This invention relates to array speaker systems in which a plurality of speaker units are arrayed in a one-dimensional manner or a two-dimensional manner.
Conventionally, array speaker systems in which a plurality of speakers are regularly arranged so as to reproduce and output sounds are known. In these array speaker systems, as a form of trouble due to the use of plural speakers, there occurs a phenomenon in which as reproduced audio frequencies become higher, so-called beams and comb shapes (i.e., sounds are spread in a comb-shape manner) emerge in audio emission characteristics, which vary in response to frequencies and which make it difficult to realize audition of high-frequency sound outside of an audio emission center position, or in which frequency characteristics greatly vary in response to listening positions.
As shown in the aforementioned drawings, beams and comb shapes apparently occur in audio emission characteristics with respect to audio frequencies of several kilo Hz or higher.
In order to avoid the occurrence of this phenomenon, a Bessel array method in which by imparting weights using a string of coefficients based on a first-order Bessel function to a string of regularly arranged speakers, audio emission characteristics are made to be spherical is known. For example, Japanese Examined Patent Application Publication No. HO 1-25480 discloses a simplified Bessel array.
Herein, the weight coefficients C1 to C15 are each calculated based on the first-order Bessel function that is defined by the following equation.
In this example in which fifteen speaker units are used, values of J−7(x) to J7(x) according to the aforementioned equation are used. When x=6.0, it is possible to produce weight coefficients C1 to C15 imparted to the fifteen speakers as follows:
C1=J−7(6)=−0.1296
C2=J−6(6)=0.2458
C3=J−5(6)=−0.3621
C4=J−4(6)=0.3576
C5=J−3(6)=−0.1148
C6=J−2(6)=−0.2429
C7=J−1(6)=0.2767
C8=J0(6)=0.1506
C9=J1(6)=−0.2767
C10=J2(6)=−0.2429
C11=J3(6)=0.1148
C12=J4(6)=0.3576
C13=J5(6)=0.3621
C14=J6(6)=0.2458
C15=J7(6)=0.1296
Compared with
However, as the weight coefficients C1 to C15 based on the Bessel function include negative values, audio emission characteristics in low frequency ranges may deteriorate; therefore, it is difficult to reproduce low-frequency sound. In particular, such a phenomenon brings a bad result in array speaker systems in which plural speaker units are installed in common enclosures or common enclosures of the bass-reflex type.
In consideration of the aforementioned circumstances, it is an object of the present invention to provide an array speaker system in which in a broad range of frequencies ranging from low frequencies to high frequencies, it is possible to avoid the occurrence of beams and comb shapes in audio emission characteristics and to efficiently realize audio emission.
An array speaker system of this invention is constituted by arraying a plurality of speaker units, wherein all speaker units are driven with the same phase in response to signals of low-frequency ranges, while the speaker units are separately driven with weight coefficients based on a Bessel function in response to signals of high-frequency ranges.
Alternatively, it is possible to drive all speaker units with the same phase and with the same gain in response to-signals of low-frequency ranges.
In addition, all-pass filters that are set up to realize phase rotation of 180° in high-frequency ranges are arranged, so that speaker units whose weight coefficients based on the Bessel function have negative values are driven with absolute values of weight coefficients, which are imparted to signals supplied thereto by way of the all-pass filters, while other speaker units whose weight coefficients based on the Bessel function do not have negative values are directly driven with the weight coefficients thereof without the intervention of the all-pass filters.
Furthermore, in an array speaker system of this invention, there are provided all-pass filters that are set up to realize phase rotation of 180° in high-frequency ranges, means that are respectively connected to speaker units whose weight coefficients based on the Bessel function have negative values so as to impart gain characteristics corresponding to absolute values of weight coefficients to signal components of high-frequency ranges within signals input thereto by way of the all-pass filters, and means that are respectively connected to speaker units whose weight coefficients based on the Bessel function do not have negative values so as to impart gain characteristics corresponding to weight coefficients to signal components of high-frequency ranges.
The aforementioned all-pass filters can be set up in such a way that the phase rotation thereof is set to 90° with respect to frequencies in proximity to frequencies corresponding to wavelengths corresponding to widths of speaker units.
