DE102013006068A1 - "Vehicle with audio system" - Google Patents

Abstract

Vehicles (10) are provided with an audio system including left speakers (16-18), right speakers (19-21), and a center speaker assembly (22). Sound-proof surfaces (28) can be used to generate virtual loudspeakers (25, 26) outside the vehicle (10).

Description

The present application relates to a vehicle equipped with an audio system, such as a passenger car or a truck.

Audio systems are used in vehicles for the reproduction of audio signals, for example for the reproduction of speech or music. As a source for such audio signals, for example, radio receivers, CD or DVD players, coupled to the vehicle MP3 playback devices such as mobile phones, or navigation devices with voice output can serve. Several of these options can be combined in a single device.

For this purpose, for example, audio systems are known in vehicles, which for stereo transmission an audio signal in each case in a left and right channel separated via at least one arranged on a left side of the vehicle speakers and at least one arranged on the right side of the vehicle speakers. The speakers can be located, for example, in a front dashboard near the respective side windows and / or in the driver and passenger door below the window edge, for example, near the door hinge on the A-pillar. In order to produce a good stereo sound, the at least one left speaker should be sufficiently far apart from the at least one right loudspeaker, with occupants of the vehicle, such as driver or passenger, preferably being in the center of a so-called stereo triangle. Due to the different seating positions of the driver and front passenger in such an approach, an interpretation of the audio system, which ensures good stereo performance for both driver and front passenger, always a compromise solution. In addition, the distance in which the at least one left-hand loudspeaker and the at least one right-hand loudspeaker can be located is limited by the dimensions of a passenger compartment of the vehicle, whereby structural conditions can lead to further restrictions.

Furthermore, communication systems are known which reproduce seating-related audio signals and are designed above all for the transmission of speech and for enabling communication between vehicle occupants with one another. Such an audio system is for example in the DE 199 38 171 C2 described.

From the US 4,769,843 For example, there is known an audio system for a vehicle having left and right speakers at the sides of a passenger compartment to which the left (L) and right (R) channel signals of an X / Y stereo signal are supplied for reproduction. In addition, in the system disclosed in this document, two center loudspeakers are arranged in a dashboard midway between the front seats. The sound signal radiated by the center speaker is based on a sum signal of the left and right channels (L + R), which is emitted with a time offset to the signal of the left channel L and the right channel R.

From the DE 10 2008 013 979 A1 It is known to arrange loudspeakers of an audio system in a vehicle closely adjacent to one another in front of respective seats and to generate a virtual stereo base by means of signal processing via inverse convolution with corresponding transfer functions.

From the US 7,561,706 B2 It is known to arrange a center speaker in the middle between seats of a vehicle and to generate a phantom position of the radiation in front of the driver by signal adjustments such as time delay adjustments or frequency adjustments.

From the US 6,069,962 For example, a loudspeaker system is known in which three loudspeakers are accommodated in a common housing, wherein an L - R signal is output from a loudspeaker, an R + L signal from a loudspeaker and an R - L signal from a loudspeaker.

However, there is still a need for audio systems which can provide enhanced stereo sound in narrow space vehicles, particularly a vehicle cabin of a vehicle. It is therefore also an object of the present invention to provide a vehicle with a corresponding audio system.

This object is achieved by a vehicle according to claim 1. The dependent claims define further embodiments.

According to the invention, a vehicle is provided, comprising:
a passenger compartment with a left front seat and a right front seat,
at least one left speaker disposed to the left of a longitudinal center axis of the vehicle,
at least one right speaker, which is arranged to the right of the longitudinal center axis of the vehicle,
a center speaker assembly having a first center speaker and a second center speaker, wherein the center speaker assembly is arranged at the longitudinal center axis of the vehicle, and
a drive device, wherein the drive device is set up to control the at least one left loudspeaker with a signal of a left audio channel of an XY stereo signal, to drive the at least one right loudspeaker with a signal of a right audio channel of the XY stereo signal, the first center loudspeaker ( 23 ) with a sum signal from a center channel and a side channel of the XY stereo signal in center sideband stereophonic encoding and the second center speaker ( 24 ) with a difference signal from the center channel and the side channel to control.

In such a vehicle, improved surround sound can be generated as compared with conventional systems.

