Patent Publication Number: US-2010124342-A1

Title: Forced acoustic dipole and forced acoustic multipole array using the same

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims the benefit of Korean Patent Application Nos. 10-2008-0113832, filed Nov. 17, 2008, and 10-2009-0030182, filed Apr. 8, 2009, the disclosures of which are hereby incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a forced acoustic dipole and a forced acoustic multipole array using the same, and more particularly, to a forced acoustic dipole in which a direction of an acoustic lobe can be freely steered and a forced acoustic multipole array using the same. 
     2. Description of Related Art 
     When an ordinary speaker is used for reproducing sound, there is auditory disturbance to others because of a natural radiating characteristic of sound. For this reason, headphones and earphones are used as personal acoustic devices for minimizing auditory disturbance to others and maintaining privacy, but this introduces a problem of sensory occlusivity. Accordingly, a personal acoustic system capable of minimizing auditory disturbance to others while overcoming the problem of sensory occlusivity is required. 
     As an example of such a personal acoustic system, a line speaker array system generating a directional lobe using a line speaker array has been disclosed. 
     The line speaker array system is configured to make an acoustic signal pass through a digital filter adjusted to be directional and output it, and thus it is possible for a sound to be heard at a designated location. 
     However, the line speaker array system has the following disadvantages. Since a filter must be attached to each speaker, the greater the number of speakers, the more complicated the structure of the system becomes. A side lobe is generated due to bad spatial resolution in high frequencies. Further, since a length of the speaker array should be lengthened in proportion to a wavelength to control sound in low frequencies, a range of controllable frequencies is limited by the length of the speaker array. In particular, because an optimum directional characteristic changes according to a frequency due to a fixed location of the speakers, many filters are required and optimum filter coefficients must be calculated one by one to obtain optimum directional characteristics at each frequency. 
     Recently, a simple speaker system using an acoustic dipole has been disclosed in order to overcome the above problems. However, this speaker system has a limit in that a direction of an acoustic lobe in which a sound can be heard cannot be freely steered due to characteristics of an acoustic dipole. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to providing a forced acoustic dipole in which a direction of an acoustic lobe can be freely steered and a forced acoustic multipole array using the same. 
     One aspect of the present invention provides a forced acoustic dipole including: a phase and sound pressure adjustment circuit configured to adjust phase and sound pressure of input signals; and first and second sound sources configured to receive the input signals whose phase and sound pressure are adjusted by the phase and sound pressure adjustment circuit, respectively, and output the received signals as first and second acoustic signals in an audible frequency. 
     Meanwhile, another aspect of the present invention provides a forced acoustic multipole array including a plurality of forced acoustic dipoles which are arranged in a matrix. Here, each of the forced acoustic dipoles includes: a phase and sound pressure adjustment circuit configured to adjust phase and sound pressure of input signals; and first and second sound sources configured to receive the input signals, respectively, and output the received signals as first and second acoustic signals in an audible frequency. 
     The first and second acoustic signals output from the first and second sound sources may be offset or amplified by the phase and sound pressure adjustment circuit to steer a direction of an acoustic lobe according to the first and second acoustic signals in a particular direction. 
     The phase and sound pressure adjustment circuit may include an inverting circuit configured to input signals having opposite phases to each other into the first and second sound source, respectively. The inverting circuit may include: a connecting line configured to input the input signals into terminals having different polarities from each other of the first and second sound source; and an inverter or a digital signal processor configured to invert the phase of the input signal input into the first sound source and input the phase-inverted signal into the second sound source. 
