EP3840399A1

EP3840399A1 - Loudspeaker and soundbar

Info

Publication number: EP3840399A1
Application number: EP19218959.5A
Authority: EP
Inventors: Peter MØLLER; Facundo Ramon; Martin Rung
Original assignee: GN Audio AS
Current assignee: GN Audio AS
Priority date: 2019-12-20
Filing date: 2019-12-20
Publication date: 2021-06-23

Abstract

The present invention relates to a loudspeaker (40) and to a soundbar (50) comprising such a loudspeaker (40).

The loudspeaker (40) comprises a first speaker unit (1), a second speaker unit (1) and a support structure (41). Each speaker unit (1) comprises a tubular side wall (2), a rear wall (3) and a speaker driver (4) comprising a speaker diaphragm (9) arranged to reciprocate in an axial direction parallel to a center line (10) extending through the center of the speaker diaphragm (9). For each speaker unit (1), the speaker driver (4) and the rear wall (3) are arranged at opposite ends (5, 6) of the side wall (2) to separate a rear cavity (7) from the environment (8). Both the volumes of the rear cavities (7) and the areas of the speaker diaphragms (9) of the first and the second speaker units (1) are equal.

Furthermore, the support structure (41) mechanically maintains the first and the second speaker unit (1) in an arrangement wherein: their center lines (10) coincide and their speaker drivers (4) face each other to delimit a front cavity (43); the support structure (41) provides one or more openings (44) between the side walls (2) of the first and the second speaker units (1) fluidly connecting the front cavity (43) with the environment (8) and thereby defining a primary acoustic passageway (45) for sound waves to escape from the front cavity (43) to the environment (8); and the maximum axial extension of the primary acoustic passageway (45) is shorter than the maximum radial extension of the speaker diaphragms (9).

The invention may e.g. be used to reduce sound-induced vibrations in a loudspeaker (40) or in a soundbar (50) and connected equipment.

Description

TECHNICAL FIELD

The present invention relates to a loudspeaker and to a soundbar comprising such a loudspeaker. The invention may e.g. be used to reduce sound-induced vibrations in a loudspeaker or in a soundbar and connected equipment.

BACKGROUND ART

Soundbars are typically used for providing sound during display of video content on flat video displays. Soundbars exist in many variations including e.g. configurations specific to providing mono, stereo or surround-sound. A soundbar is typically mounted mechanically separated from the video display.
With the advent of video conferencing, it has become convenient to arrange video cameras in soundbars. In such a soundbar, vibrations from the loudspeakers may propagate to the camera and may thus cause a distortion of the video signal provided by the camera. Some cameras further process signals from individual pixels, or groups of pixels, in their sensors e.g. to detect movements of conference participants in a meeting or lip movements, to stitch multiple sensor images into a combined video image, or to otherwise enhance the video image, and such cameras may be more sensitive to vibrations.
There is thus a need for a loudspeaker that vibrates less than prior art loudspeakers. There is further a need for a soundbar that vibrates less than prior art soundbars.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a loudspeaker that is specifically configured to suppress or avoid mechanical vibrations. It is a further object to provide a soundbar comprising such a loudspeaker and with similar advantages.
These and other objects of the invention are achieved by the invention defined in the independent claims and further explained in the following description. Further objects of the invention are achieved by embodiments defined in the dependent claims and in the detailed description of the invention.
Within this document, the singular forms "a", "an", and "the" specify the presence of a respective entity, such as a feature, an operation, an element or a component, but do not preclude the presence or addition of further entities. Likewise, the words "have", "include" and "comprise" specify the presence of respective entities, but do not preclude the presence or addition of further entities. The term "and/or" specifies the presence of one or more of the associated entities.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in more detail below together with preferred embodiments and with reference to the drawings in which:

FIG. 1 shows an embodiment of a speaker unit,
FIG. 2 shows a further embodiment of a speaker unit,
FIG. 3 shows details of the embodiment of FIG. 2,
FIG. 4 shows an embodiment of a loudspeaker comprising two speaker units, and
FIG. 5 shows an embodiment of a soundbar comprising a loudspeaker.

