EP2050303A2

EP2050303A2 - A loudspeaker system having at least two loudspeaker devices and a unit for processing an audio content signal

Info

Publication number: EP2050303A2
Application number: EP07789646A
Authority: EP
Inventors: David Corynen
Original assignee: PSS Belgium NV
Current assignee: PSS Belgium NV
Priority date: 2006-07-13
Filing date: 2007-07-12
Publication date: 2009-04-22
Also published as: TW200818964A; JP5215299B2; WO2008010086A3; JP2009543496A; WO2008010086A2

Abstract

A loudspeaker system includes at least two stand-alone multiple loudspeaker devices (1L, 1R), each comprising a frame (3) with a horizontally oriented array (5) of first loudspeakers (7) for reproducing sound in a higher frequency range The system further includes a second loudspeaker (11) for reproducing sound in a lower frequency range, the frequency ranges having a crossover frequency fc The first loudspeakers each have a first radiation surface (9) of maximal 1000 mm2 and the second loudspeaker has a second radiation surface (13) In each device (1L, 1R) a central area (9a) of each first radiation surface being situated at a vertical distance d, from a central area (13a) of the second radiation surface wherein 750 Hz ≤fc ≤3000 Hz and d ≥2.λ fc, wherein λ fc is the wavelength of the reproduced sound at the crossover frequency and wherein d is minimal 75 mm and maximal 3000 mm The system also includes a means for processing an audio content signal to generate individual signals for input to the first loudspeakers resulting, during use of the system, in a directional acoustic signal of the array of first loudspeakers of each de\ ice This system is able to reproduce sound of high fidelity qualification

Description

A loudspeaker system having at least two loudspeaker devices and a unit for processing an audio content signal

The invention relates to a loudspeaker system including at least two standalone loudspeaker devices each comprising a frame with at least one array of first loudspeakers for reproducing sound in a higher frequency range, and at least one second loudspeaker for reproducing sound in a lower frequency range.

It is known in the field that the ideal loudspeaker can only be approximated by a very small pulsating point source generating the full audible frequency spectrum from 20 Hz to 20 kHz without distortion or compression. A single full-range loudspeaker always suffers from compromising on performance, because of its physical limitations with regard to its non-linear behavior. For this reason arrangements of two loudspeakers, i.e. a first loudspeaker - usually mentioned tweeter - for reproducing sound in a higher frequency range and a second loudspeaker - usually mentioned woofer - for reproducing sound in a lower frequency range, are used to reproduce high quality audio, each loudspeaker working in a specific frequency range. Pursuant to current teaching the loudspeakers in such arrangements ^• are positioned close to each other to come close to the ideal full-range point source. However, such multiple loudspeaker devices are far from ideal and suffer from acoustic phase, level and power irregularities around the crossover frequency, resulting in blur and coloration of the reproduced sound. It is to be noted that the term "crossover frequency" means in this paper the frequency at which the electrically and/or mechanically and/or acoustically reduced sound level of the first loudspeaker and the electrically and/or mechanically and/or acoustically reduced sound level of the second loudspeaker are the same, wherein the sound pressure level of the combination of first and second loudspeaker is substantially balanced, measured at a distance of at least three meters from said combination.

An electrical filter may be used to direct appropriate frequencies to a first speaker or a second speaker of a loudspeaker system and thus to reduce the sound level at other frequencies. To improve the characteristics perceived by a listener, multi-channel audio systems are known which comprise sound channels in addition to left and right sound channels. These systems are becoming more and more common in consumer's homes. A disadvantage of such a multi-channel audio system is the large number of transducers distributedly arranged in the listener's room. Moreover the necessary wiring is not always desirable.

An alternative for the above described multi-channel audio systems, which alternative mostly better fits in the rooms of ordinary houses, is the application of devices each including an array of electro-acoustic transducers capable of generating beams of audible sound. Such array devices are capable of receiving multi-channel audio input signals and to produce steered beams of audible sound from different channels to create virtual sound sources with the aid of reflectioiis on wall and/or ceiling boundaries. In such an array device phase shifting, delaying and/or leveling applied on an input signal may be used to realize the beaming. A system with such a device is known from WO 2004/075601 Al . This known system includes low-frequency transducers arranged at the perimeter of an array of electro- acoustic high frequency transducers. This array device is capable of receiving multiple audio or multi-channel audio input signals and to produce independently steerable and focusable beams of audible sound.

