EP4049460A2 - Second-order gradient loudspeaker system, as well as second-order gradient line array speaker and plane wave speaker constructed from such loudspeaker systems - Google Patents

Second-order gradient loudspeaker system, as well as second-order gradient line array speaker and plane wave speaker constructed from such loudspeaker systems

Info

Publication number
EP4049460A2
EP4049460A2 EP19958748.6A EP19958748A EP4049460A2 EP 4049460 A2 EP4049460 A2 EP 4049460A2 EP 19958748 A EP19958748 A EP 19958748A EP 4049460 A2 EP4049460 A2 EP 4049460A2
Authority
EP
European Patent Office
Prior art keywords
order gradient
order
loudspeaker
acoustic
gradient
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Pending
Application number
EP19958748.6A
Other languages
German (de)
French (fr)
Inventor
Géza Zsolt BALOGH
András CSEREPES
Géza BALOGH
Balázs Géza MAGOS
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Interton Elektroakusztikai Kft
Original Assignee
Interton Elektroakusztikai Kft
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Interton Elektroakusztikai Kft filed Critical Interton Elektroakusztikai Kft
Publication of EP4049460A2 publication Critical patent/EP4049460A2/en
Pending legal-status Critical Current

Links

Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/32—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only
    • H04R1/40—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers
    • H04R1/403—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired directional characteristic only by combining a number of identical transducers loud-speakers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R3/00—Circuits for transducers, loudspeakers or microphones
    • H04R3/12—Circuits for transducers, loudspeakers or microphones for distributing signals to two or more loudspeakers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
    • H04R1/28—Transducer mountings or enclosures modified by provision of mechanical or acoustic impedances, e.g. resonator, damping means
    • H04R1/2807—Enclosures comprising vibrating or resonating arrangements
    • H04R1/2815—Enclosures comprising vibrating or resonating arrangements of the bass reflex type
    • H04R1/2819—Enclosures comprising vibrating or resonating arrangements of the bass reflex type for loudspeaker transducers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R1/00—Details of transducers, loudspeakers or microphones
    • H04R1/20—Arrangements for obtaining desired frequency or directional characteristics
    • H04R1/22—Arrangements for obtaining desired frequency or directional characteristics for obtaining desired frequency characteristic only 
    • H04R1/28—Transducer mountings or enclosures modified by provision of mechanical or acoustic impedances, e.g. resonator, damping means
    • H04R1/2869—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself
    • H04R1/2876—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself by means of damping material, e.g. as cladding
    • H04R1/288—Reduction of undesired resonances, i.e. standing waves within enclosure, or of undesired vibrations, i.e. of the enclosure itself by means of damping material, e.g. as cladding for loudspeaker transducers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04R—LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; DEAF-AID SETS; PUBLIC ADDRESS SYSTEMS
    • H04R27/00—Public address systems