The figures are schematic and simplified for clarity, and they just show details essential to understanding the invention, while other details may be left out. Where practical, like reference numerals and/or labels are used for identical or corresponding parts.

MODE(S) FOR CARRYING OUT THE INVENTION

The speaker unit 1 shown in an axial section in FIG. 1 comprises a tubular side wall 2, a rear wall 3 and a speaker driver 4. The side wall 2 has a front end 5 and a rear end 6. The speaker driver 4 is arranged at the front end 5 of the side wall 2. The rear wall 3 is substantially circular and is arranged at the rear end 6 of the side wall 2. The side wall 2, the rear wall 3 and the speaker driver 4 together separate a rear cavity 7 from the environment 8. The speaker driver 4 comprises a speaker diaphragm 9 arranged to reciprocate in an axial direction parallel to a center line 10 that extends through the center 11 of the speaker diaphragm 9. The side wall 2 has a substantially circular-cylindric shape, and the center line 10 coincides with the cylinder axis of the side wall 2. The speaker driver 4 may be connected to a power amplifier (not shown) providing an electric driver signal, and the speaker driver 4 comprises a transducer mechanism 12 that causes the speaker diaphragm 9 to reciprocate in dependence on the driver signal. Examples of suitable transducer mechanisms 12 include e.g. electrodynamic, electromagnetic, electrostatic, piezoelectric and/or thermoelectric electroacoustic or electromechanics mechanisms.
Note that in the present context, the terms "axial" and "radial" refer to the respective commonly known directions in a cylindrical coordinate system with the center line 10 as longitudinal axis.
Correspondingly, the term "tangential" refers to directions relative to a point in space at a non-zero distance from the center line 10, wherein the directions are perpendicular both to the center line 10 and to a radial line from the center line 10 through that point. Furthermore, the term "front" refers to a direction from the rear end 6 towards the front end 5, and the term "rear" refers to the opposite direction.
In the shown example, the speaker diaphragm 9 is circular with a diameter of 50 mm. The maximum radial extension of the speaker diaphragm 9 is thus also 50 mm. The speaker driver 4 has an annular mounting flange 13 with an outer diameter f of 55 mm, slightly larger than the diameter of the speaker diaphragm 9. The outer diameter of the side wall 2 is 60 mm, slightly larger than the diameter of the mounting flange 13, such that the speaker driver 4 can be mounted with the mounting flange 13 at the front end 5 of the side wall 2 without extending radially outside the side wall 2. The length of the side wall 2 is 110 mm, providing a volume of the rear cavity of about 0.3 liters. These dimensions enable a flat frequency response of the speaker unit 1 with a maximum deviation of about ±6 dB in a frequency range from well below 200 Hz to well above 1,000 Hz. In the following, the term "frequency range" refers to this continuous portion of the frequency scale wherein the frequency response of the speaker unit 1 is flat within ±6 dB. As is well known in the art, other dimensions may be chosen, both larger and smaller, e.g. to adapt the speaker unit 1 to other frequency ranges and/or to specific size constraints.
The side wall 2 and the rear wall 3 are mechanically connected to function as a loudspeaker enclosure. As is well known in the art, the moving mass and the compliance of the speaker driver 4 determines its resonant frequency. The low-frequency response of the speaker unit 1 is further affected by properties of the loudspeaker enclosure 2, 3, and may further be affected by filter circuits and/or the transducer mechanism 12. This typically results in the speaker unit 1 having a frequency-dependent electrical impedance with a peak at the lower end of its frequency range, which peak defines the system resonant frequency.
