device (120) with a signal source (130) to provide a source signal and a measuring device (140) for the recording of a measuring signal as a function of the source signal. Both said signal source and said measuring device are coupled to the output terminal (2). The measuring device (120) is set up to determine at least one parameter for the sound transducer (3) in accordance with the measuring signal, from which parameter the dependence of the sound level can be derived from the voltage at the input point (30, 31, 32) of the sound transducer (3).

Description

description

Reproduction device and method for calibrating a reproduction device

The invention relates to a display device and a method for calibrating a display device.

Nowadays, audio players are often offered in which a playback of the audio signals such as music is done via headphones or earphones. However, a playback on conventional speakers is possible. The described reproduction options have in common that an electrical signal can be converted via a sound transducer into an acoustic signal or sound. In the

Use of headphones or earphones, which are operated for example in the ear canal of the human ear, the reacted sound acts almost directly on the sensory organs of the ear. If the sound level generated by the transducer exceeds certain levels, or if human hearing is affected for a prolonged period of time at certain levels, this may result in hearing loss. Especially with children, it can lead to increased health damage, as these often underestimate the risk of hearing damage.

For this reason, in current playback devices for reproducing audio signals, attempts are made to limit the sound level generated by a connected loudspeaker or headphones. This can be achieved, for example, by limiting a volume control of the playback device to a certain value. However, this limit is only valid for a certain head- or headphone type and results from a value for a maximum sound level and an associated rms value of an input signal at the input of the headphones at this sound level. Accordingly, the volume gain of the reproducing apparatus can be limited to a value at which the rms value of the input signal of the headphone or the speaker is not exceeded. A measurement of the corresponding signals and the derivation of the maximum value for the volume setting are made before the delivery of the playback device in the laboratory.

However, if the operation of the playback device uses a headphone or speaker other than that for which the corresponding volume limit has been determined, it may happen that, for example due to a different type of headphone or speaker used, the sound level is too high despite the volume limit which in turn can lead to hearing loss.

An object of the invention is to provide a display device in which a limitation of a sound level for different connectable sound transducer is simplified possible. It is also an object of the invention to provide a method for calibrating a display device, which can be used to avoid hearing damage when using the display device simplified.

These objects are achieved with the subject matters of the independent claims. Embodiments and further development of the invention are the subject matter of the subclaims.

In an exemplary embodiment, a display device includes an output port to which a sound transducer and an amplifying means having an adjustable gain factor having an output coupled to the output terminal. Furthermore, a control device is provided for setting the amplification factor as a function of a sound level. Of the

Sound level can be emitted from a sound transducer connected to the output terminal during operation of the display device and depends on a voltage at the input of the sound transducer.

In this case, the control device can set the amplification factor at the amplification device such that it outputs an output voltage at its output such that the sound transducer just connected, for example a loudspeaker or headphones, emits a sound level which does not exceed a predefined or specifiable limit value , Thus, hearing damage due to high sound levels can be prevented.

The control device has a measuring device via which at least one parameter can be determined in the case of the sound transducer connected to the output connection during operation of the display device. From the at least one parameter, in turn, a dependence of the sound level on the voltage at the input of the sound transducer can be derived.

For this purpose, a signal source such as a current source or a voltage source can be provided in the measuring device, for example, which outputs a signal to the terminals of the sound transducer via the output connection. A corresponding response signal, which results at the terminals of the sound transducer, can be used as a measurement signal from a measuring device be recorded. The measuring device is thus able to determine the least one parameter from the emitted source signal and the resulting measurement signal.

For example, the control device is set up to determine a maximum permissible amplification factor of the amplification device and / or a maximum permissible voltage at the output of the amplification device as a function of a maximum value of the sound level for the connected sound converter and to set it on the amplification device. Alternatively or additionally, an output current or an output power of the amplification device can also be determined as a function of the maximum value of the sound level.

In one embodiment, the control device has a memory device in which a value can be stored that is derived from the maximum permissible amplification factor and / or the maximum permissible voltage. Accordingly, the controller may derive or recover corresponding adjustment values for the amplification means from the at least one stored value. For example, different values for different connectable sound transducers can be stored in the memory device, it being possible, during operation of the display device, to determine and use the value for the gain setting suitable for the connected sound transducer.