Definitions

  • the present invention relates to a second-order gradient loudspeaker system comprising at least two first-order gradient, e.g. cardioid, loudspeaker systems, wherein the two first- order gradient loudspeaker systems are spaced apart with a distance d and arranged preferably one behind the other. Furthermore, there is a cavity of width h between the two first-order gradient loudspeaker systems, the volume of which has an acoustic ca pacity CK.
  • the invention also relates to a second-order gradient line array speaker and a second-order gradient plane wave speaker constructed from such second-order gradi ent loudspeaker systems.
  • Ensuring proper speech intelligibility is a major challenge when sound reinforcing of spaces of high reverberation, such as typically railway stations, large-volume halls, sports facilities (swimming pools, sports halls), road-railway tunnels, airports, etc. takes place. Informing those present in these spaces is vital, but it can only be done with the help of a public loudspeaker system capable of producing adequate speech intelligibility. Speech intelligibility is of high importance in emergencies wherein announcement is of ten the only way to communicate pieces of information effectively. To minimize environ mental noise load, it is equally important to ensure adequate directivity in the open air.
  • Speech intelligibility is measured nowadays quantitatively, with a metric between 0 and 1 , provided by STI (Speech Transmission Index).
  • the value of the STI is related to the so-called critical distance, also known as the Hall radius.
  • speech intelligibility is adequate within the critical distance.
  • the square of the critical dis tance is directly proportional to the directivity factor Q of the loudspeaker system and inversely proportional to the reverberation time of the room [cf. K.B.Ginn: Application of B&K Equipment to Room Acoustics; 1978, Bruel, Naerum Offset, p.29 and H.
  • One way to increase the directivity factor Q is to use a first-order gradient loudspeaker system.
  • Gradient generation can be performed with active electrical elements and two loudspeakers or passive acoustic elements and a single loudspeaker.
  • Another technique is the so-called use of line array speakers. Although it does not change the horizontal directivity, but the vertical directivity can be increased depending on the length of the line array speaker.
  • An object of the present invention is to increase the directivity of the loudspeaker systems in both the horizontal and vertical planes.
  • the second-order gradient principle has been found to be the most suitable.
  • Second-order pressure gradient loudspeaker systems increase the directivity in both the horizontal and vertical planes, and also pro vide a second-order cardioid, hypercardioid, or “8”-shaped polar pattern in both planes (with a maximum Q value ranging from 5 to 8).
  • an object of the present invention is to eliminate or at least alleviate the problems emerging when the cardioid principle is applied in such a way that the loudspeaker systems constructed on the basis of said principle remain as simple as possible.
  • a yet further object of the present inven tion is to construct a line array speaker and a plane wave speaker with second-order gradient loudspeaker systems, thereby increasing further the directivity factor Q of the loudspeaker system at medium and low frequencies.
  • T o this end, specific geometric and acoustic conditions should be met.
  • the second-order gradient principle raises several application problems. The most un pleasant of these is that the cardioid polar pattern gets significantly distorted when mov ing towards higher frequencies, and the frequency response falls strongly towards low frequencies, with a slope of essentially 12 dB/octave. This results in a narrow transmis sion band [cf. H.F. Olson: Gradient Loudspeakers, JAES Vol. 21, pp. 83-93, 1973.
  • Known second-order gradient loudspeaker systems mostly contain active first-order loudspeaker systems, i.e., four loudspeakers, four amplifiers, and active circuits.
  • the at least four loudspeakers which are necessarily arranged close to each other, interact with each other.
  • diffractive sound reflections due to the at least four loudspeakers close to each other and/or the effect of the at least three narrow, nearly closed spaces (cavi ties) therebetween disturb significantly the operation.
  • such a solution is rather costly due to the aforesaid reasons.
  • the present invention is based on several findings. If the first-order gradient generation is implemented with passive acoustic elements, a passive acoustic phase rotator, the practical realization of a second-order gradient loudspeaker system becomes simpler and thus less expensive, since in this way only two loudspeakers and up to two amplifiers have to be used. Thus, in such a design, fewer loudspeakers are present, so there is less adverse interaction between them, which results in the problem of only a single narrow, nearly closed space (i.e., a cavity representing an acoustic capacity CK) and/or a single diffraction interaction to be solved/handled. Said interaction narrows the trans mission band and is thus disadvantageous.
  • the objects of the present invention are achieved by a second-order gradient loud speaker system according to Claim 1. Further preferred exemplary embodiments of the second-order gradient loudspeaker system of the invention are set forth in Claims 2 to 19. The objects of the present invention are further achieved by a second-order gradient line array speaker according to Claim 20 and a second-order gradient plane wave speaker according to Claim 21.
  • the main advantage of the second-order gradient loudspeaker system according to the invention is that its directivity factor Q is significantly higher at any frequencies in the frequency range of 50-2000 Hz than that of conventional loudspeaker systems, as well as conventional line array and plane wave speakers. Thereby, speech intelligibility im proves, especially in reverberant rooms, and the area where reinforced speech is well understood increases significantly, too.
  • the second-order gradient loudspeaker system according to the invention increases the directivity in that frequency band wherein the room has the largest reverberation time and thus a high directivity factor is most needed. In outdoor spaces, the increased directivity of the loudspeaker system according to the invention reduces the environmental sound pollution.
  • a further advantage of the second- order gradient loudspeaker system according to the present invention is that it can be produced at a relatively low cost.
  • FIG. 1 shows a known first-order cardioid loudspeaker system
  • FIG. 2 shows an equivalent electrical circuit diagram of the first-order cardioid loud speaker system illustrated in Figure 1;
  • FIG. 3 shows the transfer function Ai(kd,0), i.e. the frequency response, at different angles of a gradient generation which leads to a cardioid characteristic curve;
  • FIG. 4 shows a series of polar patterns for a gradient generation leading to a cardioid characteristic curve
  • FIG. 5 illustrates the directivity factor Q as a function of (kd), i.e. frequency, for a gradient generation leading to a cardioid characteristic curve
  • - Figure 6 shows the polar pattern of a second-order cardioid characteristic curve dis torted due to diffraction
  • - Figure 7 shows a second-order gradient loudspeaker system according to the invention in side view and in cross-section;
  • FIG. 8 is a block diagram of an amplifier and passive filters section of a second-order gradient loudspeaker system according to the invention.
  • FIG. 9 is a block diagram of an amplifier and active filter section of a second-order gradient loudspeaker system according to the invention.
  • FIG. 10 shows a line array speaker constructed by arranging second-order gradient loudspeaker systems according to the invention above one another;
  • FIG. 11 shows a plane wave speaker constructed by arranging second-order gradi ent loudspeaker systems according to the invention above and beside one another.
  • ..loudspeaker refers to a stand-alone electroa coustic transducer that converts electrical energy into acoustic energy with no additional components i.e. that generates sound waves in the air.