The loudspeaker enclosure 2, 3 functions as a "sealed" loudspeaker enclosure. In speaker units 1 with such enclosures, the frequency response decreases by 12dB/octave when the frequency moves below the system resonant frequency. Compressible air trapped in the rear cavity 7 inside the loudspeaker enclosure 2, 3 acts as a spring that returns the speaker diaphragm 9 to the "zero" position in the absence of a driver signal. The compressible air thus provides an acoustic compliance to sound generated by the speaker diaphragm 9. The above-mentioned example dimensions of the rear cavity 7 cause the trapped air to provide an acoustic compliance of about 2·10^-9 m⁵/N. The speaker unit 1 may comprise a filling of fibrous material, such as fiberglass, bonded acetate fiber (BAF) or long-fiber wool, arranged in the rear cavity 7 to increase its acoustic compliance and thus lower the system resonant frequency.
The speaker unit 1 may preferably comprise a leak opening 14, e.g. through the side wall 2 and/or the rear wall 3, that provides a small leak between the rear cavity 7 and the environment 8 so that internal and external pressures can equalise over time, e.g. over one or more minutes, or over an even longer time, to compensate for e.g. barometric pressure variations. The leak opening 14 may have a cross-sectional area of e.g. about 1 mm², or even smaller. In some embodiments, one or more leak openings 14 may instead or additionally be provided by a porous speaker diaphragm 9 and/or by an intentionally imperfect sealing of the loudspeaker enclosure 2, 3.
In speaker units 1 with sealed enclosures, the main cause of mechanical vibration is typically the vibration of the speaker diaphragm 9. The speaker diaphragm 9 itself and parts of the transducer mechanism 12, such as e.g. an electric coil, attached to it constitute a vibrating mass that exerts an axial vibration force onto the loudspeaker enclosure 2, 3. Furthermore, the acoustic impedances of air in the environment 8 and air in the rear cavity 7 exert reactive axial vibration forces on the speaker diaphragm 9, and these vibration forces are also transferred to the loudspeaker enclosure 2, 3, thereby increasing mechanical vibration of the speaker unit 1. Mechanical vibrations may generally be confined to mainly the axial direction by providing a sufficiently rigid side wall 2 and by centering the speaker diaphragm 9 with respect to the side wall 2.
In some embodiments, the side wall 2, the rear wall 3 and/or the speaker driver 4 may have non-circular shapes or cross-sections, such as e.g. rectangular, quadratic or hexagonal shapes or cross-sections. In some embodiments, the side wall 2 may have a non-cylindric shape, such as e.g. a tapered or a frusto-conical shape.
The embodiment of the speaker unit 1 shown in FIG. 2 equals the embodiment of the speaker unit 1 of FIG. 1 with the exception that the leak opening 14 is replaced with or complemented by a first and a second rear vent 20 that each fluidly connects the rear cavity 7 with the environment 8 and provides a significantly increased acoustic inertance, or "acoustic mass", to sound waves passing through. In this embodiment, the loudspeaker enclosure 2, 3 thus functions as a "bass reflex" loudspeaker enclosure. In contrast to the leak opening 14, the rear vents 20 are dimensioned to allow low-frequency sound waves to pass through, and the pressure equalisation thus happens in fractions of a second, such as e.g. faster than 0.3 seconds or faster than 0.1 seconds. Sound generated by the speaker diaphragm 9 causes air to reciprocate in the rear vents 20, and the reciprocating air constitutes a moving mass with an inertia that provides an acoustic inertance. The acoustic inertance interacts with the acoustic compliance of compressible air in the rear cavity 7 to form a Helmholtz resonator with a usually well-defined vent resonant frequency.
The vent resonant frequency may be adjusted by modifying properties of the moving air mass, e.g. by modifying the cross-sectional area of the rear vent 20, by modifying the length of the rear vent 20, and/or by providing dampening material in the rear vent 20. The vent resonant frequency is typically tuned to a frequency slightly below the system resonant frequency, such that low-frequency sound radiated through the rear vents 20 extend the frequency range of the speaker unit 1 further downwards. The Helmholtz resonator causes the frequency response of the speaker unit 1 to decrease by 24dB/octave when the frequency moves below the vent resonant frequency. The speaker unit 1 may further comprise a filling of fibrous material like in sealed embodiments. In some embodiments, one or more of the rear vents 20 may comprise a dampening material, such as e.g. fibrous material and/or a porous membrane at either or both ends of the rear vent 20. Such dampening material may be used to reduce the magnitude of the impedance peak at the vent resonant frequency.
