WO2010121916A1

WO2010121916A1 - Cross-barrier communication system and method

Info

Publication number: WO2010121916A1
Application number: PCT/EP2010/054765
Authority: WO
Inventors: Morten Kjær Johansen; Flemming Stig Hansen
Original assignee: Phonic Ear A/S
Priority date: 2009-04-23
Filing date: 2010-04-12
Publication date: 2010-10-28

Abstract

A relatively simple communication system (1) is able to receive sound signals comprising useful signals and noise signals on a client side (5) of a sound barrier (2) and transmit the sound signals to an attendant side (6) of the sound barrier. The noise signals are transmitted at a lower system gain than the useful signals. The communication system (1) comprises two microphones (14, 15) and a loudspeaker(19). The microphones(14, 15) are arranged to receive a first and a second acoustical input signal from different locations on the client side (5). The loudspeaker (19) is arranged to radiate an acoustical output signal to an attendant (18) in the attendant space (6). The communication system (1) is adapted to generate the acoustical output signal by subtracting the first acoustical signal from the second acoustical input signal and amplifying the difference signal.

Description

CROSS-BARRIER COMMUNICATION SYSTEM AND METHOD

TECHNICAL FIELD

The present invention relates to cross-barrier communication systems. More specifically, the present invention relates to electronic communication systems enabling persons to communicate acoustically across a sound barrier, such as e.g. a glass pane.

The invention may e.g. be useful in applications such as ticket booths and secured bank counters.

BACKGROUND ART

Ticket booths and bank counters are often provided with barriers dividing a room into a client space and an attendant space, typically in the form of glass panes. The purpose of such barriers may be various, e.g. to protect one or more attendants working in the attendant space from assault, to prevent theft from the attendant space or to allow better control of the attendants' working conditions. A further important purpose is to prevent noise in the client space from reaching and potentially stressing the attendants, and such barriers are therefore typically soundproof, at least to some extent. It is, however, often desirable to allow the attendants to communicate acoustically with clients or customers in the client space, wherefore such barriers are typically provided with two-way communication systems, which receive sound signals on each side of the barrier and reproduce the sound signals on the respective opposite sides of the barrier.

Simple two-way communication systems in the prior art comprise two independent and oppositely directed one-way communication systems, each comprising a microphone, an amplifier and a loudspeaker. The microphone receives acoustical input signals, converts them into electrical signals, which it feeds to the amplifier. The amplifier amplifies the electrical signals and feeds the amplified electrical signals to the loudspeaker, which converts these into acoustical output signals and radiates the acoustical output signals. The sensitivities of the microphone and the loudspeaker as well as the gain of the amplifier combine into a system gain, which determines the difference between the sound pressure level received by the microphone and the sound pressure level radiated by the loudspeaker.

Such simple two-way communication systems may - depending on the system gain - cause an increase in the amount of noise present in the attendant space. Furthermore, the acoustical output signals radiated by the loudspeaker of one of the one-way communication systems may be received by the microphone of the other one-way communication systems and vice versa, which - depending on the system gains and the distances between the respective loudspeakers and microphones - may cause audible artefacts, such as echoes and howling. Such artefacts may make understanding in both directions poorer and further stress the attendants. Various improved two-way communication systems have therefore been invented with the aim to reduce the amount of noise signals transmitted to the attendant space and/or reduce the amount of audible artefacts in the transmitted sound signals.

US patent 5,940,486 to Schlaff discloses a two-way communication system, which enables communication in one direction in response to the detection of communication in the other direction and disables communication in the first direction after a period of inactivity. The transmission of sound signals - including noise signals - from the client space to the attendant space may thus be normally disabled, and an attendant may enable the transmission simply by speaking into the communication system. The attendant will thus be subjected to noise signals from the client space only while communicating with a client.

Other known systems enable and disable communication in response to the detection of various events, such as the client or the attendant pressing a button, the level of the sound signal received from the client space rising above or falling below a predefined level, or the client arriving in or leaving a predefined portion of the client space. The detection of such triggering events may comprise the use of e.g. sound level detectors, motion detectors etc.