  • the term ..loudspeaker system is, however, used to refer to a device obtained by assembling one or more such loud speakers with one or more mechanical and/or acoustical and/or electrical components (e.g. a housing, funnel, sound guide, electronic components, etc.) to improve and/or modify the sound waves generated.
  • Figure 1 shows a known first-order cardioid loudspeaker system.
  • a first-order gradient more precisely a first-order cardioid-type loudspeaker system can be seen in a side view and in cross-section.
  • the box resonances are attenuated by a fibrous material E, e.g. rock wool or glass wool or foamed plastic, as sound absorbing material.
  • the acoustic impedance Zi is or may be composed of the acoustic resistance Ri and the acoustic mass Mi, wherein, generally, the acoustic resistance Ri is dominant.
  • P denotes a cover that protects the acoustic resistance from mechanical impacts, the cover P is usually formed as a perforated plate.
  • Figure 2 shows an equivalent electrical circuit diagram of the first-order cardioid loud speaker system of Figure 1.
  • the loudspeaker LS is represented by an acoustic impedance ZM, which consists of an acoustic mass MM and an acoustic capacity CM, as well as an acoustic resistance RM.
  • the gradient generation is performed by a network of acoustic elements (phase shift, phase rotator), namely the acoustic mass Mi, the acoustic resistance Ri, and the acous tic capacity Co formed by the volume located behind the membrane of the loudspeaker LS.
  • Figure 3 illustrates the transfer function Ai(kd,0), i.e. the frequency response, at different angles of a gradient generation leading to a cardioid characteristic curve.
  • f stands for the frequency
  • c the speed of sound measured in air
  • d the effective distance between two sound gates.
  • This upper limit depends on the type of polar pattern, i.e. the value of a (which varies between p and 2p).
  • the limit for the operating frequency must be set lower than the upper limit, which corresponds to said cutoff frequency f t , to avoid distortions. It is pref erable to choose the limit for the operating frequency at the value of (kd) t /1.5, i.e. at which (kd) ⁇ 2 holds. Substituting the cutoff frequency f t and then arranging the relations, one gets that
  • Figure 4 shows a series of polar patterns for a gradient generation leading to a cardioid characteristic curve, that is, it shows a series of relative polar patterns D rei (kd,0) of the transfer function Ai(kd,0) for different (kd) parameters.
  • Figure 5 shows the directivity factor Q as a function of (kd) for the gradient generation leading to a cardioid polar pattern, i.e. the frequency response of the directivity factor Q.
  • Figure 6 shows the polar pattern of a second-order cardioid characteristic curve distorted due to diffraction.
  • Figure 6 presents measurement data. Second-order cardioid polar patterns are distorted not only by the cutoff frequency of the gradient generation, but also by the interaction of two radiator elements arranged close to each other, as well as diffraction.
  • Figure 7 shows two first-order gradient loudspeaker systems 1 , 2 arranged in close proximity to each other, one behind the other.
  • a lower frequency (kd) 0.6
  • an almost ideal second-order cardioid polar pattern can be seen.
  • the polar pattern is already distorted, partly due to the proximity of the cutoff frequency, partly due to the diffraction effect caused by the first loudspeaker system, and partly due to the effect of the cavity with width h (see Figure 7).
  • FIG. 7 illustrates a second-order gradient loudspeaker system according to the invention in a side view and in cross-sectional view.
  • the second-order gradient loudspeaker system consists of two first-order gradient loudspeaker systems 1, 2.
  • Both loudspeaker systems 1, 2 have a single built-in loudspeaker LSi, LS2, respectively.
  • the internal damping of the box is due to a fibrous material E, in the form of e.g. rock wool, glass wool, or a special foamed plastic.
  • the loudspeakers LSi, LS2 are separated from one another by a distance d, while a cavity of width and/or height h is formed between said loudspeakers.
  • this cavity is partially or completely filled with a sound-absorbing material EK.
  • the sound-absorbing material EK can be rock wool, glass wool or a special foamed plastic.
  • a protective grille (or mesh) P of each loudspeaker system 1, 2 is covered on the inside with a grille cloth T, preferably made of a non-woven textile material (e.g. vetex), wherein the sound-absorbing material EK and the grille cloth T together provide an acoustic impedance ZK(RK,MK).
  • Figure 8 shows the block diagram of an amplifier and passive filters section of a second- order gradient loudspeaker system according to the invention.
  • a series connected second-order all-pass filter APFi, low-pass filter LPFi, and delay circuit n are connected to the loudspeaker LSi of the first-order gradient loudspeaker system 1.
  • a series connected second-order all-pass filter APF2, low-pass filter LPF2, and delay circuit 12 are connected in reversed phase to the loudspeaker l_S2 0f the other first-order loudspeaker systems 2.
  • the all-pass filters, the low- pass filters, and the delay circuits are all fabricated with passive electrical elements.
  • the term termed “bulall-through filter” refers to a filter that transmits a signal without any modification in its amplitude, i.e. , its frequency response is straight, but varies the phase of the signal passing through it as a function of frequency.
  • a modified audio frequency electrical signal drives the first-order gradient loudspeaker systems 1, 2 through the above-listed elements, wherein the elec trical signal is modified differently by each enlisted element: the all-pass filters APF mod ify it in phase and running time, the low-pass filters LPF in phase, running time and am plitude, and the delay circuit t in running time and phase, to e.g. varying degrees de pending on the frequency.
  • Figure 9 shows the block diagram of an amplifier and active filters section of a second- order gradient loudspeaker system according to the invention.
  • a series connected second-order all-pass filter APFi, low-pass filter LPFi, and delay circuit n are connected to the input of a power amplifier Ampi, and then the output of the power amplifier Ampi is connected to the loudspeaker LSi of the first-order gradient loudspeaker system 1.
  • a series connected second-order all-pass filter APF2, low-pass filter LPF2, and delay circuit 12 are connected to the input of a power amplifier Amp2, and then the output of the power amplifier Amp2 is connected in reversed phase to the loudspeaker LS2 of the first-order gradient loud speaker system 2.
  • Each all-pass filter and low-pass filter, as well as the delay circuits, are implemented with digital and/or analog electrical elements, preferably in a digital sig nal processor DSP, as is apparent to those skilled in the art.
  • Figure 10 shows a line array speaker obtained by stacking several second-order gradient loudspeaker systems according to the present invention on top of each other.
  • the figure shows a line array speaker arrangement formed of second-order cardioid loudspeaker systems.
  • the second-order gradient loudspeaker system in this case a cardioid loudspeaker system
  • the individual units are placed one above the other, arranged e.g. in a frame or rack adapted to receive said loudspeaker systems.
  • the shown horizontal second-order cardioid characteristic curve is enhanced vertically with an additional control gain, i.e. the directivity factor Q is further increased: a vertically enhanced, so-called bundled polar pattern is obtained.
  • Fig. 11 shows a plane wave speaker obtained by arranging several second-order gradi ent loudspeaker systems according to the present invention on top of each other and next to each other.
  • the second-order gradient loudspeaker systems are placed not only on top of each other, but also next to each other, arranged in suitable frames or racks, so that they essentially form a plane wave speaker.
  • the col umn effect also increases the directivity factor Q from both directions and narrows the polar pattern, increasing thereby significantly the value of said directivity factor Q.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • Otolaryngology (AREA)
  • General Health & Medical Sciences (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Obtaining Desirable Characteristics In Audible-Bandwidth Transducers (AREA)