Each of the rear vents 20 has a vent outlet 21 through which sound exits towards the environment 8. The direction of the vent outlet 21, indicated by arrows 22, is defined as the direction in which the main part of air leaves the respective rear vent 20 into the environment 8. The acoustic impedance of air in the environment 8 exerts a reactive vibration force on air reciprocating in the rear vents 20, mainly in the vent directions 22, and mainly at low frequencies around the vent resonant frequency. This vibration force is transferred to the loudspeaker enclosure 2, 3 and may thus cause mechanical vibration of the speaker unit 1. Depending on the direction 22 as well as the radial and axial location of the vent outlets 21, the vibrations force from the vent outlets 21 may cause radial, axial and/or tangential vibration of the speaker unit 1 as well as rotational vibrations.
Low-frequency sound typically causes both a larger excursion of the speaker diaphragm 9 and a larger displacement of air than high-frequency sound, and a loudspeaker will thus generally cause larger mechanical vibrations at low frequencies. The rear vents 20 radiate low-frequency sound, and correspondingly, reactive vibration forces caused by the rear vents 20 may be relatively large. In order to reduce mechanical vibrations of the speaker unit 1, the vent outlets 21 may preferably be directed and dimensioned to at least partially balance reactive forces created by exiting low-frequency sound waves. In the speaker unit 1 of FIG. 2, the vent outlets 21 are arranged in the side wall 2, axially adjacent each other and at tangential positions close to each other. The vent outlets 21 are directed tangentially in substantially opposite directions 22. This may cause a reduction of both radial vibrations and rotational vibrations.
Some embodiments may comprise only one rear vent 20. In some embodiments, one or more of the vent outlets 21 may be arranged in the rear wall 3 and directed partially or entirely axially. A partially or entirely axial vent outlet direction 22 may be preferable in embodiments comprising only one rear vent 20.
FIG. 3 shows a section 30 through the speaker unit 1. The section 30 is in a radial plane (see dashed line 23 in FIG. 2) that is perpendicular to the center line 10 and intersects the first rear vent 20. The section is seen from the first end 5 of the speaker unit 1 and it is oriented such that the vent outlet 21 of the first rear vent 20 is on the right-hand side. The first rear vent 20 comprises a tubular wall 31. The tubular wall 31 comprises a radially inner wall 32 arranged to extend tangentially along a portion 33 of the side wall 2 at a radial distance from the side wall 2 to provide a tangentially extending acoustic passageway 34. The acoustic passageway 34 preferably extends tangentially along the side wall for at least 225°, or even at least 270° of the full rotation around the center lines 10. The acoustic passageway 34 is delimited on the radially outer side by the portion 33 of the side wall 2 and axially by radially and tangentially extending intermediate walls (see dotted wall lines 24 in FIG. 2) that are also comprised by the tubular wall 31, such that the acoustic passageway 34 constitutes an open tube with a vent inlet 35 and the vent outlet 21 at respective ends through which the acoustic passageway 34 fluidly connects the rear cavity 7 with the environment 8. The intermediate walls 24 preferably extend radially only between the radially inner wall 32 and the side wall 2, such that the radially inner space is free for air to move back and forth between the speaker diaphragm 9 and the rear wall 3.