     Meanwhile, the phase and sound pressure adjustment circuit may include a digital signal processor configured to adjust phase and sound pressure of the input signal in a time domain or a digital signal processor configured to adjust phase and sound pressure of the input signal in a frequency domain. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The above and other features of the present invention will be described in reference to certain exemplary embodiments thereof with reference to the attached drawings in which: 
         FIGS. 1A and 1B  are diagrams for describing a basic configuration of a forced acoustic dipole; 
         FIG. 2  illustrates an inverting circuit for inputting input signals having opposite phases to each other into first and second sound sources of a forced acoustic dipole, respectively, according to a first exemplary embodiment of the present invention; 
         FIG. 3  illustrates an inverting circuit for inputting input signals having opposite phases to each other into first and second sound sources of a forced acoustic dipole, respectively, according to a second exemplary embodiment of the present invention; 
         FIG. 4  illustrates an inverting circuit for inputting input signals having opposite phases to each other into first and second sound sources of a forced acoustic dipole, respectively, according to a third exemplary embodiment of the present invention; 
         FIGS. 5A ,  5 B and  5 C are diagrams for explaining why an acoustic radiating characteristic of a forced acoustic dipole varies; 
         FIG. 6  is a diagram illustrating a direction of an acoustic lobe generated when a forced acoustic multipole array is configured by arranging two forced acoustic dipoles of the present invention in one row and two columns; 
         FIG. 7  is a diagram illustrating a direction of an acoustic lobe generated when a forced acoustic multipole array is configured by arranging four forced acoustic dipoles of the present invention in two rows and two columns; 
         FIG. 8  illustrates a phase and sound pressure adjustment circuit for adjusting phase and sound pressure of an input signal input into first and second sound sources of a forced acoustic dipole, respectively, according to a first exemplary embodiment of the present invention; 
         FIGS. 9A and 9B  illustrate a phase and sound pressure adjustment circuit for adjusting phase and sound pressure of an input signal input into first and second sound sources of a forced acoustic dipole, respectively, according to a second exemplary embodiment of the present invention; and 
         FIG. 10  is a diagram illustrating a direction of an acoustic lobe generated when a forced acoustic multipole array is configured by arranging forced acoustic dipoles having adjustable phase and sound pressure in n rows and m columns. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinafter, exemplary embodiments of the present invention will be described in detail. 
     To facilitate understanding of the present invention, a forced acoustic dipole will be described in brief below. 
       FIGS. 1A and 1B  are diagrams for describing a basic configuration of a forced acoustic dipole. 
     Referring to  FIG. 1A , when an input signal of in-phase Φ is input into a positive terminal (+) of a first sound source  110 , a diaphragm vibrates forward and an acoustic signal of in-phase θ is output. When an input signal of out-of-phase −Φ is input into a positive terminal (+) of a second sound source  120 , a diaphragm vibrates in a reverse direction and an acoustic signal of out-of-phase −θ is output. 
     The forced acoustic dipole uses acoustic characteristics of the first and second sound sources  110  and  120  as above. As shown in  FIG. 1B , when the forced acoustic dipole is configured to arrange the first sound source  110  for outputting an acoustic signal of in-phase θ and the second sound source  120  for outputting an acoustic signal of out-of-phase −θ to be adjacent to each other, the two acoustic signals θ and −θ output from the first and second sound sources  110  and  120  are offset or amplified, and thus an acoustic lobe is generated in front and rear directions of the forced acoustic dipole  100 . 
     Herein, the first and second sound sources  110  and  120  may be implemented with one of a Voice Coil Motor type speaker, a piezoelectric speaker, an ultrasonic transducer and so on, in order to convert an input signal into an acoustic signal of audio frequency and output it. 
     In the forced acoustic dipole  100  according to the present invention, the direction of the acoustic lobe can be freely steered by controlling the phase and sound pressure of the input signals input into the first and second sound sources  110  and  120 . This will be described in further detail below. 
     An inverting circuit for inputting input signals having opposite phases to each other into the first and second sound sources, respectively, will be first described, and thereafter, a phase and sound pressure adjustment circuit for adjusting phase and sound pressure of the input signals input into the first and second sound sources will be described. 
       FIG. 2  illustrates an inverting circuit for inputting input signals having opposite phases to each other into the first and second sound sources  110  and  120  of the forced acoustic dipole  100 , respectively, according to a first exemplary embodiment of the present invention. 
     Referring to  FIG. 2 , an input signal of in-phase Φ is input into a positive terminal (+) of the first sound source  110 , and a ground is connected to a negative terminal (−) of the first sound source  110 . On the other hand, in the second sound source  120 , a ground is connected to a positive-terminal (+), and an input signal of in-phase Φ is input into a negative-terminal (−). 
     In this way, the input signal of in-phase Φ is input into terminals having different polarities from each other of the first and second sound sources  110  and  120 , and thus input signals having opposite phases to each other are input into the first and second sound sources  110  and  120 , respectively. 
       FIG. 3  illustrates an inverting circuit for inputting input signals having opposite phases to each other into the first and second sound sources  110  and  120  of the forced acoustic dipole  100 , respectively, according to a second exemplary embodiment of the present invention. 
     Referring to  FIG. 3 , an input signal of in-phase Φ is input into a positive terminal (+) of the first sound source  110 , and the input signal of in-phase Φ is inverted by an inverter IVT so that an input signal of out-of-phase −Φ is input into a positive terminal (+) of the second sound source  120 . 
       FIG. 4  illustrates an inverting circuit for inputting input signals having opposite phases to each other into the first and second sound sources  110  and  120  of the forced acoustic dipole  100 , respectively, according to a third exemplary embodiment of the present invention. 
