DE19938171C2 - Process for processing acoustic signals and communication system for occupants in a vehicle - Google Patents

Abstract

For a particularly good communication between all occupants and for the participation of other occupants in voice-operated systems, such as. B. hands-free system, in a vehicle according to the invention in a method for processing acoustic signals for at least one position (P1 to P5) in the vehicle position-dependent different acoustic signals are controlled such that at least one acoustic zone (Z1 to Z5) is set up.

Description

The invention relates to a method for processing acoustic Signals for at least one position in a vehicle. Furthermore concerns the Invention a communication system for occupants in a vehicle, especially in a passenger car.

A similar topic is in the simultaneously filed application "Procedure and Device for compensating losses of a signal "treated, the Disclosure content of this application is attributable. The aforementioned registration received our internal file number P 111 438 and the official file number DE 199 38 158.5-53.

In a vehicle, e.g. B. in a passenger car, there is impairment of communication between vehicle occupants due to ambient noise. On the one hand, the communication is influenced by the position of the occupants relative to one another. The quality of communication in positions arranged in rows is particularly determined by the direction of speech (signal propagation) and, as a result, by corresponding signal losses on the transmission path. On the other hand, communication between the occupants is impaired, for example, by driving or wind noises, as well as by blower noises or music. To improve communication in the interior of the vehicle, anti-noise systems are usually used, which primarily reduce ambient noise, in particular driving noise. For this purpose, such anti-noise systems have, for example, a microphone near the head of the occupants, which is used to detect the broadband noise signal. A signal, a so-called anti-sound signal, is output via a loudspeaker. Such an anti-noise system is e.g. B. in the article by Garcia-Bonito et al .: Generation of Zones of Quiet Using a Virtual Microphone Arrangement, Journal Acoustical Society of America, 101, June 1997 , pages 3498 to 3516. The disadvantage here is that the linguistic communication between the occupants is still significantly impaired by acoustically unfavorable positions in the vehicle.

In addition, there is a hands-free system for radio telephones in today's vehicles provided that enables communication with remote participants. Here too there is usually a reduction in ambient noise in the vehicle interior for improved communication in the foreground. In addition, at such hands-free devices due to particularly long signal delays in Telephone network to compensate for electrical and acoustic echoes that occur also significantly impair communication. This is usually done Echo cancellers used. Due in particular to the driver of the vehicle aligned microphone, but is also a use of the handsfree for other occupants very much due to the acoustically unfavorable position in the vehicle limited.

In addition, EP 0 903 726 A2 describes a communication system for active Known noise and echo cancellation, in which a model-based, adaptive Control system using correlation filters using a variety of adaptive Compensation models compensates for noise and / or echoes.

Furthermore, DE 195 33 541 C1 describes a device for automatic control a device known by voice commands, which in particular the driver of the Vehicle voice-operated control of various systems, such as. B. radio, Air conditioning, navigation system, enables. The disadvantage here is that here too  other occupants of the vehicle excluded from the use of this device are.

The invention is therefore based on the objects of a method for processing acoustic signals indicate communication between all occupants is sufficiently well possible and participation of other occupants voice operated systems, such as B. hands-free system is enabled. Furthermore, it is The object of the invention is a communication system for occupants in a vehicle indicate the improved communication compared to the prior art between the occupants.

The first-mentioned object is achieved according to the invention in a processing method solved by acoustic signals for at least one position in a vehicle by position-dependent different acoustic signals are controlled such that at least one acoustic zone is set up.

The invention is based on the consideration that occupants in a vehicle have individual acoustic needs, such as B. Sufficiently good communication between occupants, communication via a hands-free system from if possible all positions, sufficiently good radio reception as well as acoustic Signal reception from other systems, such as a navigation system if possible, all positions in the vehicle and reduction of all, if possible Communication and ambient noise impairing signal reception. In addition, it occurs due to various positions in the vehicle different transmission paths to a different impairment of the Communication and acoustic signal reception. Through the position-dependent or position-based control of the different acoustic signals, such as. B. Voice signal, sound signal or noise signal, is within the range of an acoustic zone. The acoustic zone either completely or partially generated for the respective position. Due to the The complexity of acoustic systems in the vehicle interior is preferred respective position in different acoustic zones with different acoustic Properties divided. Thus both a reduction of  Ambient noise as well as a compensation for the impairment of the Allows signal reception for various positions in the vehicle.