Abstract

The present invention relates to a second-order gradient loudspeaker system comprising two first-order gradient loudspeaker systems (1, 2) with loudspeaker (LS1, LS2) arranged at a distance d from one another, said two first-order gradient loudspeaker systems (1, 2) are located substantially one behind the other and a cavity of width h is present therebetween, the cavity has a volume with an acoustic capacity CK. The first-order gradient loudspeaker systems (1, 2) according to the invention are of passive design, that is, each of said systems (1, 2) is formed as an acoustic network consisting of passive acoustic elements having at least one of a passive acoustic mass (M), acoustic resistance (R) and acoustic capacity (C). Said acoustic network comprises at least one phase rotating member capable of passive gradient generation, wherein said first-order gradient loudspeaker systems (1, 2) are driven by modified audio frequency electrical signals directly or through at least one element selected from the group consisting of all-pass filters (APF), low-pass filters (LPF) and delay circuits (τ) in such a way that the rear first-order gradient loudspeaker system (2) is in reversed phase compared to the front first-order gradient loudspeaker (1), and the driving electrical signal of the rear system (2) is delayed by a total delay time τ compared to the driving electrical signal of the front system (1), the total delay time τ is given by Formula (I) wherein c is the sound propagation velocity in air at a given temperature; and α is a factor that defines the required type of the polar pattern of the second-order gradient loudspeaker system within a range extending from cardioid to „8"-shaped, or bidirectional.