The measurement in the measuring device can be done as a DC signal measurement, so that, for example, a DC impedance of the transducer is measured. In another embodiment, the signal source outputs a pulse-shaped source signal or a source signal with alternating components such as, for example, alternating voltage components or alternating current components, so that the measuring device can record a pulse response, a step response or another transient signal as the resulting measurement signal. For example, it is thus possible to determine a complex impedance of the sound transducer and / or a transmission function of the sound transducer. The measuring device can have an analog-to-digital converter for measuring the resulting signal, which can be suitable both for a DC signal measurement and for the measurement of transient signals with alternating components.

From the at least one parameter which is determined by the measuring device, it is possible to deduce the type of the connected sound transducer. With the information thus obtained, for example, from a value table, English look up table, a corresponding gain setting for the amplification device can be read with which a predetermined limit value for a sound level to be output can be maintained.

In one embodiment, the display device is provided for operation with a sound transducer, which is a

Identification unit, in which information about the type of sound transducer are stored. In this case, the measuring device is able to read out the identification unit via a corresponding signal and, on the basis of the read-out information, which includes, for example, the at least one parameter, to make the corresponding settings on the amplifying device. Beispielswei- The at least one parameter comprises a digital identification word.

In a further embodiment, the playback device can be operated with a sound transducer, which is embodied, for example, as a headphone or earphone, wherein a microphone is provided or integrated in the headphone or earphone. The playback device has for this purpose an additional input terminal to which the microphone is connected. The measuring device can be activated via a signal at

Input terminal, which is generated by the microphone, determine a current or current sound level in the headphones or earphones. On the basis of the determined sound level or of a signal derived therefrom, for example by filtering, the control device can if necessary make a corresponding adjustment of the gain setting and / or the amplification factor. For example, a low-pass filtering or an averaging or an integration of a current sound level can be performed.

In an exemplary embodiment of a method for calibrating a display device, at least one parameter of a sound transducer, which is connected to an amplification device of the display device, is determined. From the at least one parameter, a reference variable is derived. The reference value indicates a dependence of a sound level on a voltage at an input of the sound transducer. A maximum output voltage can be determined as a function of a maximum permissible sound level and the reference value. The amplification device is set such that the determined maximum output voltage is not exceeded. Thus, a setting of an amplifying device in a display device adapted for a respective connected sound transducer can be made so that a certain sound level is not exceeded in the transducer during operation. In this way, the risk of hearing damage resulting from excessive noise levels can be reduced.

The invention will be explained in more detail with reference to several exemplary embodiments with reference to the figures. Function or effect elements have the same reference numerals.

Show it:

1 shows a first embodiment of a display device with a connected sound transducer,

2 shows a second embodiment of a display device with connected sound transducer,

FIG. 3 shows a third exemplary embodiment of a display device with a connected sound transducer,

FIG. 4 shows a first exemplary embodiment of a sound transducer,

5 shows a second embodiment of a sound transducer,

Figure 6 shows a third embodiment of a sound transducer and Figure 7 shows an embodiment of a control device with a connected transducer with integrated microphone.

Figure 1 shows a first embodiment of a display device 1, which has an output terminal 2, to which a sound transducer 3 is connected. The reproduction device 1 comprises an amplification device 200 with an adjustable amplification factor, which can be controlled via a control signal at a control input 215 of the amplification device 200. The amplifying means has a signal output 210 coupled to the output terminal 2. The reproduction device 1 further comprises a control device 100, which has a control output 115, which is coupled to the control connection 215 of the amplification device 200. The control device 100 additionally has a connection 110 which is coupled to the output 210 or the output connection 2.

In this case, the control device 100 serves to set the amplification factor of the amplification device 200 via the connections 115, 215. The amplification factor is set as a function of a sound level which is emitted or emitted by the sound transducer 3 during operation of the illustrated arrangement. The sound level depends on a voltage at the input 30 of the sound transducer 3, which is coupled to the output terminal 2. The dependence of the sound level which is emitted by the sound transducer 3 as a function of the voltage at the terminal 30, can also be referred to as sensitivity, and depends, among other things, individually on the type of construction, design and lower parameters of each connected sound transducer 3 from.

The sound transducer 3 may comprise, for example, a conventional loudspeaker or a headphone or earphone. The reproducing device 1 is comprised, for example, of an audio player such as an MP3 player, a mobile phone, a personal digital assistant (PDA) or other device having a music playing function and / or a sound reproducing function.