Compact, i.e. small size, speaker array systems for domestic applications need small wide bandwidth transducers for covering the audible frequency range above about 100 to 200 Hz, in combination with a subwoofer for covering the frequency range below about 100 to 200 Hz. An efficient beaming of the low frequency content of an audio signal by means of a number of transducers requires a minimum distance of about half the wavelength of the reproduced sound between the outer transducers of an array of transducers. Therefore it is not easy to obtain beamed sound content of low to medium frequencies with a compact array system. On the other hand the highest frequency content of an audio signal that can be beamed efficiently depends on the distance between neighboring transducers in the array; more precisely, this beaming requires small distances between the transducers. However, the distance between the transducers is limited by the transverse dimensions, usually the diameter, of the transducers. In view of the required sound pressure level at low frequencies relatively large transverse dimensions are required. This means that the distance between the transducers in a speaker array device cannot be as small as desired for generating beamed high frequency sound output. In other words the conventional compact array technology is a compromise on performance wherein use is made of transducers which each have to cover a wide bandwidth.

An object of the invention is to provide a loudspeaker system of the kind as described in the preamble, which is able to reproduce sound of an improved quality with respect to the known similar systems.

This object is achieved by the loudspeaker system according to the invention, λvhich system includes at least two stand-alone multiple loudspeaker devices, each comprising a frame with at least one array of first loudspeakers (further also called tweeters) for reproducing sound in a higher frequency range, and at least one second loudspeaker (further also called woofer) for reproducing sound in a lower frequency range, the frequency ranges having a crossover frequency f_c, which first loudspeakers each have a first radiation surface of maximal 1000 mm² and which second loudspeaker has a second radiation surface, in each device a central area of each first radiation surface being situated at a distance d, being a vertical distance, considered during use of the system, from a central area of the second radiation surface, wherein 750 Hz < f_c < 3000 Hz. and d < 2. λ_f , wherein /L is the wavelength of the reproduced sound at the crossover frequency, and wherein d is minimal 750 mm and maximal 3000 mm. and which system includes a means for processing sound content to generate individual signals for the first loudspeakers resulting, during use of the system, in a directional acoustic signal of the array of first loudspeakers of each device.

The measures applied into the loudspeaker system according to the invention are based on a new design philosophy. This philosophy implies that there should be little or preferably no interference between the sound of the second loudspeaker- or loudspeakers - and the direct sound of the first loudspeakers. In this context it is to be noted that the term "direct sound" means in this paper the sound that arrives at a certain place directly from the sound source, thus without reflection. Due to the location of the second loudspeaker at a certain minimum distance d from the first loudspeakers - as worded above - a reduced interference is obtainable. For the sake of clarity it is noted that on normal use conditions the first loudspeakers are positioned above the second loudspeaker. By positioning the second loudspeaker near a partition, such as a floor, diffuse sound can be created in those places where the sound frequencies of first and second loudspeakers cross each other. In this context it is to be noted that the term "diffuse sound" means in this paper the sound that arrives at a certain place not directly from the sound source, but after reflection. The applied design philosophy further implies that the loudspeaker system is capable of effectively generating sound content without compromising the quality of the audio reproduction The combination of arrays of tweeters, as defined above, and the descπbed means for processing enables the loudspeaker system according to the invention to process the frequency content of audio signals to generate individual signals and to direct these signals to the tweeters, whereby the arrays of tweeters generate well-defined sound beams in desired directions for different audio signals

In this context it is noted that an essential aspect of the invention is that the frequency range of the beamed sound and the frequency range of the tweeters in the arrays of tweeters match, whereby a high quality of sound is guaranteed

The sound quality of the loudspeaker system according to the invention is improved in terms of definition, clarity and holographic imaging w ith respect to similar state of the art loudspeaker systems For this reason the loudspeaker system according to the imention is suitable as a high fidelity device for audio reproduction as w ell as for TV, video and multi media sound reinforcement It offers a solution for current design and performance limitations related to multi-way loudspeaker arrangements