Description

SECOND-ORDER GRADIENT LOUDSPEAKER SYSTEM, AS WELL AS SECOND-ORDER GRADIENT
LINE ARRAY SPEAKER AND PLANE WAVE SPEAKER CONSTRUCTED FROM SUCH
LOUDSPEAKER SYSTEMS
The present invention relates to a second-order gradient loudspeaker system comprising at least two first-order gradient, e.g. cardioid, loudspeaker systems, wherein the two first- order gradient loudspeaker systems are spaced apart with a distance d and arranged preferably one behind the other. Furthermore, there is a cavity of width h between the two first-order gradient loudspeaker systems, the volume of which has an acoustic ca pacity CK. The invention also relates to a second-order gradient line array speaker and a second-order gradient plane wave speaker constructed from such second-order gradi ent loudspeaker systems.
Ensuring proper speech intelligibility is a major challenge when sound reinforcing of spaces of high reverberation, such as typically railway stations, large-volume halls, sports facilities (swimming pools, sports halls), road-railway tunnels, airports, etc. takes place. Informing those present in these spaces is vital, but it can only be done with the help of a public loudspeaker system capable of producing adequate speech intelligibility. Speech intelligibility is of high importance in emergencies wherein announcement is of ten the only way to communicate pieces of information effectively. To minimize environ mental noise load, it is equally important to ensure adequate directivity in the open air. In order the communication of information take place in a comprehensible manner in these situations and locations, the so-called directivity of loudspeaker systems need to be increased. Echo is not indifferent either when it comes to musical sound; it becomes highly unpleasant especially when the music contains vocals and a lot of bass. Reflection of bass sounds can cause particularly unpleasant subjective effects.
Speech intelligibility is measured nowadays quantitatively, with a metric between 0 and 1 , provided by STI (Speech Transmission Index). The value of the STI is related to the so-called critical distance, also known as the Hall radius. In general, speech intelligibility is adequate within the critical distance. In an echo room, the square of the critical dis tance is directly proportional to the directivity factor Q of the loudspeaker system and inversely proportional to the reverberation time of the room [cf. K.B.Ginn: Application of B&K Equipment to Room Acoustics; 1978, Bruel, Naerum Offset, p.29 and H. Kuttruff: Room Acoustics 1979, Applied Science Publishers Ltd., London, X.2] Consequently, for good speech intelligibility, the longer the reverberation time of a given room, a loud speaker system with the higher directivity factor Q should be used.
The polar pattern of a standard loudspeaker system is nearly circular at low frequencies in both horizontal and vertical directions, thus, its directivity factor is Q ~ 1 [cf. L.L. Beranek: Acoustics. 1986 Edition, Cambridge, USA, p.111,114]. In echo rooms, i.e. , in rooms with a reverberation time of 4-10 seconds, such loudspeakers are practically use less for sound reinforcing tasks. This is because the direct sound of the loudspeaker system decreases so much at a distance of a few meters compared to the so-called diffuse sound representing the echo that the direct sound carrying the information is sup pressed by the diffuse one, and hence, speech can only be heard but not understood.
One way to increase the directivity factor Q is to use a first-order gradient loudspeaker system. Gradient generation can be performed with active electrical elements and two loudspeakers or passive acoustic elements and a single loudspeaker. Although its appli cation is limited due to frequency response and polar pattern problems, the method in creases both horizontal and vertical directionality and results in a cardioid, hypercardioid, or “8” shaped polar pattern in both planes (with a maximum directivity factor Q = 3 to 4). Another technique is the so-called use of line array speakers. Although it does not change the horizontal directivity, but the vertical directivity can be increased depending on the length of the line array speaker.
An object of the present invention is to increase the directivity of the loudspeaker systems in both the horizontal and vertical planes. To this end, the second-order gradient principle has been found to be the most suitable. Second-order pressure gradient loudspeaker systems increase the directivity in both the horizontal and vertical planes, and also pro vide a second-order cardioid, hypercardioid, or “8”-shaped polar pattern in both planes (with a maximum Q value ranging from 5 to 8). In light of this, an object of the present invention is to eliminate or at least alleviate the problems emerging when the cardioid principle is applied in such a way that the loudspeaker systems constructed on the basis of said principle remain as simple as possible. A yet further object of the present inven tion is to construct a line array speaker and a plane wave speaker with second-order gradient loudspeaker systems, thereby increasing further the directivity factor Q of the loudspeaker system at medium and low frequencies. T o this end, specific geometric and acoustic conditions should be met. The second-order gradient principle raises several application problems. The most un pleasant of these is that the cardioid polar pattern gets significantly distorted when mov ing towards higher frequencies, and the frequency response falls strongly towards low frequencies, with a slope of essentially 12 dB/octave. This results in a narrow transmis sion band [cf. H.F. Olson: Gradient Loudspeakers, JAES Vol. 21, pp. 83-93, 1973. March] The second-order gradient principle intensifies the difficulties arising when first- order gradient loudspeaker systems are applied. In practice, to simplify the problems and difficulties, an electronic, i.e. active, phase rotator is mostly used, which means that the first-order gradient generation is implemented with two loudspeakers, two amplifiers and active signal shaping circuits [cf. Geo D System brochure of Nexo SA, and Axys and subwoofer brochures of Duran Audio BV.]. Here, and from now on, such an arrangement will be referred to as an active first-order gradient loudspeaker system.
Known second-order gradient loudspeaker systems mostly contain active first-order loudspeaker systems, i.e., four loudspeakers, four amplifiers, and active circuits. The at least four loudspeakers, which are necessarily arranged close to each other, interact with each other. Thus, diffractive sound reflections due to the at least four loudspeakers close to each other and/or the effect of the at least three narrow, nearly closed spaces (cavi ties) therebetween disturb significantly the operation. Moreover, such a solution is rather costly due to the aforesaid reasons.