For example, to reduce the risk of hearing damage when operating with a headset, the controller 100 may be used to set a maximum allowable gain on the gain device 200. Alternatively or additionally, the control device can also determine a maximum permissible voltage at the output 210 of the amplification device 200 and adjust it at the amplification device 200, wherein the respective setting is based on a predetermined maximum value of a sound level. In other words, due to the settings of the control device 100, the maximum value of the sound level in the presence of the maximum permissible voltage at the output 210 is not exceeded.

In one embodiment, the controller

100 via the terminal 110 one or more parameters, ie determine at least one parameter of the sound transducer 3, from which can derive the corresponding necessary gain settings for the amplifying device 200 sen to comply with the condition of maximum sound level.

In another embodiment, the control device 100 has a storage device, not shown here in which one or more parameters are stored for one or more connectable sound transducers. By appropriate programming of the control device, it can be determined, for example, that it selects from the storage device a specific parameter or parameter set which corresponds to a connected or to be connected sound transducer. Thus, a dependent on the type of the transducer 3 setting can be made in the playback device 1, each ensures that when a match between set and connected type of transducer a maximum sound level is not exceeded.

FIG. 2 shows a further exemplary embodiment of a playback device 1 with a sound transducer 3. In this exemplary embodiment, the amplification device 200 has a digital-to-analog converter 220 and a downstream amplifier 230 whose output is coupled to the output 210 of the amplification device 200.

The control device 100 comprises a measuring device 120, which has a signal source 130 and a measuring device 140. The measuring device 140 is designed, for example, as an analog-digital converter. The controller 100 further includes a digital signal processor 160 to which a memory device 150 is connected. The signal processor 160 is further coupled to the control terminal 115 as well as to the signal source 130 and the measuring device 140. The signal source 130 and the measuring device 140 each have a first connection 131, 141, which are coupled to the output connection 2 or the connection 110 of the control device 100. A respective second terminal 132, 142 of the signal source 130 and the measuring device 140 is electrically connected to a reference potential terminal. The amplification device 200 and the sound transducer 3 are also coupled to the reference potential connection 4.

The digital-to-analog converter 220 in the amplification device 200 is used, for example, for converting digitally present audio signals which are to be reproduced into corresponding analog audio signals. These can be amplified by the downstream amplifier 230 to the respectively required output level. The setting of the amplification factor at the amplification device 200 may, for example, be digital, so that a corresponding adjustment word can be output directly and / or without further conversion from the digital signal processor 160.

In one embodiment, the gain factor may be made by programming the digital-to-analog converter 220 appropriately. Alternatively or additionally, a gain setting can also be made on the downstream amplifier 230. It is desirable that there be a unique relationship between the adjusted gain and the voltage output by the gain device 200.

Although only a single amplifier path for a reproduction channel is shown schematically in FIG. 2, the amplification device 200 can be provided for the reproduction or amplification of a plurality of reproduction channels. For example, the amplifying device 200 has a second digital-to-analog converter with a downstream amplifier, which is arranged parallel to the illustrated digital-to-analog converter 220 and the amplifier 230. As explained briefly above, at least one parameter of the sound transducer 3 can be determined for the measuring device 120, wherein the at least one parameter comprises, for example, an impedance of the sound transducer. Furthermore, information about the relationship between the sound level and the corresponding voltage at the output terminal 2 or at the input 30 of the sound transducer for different types of sound transducers can be stored in the memory device 150, with an assignment to a parameter being present, at least corresponds to a parameter that can be determined via the measuring device 120. The measured parameter or parameters can now be compared with the parameters stored in the memory device 150 in order to detect whether the connected sound transducer 3 corresponds to a sound transducer which can be considered to be known according to the memory device 150.

In the case of a match, the corresponding gain settings may be read from the memory unit 150 and used to adjust the gain device 200. However, if the connected transducer 3 can not be recognized as a known transducer, a standard gain setting may be selected in which, for example, a maximum output voltage of the amplifier 200 is so low that conventional sound transducers are not expected to produce sound levels that cause hearing damage could. For example, a safety factor may be provided in this case, which limits the output voltage of the amplification device 200 to a specified factor based on a theoretically maximum possible output voltage, such as one-tenth of the theoretically maximum possible output voltage. The dependence of the sound level on the voltage at the input of the sound transducer, ie the sensitivity of the sound transducer, can be predetermined for different types of sound transducers, for example by means of a calibration, and stored together with the one or more parameters in the memory device 150, wherein the parameters of the respectively connected sound transducer 3 can be determined during operation of the display device 1 via the measuring device 120.