In a practical embodiment of the loudspeaker according to the invention the means for processing an audio content signal includes a unit for phase shifting, a unit for delaying and/or a unit for le\ehng dif ferent signals Such units are known per se Methods for processing audio signals are e g descπbed in W 02005/091678A 1 , WO02/078388A2,

US 4,349,328 and already mentioned WO2004/075601 Al (all these documents are herew ith incorporated by reference)

WO2005/091678A1 describes a method for processing sound signals for a surround left channel and a surround πght channel Thereby, a continually varying delay betw een the resulting signals of these channels is generated

WO02/078388A2 describes a method and apparatus for taking an input signal, replicating it a number of times and modifying each of the replicas before routing them to respective output transducers such that a desired sound field is created This sound field may compπse a directed beam, focused beam or a simulated oπgin US 4,399,328 descnbes an electro-acoustic arrangement comprising a plurality of transducer units including an unev en number of spaced transducers situated in line and at an equal distances from each other These transducers are accommodated in a cabinet Connection terminals of the transducers are connected to an electrical transmission channel via individual amplitude control devices The amplitude control devices amplify or attenuate a signal and may have a phase-shifting or merely an invertion action. To this end the control devices are constituted by amplifiers or attenuators or by components such as resistors. The control devices are adjusted so that the ratios between conversion factors of the arrangement form a special relationship. A preferred embodiment of the loudspeaker device according to the invention has the parameters 1000 Hz ≤f_c <2000 Hz and ό ≥3. λ_f , particularly

1000 Hz <f_c <1500 Hz.

The lower- frequency range, i.e. the frequency range of the second loudspeaker, extends from a resonance frequency up to the crossover-frequency. The second loudspeaker may have a frequency range from 20Hz to 1 OkHz (typical 50Hz-5kHz). The higher frequency range, i.e. the frequency range of the first loudspeakers, extends upwardly from the crossover frequency. The first loudspeakers may have a frequency from 500Hz to 10OkHz (typical 800Hz-40kHz).

Experiments have been done with a stereophonic arrangement having a pair of second loudspeakers (woofers) positioned close to the floor of a room and an array of first loudspeakers (tweeters) positioned at the required distance d above the second loudspeakers. Instead of the expected split-up of the reproduced stereo sound (music) image in a low- frequency content localized in a zone near the floor and a high-frequency content localized in a higher zone, it λvas surprisingly found that the stereo sound image was very stable positioned in the vertical plane just below (or near) the first loudspeakers, regardless of the frequency content of the reproduced sound. Most surprisingly was, moreover, the extremely high sound quality of the sound reproduction in terms of clarity, staging, homogeneity and transparency, and thus a true sensation of holographic stereo imaging was obtained. Specific parameters of the experiments are: a crossover frequency of 1 kHz; a vertical distance d between the array of first loudspeakers and the pair of second loudspeakers of 1 m; and the use of first loudspeakers each having a dome-shaped membrane with an effective diameter of 30 mm.

For the sake of completeness it is here reported that the above-mentioned holographic capacity of the arrangement is completely lost if the array of tweeters is mounted according to current principles, i.e. close to the second loudspeakers, but without changing the other parameters and with making use of the same filter and same components.

Similar effects, excepting the stereo image, have been obtained with a monophonic arrangement having the woofer positioned close to the floor of a room and the array of tweeters positioned at the required distance d above the woofer. A practical embodiment of the loudspeaker device according to the invention has the feature that the first radiation surface of the first loudspeaker has a circular outline and a diameter of 35 mm at the most. For reasons already mentioned above, the direct radiation surface is preferable a part of a dome-shaped membrane. For practical reasons the second loudspeaker is situated underneath the arrays of first loudspeakers.

Usually, the arrays of first loudspeakers are oriented substantially horizontally, at least during use of the system according to the invention. Generally, the first loudspeakers of an array are situated in line, and may be positioned at equal distances from each other. Each device may be provided with more than one array of first loudspeakers. This feature offers the possibility to beam in a vertical direction.

The array or arrays of first loudspeakers may be curved. This feature improves the beaming of very high frequency signals.

The number of first loudspeakers in an array is preferably at least three. Three or more speakers enable beaming of signals in a wide frequency bandwidth. Optimizing of distances between tweeters is possible.

Preferred embodiments of the system according to the invention have been mentioned and formulated in the Claims 2 to 12.