The present invention is based on several findings. If the first-order gradient generation is implemented with passive acoustic elements, a passive acoustic phase rotator, the practical realization of a second-order gradient loudspeaker system becomes simpler and thus less expensive, since in this way only two loudspeakers and up to two amplifiers have to be used. Thus, in such a design, fewer loudspeakers are present, so there is less adverse interaction between them, which results in the problem of only a single narrow, nearly closed space (i.e., a cavity representing an acoustic capacity CK) and/or a single diffraction interaction to be solved/handled. Said interaction narrows the trans mission band and is thus disadvantageous. In our studies, we have recognized how it is possible to take advantage of this detrimental interaction and thereby to expand the fre quency band. This is a particularly important finding because gradient generation, espe cially second-order gradient generation, can only be used in a narrow transmission band. We have further found that the bandwidth of a transmission band can be increased by reducing the delay time required in the second gradient generation at higher frequencies. The objects of the present invention are achieved by a second-order gradient loud speaker system according to Claim 1. Further preferred exemplary embodiments of the second-order gradient loudspeaker system of the invention are set forth in Claims 2 to 19. The objects of the present invention are further achieved by a second-order gradient line array speaker according to Claim 20 and a second-order gradient plane wave speaker according to Claim 21.
The main advantage of the second-order gradient loudspeaker system according to the invention is that its directivity factor Q is significantly higher at any frequencies in the frequency range of 50-2000 Hz than that of conventional loudspeaker systems, as well as conventional line array and plane wave speakers. Thereby, speech intelligibility im proves, especially in reverberant rooms, and the area where reinforced speech is well understood increases significantly, too. The second-order gradient loudspeaker system according to the invention increases the directivity in that frequency band wherein the room has the largest reverberation time and thus a high directivity factor is most needed. In outdoor spaces, the increased directivity of the loudspeaker system according to the invention reduces the environmental sound pollution. A further advantage of the second- order gradient loudspeaker system according to the present invention is that it can be produced at a relatively low cost.
In what follows, some possible embodiments of a second-order gradient (e.g., second- order cardioid) loudspeaker system according to the invention are exemplified, and its operation and properties will be described in more detail with reference to the drawings, in which
- Figure 1 shows a known first-order cardioid loudspeaker system;
- Figure 2 shows an equivalent electrical circuit diagram of the first-order cardioid loud speaker system illustrated in Figure 1;
- Figure 3 shows the transfer function Ai(kd,0), i.e. the frequency response, at different angles of a gradient generation which leads to a cardioid characteristic curve;
- Figure 4 shows a series of polar patterns for a gradient generation leading to a cardioid characteristic curve;
- Figure 5 illustrates the directivity factor Q as a function of (kd), i.e. frequency, for a gradient generation leading to a cardioid characteristic curve;
- Figure 6 shows the polar pattern of a second-order cardioid characteristic curve dis torted due to diffraction; - Figure 7 shows a second-order gradient loudspeaker system according to the invention in side view and in cross-section;
- Figure 8 is a block diagram of an amplifier and passive filters section of a second-order gradient loudspeaker system according to the invention;
- Figure 9 is a block diagram of an amplifier and active filter section of a second-order gradient loudspeaker system according to the invention;
- Figure 10 shows a line array speaker constructed by arranging second-order gradient loudspeaker systems according to the invention above one another; and
- Figure 11 shows a plane wave speaker constructed by arranging second-order gradi ent loudspeaker systems according to the invention above and beside one another.
Throughout this specification, the term ..loudspeaker” refers to a stand-alone electroa coustic transducer that converts electrical energy into acoustic energy with no additional components i.e. that generates sound waves in the air. The term ..loudspeaker system” is, however, used to refer to a device obtained by assembling one or more such loud speakers with one or more mechanical and/or acoustical and/or electrical components (e.g. a housing, funnel, sound guide, electronic components, etc.) to improve and/or modify the sound waves generated.
Figure 1 shows a known first-order cardioid loudspeaker system.
In Figure 1, a first-order gradient, more precisely a first-order cardioid-type loudspeaker system can be seen in a side view and in cross-section. In a cavity with the capacity of Co behind a loudspeaker LS, the box resonances are attenuated by a fibrous material E, e.g. rock wool or glass wool or foamed plastic, as sound absorbing material.
As shown, the acoustic impedance Zi is or may be composed of the acoustic resistance Ri and the acoustic mass Mi, wherein, generally, the acoustic resistance Ri is dominant. P denotes a cover that protects the acoustic resistance from mechanical impacts, the cover P is usually formed as a perforated plate.
Figure 2 shows an equivalent electrical circuit diagram of the first-order cardioid loud speaker system of Figure 1.
The loudspeaker LS is represented by an acoustic impedance ZM, which consists of an acoustic mass MM and an acoustic capacity CM, as well as an acoustic resistance RM. The gradient generation is performed by a network of acoustic elements (phase shift, phase rotator), namely the acoustic mass Mi, the acoustic resistance Ri, and the acous tic capacity Co formed by the volume located behind the membrane of the loudspeaker LS.
Figure 3 illustrates the transfer function Ai(kd,0), i.e. the frequency response, at different angles of a gradient generation leading to a cardioid characteristic curve.
The variable (kd) is proportional to the frequency, since k denotes the wavenumber, i.e. k = 2pί/o, that is, kd = 2nf*d/c can be written. Here, f stands for the frequency, c is the speed of sound measured in air, and d is the effective distance between two sound gates.
For Q = 0° (0 rad), the upper limit of cardioid gradient generation clearly locates at (kd)t = p. This upper limit depends on the type of polar pattern, i.e. the value of a (which varies between p and 2p). The transmission is discontinuous at this point, Ai(p,O) = 0 in the Figure, the corresponding frequency is the cutoff frequency ft of the gradient gener ation. It also follows that the limit for the operating frequency must be set lower than the upper limit, which corresponds to said cutoff frequency ft, to avoid distortions. It is pref erable to choose the limit for the operating frequency at the value of (kd)t/1.5, i.e. at which (kd) ~ 2 holds. Substituting the cutoff frequency ft and then arranging the relations, one gets that
