WO2006075275A1

WO2006075275A1 - Audio entertainment system, method, computer program product

Info

Publication number: WO2006075275A1
Application number: PCT/IB2006/050068
Authority: WO
Inventors: Vincent P. Buil; Daniel W. E. Schobben
Original assignee: Koninklijke Philips Electronics N.V.
Priority date: 2005-01-12
Filing date: 2006-01-09
Publication date: 2006-07-20

Abstract

An audio entertainment system (100) having an earbud (103) having an electro- acoustic transducer (104) is arranged to detect e.g. tapping on the earbud (103) for obtaining user input for e.g. controlling a game, setting a volume level or detecting (302) the earbud (103) being inserted, by measuring a change (108) in an electrical characteristic (109) of the electro- acoustic transducer (104).

Description

Audio entertainment system, method, computer program product

The invention relates to an audio entertainment system comprising: an earbud comprising an electro-acoustic transducer for converting an electric audio signal into sound.

The invention also relates to a method and to a computer program product for use in such a system.

An example of an audio entertainment system as described in the opening paragraph is described in the non-prepublished European patent application 04 101 398 (PHNL040356). Said patent application describes an audio entertainment system with an audio device and an earbud for transducing audio. The earbud has input means with a touch sensitive area for controlling the audio device. In response to a tap on the touch sensitive area, the audio device may for example toggle between a play and a pause mode.

It is a drawback of the system described in the patent application that a conventional earbud cannot be used, because an earbud having input means with a touch sensitive area is required.

It is an object of the invention to provide a system of the kind described in the opening paragraph that can be used with a conventional earbud. The object is realized in that the system comprises a detector for detecting a tap on the earbud, wherein the detector is arranged to detect the tap on the earbud in dependence of a change in an electrical characteristic of the electro-acoustic transducer.

By the detector being arranged to detect the tap on the earbud in dependence of a change in an electrical characteristic of the electro-acoustic transducer, no additional wiring is required, and no input means dedicated to receiving the tap are needed, such that the detector may be used with a conventional earbud.

In prior art solutions, the earbud needs input means like e.g. a button or a touch sensitive area, which in turn typically requires additional wiring between the earbud and an audio source where the detector is typically located. With the system in accordance with claim 1, the wire pair running to the transducer suffices to couple the detector to the transducer.

The audio entertainment system may comprise or be part of e.g. a media player, a gaming device, a communication device, a computing device, a personal digital assistant, a smartphone, a portable computer, a palmtop, a tablet computer, an organizer. The audio entertainment system may further comprise other input means or other output means, for example a video display, a game pad, a keyboard.

The audio entertainment system may comprise a source of the audio signal. The source may comprise the detector or part of the detector. The audio entertainment system may comprise an audio amplifier. The audio amplifier may advantageously be adapted to comprise at least part of the detector, for instance by including means for determining the electrical characteristic, like a resistor or inductance for measuring a current through the transducer, or an impedance of the transducer.

The electric audio signal may originate from an output of the audio amplifier, which may be coupled to the transducer with a single wire pair that carries the electric audio signal.

The electric audio signal transduced may be generated by a source within in the audio entertainment system, for example by playing it from a medium e.g. an optical disk such as a BluRay disc, a DVD, or a CD, or a hard-disc, a solid state memory. The audio transduced may alternatively or additionally, be received from a source outside the audio entertainment system, for example via a wireless interface like an antenna coupled to e.g. an analog or digital tuner for radio frequencies, a wireless LAN or PAN, WiFi, a mobile network like GSM, GPRS or UMTS, or via a wired interface e.g. USB, Fire Wire, LAN, Ethernet, or via still another interface. The earbud may be an in-ear type of headphone or earpiece, or a headset with a boom or a headband with a cup or a still other type of earbud or headphone.

The electro-acoustic transducer may comprise a voice coil speaker, a piezo speaker, a membrane speaker, or be based on a still other operating principle.