The invention further relates to a loudspeaker housing. This housing is in principle based on the same recognition as described in the foregoing paragraphs, particularly the issue that the second loudspeaker or loudspeakers must be positioned with respect to the array or arrays of first loudspeaker at such a distance that there is no or only minimal interference between the sound emanating from both kinds of speakers, and the issue of applying means for processing audio content for generating individual signal for input to the first loudspeakers resulting in stereo sound beams emanating from the array or arrays of first loudspeakers.

The loudspeaker housing according to the invention accommodates at least one array of first loudspeakers for reproducing sound in a higher frequency range, at least one second loudspeaker for reproducing sound in a lower frequency range, the frequency ranges defining a crossover frequency f_c, which array of first loudspeakers is situated in a first face, preferably a front face, of the housing, wherein each first loudspeaker has a first radiation surface of maximal 1000 mm², and which second loudspeaker is situated in a second face, not being the first face, of the housing and has a second radiation surface, a central area of each first radiation surface being situated, at least during use, at a vertical distance d with regard to a central area of the second radiation surface, wherein 750 Hz <f_c <3000 Hz, preferably 1000 Hz <f_c <2000 Hz, particularly 1500 Hz f_c <2000 Hz, and 150 mm <d <

1000 mm, and wherein a means for processing an audio content signal is provided to generate individual signals for input to the first loudspeakers resulting, during use, in a directional acoustic signal from the array of first loudspeakers. The loudspeaker housing of the invention has the same benefits of the invention as aforesaid with reference to the loudspeaker system.

Preferred embodiments of the loudspeaker housing according to the invention and preferred parameters for implementation of this housing have been mentioned and formulated in the Claims 14 to 22. A particular, specific and surprising characterizing feature of the loudspeaker housing of the invention is that the first loudspeakers are used for providing a direct sound field and the second loudspeaker(s) is/are used for providing a diffuse sound field, i.e. a field obtained after reflections.

The invention also relates to an audio and/or video apparatus provided with a loudspeaker arrangement formed by the system according to the invention or having the housing according to the invention. The loudspeaker housing may be the housing of the apparatus itself or may be a kind of subhousing. As a result of the applied principles, as explained in the foregoing, the sound quality of the apparatus according to the invention is of a high-end level. In the context of this paper the video apparatus may be a monitor.

Furthermore the invention relates to a stand-alone device meant and thus designed and constructed for use in the system according to the invention. This stand-alone device is defined in Claim 24.

It is to be noted that the German Gebrauchsmuster No. 83 04 832 discloses a loudspeaker arrangement in a TV apparatus. This known arrangement comprises more than one loudspeaker in case of mono sound reproduction and more than two loudspeakers in case of stereo sound reproduction. Particularly, the known arrangement comprises a high- frequency loudspeaker and a low-frequency loudspeaker called subwoofer, and optionally comprises a middle-frequency loudspeaker. The high-frequency loudspeaker - and if present the middle- frequency loudspeaker - radiates from a front wall portion of the TV apparatus, while the subwoofer, which has a frequency range of 40 to 200 or 300 Hz, makes use of air openings to radiate from the rear side or bottom side of the TV apparatus. Thus, the known loudspeaker arrangement applied in the known TV apparatus has hardly any resemblance as to sound aspects with the loudspeaker arrangement applied in the apparatus according to the invention. It is further to be noted that the German Gebrauchsmuster 16 87 888 discloses a loudspeaker box which is provided with a high-frequency sound system and low-frequency speaker or a broadband system. The high-frequency sound system is such designed and arranged that it radiates sound with frequencies of about 1.000 Hz or higher not only from a front side but also in other directions, such as backwards. For this reason the applied high- frequency sound system has the specific feature of having a plurality of radiation surfaces. By this feature, among others, the known loudspeaker box is essentially different from the loudspeaker structures according to the invention.

With reference to the Claims it is to be noted that various combinations of features as defined in the Claims are possible and intended within the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The already above-mentioned and other objects, features and advantages of the present invention will become readily apparent from the following detailed exemplary description read in conjunction with the accompanying drawings, in which:

Figs. 1 to 5, 6A to 6C , and 7 are schematic representations of embodiments of loudspeaker devices of the loudspeaker system according to the invention;

Fig. 8 is a schematic front view of an embodiment of the loudspeaker housing according to the invention, applied in a TV-set; Fig. 9 is a schematic front view of an embodiment of the apparatus according to the invention; and

Fig. 10 is a block diagram showing an arrangement of speakers and a processing unit in accordance with an embodiment of the loudspeaker system according to the invention.