At least one listening zone, speaking zone, is expediently used as the acoustic zone and / or creates a quiet zone. The listening zone has the functionality Reception of sound events occurring in this zone. The Speech zone serves in particular to ensure that acoustic signals are only output in this zone Signals are processed, signals output outside the speech zone remain disregarded. The rest zone is characterized in that in this area occurring acoustic signals are hidden. The individual zones through a particularly simple alignment of the acoustic transmission and Received signals generated. The separation or division of the position range into such individual acoustic zones causes each position in terms of their Acoustic conditions is structured. This makes it particularly flexible for every position Access to individual acoustic communication, information acquisition as well as for acoustic operation of functions such. B. the navigation system, enables.

At least one of the acoustic signals is advantageously position-dependent spent purposefully. This enables the generation of at least one hearing aid. Zone for the position in question. The listening zone is generated by acoustic Signals or sound events for the position in question only in this defined hearing Zone are audible. For the area outside the listening zone corresponding signals are hidden accordingly. For example acoustic signals from neighboring positions are so strongly damped, for example by anti-noise that a transmission of the signals to the position in question is avoided as safely as possible.

At least one of the acoustic signals is preferably position-dependent directed, in particular by means of a directional microphone. This is for the position in question creates a speech zone. Thereby, for the concerned Position only processes those acoustic signals, especially those received have been created within the speech zone. Acoustic signals outside of this  Speech zone are disregarded by the spatial area outside the Speech zone is acoustically separated. Such a position-related speaking zone Allows a single occupant to enter an acoustic signal in the Speech zone while entering acoustic signals of other occupants of others Positions in the relevant speech zone are not received.

It is expedient depending on the acoustic signal received output at least one acoustic signal. This ensures that in Dependence on the received signal, in particular depending on the Signal type and / or the signal intensity, the same or a different acoustic signal is output based on location or position in the vehicle interior. For example is a voice signal from a hands-free system as an acoustic reception signal Radiotelephones identified depending on the positions occupied in the vehicle is at these relevant positions this voice signal in the associated Listening zone output. At the same time, a sound signal from a music system is Zones of the relevant positions are hidden by the signal level of the sound signal correspondingly strong on the electrical signal path and / or on the acoustic Signal path is dampened by anti-noise.

In an advantageous embodiment, at least one of the acoustic signals is position-dependent Signals is eliminated. In particular, interference signals, such as Driving, wind or blower noises, so strongly damped or with opposite phases equally strong signals superimposed that only the signals relevant to information are received or output. To be favoured in the quiet zone, as far as possible, all acoustic signals or sound events hidden. Disturbing noises are particularly noticeable in the quiet zone compensated.

According to the invention, the second-mentioned object is achieved in a communication system for Occupants in a vehicle through an acoustic processing system Signals solved that for at least one position in the vehicle interior is that position-dependent by controlling different acoustic signals at least one acoustic zone is set up.  

Speech signals, interference signals and / or are preferred as acoustic signals other sound signals controllable. Depending on the functionality and the information content in particular the voice and / or sound signals positionally strengthened or damped depending on the position. Preferably is individual each position adjustable with regard to its acoustics. On the one hand, this can done automatically, e.g. B. is for incoming calls from the speakerphone the mobile phone automatically sends the voice signal to the occupants Positions increasingly issued. Alternatively, the output can be entered manually the sound signal individually controlled for a given position, e.g. B. strongly damped if the occupant so desires in this position.

Depending on the position, the acoustic zone expediently comprises at least in each case a listening zone, a speaking zone and / or a quiet zone. Here are the listening zone, the speaking zone and / or the resting zone for the associated position acoustically separated from each other. As a result, it is especially tailored to the position acoustic function division enables. For example, the position of the All acoustic zones. That is, the driver can be both voice controlled Operate systems via the assigned language zone, as well as information about the assigned listening zone received. In contrast, the position includes, for example another occupant (passenger) only one listening zone, so that this occupant acoustically is not connected to a language zone and therefore z. B. the voice-controlled System cannot operate. Advantageously, for the respective position in Depending on acoustically received signals, the signals to be output acoustically controllable by defining the assignment of the zones. The control the signals are both automatic and manual.