The description of the signals used to drive the loudspeakers in various encodings such as XY stereo signal or mid-sideband stereophonic encoding does not mean that the signals must be explicitly present in each of the encodings. For example, the sum signal and the difference signal can be determined directly from the signal for the left audio channel and the signal for the right audio channel without first determining a signal for the center channel and a signal for the side channel.

In this case, in particular, the first center loudspeaker can be arranged to the left of the longitudinal center axis and the second center loudspeaker can be arranged to the right of the longitudinal center axis, the first center loudspeaker and the second center loudspeaker being arranged adjacent to one another. Such an arrangement allows in particular the generation of virtual speakers by reflection.

The center speaker arrangement can be arranged in particular in the longitudinal vehicle direction behind the left front seat and the right front seat.

The passenger compartment can have reverberant surfaces such that at least one virtual loudspeaker can be generated outside the vehicle via reflection from the center loudspeaker arrangement, in particular a first virtual loudspeaker on the left outside of the vehicle and a second virtual loudspeaker on the right outside the vehicle. By such a measure, an effectively resulting stereo stage can be widened, which can provide for improved surround sound, especially in small vehicle cells.

In this case, the center loudspeaker arrangement can be arranged such that a sound intensity radiated in the direction of the left front seat and the right front seat is less than a sound intensity radiated in the direction of the at least one reverberant surface. For example, the difference of the sound intensities may be 5 dB or more, preferably 10 dB or more. As a result, a sound signal heard by an occupant from the direction of the at least one virtual loudspeaker is emphasized in comparison with a sound signal received directly by the center loudspeaker arrangement.

With sound signal here by loudspeakers or similar devices output sound waves are referred to, while otherwise signals refer to electromagnetic signals, the z. B. can serve to control speakers.

The center loudspeaker arrangement as well as the at least one left loudspeaker and the at least one right loudspeaker can be arranged in particular such that a sound signal from the at least one left loudspeaker or the at least one right loudspeaker in front of a sound signal from the center loudspeaker arrangement at one of the left front seat or the right Arrives at the front seat assigned seating position, wherein a sound coming from the center speaker assembly directly to the seating position within a Haas curve for the sound coming from the at least one left speaker or at least one right speaker, while one of the center speaker assembly via a reflection on the at least one sound-hard surface to the sitting position reaching sound signal is outside the Haas curve. As a result, it can be achieved that the direction of the center loudspeaker arrangement is not perceived as direction-determining, while the direction from which the reflection comes, that is to say, the direction of the center loudspeaker arrangement. H. the direction of the at least one virtual loudspeaker is perceived as being direction-determining. In particular, the abovementioned emission characteristic of the center loudspeaker arrangement can also contribute to this.

The reverberant surfaces may in particular include windows of the vehicle. Since such windows are already provided in the vehicle, then no additional measures are required.

The loudspeaker arrangements and techniques discussed above are particularly suitable for small passenger compartments, particularly passenger compartments of two-seat vehicles, ie only the left front seat and the right front seat, since it is sometimes difficult for such vehicles to without adequate measures to achieve a sufficiently good stereo reproduction.

The present invention will be explained in more detail by means of embodiments with reference to the accompanying drawings. Show it:

1 a vehicle according to an embodiment,

2 a detailed diagram for explaining an audio system of the vehicle of 1 .

3 a diagram to illustrate runtime differences,

4A - 4C Diagrams illustrating the utilization of the Haas effect in embodiments, and

5 a diagram illustrating intensity ratios of different sound signals in embodiments of the invention.

In the following, various embodiments of the present invention will be explained in detail.

It should be understood that the illustrated embodiments are for illustration only and are not to be considered as limiting the scope of the present invention. In particular, embodiments need not necessarily have all features illustrated and illustrated, and features of various embodiments may be combined with each other unless otherwise specified.

In 1 is a vehicle 10 illustrated according to an embodiment of the invention. The vehicle 10 has a passenger compartment 27 on, in the left front seat 11 , which is a seating position for a driver 12 provides, and a right front seat 14 , which is a seating position for a passenger 15 provides arranged. With 13 is called a steering wheel. Thus, the illustrated vehicle is a left-hand drive, as commonly used in countries with legal traffic. In other embodiments, the steering wheel 13 also on the right side, for example on vehicles intended for countries with left-hand traffic. While in the embodiment of the 1 two seats 11 . 14 are provided, in other embodiments, more seats, for example in the form of a back seat, be provided.