DETAILED DESCRIPTION OF EMBODIMENTS

With reference to Fig. 1, there can be seen an arrangement of two stand-alone multiple loudspeaker devices YL and FR positioned on the left hand and the right hand, respectively, and in front of an imaginary listener 100 present in a room having a floor 4a and a wall 4b. Each loudspeaker device FL, FR has a frame 3, which comprises a box 3a and a stem 3b, of e.g. a rod-like shape. A low end of the stem 3b is secured to the box 3a. The boxes 3a are meant for resting upon a face, such as the floor 4a or the like. An upper end of each stem 3b is provided with an array 5 of tweeters (first loudspeakers) 7 for reproducing sound in a higher-frequency range. Each tweeter 7 has a first radiation surface 9. Each box 3a is provided with a woofer (second loudspeaker) 1 1 having a second radiation surface 13 for reproducing sound in a lower-frequency range.

The woofers 11 may be known woofers. The tweeters 7 may be conventionally available tweeters have e.g. dome-shaped membranes, however with the additional condition that the diameter of their effective radiation surfaces is maximal 35 mm, preferably smaller. In this example the diameter of the effective radiation face of each tweeter 7 is 30 mm. In this example, the crossover frequency f_c of the speaker arrangement is 1.5 kHz. The frequency range of the tweeters 7 is 900 Hz to 30 kHz and the frequency range of the woofers 1 1 is 60 Hz to 5 kHz. The minimally required distance between the tweeters 7 and the woofer 1 1 , i.e. the vertical distance d measured from a central area 9a to a central area 13a of the tweeters 7 and the woofers 1 1 , respectively, of each device YL, LR, is at least two times the wavelength λ_f of the reproduced sound at the crossover frequency; or in another notation d > 2. A^ . In this example d is 900 mm.

As generally known, the wavelength λ_f at the crossover frequency can be determined by the quotient of sound velocity in air (about 340 m/s) and the crossover

frequency f_c: or in another notation λ, (in m). fc

The arrays 5 in the system depicted in Fig. 1 are substantially horizontally oriented. Each device YL, JR. may be provided with more than one array of tweeters 7 as is shown by way of example in Fig. 3. Each device JLL, YR may also be provided with more than one woofer 1 1 as is shown by way of example in Fig. 5. In this context it is noted that it is even possible within the scope of the invention to apply stand-alone loudspeaker devices without a woofer, thus having only one or more arrays of tweeters. In such case one or more stand-alone woofers are provided.

The system according to the invention is provided with a means for processing audio content signals to generate individual signals for input to the tweeters 7, whereby the arrays 5 are capable of radiating directional acoustic signals, In Fig. 10 an example of such a means for processing audio content signals is diagrammatically shown. As can be seen in Fig. 1 the array 5 of tweeters 7 of the device IL is capable of producing a surround left audio beam Bu and a front left and center audio beam B_L2. The array 5 of tweeters 7 of the device ]_R is capable of producing corresponding beams, i.e. a surround right audio beam B_rj and a front right and center audio beam B_R2. It is to be noted that in principle the same reference signs will be used in the following description relating to the embodiments of the Figs. 2 to 5, 6A to 6C and 7 for parts corresponding to similar parts in the embodiment of Fig. 1, however embodiments relating to stand-alone multiple loudspeaker devices are also indicated by the numeral L The embodiment disclosed in Fig. 2 has a base 3a and a stem 3b, the base 3a being provided with a foot 10 for resting on a face, particularly a floor. The base 3a accommodates a woofer 1 1 with a radiation surface 13 positioned perpendicular to said face. The stem 3b carries an array 5 of three tweeters 7 each provided with a radiation surface 9 positioned parallel to the stem 3b for radiating sound toward a listener being in front of the loudspeaker device.

The embodiment disclosed in Fig. 3 has a base 3a accommodating a woofer 1 1 with a second radiation surface 13 oriented perpendicular to a stem 3b.