The sound may for example be music, voice and is typically listened to by the wearer of the earbud. The sound may serve purposes like communication, signaling, entertainment, translation, monitoring.

The tap on the earbud comprises a temporary contact between an object and the earbud. The object may e.g. be a finger, a thumb, a hand, a wrist, a nail, a stylus or a pencil. The temporary contact may have a relatively short duration e.g. like a tick, or it may have a relatively long duration, e.g. like a gentle press. The temporary contact may recur, for instance in case of the object bouncing twice on the earbud. The tap may be forceful or rather weak. The tap may also comprise a time interval wherein the outer surface of the earbud is rubbed or scratched with the object. The audio entertainment system may comprise a controller coupled to the source, for controlling a property of the electric audio signal or of the source. The controller may be arranged to change the property in response to the detector detecting the tap. The tap detected may be used for controlling the source. The controller may e.g. be increasing or decreasing a setting, for example an audio volume, an audio balance, a tone color, or any setting for an audio effect like reverberation, chorus and so on. The controlling may pertain to the audio content, for example selecting an artist, an album, a track, a position in time of a track, a play back speed.

The detector may be further arranged to determine an attribute of the tap or of the object, like a duration, an intensity, a pressure, a speed, a rhythm, an attack, a decay, a sustain, a release, a frequency. The controller may be further arranged to change the property in dependence of the attribute of the tap determined. In controlling an audio volume for instance, the speed of changing the volume during the tap may increase with an increasing pressure exerted on the earbud. This offers the advantage that the detector provides for a more convenient and versatile interface to the user or the operator. In a particular combination, the speed or velocity of rubbing may be derived from the frequency or the pitch of the detected signal.

The electrical characteristic of the electro-acoustic transducer may be a quantity like a voltage, a current, an impedance, a capacitance, a resistance, an inductance, a frequency. The electrical characteristic may also be a measure on a history of one or more of such quantities. Examples of such a measure are an average impedance, an average electrical power absorbed by the transducer, an impedance averaged over a frequency range, a resonance frequency, a peak or a slew rate of a voltage induced over the transducer.

The electrical characteristic is determined from the electrical domain of the transducer, such that the existing two wires of the transducer suffice for determining the change in the electrical characteristic. Due to the coupling via the transducer with the acoustical domain of the transducer, a physical change in the vicinity of the transducer or the earbud causes an electrical change of the transducer. Examples of the physical change are the tap on the earbud, rubbing a finger over the outer surface of the earbud, insertion of the earbud in an ear, and pinching the earbud between e.g. a thumb and a folded index finger. The change of the electrical characteristic may be an absolute increase or decrease, but it may also be a relative increase or decrease or a rate of changing over time.

The detector may be partly or as a whole be implemented with hardware like an electronic detecting circuit known in the art. This may be cheaper than a processor that runs software.

The detector may be partly implemented with software, particularly as a computer program product running or executed on a digital signal processor. This may be more flexible than a hardware only solution, because only the program needs to be replaced to change the behavior of the detector. The detector may be calibrated prior to use. The detecting of the detector may be improved by adapting the detector to the model and make of the earbud, or additionally or alternatively to the particular earbud, or additionally or alternatively to the particular operator or user.

The system may be responsive to an input means receiving an input for calibration, such that a user or operator may initiate the calibrating. The detector may be arranged to execute a calibration in response to the earbud being inserted in an ear.

The detector may be adapted to detect that the earbud is substantially coupled acoustically to a chamber resembling a human ear auditory canal, such that the adapted detector may be applied for deciding if the earbud is inserted in the ear. This deciding may trigger the calibration as well.