For orientation is also a longitudinal central axis 29 drawn in the vehicle, with longitudinal or longitudinal direction in the context of this application that direction is designated, in which the vehicle 10 moved straight ahead. The vehicle 10 also has left speakers 16 - 18 which is to the left of the longitudinal central axis 29 and preferably to the left of the driver's seating position 12 are arranged, and right speakers 19 - 21 which is to the right of the longitudinal center axis 29 and preferably to the right of the seated position of the passenger 15 are arranged on. The terms "left" and "right" are used in the context of this application from the perspective of the driver or front passenger who looks in the forward direction of the vehicle.

In the embodiment of the 1 are three left speakers 16 - 18 and three right speakers 19 - 21 intended. These can for example each form a tweeter, midrange and woofers, and be controlled via a corresponding crossover. In other embodiments, a different number of left speakers and / or a different number of right speakers may be provided, for example, two speakers or only a single speaker. In the illustrated embodiment, the speakers 16 . 17 . 19 and 20 for example, in a dashboard of the vehicle 10 accommodated. The speaker 18 and 21 For example, woofers can be used in vehicle doors 10 be housed. Depending on the space available in a particular vehicle, other arrangements can be selected.

In addition, the audio system of the vehicle 10 a center speaker assembly 22 with a first center speaker 23 and a second center speaker 24 on. The center speaker arrangement 22 is at the longitudinal center axis 29 , for example, symmetrically this, arranged. The first center speaker 23 and the second center speaker 24 are preferably arranged immediately adjacent to each other. In the embodiment of the 1 is the center speaker arrangement 22 in the longitudinal direction behind the seats 11 . 14 arranged, with other arrangements are possible. It should be noted that in other embodiments, the center speaker assembly may also include more than two speakers. As by arrows 210 indicated and as will be explained in more detail later, by means of the center speaker arrangement 22 by reflection on reverberant surfaces such as a back surface 28 virtual speakers 25 . 26 especially outside the vehicle 10 be generated. Under virtual speakers or virtual sound sources are to be understood places, of which sound for the occupants 12 . 15 apparently going out. A reverberant surface is to be understood as meaning an area which contains sound for the most part, For example, at least 50%, at least 60% or at least 70%, reflected. As such sound-resistant surfaces can, for example, windows of the vehicle 10 or other suitable areas.

The generation of virtual speakers will now be described with reference to FIGS 2 - 5 explained in more detail.

In 2 FIG. 12 is a more detailed schematic of an audio system according to one embodiment, for example, the vehicle audio system of FIG 1 represented. In the audio system of 2 For the sake of simplicity, this is just a left speaker 30 and only a right speaker 31 which, for example, the left speakers 16 - 18 or the right speakers 19 - 21 represent. In addition, as in 1 the driver 12 and the passenger 15 as well as through the center speaker 23 and 24 formed center speaker assembly shown. A position 34 would be an optimal seating position according to the so-called stereo triangle to pass through the speakers 30 and 31 to experience an optimal stereo sound. As you can see drivers are 12 and co-driver 15 not at this optimal position, which in principle can be difficult to achieve in the spatial conditions in a vehicle.

About an audio source 33 becomes the left speaker 30 is driven with a signal of a left channel L of an XY stereo signal. The right speaker 31 is correspondingly driven with a signal of a right channel R of the XY stereo signal. The audio source 33 may include, for example, a radio receiver, a CD or DVD player or a navigation system, a hands-free device and / or an MP3 player.

In addition, the audio signal of a converter device 32 which converts the XY stereo signal into a sum signal M + S and a difference signal M-S according to a coding corresponding to a center sideband stereophonic having a Mitenkanal M and a Seitenkanal S. The converter device 32 then controls the speakers 23 and 24 such that the first center speaker 23 the sum signal M + S and the second center speaker 24 the difference signal M - S receives. These signals M + S and M-S may be formed of the signal L of the left audio channel and the signal R of the right audio channel according to: M + S = (L + R) + (L - R) = 2L and M - S = (L + R) - (L - R) = 2R, where L + R corresponds to the center signal S and L - R corresponds to the sideband signal S.