In other words, the sensitivity of the connected sound transducer is not directly determined by the measuring device 120, but instead a parameter which, with the aid of previously determined values, enables a clear inference to the sensitivity of the connected sound transducer. Since even in the event that the connected transducer is not known, a safety limitation of the output voltage or the sound level, hearing damage can be prevented or the risk of hearing damage can be significantly reduced.

For example, an impedance of the connected sound transducer 3 is determined by the measuring device 120. For this purpose, the signal source can emit a current which results in a voltage across the terminals 30, 31 of the sound transducer 3. This voltage can be detected by the measuring device 140, for example by analog-to-digital conversion of the applied voltage, so that an impedance value can be determined from the known output current and the measured voltage. Of course, the just described impedance measurement can also be performed by delivering a voltage signal and measuring a resulting current.

In one embodiment, the signal source 130 is on

Output 131 from a direct current, which accordingly results in a measured DC voltage across the terminals 30, 31 of the transducer 30. In other words, in this embodiment, a DC impedance is determined in the connected sound transducer 3.

In another embodiment, the signal source 130 outputs at the output 131 a pulsed current signal, which accordingly also comprises alternating current components. This results accordingly in a voltage response at the input

30, 31 of the sound transducer 3, the AC components comprises. For example, the voltage response of the sound transducer 3 at the input 141 can be detected as a transient signal via the analog-to-digital converter 140 in order to determine, for example, an alternating-current impedance in the sound transducer 3. However, the transient signal recorded by the measuring device 140 can also be compared with stored transient curves of known sound transducers so that a specific sound transducer can be uniquely identified by the transient course of its voltage response. The evaluation of the measured signals or transient curves can be carried out via the signal processor 160.

The source signal output by the signal source 130 may also be a signal with alternating components such as alternating current components. For example, from the signal source 130 a two-tone signal, English dual-tone signal or a multi-tone signal is emitted, which sine waves of two or several different frequencies. In other words, two or more sinusoidal vibrations of different frequencies may be superimposed in the source signal. The source signal may thus have different frequency components. This in turn results in a voltage response at the input 30, 31 of the sound transducer 3, which comprises AC components and can be recorded by the analog-to-digital converter 140. Accordingly, the measurement signal may also have different frequency components.

The determination of the respectively connected type of sound transducer and the provision of the corresponding amplification settings can be effected, for example, when the reproduction device 1 is switched on or at a point in time at which the connection of a respective sound transducer is detected. Such a detection can be realized, for example, by a corresponding contact in a connector provided for a connection of the sound transducer.

Alternatively or additionally, gain settings can also be stored in the memory device 150, which can be retrieved by appropriate programming. For example, transducers such as headphones may be classified into different classes, with a particular class indicating a range of maximum sound levels with respect to an effective input voltage VRMS. The corresponding class can be permanently set by programming the control device.

Table 1 shows possible parameters that can be stored in the memory device 150 for different classes of sound transducers. Table 1

For example, with the values of Table 1 for a Class 2 transducer, a sound level of 100 dB results for an effective input voltage of 1 volt. At a maximum permissible sound level of 90 dB, this results in a maximum permissible effective output voltage of the amplification device of 0.316 volts. Sound transducers of other classes result in correspondingly different values, which are given by way of example in Table 1.

FIG. 3 shows a further exemplary embodiment of a display device 1. As in the exemplary embodiment of FIG. 2, the amplification device 200 comprises a digital-to-analog converter 220, which is used, for example, for converting digitally present audio data, and a downstream amplifier 230. Both the digital Analog converter 220 as well as the amplifier 230 can be adjusted in their output level, for example via a gain factor.

The playback device 1 further includes the signal source 130, which in this embodiment as a power source for Output of a _test current I _{test is} formed. The current source 130 can be embodied as a direct current source or as a pulsed current source. To record the resulting measurement signal, the measuring device 140 designed as an analog-to-digital converter is provided. Such an analog-to-digital converter 140 can also be used for other measuring tasks, such as the measurement of a chip temperature or the monitoring of supply voltages.

Further elements of the control device 100, which for

Figure 2 is explained in detail, are not shown for reasons of clarity in Figure 3. Otherwise, however, the functions in particular of the current source 130 and the analog-to-digital converter 140 correspond to those described for FIG.