At least one is expediently integrated in the vehicle interior Speaker-microphone system provided. The speaker microphone System is designed such that the entire vehicle interior and / or at least a position in the vehicle interior acoustically separated from one another at least one Has listening zone and a speaking zone. Depending on the type and size of the The vehicle interior can also have multiple loudspeaker-microphone systems, in particular one for each position. With such a loudspeaker  Microphone system, in particular through a position-related loudspeaker-microphone System, acoustic functionality in the passenger compartment can be individually achieved and controllable.

The loudspeaker-microphone system is preferably in the upper region of the Arranged vehicle interior. This is a particularly short transmission path between transmitter (= mouth of the occupant or loudspeaker of the loudspeaker microphone Systems) and receiver (= microphone of the loudspeaker-microphone system or ear of the occupant), which limits interference.

In order to achieve a position-specific sound, in particular, is used advantageously as a loudspeaker of the loudspeaker-microphone system at least one Directional speaker. The directional loudspeaker indicates its directionality particularly good near field properties. For example, as a directional speaker open loudspeaker (= loudspeaker without housing) used. The sound field of the open speaker has a sound radiation in the form of a dipole and is can thus be used in particular for a near-field sound system in which the ear is in is in close proximity to the speaker. Alternatively, as a directional speaker a gradient speaker can be used. The sound field of the Gradient speaker has a sound radiation in the form of a kidney. This means that there is a greater distance from the open loudspeaker sufficiently good sound reinforcement of the position. Another alternative is through allows a speaker array. Here the directivity is determined by a plurality achieved by speakers and their corresponding orientation.

A distance of approximately 5 to 30 cm from the loudspeaker has proven to be particularly advantageous to the top of the position, e.g. B. to the ear area of the occupant on the position in question. The level loss is kept particularly low. In addition, there are possible interferences and a resulting one Limited impact on reception. It is also suitable as a position-dependent Installation location of the loudspeaker in the vehicle interior, in particular the vehicle roof, the headrest and / or the backrest.

To enable position-related input of acoustic signals, as is  The microphone of the loudspeaker-microphone system is preferably a directional microphone intended. By using the directional microphone, the acoustic signal is off one main direction recordable, whereas the directional microphone for other directions is at least largely insensitive. Thus, the input is impaired of acoustic signals at the position in question by signals, e.g. B. voice or Interference signals from neighboring positions, or particularly safe due to ambient noise avoided. Alternatively, a microphone array can also be used as a microphone, which further increases the directivity. This is expedient Microphone at a distance of about 20 to 50 cm from the occupant's mouth arranged.

The advantages achieved by the invention consist in particular in that position-based control of different acoustic signals the or each Position can be individually aligned with regard to their acoustic functionality can. Thus, even from acoustically unfavorable positions is a carefree one Communication and participation of the persons concerned in acoustic Interactions such as B. voice-guided navigation system.

Embodiments of the invention are explained in more detail with reference to a drawing.

In it show:

Fig. 1 shows schematically a communication system for occupant in a vehicle with a plurality of loudspeaker-microphone systems,

Fig. 2 shows schematically the vehicle interior of FIG. 1 with a plurality of acoustic zones,

Fig. 3 shows schematically a position-related acoustic opening zone,

Fig. 4 shows schematically a position-related acoustic rest zone,

Fig. 5 shows schematically a position-related acoustic listening zone,

Fig. 6 shows schematically the communication system of FIG. 1 with a system for the processing of acoustic signals,

Fig. 7 is a diagram for the directivity of a directional loudspeaker in the vicinity (Fig. 7a) and in the far field (Fig. 7b),

Fig. 8 shows schematically the electrical circuit for a gradient speaker, and

Fig. 9 is a diagram for the directional effect of the gradient in the vicinity of the speaker (Fig. 9a) and in the far field (Fig. 9b).

Identical parts are provided with the same reference symbols in all figures.

In Fig. 1, a passenger compartment 1 is shown with a communication system 2 having five positions P1 to P5 as space. Positions P1 to P4 each include at least one receiving location 4 and at least one transmitting location 6 . Depending on the size of the vehicle interior 1 , this can also include fewer or more positions than P1 to P5. At least one microphone M1 to M4 is provided as a transmitter in the vehicle interior 1 at the respective transmission location 6 . For example, a microphone array comprising a plurality of microphones can also be used instead of the microphone M1 to M4. The microphone M1 to M4 is preferably arranged at a distance of approximately 20 to 50 cm from the mouth area of a person belonging to the respective positions P1 to P4. For example, the microphone M1 to M4 is integrated in the vehicle roof 7 or in the lateral surfaces of the vehicle interior 1 .