DISCLOSURE OF INVENTION

A main disadvantage of the above mentioned prior art communication systems is that the noise signal is transmitted whenever the useful signal is transmitted, so that the attendant may experience difficulties understanding the speech of the clients. A further disadvantage is that the means for detecting the triggering events may raise false alarms or fail, thus causing e.g. spurious noise bursts or cutting-off of parts of a client's speech. Over long time periods, such system behaviour may stress the attendants. A further disadvantage is that the means for detecting the triggering events tend to make the known communication systems more complicated and thus typically more expensive, not only with respect to development and manufacture, but also with respect to installation and maintenance of the systems. Typically, such means for detecting the triggering events need regular adjustment in order to reliably avoid false alarms and failures.

There is therefore a need for a relatively simple communication system, which is able to receive sound signals comprising useful signals and noise signals on one side of a sound barrier and transmit the sound signals to the other side of the sound barrier, the noise signals being transmitted at a lower system gain than the useful signals. It is an object of the present invention to provide such a communication system.

It is a further object of the present invention to provide a relatively simple two-way communication system, which produce less audible artefacts, such as echoes and howling.

Objects of the invention are achieved by the invention described in the accompanying claims and as described in the following.

An object of the invention is achieved by a communication system for transmitting acoustical signals, the communication system comprising a sound barrier, a first microphone and a first loudspeaker. The sound barrier delimits a client space on one side and an attendant space on the opposite side. The first microphone has a first sound receiving area, which is arranged to receive a first acoustical input signal from the client space. The first loudspeaker is arranged to radiate a first acoustical output signal to a person in the attendant space. The communication system according to the present invention further comprises a second sound receiving area, which is arranged to receive a second acoustical input signal from the client space, and the communication system is adapted to generate the first acoustical output signal based on a difference between the first and the second acoustical input signals. Subtracting one of the first and the second acoustical input signals from the other one may be performed very easily and may thus enable the communication system to be very simple and at the same time amplify noise signals from the client space at a lower system gain than useful signals. In the present context, the term "sound receiving area" denotes any area or opening to or through which a sound signal must propagate in order to be received by a microphone. A sound receiving area may thus be formed e.g. by a microphone diaphragm or by a sound inlet being acoustically connected to a microphone diaphragm. In the present context, an opening or inlet may comprise several smaller openings or inlets without deviating from the concept of forming a single sound receiving area, provided that the several smaller openings or inlets are mutually acoustically connected.

Advantageously, the acoustical centres of the first and second sound receiving areas are arranged on or close to a main surface of the sound barrier and at a mutual distance of 5 cm or less, preferably 3 cm or less, and even more preferably about 1.5 cm. Experiments have shown that these distances may enable the communication system to provide improved understandability of speech signals from the client space.

Advantageously, the sound barrier has a focus area, and the acoustical centres of the first and second sound receiving areas are arranged along a line directed towards the focus area. This allows for guiding the clients to locate their mouths at a location where the communication system may provide an improved understandability of speech signals. Advantageously, the acoustical centres of the first and second sound receiving areas are arranged at a distance of about 20 to 80 cm, preferably between 20 and 50 cm and more preferably between 20 and 30 cm from the centre of the focus area. Experiments have shown that these distances may enable the communication system to provide improved understandability of speech signals from the client space without decreasing the reception level substantially.

The communication system may further comprise a second loudspeaker, which is arranged to radiate a second acoustical output signal into the client space via a sound radiating area. Advantageously, the distance between the acoustical centre of the sound radiating area and the acoustical centre of the first sound receiving area equals the distance between the acoustical centre of the sound radiating area and the acoustical centre of the second sound receiving area. This may enable the communication system to radiate less audible artefacts, such as echoes and howling, to the attendant. In the present context, the term "sound radiating area" denotes any area or opening from or through which a sound signal generated by a loudspeaker is radiated into a space. A sound radiating area may thus be formed e.g. by a loudspeaker diaphragm or by a sound outlet being acoustically connected to a loudspeaker diaphragm. In the present context, an opening or outlet may comprise several smaller openings or outlets without deviating from the concept of forming a single sound radiating area, provided that the several smaller openings or outlets are mutually acoustically connected.

Advantageously, the first microphone is acoustically connected to the first sound receiving area, and the communication system further comprises a second microphone, which is acoustically connected to the second sound receiving area, and the communication system is adapted to convert the first and the second acoustical input signals into a first and a second electrical signal, respectively, and to subtract the second electrical signal from the first electrical signal. Subtraction of electrical signals may be performed very easily, thus enabling the communication system to be very simple. In the present context, a microphone diaphragm forming a sound receiving area shall be regarded as being acoustically connected to that sound receiving area.