FIG. 4 shows an exemplary embodiment of a sound transducer 3 with a first and a second reproduction channel, which is illustrated by loudspeakers 310, 320 for a stereo signal, by way of example. The right channel speaker 310, R is connected to a first terminal 30 and a second terminal 31. The second loudspeaker 320, L is accordingly connected to a third terminal 32 and to the common second terminal 31. Between the first and the third terminal 30, 32 an impedance element 315 is provided. The output terminal 2 has a first pad 20 for a first playback channel coupled to the terminal 30 of the acoustic transducer 3, a second pad 22 for a second playback channel coupled to the terminal 32, and a third pad 21 for a common one Reference voltage, which is coupled to the reference potential terminal 4 and the terminal 31. The sound transducer 3 comprises in this embodiment, for example, a headphone or earphone. In addition to the impedances which result from the electrical properties of the loudspeakers 310, 320, the further impedance element 315 is provided whose impedance value corresponds, for example, to a specific sensitivity or from which, as explained above, a sensitivity of the sound transducer 3 or the loudspeakers 310, 320 can be deduced. The impedance value of the impedance element 315 can be measured or determined, for example, via the measuring device 120, which is illustrated in detail in FIG. 1 and explained in detail there. With a corresponding evaluation of the determined impedance value of the impedance element 315, in turn gain settings for the amplification device 200 can be derived, for example by comparison with values stored in the memory device 150. In other words, can be coded by the impedance value of the impedance element 315, a certain sensitivity of the transducer 3. It is desirable that the coding for sound transducers from different manufacturers is uniform.

In addition to determining the impedance value of the impedance element 315, the impedance of the first and / or the second loudspeaker 310, 320 between the third contact point 21 and the first and / or the second contact point 22 can also be determined and used to derive the gain settings.

FIG. 5 shows a further exemplary embodiment of a sound transducer 3. In this exemplary embodiment, an identification unit is provided between the first and the second connection 30, 31 of the loudspeaker 310, in which, for example, a digital identification word is stored. Controlled for example by a corresponding high-frequency signal, which is generated by the signal source 130, the Identification unit in one embodiment, the digital identification word as a corresponding high-frequency voltage signal between the terminals 30, 31 back. This can be detected by the measuring device 140 and evaluated by the signal processor 160. The digital identification word can be used to read out corresponding gain settings from the memory unit 150. In a further embodiment, the digital identification word itself contains information about the sensitivity of the sound transducer 3 or the loudspeakers 310, 320.

FIG. 6 shows a further exemplary embodiment of a sound transducer 3, wherein, with reference to FIG. 5, in this exemplary embodiment the identification unit 330 is provided between the terminations 31, 32, ie the connections of the second loudspeaker 320.

FIG. 7 shows an exemplary embodiment of a control device 100 and a sound transducer 3, in which the sound transducer 3 comprises, in addition to the loudspeakers 310, 320, a microphone 340 which is coupled to a microphone connection 33. In this exemplary embodiment, the reproduction device 1 or the control device 100 additionally comprises an input connection 5, which is coupled to the microphone connection 33. Furthermore, the signal source 130 and the measuring device 140 of the measuring device 120 are connected to the input terminal 5.

The microphone 340 is for example integrated with one of the speakers rather 310, 320 together in a headphone. By evaluating the microphone signal via the measuring device 120, a sound level which is generated by the respective loudspeaker can be determined. Due to the design of the Headphone should be ensured that the level in the microphone 340 is proportional to the sound level in the ear. The measured sound level can accordingly be compared with a maximum permissible sound level in order to make a corresponding adjustment of the gain settings.

This allows control of the gain settings in the operation of the playback device. In a further embodiment, it is also possible to provide a second microphone for the respective other loudspeaker.

The embodiment shown in FIG. 7 can also be combined with the previously described embodiments.

Claims

claims

1. playback device (1), comprising an output terminal (2) to which a sound transducer (3) can be connected, from which during operation of the display device (1) a sound level in response to a voltage at the input (30, 31, 32) of the sound transducer (3) is deliverable; amplifying means (200) having an adjustable gain factor and having an output (210) coupled to the output terminal (2); and control means (100) for adjusting the gain as a function of a dependence of the sound level on the voltage at the input (30, 31, 32) of the sound transducer (3); wherein the control device (100) has a measuring device (120) with a signal source (130) for outputting a source signal and a measuring device (140) for receiving a measuring signal as a function of the source signal, which are each coupled to the output terminal (2); and wherein the measuring device (120) is set up to determine at least one parameter in the sound converter (3) connected to the output terminal (2) as a function of the measuring signal, from which the dependence of the sound level of the voltage at the input (30, 31, 32) of the transducer (3) can be derived.