The detector may replace an existing detector operating on a principle like, for example, closing an electrical circuit between a pair of e.g. skin contacts, or spring switch contacts, or detecting an infrared radiation, or detecting a presence of an ear lobe, or a still further operating principle. Alternatively, combining the detector with other existing detectors may enhance the reliability of the detecting. The detector may for example improve determining an instant at which the tap begins, because the onset of the contact between the object and the earbud may be determined with a relatively high accuracy in time. This may enable using a capacitance sensor for an application, where this would be not possible without the detector. The detector may advantageously operate in a first or a second mode, in dependence of the sound level transduced. In a first mode, the transducer produces sound while being acoustically substantially coupled to an ear. The tap causes the earbud to move with respect to the ear, resulting in the electrical characteristic of the electro-acoustic transducer being changed temporarily. In a second mode, the transducer may be used as a microphone, picking up noise generated by the tap. The noise picked up is by monitored the detector for the particular noise of the tap. The detector may operate in the first mode as long as the signal level is above a first threshold, and switch to the second mode if the signal level is below the first threshold, subsequently switching back to the first mode when the signal level exceeds a second threshold above the first threshold again.

In an especially advantageous combination, a tap and hold detector combines detection of the impact of the tap with detection of holding a pressure by a change in impedance. These two detection principles combine especially advantageously, because the impact detection provides for accurate start and stop points in time which collide with the transients of hitting the earphone and letting go of it, while the impedance detection provides for an accurate holding time pressure.

The taps detected may be used for various applications. In a first application, the taps detected control or select a source of the audio signal. In a second application, the taps detected control a setting for a property of the audio signal, like a volume level. In a third application, the taps detected control another function of the device.

A particular function that is suitable to be controlled is a gaming function of the device. In this case, the earbuds serve as game pads. The earbuds may be taken out of the ears, and be held in the hand while serving as game pads.

Any existing type of earbud may thus serve as input means for controlling a gaming function of an audio device. This has the advantage that the earbud serves both the purpose of transducing audio and the purpose of input means for game control, thus alleviating the need for a separate input means. Additionally, the earbud may be very simple and therefore cheap. No modifications on the earbud are required, such that an off-the-shelf earbud may be used. Also, an earbud may have to be provided with the device anyhow, so that the input means for the gaming function do not add to the bill of materials.

The earbud thus serve multiple purposes. The earbud may serve as a low-cost game pad, is light-weight, and is readily available for most portable equipment. The earbud, when used as a game pad, allows the controlled device to be lying on the lap or on a desk, and allows for multi-player games to be controlled easily without the players interfering with each other on a tiny keypad. The earbud also allows players to take a distance from the device while still controlling it.

A first player may use a keypad on the device and a second user may use an earbud, such that both players can control the device. Alternatively, the first user may use a first earbud and the second user may use a second earbud, offering the advantage that both players may move freely in the vicinity of the controlled device, be it under a possible constraint from a wire coupling the earbud to the controlled device. Still alternatively, the first user may use a first set of earbuds and the second user may use a second set of earbuds. This offers the advantage that each user benefits from having two input means, which may result in a more intuitive user interface. In an example of such user interface a plane is controlled, whereby the difference between measured impedances of the left and the right earbud determines the plane turning right or left, such that pressing the left earbud harder than pressing the right earbud results in the plane turning left.

Holding the earbuds in the hands also offers the advantage that when an auxiliary signal is added for improving the detecting as of claim 7, the auxiliary signal may be relatively loud without causing much to be heard of it. The detection may be improved if the auxiliary signal is relatively loud, as the signal to noise ratio will improve. Alternatively a simpler detector may be applied, e.g. with circuits that do not need to achieve high signal to noise ratios.

In an embodiment, the audio entertainment system has the features of claim 2. Voltage and current may be measured with relatively simple means, for example a shunt resistor that couples the output of an audio source to the transducer. In another embodiment, the audio entertainment system has the features of claim 3. It has been established with experiments that the electrical impedance changes notably with the size of the chamber that acoustically terminates the transducer, probably due to the stiffness of the enclosed air. The electrical impedance is less dependent of the electrical audio signal than voltage and current are, which is an advantage because the detecting should ideally hardly depend on the electrical audio signal.