In this embodiment the stand-alone loudspeaker device I comprises a frame, i.e. the stem 3b. which carries three arrays 5a. 5b. 5c of tweeters 7 each having a first radiation surface 9. The vertical distance between a central area 9a of a radiation surface 9 of a tweeter 7 of the array 5a and the radiation surface 13 of the woofer 1 1 is the required distance d as defined in this paper.

The embodiment disclosed in Fig. 4 has a support or frame 3 constituted by a rectangular box-like structure and housing an array 5 of five tweeter 7 and a woofer 1 1. The embodiment depicted in Fig. 5 includes an array 5 of five tweeters 7 as well as three or an array of three woofers 11.

The embodiment disclosed in Fig. 6A comprises an array 5 of five tweeters 7 and a woofer 11.

In this embodiment, but this may also be the case in the other embodiments, the array 5 is curved, i.e. the tweeters are situated in a curved line. In Fig. 6B the array 5 is depicted in an enlarged front view. In Fig. 6C the array 5 is depicted in a corresponding top view.

The embodiment disclosed in Fig. 7 has an array 5 of five tweeters 7 not positioned at regular distance to each other. All the embodiments depicted in the Figs. 1 to 5, 6A to 6C, and 7 have the parameters required to obtain the high quality sound effects of the invention. More specifically, each of the tweeters 7 has a first radiation surface 9 of maximal 1000 mm² , and in all cases the distance d > 2. λ_f and 750 mm < d < 3000 mm, and 750 Hz < f_c < 3000 Hz. In Fig. 6A, as well as in Fig. 1 , the distance between neighboring tweeters 7 is indicated by the letter s and the distance between the outer tweeters 7 is indicated by the letter w. It is of common knowledge that the distances s and w must fulfill certain requirements in order to be able to beam efficiently. In this context it is informed that ail embodiments meet the following requirements:

f < — ; here the distance s delivers the highest frequency to which efficient

beaming is possible;

f > ; here the distance w defines the lowest frequency to which efficient

2. w beaming is possible. It is to be noted that c is the speed of sound. To produce multi-channel sound, sets of two and if desired more of such multiple loudspeaker devices can be formed. The embodiment depicted in Fig. 1 has the following parameters: s = 30 mm w = 150 mm d = 900 mm. The effective diameter of a tweeter 7 is 25 mm.

With reference now to Figs. 8. there can be seen an embodiment of the loudspeaker housing 101 according to the invention. Jn this example the loudspeaker housing 101 is constituted by a television housing 103 of a TV set having in its front face 103a a screen 104. In this example the loudspeaker housing 101 comprises two arrays 105 of four tweeters 107 and further comprises two woofers 1 1 1. The tweeters 107 have radiation surfaces 109 which are positioned in or near the front face 103a of the television housing 103, so that they are able to radiate sound from the front face 103a. Contrary thereto the woofers 1 1 1 are mounted such that their radiation surfaces 1 13 are positioned in or near a rear face of the television housing 103, so that they radiate sound during use from that face. The tweeters 107 are mounted at a high level in the housing KM and the woofers 111 are mounted at a low level in the housing. The loudspeaker arrangements applied in the loudspeaker housing 101 fulfill the following additional requirements: (1) the radiation surfaces 109 of the tweeters 107 each have a size of maximal 1000 mm², (2) the crossover frequency f_c is lying in the range from 750 Hz to 3000 Hz and (3) the tweeters 107 on the one hand and the woofers 1 1 1 on the other hand are positioned, measured from central area 109a to central area 1 13a, at a vertical distance d in the range from 150 mm to 1000 mm. Preferably, the tweeters 107 are dome-shaped tweeters and 1500 Hz < f_c < 2000 Hz. Ln this example the distance d is 350 mm. The loudspeaker housing 101 comprises a means ex emplarity depicted in Fig. 10 for processing audio content signals.

Fig. 9 discloses an alternative for the housing depicted in Fig. 8. In this alternative loudspeaker housing 101 two arrays of 105 of four speakers 107 each are mounted in the front face 103a, at a low level in the housing. A woofer 1 1 1 is mounted in a high level. For the rest, this embodiment meets the requirements of the invention and is similar to the embodiment of Fig. 9.