The second rear vent 20 has a similar configuration as the first rear vent 20, but with a section (not shown) that is mirrored with respect to the section 30 of the first rear vent 20. Consequently, the direction of flow through the acoustic passageway 34 towards the environment 8, i.e. the direction from the vent inlet 35 through the acoustic passageway 34 to the vent outlet 21, is tangentially opposite for the two rear vents 20. At its axially rear end, the acoustic passageway 34 of the second rear vent 20 is axially delimited by the rear wall 3, while at its front end, the rearmost intermediate wall 24 of the first rear vent 20 may be shared by the two rear vents 20. In other embodiments, the acoustic passageway 34 may instead be axially delimited by one or two further intermediate walls 24 like the ones of the first rear vent 20. The opposite directions of flow through the tangentially oriented acoustic passageways 34 of the first and the second rear vents 20 further has the effect that inertial forces exerted by moving air within the acoustic passageways 34 largely balance each other.
The acoustic passageways 34 of the rear vents 20 are dimensioned to provide an acoustic inertance that in combination with the acoustic compliance of the rear cavity 7 define the vent resonant frequency such that the level of low-frequency sound radiated by the speaker unit 1 is increased. In the shown example, each of the rear vents 20 has a length (in the direction of air flow) of about 180 mm, and a consistent cross-sectional area of about 120 mm². These dimensions provide a total acoustic inertance of the rear vents 20 of about 900 kg/m⁴. The above-mentioned example acoustic compliance and example total acoustic inertance together yield a vent resonant frequency of about 115 Hz. Furthermore, the rear vents 20 may help reducing axial excursion of the speaker diaphragm 9 around its resonant frequency, such that the frequency range of the speaker unit 1 is extended downwards to about 90 Hz. In other embodiments, the rear vents 20 may be dimensioned otherwise to e.g. increase or decrease the vent resonant frequency, improve suppression of turbulence and/or allow larger air flows through the acoustic passageways 34 without increasing turbulence.
The tubular walls 31 are preferably arranged such that they create a double-wall system which improves the rigidity of the side wall 2 and further minimizes abrupt changes in the air flow directions to reduce turbulent noise.
In some embodiments, the speaker unit 1 may comprise more than two rear vents 20, such as e.g. three, four or even more rear vents 20, similarly arranged and further with their vent outlets 21 directed and dimensioned to at least partially balance reactive forces created by exiting low-frequency sound waves.
Speaker units 1 like the one shown in FIG. 2 may be used as stand-alone loudspeakers, e.g. in mono, stereo or surround-sound configurations. Alternatively, they may be combined with high-frequency speaker units to provide loudspeakers covering a wider frequency range. Speaker units 1 like the one shown in FIG. 2 may provide high-quality medium/low-frequency sound with less mechanical vibration and/or with less extension in the axial direction than speaker units of the prior art. As explained further in the following such speaker units 1, as well as speaker units 1 like the one shown in FIG. 1, may be combined and e.g. incorporated into soundbars with or without video cameras.
The loudspeaker 40 shown in FIG. 4 comprises a first and a second speaker unit 1 and a support structure 41. The speaker units 1 are preferably configured like the speaker units 1 shown in FIG. 1 or FIG. 2, and they are further configured to have equal volumes of their rear cavities 7 and equal areas of their speaker diaphragms 9. The support structure 41 comprises four rigid rods 42 that mechanically maintain the first and the second speaker unit 1 in an arrangement wherein their center lines 10 coincide and their speaker drivers 4 face each other to delimit a front cavity 43. The rigid rods 42 separate four front openings 44 between the side walls 2 of the first and the second speaker unit 1. The front openings 44 fluidly connect the front cavity 43 with the environment 8 and thereby define a primary acoustic passageway 45 for sound waves to escape from the front cavity 43 to the environment 8. The maximum axial extension of the primary acoustic passageway 45 is shorter than the maximum radial extension of the speaker diaphragms 9.