Furthermore, in an array speaker system of this invention, there are provided filter means for dividing input signals into signal components of low-frequency ranges and signal components of high-frequency ranges, weighting means that are respectively connected to speaker units so as to impart weight coefficients based on the Bessel function to signal components of high-frequency ranges, and addition means that are respectively connected to speaker units so as to add signal components of low-frequency ranges to signal components of high-frequency ranges, to which weight coefficients based on the Bessel function are imparted by the weighting means, thus outputting addition results to the speaker units.
Incidentally, in the array speaker system of this invention, a plurality of speaker units are installed in a common enclosure or a common enclosure of a bass-reflex type, for example.
Preferred embodiments of this invention will be described in detail with reference to the accompanying drawings.
First, a description will be given with respect to the basic principle of an array speaker system of this invention.
As shown in audio emission characteristics shown in
Hereinafter, a description will be given with respect to an array speaker system of this invention in which speaker units are each driven with the positive phase in low-frequency ranges and are each driven with weight coefficients based on the Bessel function in high-frequency ranges.
In addition, the present embodiment is designed such that speaker units are each driven with the positive phase in low-frequency ranges and are each driven with weight coefficients based on the Bessel function in high-frequency ranges. For this reason, the present embodiment uses all-pass filters whose phases vary by 180° in high-frequency ranges.
In
A reference numeral 3 designates an all-pass filter whose amplitude characteristics are flat over all frequency ranges and whose phase characteristics realize phase rotation of 0° in low-frequency ranges but are reversed by way of variation of 180° in high-frequency ranges.
In
That is, signals to which weight coefficients are applied in the corresponding weighting means are respectively supplied to the speaker units 1-2, 1-4, 1-7, 1-8, and 1-11 to 1-15 whose weight coefficients based on the Bessel function have positive values. In addition, weighting having the same phase (i.e., the same polarity) as the weighting applied to the speaker units whose weight coefficients based on the Bessel function have positive values is applied to the speaker units 1-1, 1-3, 1-5, 1-6, 1-9, and 1-10 whose weight coefficients based on the Bessel function have negative values with respect to low-frequency signals on which the all-pass filter 3 effects phase rotation not exceeding 90°. In contrast, with respect to high-frequency signals on which the all-pass filter 3 effects phase rotation exceeding 90°, weighting having the reverse phase (i.e., the reverse polarity) as the weighting applied to the speaker units whose weight coefficients based on the Bessel function have positive values is applied to them.
That is, in high-frequency ranges, negative weight coefficients are applied to the speaker units whose weight coefficients based on the Bessel function have negative values, thus making the weight coefficients based on the Bessel function operate effectively. In low-frequency ranges, signals having the same phase are supplied to the corresponding speaker units; therefore, it is possible to reproduce low-frequency sound with a sufficient amplitude.
Compared with the foregoing audio emission characteristics shown in
Incidentally, the all-pass filter 3 is not necessarily formed using an analog filter as shown in
For instance, suppose that the analog all-pass filter 3 shown in
It is subjected to bilinear transform in a Z-axis region by use of the following formula.
Hence, it is transformed as follows:
In the above, when C=0.047 μF, R=4.7 kΩ, and sampling frequency fs=48 Hz, it is represented as follows:
This digital filter can be formed using an IIR (Infinite Impulse Response) filter shown in
As described above, the speaker units each have different weight coefficients based on the Bessel function. For example, in the case of the weight coefficients C1 to C15 shown in
A second embodiment of this invention, which is designed to eliminate the aforementioned drawback, will be described with reference to
In the second embodiment, filters that have the same gain with respect to low-frequency ranges and that have gains in response to weight coefficients based on the Bessel function with respect to high-frequency ranges are used as weighting means. That is, a reference speaker unit is set up; then, flat gain characteristics are applied to the reference speaker unit. For the other speaker units, the same gain as the gain of the reference speaker unit is set with respect to low-frequency ranges; and filters having gain characteristics, which represent ratios of weight coefficients of the other speaker units, compared with the weight coefficient of the reference speaker unit, are used as weighting means with respect to high-frequency ranges. Incidentally, similarly to in the aforementioned first embodiment, the output of the all-pass filter 3 is directly supplied to the speaker units whose weight coefficients based on the Bessel function have negative values.