Similarly, at least one loudspeaker L1 to L4 is provided at the respective receiving location 4 . Depending on the type of embodiment, a plurality of loudspeakers L1 to L4 can also be provided per receiving location 4 . The loudspeaker L1 to L4 is preferably arranged at a distance of approximately 5 to 30 cm from the ear area of the occupant associated with the respective position P1 to P4. A headrest 8 of the associated position P1 to P4 is preferably used as the installation location for the loudspeaker L1 to L4. If there are several loudspeakers L1 to L4 per position P1 to P4, these can be arranged on both sides of the headrest 8 . Alternatively, the loudspeaker L1 to L4 can also be arranged in the backrest area 10 and / or in the vehicle roof 7 of the vehicle interior 1 . The loudspeaker L1 to L4 serves on the one hand to output acoustic signals which are relevant to information and / or entertainment for the occupant concerned. On the other hand, the loudspeaker L1 to L4 is used to generate compensation signals which the interference signals acting on the respective position P1 to P4, such as e.g. B. driving, wind, engine or blower noise, eliminate or compensate as far as possible by means of anti-noise.

Each of the positions P1 to P4 is thus characterized by an integrated loudspeaker-microphone system LM1 to LM4, which is preferably arranged in the upper area of the vehicle interior 1 , in the immediate vicinity of the vehicle roof 7 .

Depending on the type and size of the vehicle interior 1 and depending on the acoustic conditions in the vehicle interior 1 , a single loudspeaker-microphone system LM1 to LM4 can be provided for the entire vehicle interior 1 . Such a loudspeaker-microphone system LM1 to LM4 each comprises loudspeakers L1 to L4 and microphones M1 to M4, which have a particularly specific directional characteristic. Depending on the needs and design of the vehicle interior 1 , position P5 can also be designed with a loudspeaker and / or a microphone.

Fig. 2 shows the positions P1 to P5, each with at least one associated acoustic zone Z1 to Z5. Each position P1 to P5 comprises an acoustic zone Z1 to Z5 a speaking zone S1 to S5.

In Fig. 3 one of the position-related speech zones S1 is shown as personal data. The speech zone S1 for the z. B. position P1 associated person generated by directed reception of at least one acoustic signal. For this purpose, an acoustic signal, in particular the speech signal emitted by the person, is supported in the speaking zone S1. For example, this is achieved by means of a microphone M1 designed as a directional microphone according to FIG. 1. Alternatively, a microphone array can also be used as the microphone M1. Acoustic signals that are received in areas outside the speaking zone S1 are not taken into account due to the insensitivity of the directional microphone outside the speaking zone S1. Further acoustic signals or sound events occurring in the speaking zone S1, such as. B. speech signals of adjacent positions P2 to P5 or interference signals, on the other hand, are particularly strongly attenuated, in that they are preferably eliminated by superimposition with an antiphase acoustic signal.

FIG. 4 shows a position P1 and the associated person associated quiescent zone R1, as further acoustic zone Z1. The position-related rest zone R1 is characterized by the elimination of as far as possible all acoustic signals occurring in this area of the position P1, such as e.g. B. voice, sound, interference signals. This is brought about, for example, by an anti-noise system which emits a corresponding broadband anti-noise signal via the relevant loudspeaker L1. The microphone M1 of the assigned position P1 is preferably used to determine the anti-noise signal and thus to compare errors in the anti-noise system.

In FIG. 5, a hearing zone H1 is shown as a further acoustic zone for the position P1. Like the speaking zone S1 and the quiet zone R1, this listening zone H1 is also position-related. The hearing zone H1 receives as far as possible all acoustic signals arriving directly at the respective position P1, such as e.g. B. Music, language or information. The spatial area outside the hearing zone H1 of the position P1 is acoustically separated. For this purpose, the acoustic signals are output in a targeted manner to position P11 by means of a loudspeaker L1 designed as a directional loudspeaker according to FIG. 1.