The speaker units 1 are preferably generally identical or mirrored versions of each other. In some embodiments, the speaker units 1 are arranged and configured generally symmetric with respect to reflection in a symmetry plane 46 extending perpendicularly to the center lines 10. In other embodiments, the speaker units 1 are arranged and configured generally symmetric with respect to rotation around a symmetry axis (not shown) perpendicularly to and intersecting the center lines 10. In any embodiments, minor details, such as e.g. holes in the mounting flanges 13, other fastening means, wiring exits and/or smaller features in the side walls 2 or the rear walls 3 may differ between the speaker units 1. In some embodiments, the speaker diaphragms 9 have equal axial projections onto the symmetry plane 46
The rigid rods 42 are identical, have a diameter of about 5 mm and are arranged symmetrically with respect to rotation around the center lines 10. The front openings 44 are thus also arranged symmetrically with respect to rotation around the center lines 10. This means that sound may escape the front cavity 43 radially in nearly all radial directions, which contributes to balancing reactive forces exerted by the acoustic impedance of air in the environment 8 and thus also to reducing mechanical vibration of the loudspeaker. In other embodiments, the front openings 44 may be more or less evenly distributed around the center lines 10. The front openings 44 may e.g. by arranged symmetrically with respect to reflection in one or more distinct planes comprising the center lines 10.
In the shown example, the speaker units 1 are configured and dimensioned like the speaker unit 1 shown in FIGs. 2 and 3, and the distance between the side walls 2 is 15 mm, i.e. about 30% of the maximum radial extension of the speaker diaphragms 9. The maximum axial extension of the primary acoustic passageway 45 is thus shorter than the maximum radial extension of the speaker diaphragms 9, preferably shorter than 70% or most preferably shorter than 40% of the maximum radial extension of the speaker diaphragms 9. The relatively small maximum axial extension of the primary acoustic passageway 45 allows the loudspeaker 40 to efficiently radiate sound also in axial directions such that its directivity comes close to omnidirectionality within a large portion of its frequency range. In embodiments with larger or smaller speaker diaphragms 9, the frequency range of the loudspeaker will typically be shifted respectively downwards or upwards and the maximum axial extension of the primary acoustic passageway 45 should normally be adapted to fit the shifted frequency range.
The rigid rods 42 are preferably arranged to maximise the cross-sectional area of the primary acoustic passageway 45 without compromising mechanical stability of the support structure 41. The support structure 41 is thus preferably configured to provide that the smallest cross-sectional area of the primary acoustic passageway 45 is at least 60%, preferably at least 75% or even more preferably at least 90% of an available area defined as the area of the largest imaginary open cylinder that can be axially spanned between the speaker diaphragms 9 of the first and the second speaker units 1. In the example shown, this largest open cylinder is an open circular cylinder that is spanned between the outer rims of the speaker diaphragms 9, and the available area is the area of that cylinder area. With the example dimensions the available area is thus the area of an open circular cylinder with diameter of 50 mm and a length of 15 mm.
The rigid rods 42 are dimensioned to not have any inherent resonant frequencies below the upper limit of the frequency range of the loudspeaker 1, and preferably neither any within the entire audible frequency range. The support structure 41 may be made in other ways, e.g. comprising more or fewer than four rods 42 or comprising other mechanical structures providing the functions or benefits described above, such as e.g. a cage-like structure. The support structure 41 may be made of e.g. metal or hard resin.