It should be noted that the audio source 33 and the converter device 32 can also be implemented in a single device. It should also be noted that an audio source is also possible from which the center signal M and the page signal S are output. From the signals M and S can then be formed in the reverse manner as described above, the signals L and R for the left and right channel.

As by circles 43 symbolized such center-loudspeaker arrangement controlled by signals forms an acoustic dipole, in which 2 to the left and right (ie in a direction corresponding to a connecting line of the speakers 23 . 24 ) a maximum sound intensity is radiated while in a direction perpendicular thereto a minimum sound intensity is radiated.

In the arrangement of 2 will therefore be according to arrows 39 . 41 a comparatively high intensity in the direction of reverberant surfaces 36 . 37 radiated and reflected there. The sound signal thus reflected is indicated by arrows 40 . 42 symbolizes and leads by further reflection on reverberant surfaces 35 . 38 to form the virtual speaker 25 , The virtual speakers 25 . 26 can be outside the vehicle as shown. This will be a stereo stage for the driver 12 and the passenger 15 widened. The driver stops 12 in particular sound signals from the direction of the virtual speaker 25 while the passenger 15 in particular sound signals from the direction of the virtual speaker 26 hear.

The dipole characteristic causes in particular that directly to the driver 12 and co-driver 15 a lower sound intensity is emitted than to the reverberant surfaces 26 and 37 out.

The arrangement of the speakers 30 . 31 . 23 , and 24 may in particular be such that directly from the center speakers 23 . 24 to the driver 12 and the passenger 15 sound is not perceived as being directional while the sound is coming from the virtual speakers 25 . 26 can be located, ie for the driver 12 or the passenger 15 from the direction of the virtual speaker 25 respectively. 26 comes.

For this purpose, in particular the Haas effect is utilized, which states that a sound signal arriving at a listener first determines the direction alone if another similar sound signal (for example a reflection) arrives at the listener with a low propagation delay, for example below 10 ms. In this case, only one sound event is perceived.

To avoid having a direct from the center speaker assembly to the driver 12 or passenger 15 If the sound signal arriving is perceived as determining the direction, the arrangement may be selected such that a sound signal from the left loudspeaker 30 for example, shortly before the corresponding sound signal from the center speaker assembly to the driver 12 arrives so that the sound signal from the center speaker assembly is within a Haas curve for the sound signal from the left speaker.

The time delay within which a second sound event is not perceived to be directional also depends on the relative intensities of the first sound event and the second sound event. This dependence on sound intensity and time delay can be represented as a Haas curve. An example of this will be later with reference to 4 given. Sound events within the Haas curve are not perceived as direction-determining, whereas sound events outside the Haas curve are perceived as direction-determining. As in 3 For example, shown reaches a sound signal from the left speaker 30 within a running time t _L the driver 12 , With an appropriate arrangement and control, which results from the speed of sound, reaches a corresponding sound signal from the center speaker arrangement with the speakers 23 and 24 the driver 12 whereas after a time t _L + Δt. If the time difference .DELTA.t at the respective intensity ratio is selected such that the signal from the center speaker assembly is within the Haas curve, the signal from the center speaker arrangement will not be directional but only the sound signal from the left speaker L and the two sound signals will be considered a single sound event perceived.

Contributes to that, as in 4A schematically shown a sound signal 50 for example, from the left speaker 30 by the already mentioned dipole characteristic of the center speaker arrangement has a higher intensity than a later arriving sound signal 51 from the center speaker assembly. Depending on the time difference .DELTA.t is the sound signal 51 even then not perceived as direction-determining, but only the sound signal 50 even if the sound signal 51 has a higher intensity than the sound signal 50 as long as the sound signal 51 within the Haas curve for the sound signal 50 lies. For example, if the sound signal 50 has a volume (sound intensity) of 0 dB, the sound signal 51 be louder by 9 dB, if it is z. B. delayed by .DELTA.t = 10 ms arrives.

For a time t3, which requires a sound signal from a virtual speaker to the driver or passenger, for example, from the virtual speaker 26 to the passenger 15 as in 4B in contrast, it is true that it is chosen so large that the sound signal is perceived by the virtual loudspeaker as direction-determining and the virtual loudspeaker is actually perceived as an additional sound source. Specifically, the time t3 may be times t1 and t2 of the left and right speakers 30 and 31 differ so far that a corresponding point is outside the Haas curve. This larger duration may be due to the fact that as in 2 represented a sound path over the reflections on the reverberant surfaces is longer and thus the duration is longer. At least in part, the delay may also be adjusted by outputting the respective signals M + S and M-S delayed in time to the left and right speaker signals L, R to the center speaker assembly.