Advantageously, the first microphone is acoustically connected to the first and the second sound receiving areas, and the first microphone is adapted to generate an electrical signal based on a difference between the first and the second acoustical input signals. This may enable the communication system to perform a very accurate subtraction of the acoustical input signals and thus radiate even less audible artefacts, such as echoes and howling, to the attendant.

An object of the invention is achieved by a method of transmitting acoustical signals across a sound barrier delimiting a client space on a first of its sides and an attendant space on the opposite second side. The method comprises the steps of receiving a first acoustical input signal at a first location in the client space; receiving a second acoustical input signal at a second location in the client space, the second location being different from the first location; and radiating a first acoustical output signal to a person in the attendant space, the first acoustical output signal being based on a difference between the first and the second acoustical input signals.

Advantageously, the method further comprises the steps of converting the first and the second acoustical input signals into a first and a second electrical signal, respectively; and subtracting the second electrical signal from the first electrical signal.

Advantageously, the method further comprises the step of radiating a second acoustical output signal into the client space from a location, which is at equal distances from the first and the second locations.

It is intended that the structural features of the system described above, in the detailed description of 'mode(s) for carrying out the invention' and in the claims can be combined with the methods, when appropriately substituted by a corresponding process. Embodiments of the methods have the same advantages as the corresponding systems. Further objects of the invention are achieved by the embodiments defined in the dependent claims and in the detailed description of the invention.

As used herein, the singular forms "a", "an", and "the" are intended to include the plural forms as well (i.e. to have the meaning "at least one"), unless expressly stated otherwise. It will be further understood that the terms "has", "includes", "comprises", "having", "including" and/or "comprising", when used in this specification, specify the presence of stated features, integers, steps, operations, elements and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components and/or groups thereof. It will be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element, or intervening elements may be present, unless expressly stated otherwise. Furthermore, "connected" or "coupled" as used herein may include wirelessly connected or coupled. As used herein, the term "and/or" includes any and all combinations of one or more of the associated listed items. The steps of any method disclosed herein do not have to be performed in the exact order disclosed, unless expressly stated otherwise.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be explained in more detail below in connection with preferred embodiments and with reference to the drawings in which: FIG. 1 shows a typical sound barrier with a prior art communication system, FIG. 2 shows a first embodiment of a communication system according to the present invention, and FIG. 3 shows a schematic of the communication system of FIG. 2.

The figures are schematic and simplified for clarity, and they just show details, which are essential to the understanding of the invention, while other details are left out. Throughout, the same reference numerals and names are used for identical or corresponding parts. Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.

MODE(S) FOR CARRYING OUT THE INVENTION

FIG. 1 shows a section through a typical prior art sound barrier 2 with a typical prior art communication system. The sound barrier 2 consists of a glass pane 3 arranged on top of a desk or a counter 4. The sound barrier 2 delimits a client space 5 on one side and an attendant space 6 on the opposite side. The sound barrier 2 dampens acoustical signals travelling between the client space 5 and the attendant space 6. The sound barrier 2 thus makes unaided acoustical communication between a client (not shown) located in the client space 5 and an attendant (not shown) located in the attendant space 6 difficult. A two-way communication system is therefore arranged on the sound barrier 2. The system comprises a client microphone 7, an attendant loudspeaker 8, an attendant microphone 9, a client loudspeaker 10 and an amplifier unit 11. The client microphone 7 is arranged on the client side of the sound barrier 2 and is connected to the attendant loudspeaker 8 via a first amplifier (not shown) in the amplifier unit 11 , which is arranged concealed within the counter 4. The attendant loudspeaker 8 is arranged on the attendant side of the sound barrier 2. The attendant microphone 9 is arranged on the attendant side of the sound barrier 2 and is connected to the client loudspeaker 10 via a second amplifier (not shown) in the amplifier unit 11. The client loudspeaker 10 is arranged on the client side of the sound barrier 2.