Here, it has been also taken into account that the condition for an ideal theoretical cardi oid polar pattern is that the time constant d/c is equal to the delay time t between the two sound gates [cf. e.g. L.L. Beranek: Acoustics. 1986 Edition, Cambridge, USA, p. 149-150]
Figure 4 shows a series of polar patterns for a gradient generation leading to a cardioid characteristic curve, that is, it shows a series of relative polar patterns Drei(kd,0) of the transfer function Ai(kd,0) for different (kd) parameters. One can see that in the case of (kd) = 2, the cardioid characteristic curve is distorted, but it is still acceptable. In the case of (kd) = 1.5, the cardioid polar pattern is, however, almost perfect.
Figure 5 shows the directivity factor Q as a function of (kd) for the gradient generation leading to a cardioid polar pattern, i.e. the frequency response of the directivity factor Q. The figure shows that for (kd) = 2, Q ~ 1.5, and for (kd) = 1.5, Q ~ 2 holds. The values show a distortion of the polar pattern, since for an ideal cardioid, Q = 3 should hold. Figure 6 shows the polar pattern of a second-order cardioid characteristic curve distorted due to diffraction. Figure 6 presents measurement data. Second-order cardioid polar patterns are distorted not only by the cutoff frequency of the gradient generation, but also by the interaction of two radiator elements arranged close to each other, as well as diffraction. Figure 7 shows two first-order gradient loudspeaker systems 1 , 2 arranged in close proximity to each other, one behind the other. In Figure 6, at a lower frequency (kd) = 0.6, an almost ideal second-order cardioid polar pattern can be seen. At a higher frequency (kd) = 2, the polar pattern is already distorted, partly due to the proximity of the cutoff frequency, partly due to the diffraction effect caused by the first loudspeaker system, and partly due to the effect of the cavity with width h (see Figure 7).
Figure 7 illustrates a second-order gradient loudspeaker system according to the invention in a side view and in cross-sectional view. The second-order gradient loudspeaker system consists of two first-order gradient loudspeaker systems 1, 2. Both loudspeaker systems 1, 2 have a single built-in loudspeaker LSi, LS2, respectively. The internal damping of the box is due to a fibrous material E, in the form of e.g. rock wool, glass wool, or a special foamed plastic. The loudspeakers LSi, LS2 are separated from one another by a distance d, while a cavity of width and/or height h is formed between said loudspeakers. According to the invention, this cavity is partially or completely filled with a sound-absorbing material EK. The sound-absorbing material EK can be rock wool, glass wool or a special foamed plastic. Being filled with (or without) the sound-absorbing material EK, a protective grille (or mesh) P of each loudspeaker system 1, 2 is covered on the inside with a grille cloth T, preferably made of a non-woven textile material (e.g. vetex), wherein the sound-absorbing material EK and the grille cloth T together provide an acoustic impedance ZK(RK,MK).
Figure 8 shows the block diagram of an amplifier and passive filters section of a second- order gradient loudspeaker system according to the invention.
Both passive first-order gradient loudspeaker systems 1, 2, i.e. the one located forward (front) and the other located backward (rear), receive the electrical signal from a common power amplifier Amp. A series connected second-order all-pass filter APFi, low-pass filter LPFi, and delay circuit n are connected to the loudspeaker LSi of the first-order gradient loudspeaker system 1. A series connected second-order all-pass filter APF2, low-pass filter LPF2, and delay circuit 12 are connected in reversed phase to the loudspeaker l_S2 0f the other first-order loudspeaker systems 2. The all-pass filters, the low- pass filters, and the delay circuits are all fabricated with passive electrical elements. Hereinafter, as it is anyway apparent to those skilled in the art, the term „all-through filter” refers to a filter that transmits a signal without any modification in its amplitude, i.e. , its frequency response is straight, but varies the phase of the signal passing through it as a function of frequency. A modified audio frequency electrical signal drives the first-order gradient loudspeaker systems 1, 2 through the above-listed elements, wherein the elec trical signal is modified differently by each enlisted element: the all-pass filters APF mod ify it in phase and running time, the low-pass filters LPF in phase, running time and am plitude, and the delay circuit t in running time and phase, to e.g. varying degrees de pending on the frequency.
Figure 9 shows the block diagram of an amplifier and active filters section of a second- order gradient loudspeaker system according to the invention.
Both passive first-order gradient loudspeaker systems 1, 2, i.e. the one located forward (front) and the other located backward (rear), receive the electrical signal from two dif ferent power amplifiers Ampi and Amp2. A series connected second-order all-pass filter APFi, low-pass filter LPFi, and delay circuit n are connected to the input of a power amplifier Ampi, and then the output of the power amplifier Ampi is connected to the loudspeaker LSi of the first-order gradient loudspeaker system 1. A series connected second-order all-pass filter APF2, low-pass filter LPF2, and delay circuit 12 are connected to the input of a power amplifier Amp2, and then the output of the power amplifier Amp2 is connected in reversed phase to the loudspeaker LS2 of the first-order gradient loud speaker system 2. Each all-pass filter and low-pass filter, as well as the delay circuits, are implemented with digital and/or analog electrical elements, preferably in a digital sig nal processor DSP, as is apparent to those skilled in the art.
Figure 10 shows a line array speaker obtained by stacking several second-order gradient loudspeaker systems according to the present invention on top of each other.
The figure shows a line array speaker arrangement formed of second-order cardioid loudspeaker systems. One can clearly see that the second-order gradient loudspeaker system, in this case a cardioid loudspeaker system, is multiplied and the individual units are placed one above the other, arranged e.g. in a frame or rack adapted to receive said loudspeaker systems. Thus, the shown horizontal second-order cardioid characteristic curve is enhanced vertically with an additional control gain, i.e. the directivity factor Q is further increased: a vertically enhanced, so-called bundled polar pattern is obtained.
Fig. 11 shows a plane wave speaker obtained by arranging several second-order gradi ent loudspeaker systems according to the present invention on top of each other and next to each other.
Here, the second-order gradient loudspeaker systems are placed not only on top of each other, but also next to each other, arranged in suitable frames or racks, so that they essentially form a plane wave speaker. Thus, in addition to gradient generation, the col umn effect also increases the directivity factor Q from both directions and narrows the polar pattern, increasing thereby significantly the value of said directivity factor Q.