In another embodiment, the audio entertainment system has the features of claim 4. It appears from experiments that the absolute change in the impedance is relatively large at about the resonance frequency, such that detection is improved if the detector is most sensitive at about the resonance frequency. In another embodiment, the audio entertainment system has the features of claim 5. Closing the opening provides for a very clear change that is easily detected. The opening may be conveniently closed or opened with a thumb. The opening may conveniently be located at a protruding part of the earbud that typically extends in a radial direction from a disc-shaped part of the earbud, such that the opening is accessible for tapping while the earbud is inserted substantially in the ear. A gradually increasing pressure exerted by the thumb on the opening, causes the opening to be gradually closed, and causes a gradual change in the impedance to be measured. This way, the earbud may serve as a pressure sensor or pinch sensor, and the measured pressure may be applied as input to an application of the device like a game. A further refinement is to use two earbuds, one in each hand, where the difference between the measured impedances is used as input to the application. This may e.g. control the direction and speed of a moving bat in e.g. a game like Pong, Arkanoid, andsoon.

In another embodiment, the audio entertainment system has the features of claim 6. The opening may function as a bass port and enhance the low frequency response of the earbud. This has the additional advantage that closing a bass port generally causes a clear impedance change that may be easily detected.

In another embodiment, the audio entertainment system has the features of claim 7. In the absence of an electrical audio signal that carries sufficient energy for the detecting, e.g. during a silence, detection may still be achieved with the auxiliary signal providing additional energy for the detecting.

In another embodiment, the audio entertainment system has the features of claim 8. By adapting the auxiliary signal such that it is masked by the electric audio signal, the user will not perceive the auxiliary signal, while the auxiliary signal is added and the detecting improved. Various methods are known in the art to achieve the masking. In one method, the frequency of the auxiliary signal may be chosen outside the frequency band of perceptible tones. In another method, transient shadow effects, such as the impossibility of the human ear to detect sound shortly before and/or after a loud transient is exploited.

In another embodiment, the audio entertainment system has the features of claim 9. Taking the second earbud as a reference has the advantage that detecting a difference between the earbuds may be easier than detecting the change in a single earbud. In addition, the influence of a disturbing factor may be effectively reduced, for example if both earbuds suffer from the same disturbance, like variations in air stiffness, temperature, inner ear shape andsoon.

The above object and features of the audio entertainment system 100, the detector 106, the method 300 and the computer program product 400 of the present invention will be more apparent from the following description with reference to the drawings. Fig. 1 shows the measured impedance of Philips HP890 full-size headphone when free in the air (yellow) and when being worn on the head (green).

Fig. 2 shows the measured impedance of an earphone in air (yellow) and in ear (green). Fig. 3 shows a set-up for measuring the electrical output of a headphone for a tap 107.

Fig. 4 shows the measured electrical output of a headphone for a tap 107.

Fig. 5 shows an example diagram of a fork circuit.

Fig. 6 shows an example diagram of a circuit for picking up differences 202 between a left and a right channel.

Fig. 7 shows an example of operating the earbud 103 as input sensor.

Fig. 8 shows another example of operating the earbud 103 as input sensor.

Fig. 9 shows a block diagram of an audio entertainment system 100 according to the invention. Fig. 10 shows a block diagram of an audio entertainment system 100 with a second earbud 200 according to the invention.

Fig. 11 shows a flow diagram of a method 300 according to the invention.

Fig. 12 shows a computer program product 400 according to the invention.

By measuring the impedance level of the loudspeakers 104 in the headphone it is possible to detect how much air-resistance they encounter when playing sound 105. When the headphone 103 is worn this air-resistance is higher then when not worn, because the worn headphones 103, 200 create a small chamber of air around or in the ear, depending on the type of headphone 103. The differences in air-resistance create a significant change 108 in measured impedance 112 of the speaker 104 driver, as shown in Figures 1 and 2. The measured impedance can be used to detect whether the headphone 103 is being worn or not. This solution does not require modifications to existing headphones 103, 200, nor does it require extra wires between the headphone 103 and the device. Only some impedance measuring electronics in the device are added, to enable detecting 302 whether the connected headset 103 is worn or not. Any headset 103 that produces a detectable change 108 in impedance 112 between both situations may be used.