The prior art communication system functions in the following way. The client generates a first acoustical input signal by speaking into the client microphone 7, which converts it into a first electrical input signal and feeds the latter to the first amplifier. The first amplifier amplifies the first electrical input signal and feeds a corresponding first electrical output signal to the attendant loudspeaker 8. The attendant loudspeaker 8 converts the first electrical output signal into a first acoustical output signal and radiates it into the attendant space 6, where the attendant may hear it. When responding, the attendant generates a second acoustical input signal by speaking into the attendant microphone 9, which converts it into a second electrical input signal and feeds the latter to the second amplifier. The second amplifier amplifies the second electrical input signal and feeds a corresponding second electrical output signal to the client loudspeaker 10. The client loudspeaker 10 converts the second electrical output signal into a second acoustical output signal and radiates it into the client space 5, where the client may hear it. The first and second acoustical output signals as well as additional acoustical signals originating from other sources than the client and the attendant are also received by the microphones 7, 9 and therefore also amplified by the amplifiers and radiated by the loudspeakers 8, 10. The repeated amplification of the first and second acoustical output signals may cause audible artefacts, such as echoes and or howling, which may be very disturbing to both the client and the attendant. The radiated additional acoustical signals are typically perceived as noise by the client and/or the attendant and may cause difficulties in understanding each other. The radiated noise may further cause stress to and lower the working capability of any person working near the communication system for longer periods of time, i.e. the attendant. As explained further above, the prior art has taught several methods and devices for reducing the time periods in which noise is radiated in order to lower the stress level. This does, however, not improve the understandability and may even worsen it.

FIG. 2 shows a first embodiment of a communication system 1 according to the present invention. It comprises a sound barrier 2 similar to the one shown in FIG. 1 , consisting of a glass pane 3 arranged on top of a counter 4. The sound barrier 2 delimits a client space 5 on one side and an attendant space 6 on the opposite side and is viewed from the client side, i.e. the side facing the client space 5. The sound barrier 2 dampens acoustical signals travelling between the client space 5 and the attendant space 6. The glass pane 3 has a focus area 12, which is surrounded by a circle engraved in the glass and has a centre 13, which is marked by an engraved cross. Two identical client microphones 14, 15 are arranged with their acoustical centres, i.e. the acoustical centres of their diaphragms, and hence of their sound receiving areas, at a mutual distance of 1.5 cm and on a horizontal line 16, which is directed towards the centre 13 of the focus area 12. The acoustical centres of the client microphones 14, 15 are arranged at a distance of 25 cm from the centre 13 of the focus area 12. A client loudspeaker 17 is arranged with its acoustical centre, i.e. the acoustical centre of its sound radiating area, at a distance of 25 cm vertically above the acoustical centres of the client microphones 14, 15 and hence with equal distances to the acoustical centres of the two client microphones 14, 15. The client microphones 14, 15 and the client loudspeaker 17 are embedded in holes in the glass pane 3. The communication system 1 further comprises a headset 18 (show in an arbitrary location) comprising an attendant loudspeaker 19 and an attendant microphone 20, as well as an amplifier unit (not shown).

FIG. 3 shows a schematic with further details of the first embodiment of a communication system 1 shown in FIG. 2. The sound barrier 2, which is viewed from above, has two main surfaces - a client-side surface 21 facing the client space 5 and an attendant-side surface 22 facing the attendant space 6. Each of the client microphones 14, 15 is adapted to receive acoustical signals and convert the acoustical signals into an electrical signal on its output. The outputs of the client microphones 14, 15 are connected to a respective one of the two inputs of a differential power amplifier 23, which is adapted to subtract one of the electrical signals on its two inputs from the other one, amplify the difference signal and provide the amplified signal on its output. The gain of the differential power amplifier 23 is linear with frequency between an upper 3 dB limit of about 5 kHz and a lower 3 dB limit of about 200 Hz. The output of the differential power amplifier 23 is connected to the attendant loudspeaker 19, which is adapted to convert the amplified signal and radiate it towards the attendant 28 as an acoustical signal. The attendant microphone 20 is adapted to receive acoustical signals and convert them into an electrical signal on its output, which is connected to the single input of a simple power amplifier 24. The simple power amplifier 24 is adapted to amplify the signal on its input and provide the amplified signal on its output, which is connected to the client loudspeaker 17. The client loudspeaker 17 is adapted to convert the amplified signal and radiate it as an acoustical signal into the client space 5.

The functioning of the first embodiment of a communication system 1 is explained in the following with reference to FIGs. 2 and 3.