The loudspeaker enclosures 2, 3 of the two speaker units may both be sealed loudspeaker enclosures as described further above with reference to FIG. 1, or the may both be bass-reflex loudspeaker enclosures as described further above with reference to FIG. 2. In the latter case, each of the speaker units 1 comprise a number, preferably an equal number, of rear vents 20 with vent outlets 21, e.g. two rear vents 20 in each speaker unit 1. The vent outlets 21 are preferably directed 22 and dimensioned to at least partially balance reactive forces created by exiting low-frequency sound waves. Such balancing may be provided for each speaker unit 1 alone, and/or for the entire loudspeaker 40. In the example shown in FIG. 4, the vent outlets 21 are directed tangentially opposite for each of the speaker units 1 and the vent outlets 21 are further arranged symmetrically with respect to reflection in the symmetry plane 46 to further reduce mechanical vibrations.
The soundbar 50 shown in FIG. 5 comprises a soundbar housing 51, a loudspeaker 40 and a video camera 52. The loudspeaker 40 is preferably configured like the loudspeaker 40 shown in FIG. 4 or like other embodiments described above. The video camera 52 comprises three video sensors 53 and a video processor 54. The video sensors 53 are arranged and oriented to cover each their field of view. The loudspeaker 40 and the video camera 52 are both mechanically connected to the soundbar housing 51 and the video sensors 53 are thus also mechanically connected to the soundbar housing 51. As described further above, the loudspeaker 40 may cause less mechanical vibrations than similar prior art loudspeakers, and in the soundbar 50, the video camera 52 may thus receive less mechanical vibrations than in prior art soundbars and may therefore be able to provide a more stable video output signal. In other embodiments, the video camera 52 may comprises fewer or more video sensors 53, such as e.g. one, two, four or even more video sensors 53. In some embodiments, the video processor 54 may be omitted.
The video processor 54 may receive a video sensor signal from each of the three video sensors 53, retrieve image information from each of the video sensor signals and process the retrieved image information to provide a video output signal. In some embodiments, the video processor 54 may stitch multiple images into a combined image covering a larger field of view than each of the video sensor signals. In some embodiments, the video processor 54 may detect speech by analysing for moving objects in the retrieved image information.
The soundbar 50 may preferably further comprise one or more high-frequency speaker units 55 and/or one or more microphones 56 that pick-up sound from the environment 8 to complement or be embedded in the video output signal. The loudspeaker 40 is preferably oriented with its center lines 10 in a length direction of the soundbar 50. The soundbar 50 may further comprise one or more power amplifiers (not shown) to provide a driver signal for the speaker units 1 of the loudspeaker 40 and/or for the high-frequency speaker units 55.
The detailed description given herein and the specific examples indicating preferred embodiments of the invention are intended to enable a person skilled in the art to practice the invention and should thus be regarded mainly as an illustration of the invention. The person skilled in the art will be able to readily contemplate further applications of the present invention as well as advantageous changes and modifications from this description without deviating from the scope of the invention. Any such changes or modifications mentioned herein are meant to be non-limiting for the scope of the invention.
The invention is not limited to the embodiments disclosed herein, and the invention may be embodied in other ways within the subject-matter defined in the following claims. As an example, further features of the described embodiments may be combined arbitrarily, e.g. in order to adapt devices according to the invention to specific requirements.
Any reference numerals and labels in the claims are intended to be non-limiting for the scope of the claims.