Impedance measurements 112 may be taken when sound 105 is playing. In a preferred embodiment an auxiliary signal 115 is generated at moments that no sound 105 is rendered on the headphone 103. This auxiliary signal 115 preferably has a low intensity and an energy that is substantially centered on the resonance frequency 113 of the headphone

103, because most information is in this region. Figure 1 shows a measurement of the impedance 112 of one loudspeaker driver 104 in a Philips HP890 full-size headphone 103 free in air (the upper curve) and on the ear (the lower curve). A detectable change 108 is obtained. Figure 2 shows a similar measurement for a Philips in-ear headphone 103. Again, a detectable change 108 is obtained.

Alternatively or additionally, the speakers 104 of a headset 103, 200 may be used as microphones to detect tapping and rubbing on the earbuds 103, 200. An advantage is that again existing headphones 103, 200 may be used for controlling purposes, and that the two methods may be used together to further improve the detecting 302.

By applying a fork circuit, it is possible to use a speaker 104 of a headset 103 simultaneously as an output and as an input medium (i.e., loudspeaker and microphone function). Because the speakers 104 are designed for rendering audio, the effective registration capabilities are not so strong. However, tapping on an earbud 103 with built-in speaker 104 gives a strong enough impact to be detected and discriminated electronically.

The same holds for rubbing an earbud 103. The Figure 3 shows a test set-up for measuring the impact, while Figure 4 shows a typical input level obtained when tapping the headphone

103. The schematics given in Figures 5 and 6 show possible implementations of a detector 106 for detecting 302 tapping or rubbing from the signals produced by the headset speakers 104.

The circuit of Figure 5 filters the music signal by an adaptive filter (AF) so as to eliminate the contribution of the music to the signal over the series resistance (RO). The block (AF) with the arrow through it is the adaptive filter, which estimates the music component in the signal (SI) after the output resistance (RO). The signal (Output) that controls the adaptive filter should ideally contain only the tapping signal.

In the circuit of Figure 6, the earbud 103 itself is used to produce the

'subtracting impedance' required for the fork circuit. The circuit of Figure 6 may be used to process a left (L) and a right audio signal (R) for obtaining a single detectable signal that may be led to a detection circuit. In this case a tap 107 on either earbuds is detected from the asymmetry between the left and the right earbud 103 as caused by the asymmetry of the tapping. From experiments it appears that most of the energy induced by the tapping is in the lower part of the audio spectrum. In this part of the spectrum the ear is least sensitive to stereo sound 105 so it is advantageous to 'add' these components to provide the headsets with a 'mono' bass component, resulting in the addition of an auxiliary signal 115. A subtracter (SUB) cancels out the common 'driven low frequency sound'. A low pass filter (LP) removes the high frequency stereo components. Only signals generated by tapping or scratching on the headset are left after this filtering. These signals are available for further processing by a detection circuit. The detection circuit referred to from Figure 6 may be implemented with any standard pattern matching method, particularly those used in speech recognition, like Hidden Markov Models, Neural Networks, etc.

A possible user interaction mapping between tapping 107 and actions for a portable audio player 101 is:

Table 1 : Example of tapping interaction for a portable audio player

Another application for the tap 107 detector 106 is to use it as a general purpose input sensor, for instance to play a game on a mobile phone 101 or media player 101.