The acoustic zones Z1 shown in FIGS. 3 to 5 - the speaking zone S1, the quiet zone R1 and the listening zone H1 - are position-dependent. That is, Depending on the requirement, a position P1 to PS according to FIG. 1 can each comprise only one hearing zone H1 to H5, one speaking zone S1 to S5, one quiet zone R1 to R5 or any combination of all of these zones. Each position P1 to P5 can thus be individually controlled with regard to the acoustic functionality.

Fig. 6 shows the communication facility 2 with a system 12 for processing of acoustic signals, comprising the five positions P1 through P5, respectively, the integrated speaker-microphone system LM1 to LM5, the respectively associated loudspeaker L1 to L5 and the respectively associated microphone M1 to M5 and a central control unit 14 . Positions P1 and P5 are occupied by people. When the communication system 2 is in operation, acoustic signals are exchanged when the people in positions P1 and P5 communicate with one another. This signal exchange is subject to further acoustic influences, such as. B. driving noise, wind noise, noise from the blower or from an air conditioner, sound signals from a music system, information signals from a navigation system. In order to take into account the acoustic signals relevant for the communication between the people, the different acoustic signals are controlled in a position-dependent manner in such a way that at least one of the acoustic zones Z1 to Z5 according to FIGS. 2 to 5 is generated. For this purpose, the control unit 14 of the system 12 comprises a number of inputs E1 to En and a number of outputs O1 to On, by means of which the respective loudspeaker-microphone system LM1 to LM5 is controlled.

For example, if the person at position PS is actively speaking and the person is listening at position P1, the control unit 14 determines the microphone M5 associated with position PS with the highest signal level as the active microphone. At the same time, as far as possible, all acoustic signals output via the assigned loudspeaker L5 are eliminated by the control unit 14 using the corresponding output O1 to On z. B. deactivated the speaker L5. In contrast, the loudspeaker L1 assigned to the listening person is activated by means of the control unit 14 . In this case, the signal output via the loudspeaker L1 is processed in such a way by means of electronic components, not shown, for. B. amplified, delayed and filtered that a speech signal of the person from position PS is output on the speaker L1 from position P1, which results in a natural speech image at the location of the person. Usually z. B. a level balance, an amplifier, an attenuator, a timing element and / or an echo canceller between the respective elements of the loudspeaker-microphone system LM1 to LM5, which filter, attenuate or compensate for different acoustic signals. The individual components can be controlled by the control unit 14 as a function of the signal type, the signal intensity and the associated position P1 to P5. The acoustic zones Z1 to Z5 described above are thus set up in a particularly simple manner as a function of position, in that the loudspeakers L1 to L5 and the microphones M1 to M5 are controlled and set accordingly. For example, an acoustic signal received via a hands-free system, not shown, can cause the respective hearing zone H1 or H5 of the occupied positions P1 or P5 to only receive this acoustic signal. For this purpose, the acoustic signal received by the hands-free system is output via the associated loudspeakers L1 and L5 by means of the control unit 14 . The output of further acoustic signals is suppressed on these loudspeakers L1 and L5. Further examples of different position-dependent controls of different acoustic signals are possible, which are implemented by means of this communication system 2 . These examples depend on the type of signal, the signal intensity, the specified functions for the respective positions P1 to P5 and / or the configuration of the respective positions P1 to P5 with loudspeakers L1 to L5, microphones M1 to M5 and / or integrated loudspeakers -Microphone systems LM1 to LM5.

As an alternative and / or in addition to the central control unit 14 , a local control unit (not shown) can be provided for each position P1 to P5, with which the respective person can set the acoustic ambient conditions of the associated position P1 to P5 locally. A local control unit of this type thus achieves a personal setting of desired acoustic functions for the associated positions P1 to P5.

FIG. 7 shows the directivity of an individual loudspeaker L1 to L5 designed as a directional loudspeaker in the near range ( FIG. 7a) and in the far range ( FIG. 7b). An open-ended loudspeaker (without an outer housing) serves as the directional loudspeaker, which has sound radiation in the form of a dipole, particularly in the vicinity. With a greater distance, in the far range, the sound pressure generated by the open loudspeaker becomes increasingly lower. Accordingly, the loudspeaker L1 to L5, which is designed as an open loudspeaker, is used in the close range, ie at a distance of less than 20 cm from the area to be sounded, in particular the hearing zone H1 to H5, and is thus used for head-related near-field sound reinforcement.