Fig. 10 shows an example of the loudspeaker system according to the invention, including an arrangement similar to the arrangement shown in Fig. 1 and including a means for processing audio signals to generate individual signals for input to the tweeters. More specifically, the depicted system comprises (1) two loudspeaker devices IL and j_R positioned on the left hand and the right hand, respectively, of an imaginary listener, wherein each device JJL and JR including an array 5 of tweeters 7 and a woofer 1 1 , (2) a processing unit 51 , (3) a filter unit 53 and (4) an amplifier unit 55 and an input unit 57. The processing unit 51 has a high frequency processing subunit 51_h and a low frequency processing subunit 51]. The filter unit 53 has high pass filters 53j, and low pass filters 53]. The amplifier unit 55 has individual amplifiers 55; serving as simple voltage amplifiers for amplifying output signals of the processing unit 51 to the recognized level to drive the individual tweeters and woofers. The input unit 57 serves in this example for receiving three input signals, i.e. a front signal if, a surround signal i_s and a center signal i_c, wherein the front signal i_f includes a front left signal in and a front right signal i_fr and the surround signal i_s includes a surround left signal i_sl and a surround right signal i_sr. It is to be noted that digital or analogue input channels of different audio channels, in this example front, surround and center channels, may be applied. The input channels might originate from an external source or an internal source, such as a tuner, DVD device, CD-ROM device or a movie sound track, and are processed, during use of the system, such that the different input components, thus front, surround and center components, are individually available for further processing. The signals i_f, i_s and i_c pass the filter unit 53, resulting in high pass signals i_h and low pass signal ii. The reference frequency for filtering is the crossover frequency, this means that the high pass signals represent audio content above crossover frequency and low pass signals represent audio content below crossover frequency.

The high pass filter signals ii, are processed in the processing subunit 5I)₁, wherein the high pass signals i_h originating from input components, i.e. the input signals if, i_s and i_c, are mixed to complex signals I_0I and l_cr meant for input, after passing the amplifier unit 55, to the tweeters 7 of the array IL and the array IR, respectively. The phase relations in said complex signals I_c1 and I_cr are such that the arrays U, and IR radiate different audio signals in well-defined different directions. In other word, the purpose of the processor sub unit 51 _h, which may be known per se, is to mix the individual high passed components to provide audio input signals for the amplifiers of the amplifier unit 55 to achieve a desired acoustical directivity of the loudspeaker arrays JL and \R. In this way individual directivity patterns for different components can be created, so that for instance front, center and surround components are beamed into different directions, e.g. corresponding to the audio beams B_u, B_L2, B_RI and B_R2 shown in Fig. I . Algorithms may be applied in the above- described signal processing. The low pass signals i| are added to the processing sub unit 51 ]. This sub unit 51₁ serves as a mixer that runs and levels the low passed components in order to create a stereo signal J₅ meant for input, after passing the amplifier unit 55, to the woofers 1 1 , being a left positioned and a right positioned woofer. If desired, phase and/or time of the individual low -passed components can be modified to support the surround effect of the tweeter arrays JX and _T_R. By applying e.g. psycho-acoustic algorithms in the circuit of the woofers 11 virtual sound can be created for frequencies below crossover frequency. In this way the sound that is created by the arrays JX, and VR of tweeters 7 may be completed with the virtual surround sound of the woofers 1 1.

In case of two or more woofers, the audio content below crossover frequency can be processed, if desired, in a similar way as is described above in relation to audio content above crossover frequency, in order to beam sound of a frequency till a lowest frequency dependent on the distance between the outer woofers.

It is to be noted that the invention is not limited to the embodiments disclosed herein. For example a subwoofer may be additionally applied for reproducing only bass frequencies. The frequency range of such a subwoofer may be from the resonance frequency of the subwoofer to about 200 Hz.

Claims

CLAIMS:

1. A loudspeaker system including at least two stand-alone multiple loudspeaker devices, each comprising a frame with at least one array of first loudspeakers for reproducing sound in a higher frequency range, and at least one second loudspeaker for reproducing sound in a lower frequency range, the frequency ranges having a crossover frequency f_c, which first loudspeakers each have a first radiation surface of maximal 1000 mm² and which second loudspeaker has a second radiation surface, in each device a central area of each first radiation surface being situated at a distance d, being a vertical distance, considered during use of the system, from a central area of the second radiation surface, wherein 750 Hz <f_c <3000 Hz, and d ≥2. λ_f , wherein λ_f is the wavelength of the reproduced sound at the crossover frequency, and wherein d is minimal 750 mm and maximal 3000 mm, and a means for processing an audio content signal to generate individual signals for input to the first loudspeakers resulting, during use of the system, in a directional acoustic signal of the array of first loudspeakers of each device.