Figures 7 and 8 show examples of operating the earbud 103 as an input sensor. Typically an earbud 103 has a disc-shaped part that houses the transducer 104 and a protruding part that carries the wire and serves as a handle for positioning the earbud 103. As shown in Figures 7 and 8, the protruding part may extend away from the fist, see Figure 7, or largely be comprised in the fist, see Figure 8. In both situations the electrical impedance 112 of the transducer 104 changes when the earbud 103 is pinched between thumb and a folded index finger. This is believed to be caused by one or more of the variation in the size of the air chamber formed by the hand or by closure of the grill of the earphone, in the extend to which it is closed, and in the extend to which the chamber is acoustically coupled to the transducer. Other effects however, may also play an important role.

In case the protruding part has an opening or a bass port 114, the thumb may conveniently close the opening. Figure 9 shows an embodiment of the audio entertainment system 100 according to the invention. The electrical audio signal is fed to the transducer 104 of the earbud 103 via the detector 106 and the signal is converted into sound 105. The transducer 104 has a voice coil through which a current 111 flows. Between the pair of wires connecting the voice coil to a source 101 of the signal, a voltage 110 exists. The electric characteristic is the electrical impedance 112 of the transducer, which is measured by the detector 106 at or around its resonance frequency 113. The detector 106 is included in the wiring between the source 101 and the voice coil. The detector 106 may be located anywhere along these wires, e.g. inside the earbud 103, in-between earbud 103 and source 101, or inside the source 101. The detector 106 monitors the measured impedance for changes. A tap 107 with a finger onto the earbud 103 causes the acoustical environment of the transducer 104 to change 108, which may be detected as a change 108 in the electrical characteristic 109 of the transducer. If the signal conveys silence, or if the power of the signal drops below a threshold, the detector 106 has means 117 for adapting and adding a sinusoid to continue measuring the impedance. The frequency of the sinusoid may be swept over a range to determine the resonance frequency 113 and subsequently be kept around the resonance frequency 113 determined. Instead of the sinusoid colored noise may be used.

Figure 10 shows an embodiment with a second earbud 200 of the audio entertainment system 100 according to the invention. The second earbud 200 has a second transducer 201 that converts a second audio signal into a second sound 105. By measuring the second electrical characteristic 203 of the second earbud 200, a tap 107 on the second earbud 200 may be detected with a second detector 106, analogously to the system with a single earbud 103. In addition however, the earbud 103 and the second earbud 200 may be substantially identical, such that the symmetry can be exploited to enhance the detecting 302 by monitoring for a change 108 in a difference 202 between the characteristics. If the difference 202 is substantially zero or stays within a range around zero, no tap 107 is detected. If the difference 202 exceeds a positive threshold, a tap 107 on the earbud 103 is detected. If the difference 202 drops below a negative threshold, a tap 107 on the second earbud 200 is detected. Figure 11 shows the method 300 in accordance with the invention. 10. The method 300 detects a tap 107 on an earbud 103, and has the two steps of converting 301 an electric audio signal 102 into sound 105 with an electro-acoustic transducer 104 and detecting 302 the tap 107 in dependence of a change 108 in an electrical characteristic 109 of the electro-acoustic transducer 104. The step of detecting 302 may be implemented as a software routine on a processor 401 for processing the signal 102. The step of detecting 302 is typically repeated after detecting 302 a tap 107. The method 300 may additionally include steps like calibrating the detector 106, determining the resonance frequency 113, adapting parameters of the detector 106 in response to a history of detection results, andsoon. Figure 12 shows a computer program product 400 for use in the audio entertainment system 100 having a processor 401 for detecting 302 the tap 107 on the earbud 103. The computer program product 400 is designed to instruct the processor 401 to detect the tap 107 on the earbud 103 in dependence of a change 108 in an electrical characteristic 109 of the electro-acoustic transducer. This may for example be achieved if the computer program product 400 instructs the processor 401 to execute the step of detecting 302 of the method 300 in accordance with the invention. The method 300 may be implemented as an event-driven routine that submits events to an event queue, or it may also be implemented with a software or hardware interrupt. The computer program product 400 may take the form of an upgrade of firmware of the source 101 of the signal 102, like typically stored in flash memory, or a software component like a compressed archive typically downloaded from the Internet, or a plug- in for an application, or be comprised in a stand-alone application.