2. reproducing device (1) according to claim 1, wherein the control device (100) is arranged, a maximum allowable amplification factor of the amplifying means (200) and / or a maximum allowable voltage on Output (210) of the amplifying means (200) in response to a maximum value of the sound level to determine and adjust the gain means (200).

3. reproduction device (1) according to claim 2, wherein the control device (100) comprises a memory device (150) which is adapted to store at least one value derived from the maximum allowable gain factor and / or the maximum allowable voltage is.

4. reproduction device (1) according to one of claims 1 to

3, in which the measuring device (140) has an analog-to-digital converter.

5. reproduction device (1) according to one of claims 1 to

4, wherein the signal source (130) comprises a power source.

6. playback device (1) according to one of claims 1 to 5, wherein the signal source (130) is arranged, the

Deliver source signal as a DC signal.

7. reproduction device (1) according to one of claims 1 to

5, wherein the signal source (130) is arranged to deliver the source signal as a pulse-shaped signal and / or as a signal with alternating components.

8. playback device (1) according to any one of claims 1 to 7, wherein the output terminal (2) comprises: - a first contact point (20) for a first reproduction channel of a sound transducer (3); a second contact point (22) for a second reproduction channel of a sound transducer (3); and a third pad (21) for a common reference voltage of the first and second playback channels.

The display device (1) of claim 8, wherein the at least one parameter comprises an impedance of the acoustic transducer (3) and wherein the measuring device (120) is adapted to control the impedance between the third junction (21) and the first and / or the second contact point (20, 22) to determine.

The display device (1) of claim 8, wherein the at least one parameter comprises an impedance provided by the acoustic transducer (3) between the first and second contact pads (20, 22), and wherein the measuring device (120) is adapted to: to determine the impedance.

11. reproduction device (1) according to one of claims 1 to 10, wherein the measuring device (120) is adapted to read the at least one parameter from a in the sound transducer (3) provided identification unit (330).

The display device (1) of claim 11, wherein the at least one parameter comprises a digital identification word.

13. reproduction device (1) according to one of claims 1 to

12, in which the control device (100) is set up to compare the at least one parameter with stored parameters and to set the amplification factor as a function of the comparison.

14. reproduction device (1) according to one of claims 1 to

13, in which the output terminal (2) is arranged to to connect a sound transducer (3) comprising a headphone or an earphone.

15. Reproduction device (1) according to claim 14, which additionally has an input terminal (5) to which a microphone (340) integrated in the headphone or earphone is connectable, wherein the measuring device (120) is adapted to the at least one To determine parameters from a signal at the input terminal (5).

16. A display device (1) according to any one of claims 1 to 15, wherein the amplifying means (200) comprises a digital-to-analog converter (220), the signals to be reproduced are supplied digitally and in which the gain factor is digitally adjustable.

17. A method of calibrating a display device (1) comprising:

Outputting a source signal to a sound transducer (3) connected to amplification means (200) of the display device (1);

Recording a measurement signal at the input of the sound transducer (3) in response to the source signal;

Determining at least one parameter of the sound transducer (3) as a function of the measurement signal, which can be derived from the at least one parameter, a dependence of the sound level of the voltage at the input (30, 31, 32) of the sound transducer (3);

Determining a maximum output voltage as a function of a maximum allowable sound level and the at least one parameter; and

Setting the amplification device (200) such that the maximum output voltage is not exceeded.

18. The method of claim 17, wherein the adjusting comprises deriving an amplification factor from the maximum output voltage and adjusting the amplification factor at the amplification means (200).

19. The method of claim 17 or 18, wherein the source signal is delivered as a DC signal.

20. The method according to claim 17 or 18, wherein the source signal is output as a pulse-shaped signal and / or as a signal with alternating components.

21. The method of claim 17, wherein determining the at least one parameter comprises measuring an impedance.

22. The method of claim 17, wherein deriving the reference comprises comparing the at least one parameter with stored parameters, and adjusting the gain means is set in dependence on the comparison.

23. Method according to claim 17, wherein determining the at least one parameter comprises reading out the at least one parameter from an identification unit (330) provided in the sound transducer (3).

24. The method according to claim 17, wherein the sound transducer comprises a headphone or an earphone, and determining the at least one parameter comprises evaluating a signal which is produced by a microphone (340) integrated in the headphone or earphone. is delivered.