     Referring to  FIG. 4 , an input signal of in-phase Φ is input as an input signal CH 1  of the first sound source  110  via a digital signal processor DSP 1 . The input signal of in-phase Φ is inverted by a phase inverter  130  inside the digital signal processor DSP 1 , so that an input signal of out-of-phase −Φ is input as an input signal CH 2  into a positive terminal (+) of the second sound source  120 . 
     In this case, it is possible to adjust the phase of the input signal CH 1  input into the first sound source  110  according to necessity. 
     Meanwhile, the acoustic radiating characteristics of the forced acoustic dipole  100  vary according to the distance between the first sound source  110  and the second sound source  120  and a difference in phase of the input signals input into the first and second sound sources  110  and  120 , respectively. This will be described in further detail below. 
       FIGS. 5A ,  5 B and  5 C are diagrams for explaining why acoustic radiating characteristics of the forced acoustic dipole  100  vary. 
     As illustrated in  FIG. 5A , when a distance between the first sound source  110  and the second sound source  120  is d 1  and a difference in phase of input signals input into the first and second sound sources  110  and  120  is Φ 1 , acoustic signals output from the first and second sound sources  110  and  120  reinforce each other, and thus a loud sound is heard by a listener. 
     However, as illustrated in  FIG. 5B , when a distance between the first sound source  110  and the second sound source  120  is d 2  and a difference in phase of input signals input into the first and second sound sources  110  and  120  is Φ 2 , acoustic signals output from the first and second sound sources  110  and  120  are offset each other, and thus no sound is heard by the listener. 
     In this state, as illustrated in  FIG. 5C , when the difference in phase of input signals input into the first and second sound sources  110  and  120 , Φ 1 , is equal to the sum of Φ 2  and α by shifting the phase of the input signal input into the second sound source  120  by α, acoustic signals output from the first and second sound sources  110  and  120  reinforce each other, and thus a loud sound is heard again by the listener. 
     Consequently, the acoustic radiating characteristics of the forced acoustic dipole  100  vary according to the distance between the first sound source  110  and the second sound source  120  and the difference in phase of input signals input into the first and second sound sources  110  and  120 , respectively. 
     In other words, a listener can hear a sound continuously by either changing the distance between the first sound source  110  and the second sound source  120  or shifting the difference in phase of input signals input into the first and second sound sources  110  and  120 , respectively, even if the listener&#39;s location is changed. 
     But, because physically changing the distance between the first sound source  110  and the second sound source  120  whenever the listener&#39;s location is changed is very difficult, in the present invention, the acoustic radiating characteristics of the forced acoustic dipole  100  may be controlled by shifting the difference in phase of input signals input into the first and second sound sources  110  and  120 , respectively. This will be described in further detail below. 
       FIG. 6  is a diagram illustrating a direction of an acoustic lobe generated when a forced acoustic multipole array is configured by arranging two forced acoustic dipoles of the present invention in one row and two columns. For convenience of explanation, the forced acoustic dipoles shown in  FIGS. 2 to 4  are illustrated as blocks. 
     First, when input signals of in-phase and out-of-phase are input into first and second sound sources  110   a  and  120   a  of a first forced acoustic dipole  100   a , respectively, and input signals of in-phase and out-of-phase are input into first and second sound sources  110   b  and  120   b  of a second forced acoustic dipole  100   b , respectively, as shown in an acoustic lobe  610 , sound is heard only in front and rear directions of a forced acoustic multipole array  200   a , and not on left and right sides thereof. 
     Second, when an input signal of in-phase is input into the first sound source  110   a  of the first forced acoustic dipole  100   a , an input signal of out-of-phase is input into the second sound source  120   b  of the second forced acoustic dipole  100   b  and the remaining sound sources are off, an acoustic lobe  620  is generated. 
     Third, when input signals of in-phase are input into the first and second sound sources  110   a  and  120   a  of the first forced acoustic dipole  100   a  and input signals of out-of-phase are input into the first and second sound sources  110   b  and  120   b  of the second forced acoustic dipole  100   b , as shown in an acoustic lobe  630 , sound is heard only in left and right sides of the forced acoustic dipole. 
     Fourth, when an input signal of out-of-phase is input into the second sound source  120   a  of the first forced acoustic dipole  100   a , an input signal of in-phase is input into the first sound source  110   b  of the second forced acoustic dipole  100   b  and the remaining sound sources are off, an acoustic lobe  640  is generated. 