In FIG. 8, the electrical circuit is a single loudspeaker L1 configured as gradient loudspeaker shown schematically. Two opposite-phase loudspeakers L1 'and L1 "are arranged separately from one another in an associated housing 16 ' and 16 " and fed by a common amplifier, not shown. One loudspeaker L1 'is driven directly, the second loudspeaker L1 "operated in phase opposition is controlled via a delay element 18. The delay time corresponds approximately to the acoustic transit time of the signal from loudspeaker L1' to second loudspeaker L1". Now moves a sound wave from the speaker L1 'to said second loudspeaker L1 ", then the acoustic path is compensated by the electric delay member 18. The portions of sound from both speakers L1' and L1" remain in phase opposition to each other and compensate accordingly. There is a sound cancellation for the sound propagation in this direction - in the direction of the second loudspeaker L1 ". For the opposite direction there is a maximum in the sound propagation. Thus, such a gradient loudspeaker has a cardioid polar pattern, which is shown in FIG. 9 is.

The construction of the gradient loudspeaker according to FIG. 8 results in different distances in the near field from the hearing zone H1, in particular from the ear of the person belonging to the position P1. Ideally, the sound level decreases inversely proportional to the square distance. An extinction occurs only if the levels of sound and antiphase sound at the receiving location (= listening zone H1 to H5) are the same. The amplitudes of the two loudspeakers L1 'and L1 "can therefore be set differently by a near-field correction, so that a kidney shape as shown in FIG. 9a results, for example, at a distance of approximately 10 cm distance of about 60 cm as shown in Fig. 9b are set. In the examples shown in FIG. 9a followed to achieve the kidney shape at a distance of about 10 cm, the amplitude of the loudspeaker L1 'with respect to the amplitude of the second loudspeaker L1 "of about Reduced 35%. Similarly, in the example according to FIG. 9b, the amplitude of the loudspeaker L1 'was reduced by approximately 5% for a distance of approximately 60 cm.

Claims (13)

1. Method for processing acoustic signals for at least one position (P1 to P5) in a vehicle in which a single position (P1 to P5) in several acoustic Zones (Z1 to Z5) based on acoustic and / or electrical signals, which in Dependence on the respective position (P1 to P5) and / or neighboring positions (P1 to P5) can be controlled separately, is divided. 2. The method according to claim 1, wherein the acoustic zone (Z1 to Z5) at least a listening zone (H1 to H5), a speaking zone (S1 to S5) and / or a quiet zone (R1 to R5). 3. The method according to claim 1 or 2, in which at least one of the position-dependent acoustic signals are directed. 4. The method according to any one of claims 1 to 3, in which at least depending on the position one of the acoustic signals is received in a directed manner. 5. The method of claim 4, wherein depending on the received  acoustic signal at least one acoustic signal is output. 6. The method according to any one of claims 1 to 4, in which at least depending on the position one of the acoustic signals is eliminated. 7. Communication system ( 2 ) for occupants in a vehicle, in which a system ( 12 ) for processing acoustic and / or electrical signals is provided, which is designed for at least one position (P1 to P5) in the vehicle interior ( 1 ), that depending on the position (P1 to P5) or adjacent positions (P1 to P5) by separate control of different acoustic and / or electrical signals, several acoustic zones (Z1 to Z5) are set up. 8. Communication system ( 2 ) according to claim 7, wherein the acoustic signals are voice signals, interference signals and / or sound signals. 9. Communication system ( 2 ) according to claim 7 or 8, in which the acoustic zone (Z1 to Z5), depending on the position, each has at least one listening zone (H1 to H5), a speaking zone (S1 to S5) and / or a quiet zone. Zone (R1 to R5) includes. 10. Communication system ( 2 ) according to one of claims 7 to 9, in which signals for the respective position (P1 to P5) can be controlled as a function of acoustically received signals. 11. Communication system ( 2 ) according to one of claims 7 to 10, in which at least one integrated loudspeaker-microphone system (LM1 to LM5) is provided as the system ( 12 ). 12. Communication system ( 2 ) according to claim 11, wherein the loudspeaker-microphone system is arranged in the upper region of the vehicle interior. 13. Communication system ( 2 ) according to claim 11 or 12, in which at least one directional loudspeaker is used as the loudspeaker of the loudspeaker-microphone system (LM1 to LM5).