In the present context, the focus area 12 on the client side of the sound barrier 2 is to be understood as an imaginary area on the client-side surface 21 , in front of which a client 25 in the client space 5 would typically locate his mouth while speaking to an attendant 28 in the attendant space 6. In the first embodiment of a communication system 1 , the focus area 12 is marked by a circle and a cross at the centre 13 of the circle, but it may alternatively be marked on the sound barrier 2 by any shape, drawing or text, such as "Speak here", or it may be left unmarked. Furthermore - particularly in the latter case - the sound barrier 2 and/or the surroundings may be designed to guide the client 25 to the desired location or encourage him to locate himself there. For instance, a lock (not shown) for exchanging small items, such as money and tickets, between the client 25 and the attendant 28 may be arranged at the bottom of the glass pane 3. Such a lock would make the typical clients 25 speak towards imaginary points vertically above the lock, and the focus area 12 would thus be construed around these imaginary points. Also the typical working position of the attendant 28 and the average height of the clients 25 may be used to construct or estimate the location of the focus area 12 on the sound barrier 2. In the first embodiment of a communication system 1 , the sound barrier 2 is furthermore designed to encourage clients 25 to stand at a distance of about 25 cm from the glass pane 3 while speaking.

When the client 25 speaks while being in the intended location in front of the focus area 12 and at a distance of about 25 cm from the glass pane 3, he produces a speech signal, which travels towards the client microphones 14, 15 in the direction indicated by the arrow 26 and hits these at an incidence angle Ch of about 45° relative to the line 16, on which their acoustical centres are located. Since the client microphones 14, 15 are located at different distances from the client 25, they receive the speech signal at different points in time, and correspondingly, the speech signal appears with different time delays in their electrical output signals. The different delays cause a phase difference between the two signals, the phase difference increasing with increasing signal frequency. The differential power amplifier 23 subtracts the electrical output signal of one of the client microphones 14, 15 from the electrical output signal of the other one, amplifies the difference signal and provides the amplified signal on its output. The amplified signal is fed to the headset 18 and the attendant loudspeaker 19, which radiates a corresponding acoustical signal to the attendant 28. The subtraction of the signals causes an attenuation of the signals, the low frequency components of the speech signal being attenuated more than the high frequency components, which may contribute to improve understandability. The differential power amplifier 23 may be dimensioned with an increased gain at low frequencies in order to partially compensate for the effects of the subtraction, however at the risk of increasing noise at low frequencies. Acoustical signals arriving at higher incidence angles α, i.e. towards 90°, arrive with a smaller phase difference and are thus attenuated more than acoustical signals arriving at lower incidence angles α, i.e. towards 0°. Acoustical signals, such as the output signals from the client loudspeaker 17, which approach the client microphones 14, 15 from a direction perpendicular to the line 16, i.e. at an incidence angle α of 90°, cause equal electrical output signals from the client microphones 14, 15 and are thus - in theory - cancelled completely by the subtraction. However, differences between the client microphones 14, 15 as well as inbalances in the differential power amplifier 23 typically cause the attenuation to be finite. In any case, however, it should be an easy task for the person skilled in the art to dimension the communication system 1 to provide a strong attenuation of such signals, i.e. in an order of magnitude of at least 20 dB.

When the attendant 28 answers the client 25, he generates an acoustical signal, which is received by the attendant microphone 20 in the headset 18 and fed as an electrical signal to the simple power amplifier 24. The output of the simple power amplifier 24 is fed to the client loudspeaker 17, which radiates it as an acoustical signal into the client space 5. The acoustical signal travels in a direction indicated by the arrow 34 towards the client 25, but also in the directions indicated by the arrows 30, 31 towards the client microphones 14, 15, respectively. Since the acoustical centre of the client loudspeaker 17 is located at equal distances from the acoustical centres of the client microphones 14, 15, the acoustical signal arrives at the same time at the two client microphones 14, 15, and the signal is thus attenuated strongly in the amplified signal from the differential power amplifier 23. This prevents audible artefacts, such as echoes and howling, from appearing in the acoustical signal radiated by the attendant loudspeaker 19 towards the attendant 28.