It is noted that the above-mentioned embodiments illustrate rather than limit the invention, and that those skilled in the art will be able to design many alternative embodiments without departing from the scope of the appended claims. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word "having" does not exclude the presence of elements or steps other than those listed in a claim. The word "a" or "an" preceding an element does not exclude the presence of a plurality of such elements. The invention can be implemented by means 117 of hardware comprising several distinct elements, and by means 117 of a suitably programmed computer. In the entertainment device claim enumerating several means 117, several of these means 117 can be embodied by one and the same item of hardware. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

A 'computer program' is to be understood to mean any software product stored on a computer-readable medium, such as a floppy-disk, downloadable via a network, such as the Internet, or marketable in any other manner.

Claims

CLAIMS:

1. An audio entertainment system 100 comprising: an earbud 103 having an electro-acoustic transducer 104 for converting 301 an electric audio signal into sound 105; and a detector 106 for detecting 302 a tap 107 on the earbud 103, wherein the detector 106 is arranged to detect the tap 107 on the earbud 103 in dependence of a change 108 in an electrical characteristic 109 of the electro-acoustic transducer 104.

2. An audio entertainment system 100 according to claim 1, wherein the electrical characteristic 109 is a voltage 110 over and/or a current 111 through the electro-acoustic transducer 104.

3. An audio entertainment system 100 according to claim 1, wherein the electrical characteristic 109 is an electrical impedance 112 of the electro-acoustic transducer 104.

4. An audio entertainment system 100 according to claim 3, wherein the electro-acoustic transducer 104 has a resonance frequency 113 and wherein the detector 106 is arranged to detect the tap 107 by measuring the change 108 of the electrical impedance 112 substantially at the resonance frequency 113.

5. An audio entertainment system 100 according to claim 3, wherein the earbud 103 comprises an opening for improving the detecting 302, wherein the opening is arranged for: being accessible for receiving the tap 107, and - being substantially closed during the tap 107, wherein the electrical impedance 112 is substantially changed by the opening being substantially closed.

6. An audio entertainment system 100 according to claim 5, wherein the opening is a bass port 114 for improving a low frequency response of the earbud 103.

7. An audio entertainment system 100 according to claim 1, further comprising an adder 116 for adding an auxiliary signal 115 to the electric audio signal 102 for improving the detecting 302.

8. An audio entertainment system 100 according to claim 7, further comprising means 117 for adapting the auxiliary signal 115 in dependence of the electric audio signal 102, such that the auxiliary signal 115 is masked by the electric audio signal 102 in the resulting sound 105, as typically perceived by humans.

9. An audio entertainment system 100 according to claim 1, further comprising a second earbud 200 comprising a second electro-acoustic transducer 201, wherein the detector 106 is arranged to detect the tap 107 on the earbud 103 in dependence of a change 108 in a difference 202 between the electrical characteristic 109 of the electro-acoustic transducer 104 and a second electrical characteristic 203 of the second electro-acoustic transducer 201.

10. A method 300 for detecting 302 a tap 107 on an earbud 103, comprising the steps of: converting 301 an electric audio signal 102 into sound 105 with an electro-acoustic transducer 104; detecting 302 the tap 107 in dependence of a change 108 in an electrical characteristic 109 of the electro-acoustic transducer 104.

11. A computer program product 400 for use in an audio entertainment system 100, the audio entertainment system 100 comprising: an earbud 103 comprising an electro-acoustic transducer 104 for converting 301 an electric audio signal into sound 105; and - a processor 401 for detecting 302 a tap 107 on the earbud 103, the computer program product 400 being designed to instruct the processor 401 to detect the tap 107 on the earbud 103 in dependence of a change 108 in an electrical characteristic 109 of the electro-acoustic transducer 104.