Claims

A loudspeaker (40) comprising a first speaker unit (1), a second speaker unit (1) and a support structure (41), each speaker unit (1) comprising a tubular side wall (2), a rear wall (3) and a speaker driver (4) comprising a speaker diaphragm (9) arranged to reciprocate in an axial direction parallel to a center line (10) extending through the center (11) of the speaker diaphragm (9), wherein for each speaker unit (1), the speaker driver (4) and the rear wall (3) are arranged at opposite ends (5, 6) of the side wall (2) to separate a rear cavity (7) from the environment (8), and wherein further:
- the volumes of the rear cavities (7) of the first and the second speaker units (1) are equal; and

- the areas of the speaker diaphragms (9) of the first and the second speaker units (1) are equal,
characterised in that:
- the support structure (41) mechanically maintains the first and the second speaker unit (1) in an arrangement wherein their center lines (10) coincide and their speaker drivers (4) face each other to delimit a front cavity (43);

- the support structure (41) provides one or more openings (44) between the side walls (2) of the first and the second speaker units (1) fluidly connecting the front cavity (43) with the environment (8) and thereby defining a primary acoustic passageway (45) for sound waves to escape from the front cavity (43) to the environment (8); and

- the maximum axial extension of the primary acoustic passageway (45) is shorter than the maximum radial extension of the speaker diaphragms (9).
A loudspeaker according to claim 1, wherein the one or more openings (44) comprise multiple openings (44) arranged symmetrically with respect to rotation around the center lines (10) and/or with respect to reflection in one or more distinct planes comprising the center lines (10).
A loudspeaker according to claim 1 or 2, wherein the smallest cross-sectional area of the primary acoustic passageway (45) is at least 60%, preferably at least 75% or even more preferably at least 90% of an available area defined as the area of the largest imaginary open cylinder that can be axially spanned between the speaker diaphragms (9) of the first and the second speaker units (1).
A loudspeaker according to any preceding claim, wherein the maximum axial extension of the primary acoustic passageway (45) is shorter than 70% or preferably shorter than 40% of the maximum radial extension of the speaker diaphragms (9).
A loudspeaker according to any preceding claim, wherein:
- each of the first and the second speaker units (1) further comprises one or more rear vents (20) fluidly connecting the rear cavity (7) with the environment (8) and further providing a significantly increased acoustic inertance to sound waves passing through the one or more rear vents (20);

- each of the one or more rear vents (20) comprises a vent outlet (21); and

- the vent outlets (21) of the one or more rear vents (20) of the first and the second speaker units (1) are directed and dimensioned to at least partially balance reactive forces created by low-frequency sound waves exiting through the vent outlets (21) when the speaker drivers (4) of the first and the second speaker units (1) are driven in phase with each other.
A loudspeaker according to claim 5, wherein for each of the first and the second speaker units (1):
- the one or more rear vents (20) comprise at least two rear vents (20) with respective vent outlets (21) directed at least partly tangentially with respect to the center line (10); and

- the vent outlets (21) of the at least two rear vents (20) are directed and dimensioned to at least partially balance reactive tangential forces created by low-frequency sound waves exiting through the respective vent outlets (21).
A loudspeaker according to claim 5 or 6, wherein for each of the first and the second speaker units (1), at least one of the one or more rear vents (20) comprises a tubular wall (31) providing a secondary acoustic passageway (34) dimensioned to increase the level of low-frequency sound radiated by the speaker unit (1).
A loudspeaker according to claim 6, wherein for each of the first and the second speaker units (1):
- each of the at least two rear vents (20) comprises a tubular wall (31) providing a secondary acoustic passageway (34) dimensioned to increase the level of low-frequency sound radiated by the speaker unit (1) and extending tangentially along a portion (33) of the side wall (2); and

- the direction of flow through the secondary acoustic passageway (34) towards the environment (8) is tangentially opposite for at least two of the at least two rear vents (20).
A loudspeaker according to claim 8, wherein for each of the first and the second speaker units (1), each of the secondary acoustic passageways (34) of the at least two rear vents (20) extends tangentially along the side wall for at least 225°.
A soundbar (50) comprising a soundbar housing (51), a loudspeaker (40) according to any preceding claim and a video camera (52) with a video sensor (53), wherein each of the loudspeaker (40) and the video sensor (53) is mechanically connected to the soundbar housing (51).
A soundbar according to claim 10, wherein the video camera (52) comprises multiple video sensors (53) and a video processor (54), wherein the video processor (54) is adapted to receive a video sensor signal from each of the video sensors (53), retrieve image information from each of the video sensor signals and process the retrieved image information to provide a video output signal.
A soundbar according to claim 11, wherein the processing of the retrieved image information comprises stitching multiple images into a combined image covering a larger field of view than each of the video sensor signals.
A soundbar according to claim 11 or 12, wherein the processing of the retrieved image information comprises detecting speech by analysing for moving objects in the retrieved image information.