Sounds from other acoustical sources in the client space 5 may be received by the client microphones 14, 15 and thus be superimposed on the acoustical signal radiated by the attendant loudspeaker 19 towards the attendant 28, which may regard such sounds as noise causing disturbance and stress. In FIG. 3, a noise source 32 radiates a noise signal, which travels towards the client microphones 14, 15 in a direction indicated by the arrow 33 and hits the client microphones 14, 15 at an incidence angle α₂ of approximately 70°. Experiments have shown that in the amplified signal from the differential power amplifier 23, the noise signal is attenuated by about 5 to 6 dB compared to the speech signal arriving at an incidence angle Ch of 45°. This relative attenuation increases with decreasing frequency. Experiments have further shown that a large portion of the noise signals, arrive at the client microphones 14, 15 at large incidence angles α, i.e. above 45°, and are thus attenuated more than useful signals, such as speech signals, arriving at incidence angles α of 45° or lower. Hence, most noise signals will be amplified with a smaller gain than the useful signals, whereby the communication system 1 according to the present invention generally provides better speech understandability and lower stress to the attendant.

Further experiments have shown that the distance between the acoustical centres of the client microphones 14, 15 may be varied up to 3 cm or even up to 5 cm without substantially decreasing speech understandability. The difference signal increases with increasing distance, however at the cost of a somewhat higher attenuation of high frequency components in the speech signal. Experiments have also shown that the distance between the acoustical centres of the client microphones 14, 15 and the centre 13 of the focus area 12 may be varied in the range 20 to 30 cm, alternatively up to 50 cm or even up to 80 cm without substantially decreasing speech understandability. The level of the acoustical signals received by the client microphones 14, 15 decreases with increasing distance, however, and as a general rule the distance should therefore only be increased when other requirements demand this. Such requirements could e.g. be that the client microphones 14, 15 be mounted concealed to the client. A large distance may also make it difficult to place the client loudspeaker 17 in a suitable location.

In a second embodiment (not shown) of the communication system 1 , the two client microphones 14, 15 and the differential power amplifier 23 are substituted by a pressure gradient microphone and a single-input amplifier. The pressure gradient microphone may e.g. be of the kind disclosed in the European Patent Application EP 1 351 549 A2. The pressure gradient microphone has two ports or inlets, which are located in the same locations as the diaphragms of the client microphones 14, 15 in the first embodiment and the output of the pressure gradient microphone is fed to the input of the single-input amplifier. The pressure gradient microphone performs an acoustical subtraction of the acoustical signals received at its sound receiving areas instead of the electrical subtraction performed in the differential power amplifier 23 in the first embodiment of the communication system 1.

Three embodiments of a method of transmitting acoustical signals across a sound barrier is explained in the following with reference to FIGs. 2 and 3, in which a sound barrier 2 delimits a client space 5 on a first of its sides and an attendant space 6 on the opposite second side.

A first embodiment of the method comprises the steps of receiving a first acoustical input signal at a first location in the client space 5, e.g. at the acoustical centre of the first client microphone 14; receiving a second acoustical input signal at a second location in the client space 5, e.g. at the acoustical centre of the second client microphone 15, the second location being different from the first location; and radiating a first acoustical output signal, e.g. via an attendant loudspeaker 19, to a person in the attendant space 6, e.g. the attendant 28, the first acoustical output signal being based on a difference between the first and the second acoustical input signals.

A second embodiment of the method further comprises the steps of converting the first and the second acoustical input signals into a first and a second electrical input signal, respectively; and subtracting the second electrical signal from the first electrical signal, e.g. in a differential power amplifier 23.

A third embodiment of the method further comprises the step of radiating a second acoustical output signal into the client space 5 from a location, which is at equal distances from the first and the second locations, e.g. from the acoustical centre of the client loudspeaker 17.

The respective improvements of the first embodiment of the method suggested by the second and the third embodiments of the method may be implemented alternatively to each other or in combination.