In addition, the direction-determining perception of the virtual speakers 25 and 26 supported by the fact that in the illustrated embodiments by the dipole characteristic of the center speaker assembly an intensity radiated to the reverberant surfaces is increased.

For further illustration, see 4C a Haas curve 55 z. B. for a sound signal from the left speaker 30 or the right speaker 31 of the 2 which shows limit values for the direction-determining perception as intensity plotted over time. Points that are outside, ie in 4C above the Haas curve 55 are perceived to be directional (ie, sound events with larger transit time differences and / or higher intensities), while points within the Haas curve 55 (ie in 4C below the curve) are perceived as not direction-determining. For example, for a given sound level, events with a transit time difference greater than a critical time t _{K can} be perceived as direction-determining. For example, t _K may be on the order of 10 ms for a sound intensity (sound level) of 11 dB above the first signal.

For example, points can 56 and 57 Representing sound signals from an occupant such as the driver 12 or the passenger 15 directly from the speakers 23 and 24 the center speaker assembly can be obtained. These points are within the Haas curve 55 for the left or right speaker 30 . 31 and are therefore not perceived as determining the direction. Points 58 and 59 can be used as examples for sound signals from the virtual speakers 25 or 26 serve. These are outside the Haas bend 55 and are thus perceived as direction-determining.

Thus, by appropriate choice of the intensities and the delays can be achieved that only the virtual speakers 25 and 26 be perceived as a direction determining, but not a received directly from the center speaker arrangement sound signal.

Examples of usable intensity ratios are in 5 shown. In 5 represent curves 63 a radiation characteristic of an acoustic dipole generated by a center speaker assembly as discussed above. circles 60 - 62 represent a scale for the intensity, where the circle 60 for example 0 dB, the circle 61 for example -10 dB and the circle 62 for example, -20 dB. Intersections of the curves 63 with the circles 60 - 62 indicate the intensity present in the respectively radiated direction.

In the illustrated example, one is to a right ear of the driver 12 radiated sound intensity (point 64 on the bend 63 For example, -20 dB, one to the left ear of the driver 12 radiated sound intensity (point 65 on the bend 63 ) is for example -15 dB. One to create the virtual speaker 25 to the reverberant surface 35 On the other hand, the emitted sound intensity is corresponding to one point 66 on the bend 63 at - 3 dB, thus differs from the sound going directly back to the driver by more than 10 dB. In other embodiments, the difference may also be larger or smaller, for example at least 5 dB.

As mentioned above, such a radiation characteristic can support and enhance the transit time effect. In addition, sufficient strength for the virtual speakers can be ensured.

As previously discussed, the above embodiments are merely illustrative of ways of implementing the invention, and other implementations are possible. For example, a similar speaker assembly may also be used for passengers on rear seats of a vehicle. Depending on the available reverberant surfaces, the center speaker assembly may also be located elsewhere than behind the seats of the driver and front passenger.

LIST OF REFERENCE NUMBERS

10

vehicle

11

left front seat

12

driver

13

steering wheel

14

right front seat

15

co-driver

16-18

left speaker

19-21

right speakers

22

Center speaker layout

23

first center speaker

24

second center speaker

25

left virtual speaker

26

right virtual speaker

27

cabin

28

reverberant surface

29

longitudinal central axis

210

arrow

30

left speaker

31

right speaker

32

transducer means

33

audio source

34

optimal seating position for stereo triangle

35-38

reverberant surfaces

39-42

arrows

43

dipole-symbolizing circles

50

signal

51

signal

55

Haas curve

56-59

Points

60-62

scale circuits

63

Dipolabstrahlungscharakteristik

64-66

direction points

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• DE 19938171 C2 [0004]
• US 4769843 [0005]
• DE 102008013979 A1 [0006]
• US 7561706 B2 [0007]
• US 6069962 [0008]

Claims (10)