In
As absolute values of weight coefficients applied to the speaker units 1-2 to 1-4, 1-6 to 1-10, and 1-12 to 1-14 are greater than the absolute value 0.1296 of the weight coefficient applied to the reference speaker unit, high-pass filters 4-2 to 4-4, 4-6 to 4-10, and 4-12 to 4-14, each of which is a so-called shelving type, are connected to them. These high-pass filters have flat gain characteristics in low-frequency ranges; and they also have gain characteristics that are increased in response to ratios of the weight coefficients applied to the corresponding speaker units compared with the reference weight coefficient C1 (C15) with respect to high-frequency ranges.
Both of the weight coefficients applied to the other speaker units 1-5 and 1-11 are set to 0.1148, which is lower than the reference weight coefficient 0.1296. Hence, high-cut filters of the shelving type that have flat gain characteristics in low-frequency ranges and that also have gain characteristics, which are decreased in response to ratios of the weight coefficients thereof compared with the reference weight coefficient C1, are connected to them.
In the circuits shown in
In each of the high-pass filter and high-cut filter shown in
For example, with respect to the high-pass filter 4-2 having the weight coefficient C2=0.2458, circuit constants thereof (i.e., R3=36 kΩ, C=3300 pF) are determined in order for the gain thereof in high-frequency ranges to be increased by 20 log(0.2458/0.1296)=5.56 dB compared with the gain of the amplifier 4-1 connected to the reference speaker unit 1-1, i.e., it is set to 3.07+5.56=8.63 dB. With respect to the high-pass filter 4-3, circuit constants thereof (i.e., R3=18 kΩ, C=5600 pF) are determined in order for the gain thereof in high-frequency ranges to be set to 20 log(0.3621/0.1296)+3.07=12.0 dB. Similarly, with respect to the high-pass filter 4-4, the gain thereof is set to 20 log(0.3576/0.1296)+3.07=11.9 dB, which is approximately identical to the gain of the high-pass filter 4-3; hence, circuit constants thereof (i.e., R3=18 kΩ, C=5600 pF) are similarly set up. Based on similar calculations, circuit constants of R3=36 kΩ and C=3300 pF are set with respect to the high-pass filter 4-6; circuit constants of R3=30 kΩ and C=3900 pF are set with respect to the high-pass filter 4-7; circuit constants of R3=20 kΩ and C=1000 pF are set with respect to the high-pass filter 4-8; circuit constants of R3=30 kΩ and C=3900 pF are set with respect to the high-pass filter 4-9; circuit constants of R3=36 kΩ and C=3300 pF are set with respect to the high-pass filter 4-10; circuit constants of R3=18 kΩ and C=5600 pF are set with respect to the high-pass filter 4-12; circuit constants of R3=18 kΩ and C=5600pF are set with respect to the high-pass filter 4-13; and circuit constants of R3=36 kΩ and C=3300 pF are set with respect to the high-pass filter 4-14.
Furthermore, both of the high-cut filters 4-5 and 4-11 have the same weight coefficient whose absolute value is 0.1148; hence, circuit constants thereof (i.e., R3=360 kΩ, C=470 pF) are determined as shown in
As described above, in the second embodiment, in low-frequency ranges at which no problem occurs with regard to beams and comb shapes in audio emission characteristics, signals having the same phase and the same gain are supplied to the speaker units, wherein as frequencies become higher, signals given weights based on the Bessel function are supplied to them. Therefore, in the present embodiment, it is possible to prevent the audio emission efficiency in the low-frequency sound from being reduced; and it is possible to avoid the occurrence of beams and comb shapes in audio emission characteristics.