The sound barrier 2, which is comprised in the disclosed embodiments of the communication system according to the invention, and which is mentioned in the disclosed methods according to the invention, may have various configurations without deviating from the general concept that it delimits a client space 5 on one of its sides and an attendant space 6 on the opposite side. Various embodiments of a sound barrier 2 are well known in the art, and they are typically in use in ticket booths, banks and other service rooms and/or buildings, where it is desirable to have some form of protection of goods and/or attendants or other personnel servicing clients or customers. The sound barrier 2 may extend entirely to the walls, the floor and the ceiling of the room, thus separating the client space 5 and the attendant space 6 completely from each other, or it may be of smaller dimensions, in which case it may function merely as a sound shield, i.e. acoustical signals may travel around the edges of the sound barrier 2. In any case, however, it should provide some level of dampening to acoustical signals travelling directly between locations close to opposite main surfaces 21 , 22 of the sound barrier 2. It is also not required that it be plane; it might e.g. be curved horizontally and/or vertically. The sound barrier 2 may be air-tight or it may be provided with any number of openings allowing both air and acoustical signals to pass through.

The invention is defined by the features of the independent claim(s).

Preferred embodiments are defined in the dependent claims. Any reference numerals in the claims are intended to be non-limiting for their scope.

Some preferred embodiments have been shown in the foregoing, but it should be stressed that the invention is not limited to these, but may be embodied in other ways within the subject-matter defined in the following claims. For example, the features of the described embodiments may be combined arbitrarily.

Claims

1. A communication system (1 ) for transmitting acoustical signals, the communication system (1 ) comprising a sound barrier (2), a first microphone (14) and a first loudspeaker (19), the sound barrier (2) delimiting a client space (5) on a first of its sides and an attendant space (6) on the opposite second side, the first microphone (14) having a first sound receiving area being arranged to receive a first acoustical input signal from the client space (5), and the first loudspeaker (19) being arranged to radiate a first acoustical output signal to a person (28) in the attendant space (6), characterised in that the communication system (1 ) further comprises a second sound receiving area being arranged to receive a second acoustical input signal from the client space (5) and in that the communication system (1 ) is adapted to generate the first acoustical output signal based on a difference between the first and the second acoustical input signals.

2. A communication system according to claim 1 , characterised in that the acoustical centres of the first and second sound receiving areas are arranged on or close to a main surface (21 ) of the sound barrier (2) and at a mutual distance of 5 cm or less, preferably 3 cm or less, and even more preferably about 1.5 cm.

3. A communication system according to claims 1 or 2, characterised in that the sound barrier (2) has a focus area (12), and in that the acoustical centres of the first and second sound receiving areas are arranged along a line (16) directed towards the focus area (12).

4. A communication system according to claim 3, characterised in that the acoustical centres of the first and second sound receiving areas are arranged at a distance of about 20 to 80 cm, preferably between 20 and 50 cm and more preferably between 20 and 30 cm from the centre of the focus area (12).

5. A communication system according to any of the preceding claims, the communication system further comprising a second loudspeaker (17) being arranged to radiate a second acoustical output signal into the client space (5) via a sound radiating area, characterised in that the distance between the acoustical centre of the sound radiating area and the acoustical centre of the first sound receiving area equals the distance between the acoustical centre of the sound radiating area and the acoustical centre of the second sound receiving area.

6. A communication system according to any of the preceding claims, characterised in that the first microphone (14) is acoustically connected to the first sound receiving area, and in that the communication system further comprises a second microphone (15) being acoustically connected to the second sound receiving area, and in that the communication system (1 ) is adapted to convert the first and the second acoustical input signals into a first and a second electrical signal, respectively, and to subtract the second electrical signal from the first electrical signal.

7. A communication system according to any of the preceding claims 1 to 5, characterised in that the first microphone (14) is acoustically connected to the first and the second sound receiving areas, and in that the first microphone (14) is adapted to generate an electrical signal based on a difference between the first and the second acoustical input signals.

8. A method of transmitting acoustical signals across a sound barrier (2) delimiting a client space (5) on a first of its sides and an attendant space (6) on the opposite second side, the method comprising the steps of receiving a first acoustical input signal at a first location in the client space (5); receiving a second acoustical input signal at a second location in the client space (5), the second location being different from the first location; and radiating a first acoustical output signal to a person (28) in the attendant space (6), the first acoustical output signal being based on a difference between the first and the second acoustical input signals.

9. A method according to claim 8, characterised in that the method further comprises the steps of converting the first and the second acoustical input signals into a first and a second electrical input signal, respectively; and subtracting the second electrical signal from the first electrical signal.

10. A method according to claims 8 or 9, characterised in that the method further comprises the step of radiating a second acoustical output signal into the client space (5) from a location, which is at equal distances from the first and the second locations.