Vehicle ( 10 ), comprising: a passenger compartment ( 27 ) with a left front seat ( 11 ) and a right front seat ( 14 ), at least one left speaker ( 16 - 18 ; 30 ) which is to the left of a longitudinal central axis ( 29 ) of the vehicle ( 10 ), at least one right speaker ( 19 - 21 ; 31 ) which is to the right of the longitudinal center axis ( 29 ) of the vehicle ( 10 ), and a center speaker arrangement ( 22 ) with a first center speaker ( 23 ) and a second center speaker ( 24 ), wherein the center speaker arrangement ( 22 ) at the longitudinal center axis ( 29 ), and a drive device ( 32 . 33 ), which is set up, the at least one left speaker ( 16 - 18 ; 30 ) with a signal of a left audio channel of an XY stereo signal, the at least one right speaker ( 19 - 21 ; 31 ) with a signal of a right audio channel of the XY stereo channel, the first center speaker ( 23 ) with a sum signal from a center channel and a side channel of the XY stereo signal in center sideband stereophonic encoding and the second center speaker ( 24 ) with a difference signal from the center channel and the side channel to control. Vehicle ( 10 ) according to claim 1, characterized in that the first center loudspeaker ( 23 ) to the left of the longitudinal central axis ( 29 ) and that the second center speaker ( 24 ) adjacent to the first loudspeaker ( 23 ) to the right of the longitudinal center axis ( 29 ) is arranged. Vehicle ( 10 ) according to claim 1 or 2, characterized in that the center loudspeaker arrangement ( 22 ) in the longitudinal direction of the vehicle ( 10 ) behind the left front seat ( 11 ) and the right front seat ( 14 ) is arranged. Vehicle ( 10 ) according to one of claims 1-3, characterized in that one of the center speaker arrangement ( 22 ) directly to a sitting position on the left front seat ( 11 ) sound signal within a Haas curve for one of the at least one left speaker ( 16 - 18 ; 30 ) to the sitting position on the left front seat ( 11 ) is present, and / or that one of the center speaker arrangement ( 22 ) directly to a sitting position on the right front seat ( 14 ) passing sound signal within a Haas curve for one of the at least one right speaker ( 19 - 21 ; 31 ) to the sitting position on the right front seat ( 14 ) reaching sound signal is located. Vehicle ( 10 ) according to one of claims 1-4, characterized in that the vehicle has at least one reverberant surface ( 28 ; 35 ), wherein the center speaker arrangement ( 22 ) so to the reverberant surface ( 28 ; 35 - 38 ) is arranged, that via a reflection on the at least one reverberant surface ( 28 ; 35 - 38 ) at least one virtual speaker ( 25 . 26 ) is generated outside the vehicle. Vehicle ( 10 ) according to claim 5, characterized in that a transit time of a sound signal from the center speaker arrangement ( 22 ) on the reflection on the at least one reverberant surface ( 28 ; 35 - 38 ) to a sitting position of the left front seat ( 11 ) outside a Haas curve for one of the at least one left speaker ( 16 - 18 ; 30 ) to the sitting position of the left front seat ( 11 ), and / or that a transit time of a sound signal from the center speaker arrangement ( 22 ) on the reflection on the at least one reverberant surface ( 28 ; 35 - 38 ) to a sitting position of the right front seat ( 14 ) outside a Haas curve for one of the at least one right speaker ( 19 - 21 ; 31 ) to the seating position of the right front seat ( 14 ) reaching sound signal is located. Vehicle ( 10 ) according to claim 5 or 6, characterized in that one of the center speaker arrangement ( 22 ) directly to the left front seat ( 11 ) and / or right front seat ( 14 ) radiated first sound intensity is smaller than one of the center speaker arrangement ( 22 ) to the at least one reverberant surface ( 28 ; 35 - 38 ) radiated second sound intensity. Vehicle ( 10 ) according to claim 7, characterized in that the second sound intensity by at least 5 dB, preferably at least 10 dB, greater than the first sound intensity. Vehicle ( 10 ) according to claim 7 or 8, characterized in that the center loudspeaker arrangement ( 22 ) has a dipole emission characteristic. Vehicle ( 10 ) according to one of claims 5 to 9, characterized in that the at least one virtual loudspeaker has a left virtual loudspeaker ( 25 ) to the left of the longitudinal center axis ( 29 ) outside the vehicle and a right virtual speaker ( 26 ) to the right of the longitudinal center axis ( 29 ) outside the vehicle.

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