       FIG. 7  is a diagram illustrating a direction of an acoustic lobe generated when a forced acoustic multipole array is configured by arranging four forced acoustic dipoles of the present invention in two rows and two columns. 
     Referring to  FIG. 7 , in a forced acoustic multipole array  200   b  including four forced acoustic dipoles  100   a  to  100   d  arranged in two rows and two columns, a direction of an acoustic lobe is changed similarly to the forced acoustic multipole array  200   a  including two forced acoustic dipoles arranged in one row and two columns, but the width of an acoustic lobe  750  becomes narrower. 
     Consequently, by adjusting the phases of input signals which are input into the first and second sound sources  110  and  120  of each forced acoustic dipole  100 , respectively, or adjusting the sound pressures of input signals which are input into the first and second sound sources  110  and  120  including turning the first and second sound sources  110  and  120  on or off, it is possible to freely change the directions and widths of acoustic lobes of the forced acoustic multipole arrays  200   a  and  200   b.    
     Next, a phase and sound pressure adjustment circuit for adjusting phase and sound pressure of input signals input into the first and second sound sources  110  and  120 , respectively, will be described. 
       FIG. 8  is a diagram illustrating a phase and sound pressure adjustment circuit for adjusting phase and sound pressure of input signals input into first and second sound sources  110  and  120  of a forced acoustic dipole  100 ′, respectively, according to a first exemplary embodiment of the present invention. 
     Referring to  FIG. 8 , an input signal of in-phase Φ is input as an input signal CH 1  of the first sound source  110  via a digital signal processor DSP 2 . The input signal of in-phase Φ is phase-shifted by a by a phase shifter  131  inside the signal processor DSP 2  and the sound pressure thereof is adjusted by a factor of k. Then, the input signal of in-phase Φ is input as an input signal CH 2  of the second sound source  120 . 
     More specifically, the input signal of in-phase Φ is input into the first sound source  110 , but, an input signal k(Φ+α) having a phase shifted by a in comparison with the input signal of in-phase Φ and a sound pressure adjusted by a factor of k is input into the second sound source  120 . 
     In other words, when a listener&#39;s location is changed, it is possible to freely change the direction of the acoustic lobe of the forced acoustic dipole  100 ′ without changing the distance between the first sound source  110  and the second sound source  120  by adjusting phase and sound pressure of input signals input into the first and second sound sources  110  and  120 , respectively. 
       FIGS. 9A and 9B  are diagrams illustrating a phase and sound pressure adjustment circuit for adjusting phase and sound pressure of input signals input into the first and second sound sources  110  and  120  of the forced acoustic dipole  100 ′, respectively, according to a second exemplary embodiment of the present invention. 
     Referring to  FIG. 9A , an input signal of in-phase Φ is input as an input signal CH 1  of the first sound source  110  via a digital signal processor DSP 3 . The input signal of in-phase Φ is transformed into a signal of a frequency domain by a fast Fourier transform (FFT) unit  135  inside the signal processor DSP 3 . Here, the phase is shifted by a and the sound pressure is adjusted by a factor of k in each frequency spectrum by a phase and sound pressure adjustment portion  137 . The input signal having the shifted phase and adjusted sound pressure is again transformed into a signal of a time domain by an inverse FFT (IFFT) unit  139 , and thus input as an input signal CH 2  of the second sound source  120 . 
     Accordingly, as shown in  FIG. 9B , in the input signal CH 2  of the second sound source  120 , the sound pressure (amplitude) is decreased by a factor of k and the phase is shifted by α, and thus the input signal CH 2  has the same phase and sound pressure as the input signal CH 1  of the first sound source  110 . 
       FIG. 10  is a diagram illustrating a direction of an acoustic lobe generated when a forced acoustic multipole array  200   c  is configured by arranging forced acoustic dipoles  100 ′ having adjustable phase and sound pressure in n rows and m columns (where m and n are integers greater than 1). 
     Referring to  FIG. 10 , when input signals input into first and second sound sources  110  and  120  of each forced acoustic dipole  100 ′ are phase-shifted at different angles and sound pressures thereof are properly adjusted, acoustic signals having various phases and sound pressures are output, respectively, and thus the direction of an acoustic lobe can be controlled more precisely. 
     Consequently, the present invention provides a forced acoustic dipole in which a direction of an acoustic lobe can be freely steered by controlling phase and sound pressure of input signals input into first and second sound sources, respectively, and thus it is possible to output a sound in a desired location and realistic acoustic effects can be provided without auditory disturbance to others. 
     While the invention has been shown and described with reference to certain exemplary embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing from the spirit and scope of the invention as defined by the appended claims.