2. A loudspeaker system as claimed in Claim 1 , wherein the means for processing includes a unit for phase shifting and/or delaying and/or leveling different signals.

3. A loudspeaker system as claimed in Claim 1 or 2, wherein 1000 Hz <f_c ≤

2000 Hz, and d >3.λ_fC

4. A loudspeaker system as claimed in Claim 3, wherein 1000 Hz <f_c <1500 Hz.

5. A system as claimed in Claim 1 , 2, 3 or 4, wherein the lower frequency range extends from a resonance frequency up to the crossover frequency.

6. A system as claimed in Claim 1 , 2, 3 or 4, wherein the higher frequency range extends from the crossover frequency.

7. A system as claimed in Claim 1, 2, 3 or 4, wherein the first radiation surface has a circular outline and a diameter of 35 mm at the most.

8. A system as claimed in Claim 1, 2, 3 or 4, wherein the second loudspeaker is situated underneath the array of first loudspeakers.

9. A system as claimed in Claim 1, 2, 3 or 4, wherein the first radiation surface is part of a dome-shaped membrane.

10. A system as claimed in Claim 1, 2, 3 or 4, wherein the arrays of first loudspeakers are oriented substantially horizontally, at least during use of the system.

1 1. A system as claimed in Claim 10, wherein the arrays are curved.

12. A system as claimed in Claim 10 or 1 1. wherein, each device is provided with more than one array of loudspeakers, wherein the arrays of each loudspeaker are arranged one above another.

13. A loudspeaker housing accommodating at least one array of first loudspeakers for reproducing sound in a higher frequency range, and at least one second loudspeaker for reproducing sound in a lower frequency range, the frequency ranges defining a crossover frequency f_c, which array of first loudspeakers is situated in a first face of the housing, wherein each first loudspeaker has a first radiation surface of maximal 1000 mm², and which second loudspeaker is situated in a second face, not being the first face, of the housing and has a second radiation surface, a central area of each first radiation surface being situated, at least during use, at a vertical distance d with regard to a central area of the second radiation surface, wherein 750 Hz ≤f_c ≤3000 Hz, wherein d is minimal 150 mm and maximal 1000 mm and wherein a means for processing an audio content signal is provided to generate individual signals for input to the first loudspeakers resulting, during use, in a directional acoustic signal of the array of first loudspeakers.

14. A loudspeaker housing as claimed in Claim 13, wherein the means for processing includes a unit for phase shifting and/or delaying and/or leveling different signals.

15. A housing as claimed in Claim 13 or 14, wherein 1000 Hz < f_c < 2000 Hz.

16. A housing as claimed in Claim 15, wherein 1500 Hz < f_c < 2000 Hz.

17. A housing as claimed in Claims 13, 14, 15 or 16, wherein the lower frequency range extends from a resonance frequency up to the crossover frequency.

18. A housing as claimed in Claim 13, 14, 15 or 16, wherein the higher frequency range extends from the crossover frequency.

19. A housing as claimed in Claim 13, 14, 15 or 16, wherein the first radiation surface has a circular outline and a diameter of 35 mm at the most.

20. A housing as claimed in any one of the Claims 13, 14, 15 or 16, wherein the second loudspeaker is mounted in a rear wall of the housing.

21. A housing as claimed in any one of the Claims 13, 14, 15 or 16, wherein the first radiation surface is part of a dome-shaped membrane.

22. A housing as claimed in any one of the Claims 13 to 21 , wherein a further similar array of first loudspeakers and a further second loudspeaker are accommodated.

23. An audio and/or video apparatus provided with a loudspeaker arrangement formed by the system as claimed in any one of the Claims 1 to 12, or having the housing as claimed in any one of the Claims 13 to 22.

24. A stand-alone multiple loudspeaker device suitable for use in the loudspeaker system as claimed in any one of the Claims 1 to 12 and characterized as defined in any one of these claims.