Claims

1. A second-order gradient loudspeaker system comprising two first-order gradient loudspeaker systems (1, 2) with loudspeaker (LSi, LS2) arranged at a distance d from one another, said two first-order gradient loudspeaker systems (1, 2) are located substantially one behind the other and a cavity of width h is present there between, the cavity has a volume with an acoustic capacity CK, characterized in that the first-order gradient loudspeaker systems (1 , 2) are of passive design, that is, each of said systems (1, 2) is formed as an acoustic network consisting of passive acoustic elements having at least one of a passive acoustic mass (M), acoustic resistance (R) and acoustic capacity (C), said acoustic network com prises at least one phase rotating member capable of passive gradient generation, wherein said first-order gradient loudspeaker systems (1, 2) are driven by modified audio frequency electrical signals directly or through at least one element selected from the group consisting of all-pass filters (APF), low-pass filters (LPF) and delay circuits (t) in such a way that the rear first-order gradient loudspeaker system (2) is in reversed phase compared to the front first-order gradient loudspeaker (1), and the driving electrical signal of the rear system (2) is delayed by a total delay time t compared to the driving electrical signal of the front system (1), the total delay time t is given by d 0 £ t £ - , a c wherein c is the sound propagation velocity in air at a given temperature; and a is a factor that defines the required type of the polar pattern of the second- order gradient loudspeaker system within a range extending from cardioid to „8”-shaped, or bidirectional.
2. The second-order gradient speaker system according to claim 1, characterized in that each first-order gradient loudspeaker system (1, 2) has a cardioid polar pattern, and if the condition x=d/c fulfils, the polar pattern of the second-order gra dient loudspeaker system is a second-order cardioid.
3. The second-order gradient speaker system according to claim 1 or 2, characterized in that the delay time t and the cutoff frequency ft of the gradient generation fulfil the relation
4. The second-order gradient speaker system according to claim 1 or 2, characterized in that each first-order gradient loudspeaker system (1 , 2) has a hypercardioid polar pattern, and if the condition t=0 fulfils, the polar pattern of the second-order gradient loudspeaker system is the most strongly directed second-order hypercar dioid with a maximum directivity factor of Q = 8.
5. The second-order gradient speaker system according to any one of claims 1 to 4, characterized in that the value of the acoustic mass (M2) in the acoustic network of the rear first-order gradient loudspeaker system (2) is greater than the value of the acoustic mass (Mi) in the acoustic network of the front first-order gradient loud speaker system (1).
6. The second-order gradient speaker system according to any one of claims 1 to 5, characterized in that the cavity of width h and acoustic capacity CK being present between the first-order gradient loudspeaker systems (1 , 2) is at least partially filled with a sound-absorbing material (EK).
7. The second-order gradient speaker system according to claim 6, characterized in that the sound-absorbing material (EK) is at least one of rock wool, glass wool, a foamed plastic or any combination thereof.
8. The second-order gradient speaker system according to any one of claims 1 to 7, characterized in that a protective grille (P) encloses the cavity of width h and acoustic capacity CK being present between the first-order gradient loudspeaker systems (1, 2).
9. The second-order gradient speaker system according to claim 8, characterized in that the protective grille (P) is made of textile (T), preferably a non-woven textile.
10. The second-order gradient speaker system according to any one of claims 1 to 9, characterized in that the cavity of width h and acoustic capacity CK being present between the first-order gradient loudspeaker systems (1 , 2) is at least partially filled with a sound-absorbing material (EK) and enclosed by a protective grille (P), wherein the sound-absorbing material (EK) and the protective grille (P) together have an overall acoustic impedance ZK(RK, MK), and wherein the time constant of the acoustic resistance RK and the acoustic capacity CK fulfils the relation
RK ' CK < 2 ~Jt -
11. The second-order gradient speaker system according to any one of claims 1 to 10, characterized in that the delay time t of the reversed phase audio frequency elec trical signal of the rear first-order gradient loudspeaker system (2) is generated by a delay unit (12).
12. The second-order gradient speaker system according to any one of claims 1 to 10, characterized in that the rear first-order gradient loudspeaker system (2) is driven by the reversed phase audio frequency electrical signal through at most two sec ond-order low pass-filters (LPF2), and the front first-order gradient loudspeaker system (1) is directly driven by the audio frequency electrical signal and, thus, the delay time t is generated by a phase shift, i.e. delay time, of said second-order low pass-filters (LPF2).
13. The second-order gradient speaker system according to any one of claims 1 to 10, characterized in that the rear first-order gradient loudspeaker system (2) is driven by the reversed phase audio frequency electrical signal through two second-order low pass-filters (LPF2), and the front first-order gradient loudspeaker system (1) is driven by the audio frequency electrical signal through a single second-order all pass-filter (APFi), said filters being designed in such a way that the delay time t is equal to the difference between the delay time generated by said second-order low pass-filters (LPF2) and the delay time generated by said second-order all pass- filters (APF^.
14. The second-order gradient speaker system according to any one of claims 1 to 10, characterized in that the rear first-order gradient loudspeaker system (2) is driven by the reversed phase audio frequency electrical signal through at least one ele ment selected from a group consisting of n-th order low-pass filters (LPF2), n-th order all-pass filters (APF2) and a delay circuit (12), and the front first-order gradient loudspeaker system (1) is driven by the audio frequency electrical signal through at least one element selected from a group consisting of n-th order low-pass filters (LPFi), n-th order all-pass filters (APF1) and a delay circuit (n), wherein said filters are designed and/or the filtering parameters, that is, the degree (n), the resonance frequency (fo) and the quality factor (Qo) of the filters are set in such a way that the delay time t of the rear first-order gradient loudspeaker system (2) is equal to the difference between the delay time generated by said filters and the delay time gen erated by the delay circuits.
15. The second-order gradient speaker system according to any one of claims 1 to 14, characterized in that the delay time t is frequency dependent.
16. The second-order gradient speaker system according to claim 15, characterized in that the delay time t varies as a function of the frequency, preferably, the delay time t is smaller at higher frequencies.
17. The second-order gradient speaker system according to any one of claims 1 to 16, characterized in that the first-order gradient loudspeaker systems (1 , 2) are driven by an electrical signal from an output of a common power amplifier (Amp), and each all-pass filter (APFi, APF2), each low-pass filter (LPFi, LPF2) and each delay circuit (ti, 12) is fabricated with passive electric elements.
18. The second-order gradient speaker system according to any one of claims 1 to 16, characterized in that the first-order gradient loudspeaker systems (1 , 2) are driven by electrical signals from outputs of at least two different power amplifiers (Ampi, Amp2), and each all-pass filter (APFi, APF2), each low-pass filter (LPFi, LPF2) and each delay circuit (n, 12) is fabricated with passive and/or active electric elements, wherein the active electric elements and each of the all-pass filters (APFi, APF2), the low-pass filters (LPFi, LPF2) and the delay circuits (n, 12) comprise one or more digital signal processors (DSP).
19. The second-order gradient speaker system according to any one of claims 1 to 18, characterized in that the second-order gradient speaker system is designed for low frequencies and is formed as a subwoofer.
20. A second-order gradient line array speaker, characterized in that the second-or der gradient line array speaker comprises at least two second-order gradient speaker systems according to any one of claims 1 to 19 arranged on top of each other.
21. A second-order gradient plane wave speaker, characterized in that the second- order gradient plane wave speaker comprises at least two second-order gradient speaker systems according to any one of claims 1 to 19 arranged on top of each other and next to each other.
EP19958748.6A 2019-10-27 2019-10-29 Second-order gradient loudspeaker system, as well as second-order gradient line array speaker and plane wave speaker constructed from such loudspeaker systems Pending EP4049460A2 (en)

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HU1900369A HUP1900369A1 (en) 2019-10-27 2019-10-27 Second order gradient speaker further second order gradient line speaker and surface speaker built from said speakers
PCT/HU2019/050047 WO2021176240A2 (en) 2019-10-27 2019-10-29 Second-order gradient loudspeaker system, as well as second-order gradient line array speaker and plane wave speaker constructed from such loudspeaker systems

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US3283848A (en) * 1965-10-21 1966-11-08 Patti Thomas Allan Sound reproduction system
SU1184110A1 (en) * 1981-03-17 1985-10-07 Vnii Radiovesh Priema Akustiki Acoustic radiator
US5870484A (en) * 1995-09-05 1999-02-09 Greenberger; Hal Loudspeaker array with signal dependent radiation pattern
US7813516B1 (en) * 2006-07-24 2010-10-12 Graber Curtis E System for cardioid sound field generation from dissimilar sources
US10123111B2 (en) * 2016-06-03 2018-11-06 Fulcrum Acoustic, LLC Passive cardioid speaker

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