Incidentally, in the aforementioned embodiment, the speaker unit 1-1 is selected as the reference speaker unit, but this invention is not necessarily limited by the aforementioned embodiment; hence, it is possible to arbitrarily select a desired speaker unit as the reference speaker unit. In addition, it is possible to form the aforementioned high-pass filters and high-cut filters by use of digital filters, instead of analog filters.
A third embodiment of this invention, in which similarly to in the second embodiment shown in
In the third embodiment, a feedback resistor connected between the output terminal and inverting input terminal of the operational amplifier in the all-pass filter 3 shown in
Within the aforementioned weight coefficients C1 to C15, the weight coefficients C3 and C13 whose absolute values (i.e., 0.3621) are maximal are selected as reference coefficients, and are then normalized to “1”. For example, the weight coefficient C5=−0.1148 has an absolute value that is represented as 1/3.15(=0.1148/0.3621); hence, the gain applied to the corresponding speaker unit 1-5 is adjusted to have a difference of 20 log(1/3.15)=−9.97 dB compared with the gain of the other speaker unit 1-3.
The filter shown in
In the above, when circuit constants are set as C=0.1 μF, R1=4.7 kΩ, and R2=1.5 kΩ, it is possible to realize the gain characteristics shown in
Similarly to above, prescribed circuit constants can be determined in response to gain characteristics with respect to weight coefficients of filters connected to the other speaker units.
With respect to speaker units whose weight coefficients based on the Bessel function have positive values, it is possible to use filters having gain characteristics in response to ratios of the weight coefficients compared with the reference weight coefficient, and these filters can be embodied by the circuitry shown in
For example, with respect to the filter corresponding to the weight coefficient C11=0.1148, the left-side circuit portion of the filter shown in
In the above, when circuit constants are set as R1=4.7 kΩ, R2=4.7 kΩ, R3=2.7 kΩ, and C−0.1 μF, it is possible to realize the gain characteristics shown in
Similarly, prescribed circuit constants can be determined with respect to filters connected to the other speaker units whose weight coefficients have positive values.
The filter shown in
In addition, the filter shown in
As described above, in the third embodiment, the same gain having the same phase is applied to each of the speaker units with respect to low-frequency ranges having no problem regarding beams and comb shapes in audio emission characteristics, while weight coefficients based on the Bessel function are applied to each of them with respect to high-frequency ranges. Therefore, it is possible to avoid a degradation of audio emission characteristics in low-frequency sound; and it is possible to avoid the occurrence of beams and comb shapes in audio emission characteristics. Furthermore, it is possible to omit the all-pass filter, which is connected in common to all speaker units.
The aforementioned embodiment is described and embodied using analog filters, but it can be embodied using a digital filter shown in
Next, a center frequency (i.e., a frequency causing phase rotation of 90°) in the phase rotation of the aforementioned all-pass filter and the filter shown in
For example, in the aforementioned simulation, fifteen speaker units are disposed with the distance d (=2.5 cm) therebetween, wherein the overall width of the speaker unit string is 35 cm (=2.5 cm×14). Simulation is performed in consideration of the speed of sound, i.e., 340 m/sec, so that the frequency having a single wavelength corresponding to the width of the speaker unit string, i.e., 35 cm, is 34000/35=971 Hz.
As described above, it is preferable that the center frequency (corresponding to phase rotation of 90°) in the phase rotation of the all-pass filter be set in proximity to the frequency corresponding to the wavelength of the speaker unit string of the array speaker system.
The aforementioned embodiment is constituted using the all-pass filter (or the filter shown in
Reference numerals 1-1 to 1-15 designate speaker units similar to the foregoing ones; reference numeral 6 designates a low-pass filter for filtering signal components of low-frequency ranges from input signals; reference numeral 7 designates a high-pass filter for filtering signal components of high-frequency ranges from input signals; reference numerals 8-1 to 8-15 designate weighting means for imparting weights using weight coefficients C1 to C15 based on the Bessel function to signal components of high-frequency ranges supplied from the high-pass filter 7; and reference numerals 9-1 to 9-15 designate adders, which are arranged in correspondence with the speaker units 1-1 to 1-15 respectively and which add signal components of low-frequency ranges (to which a gain of 1 is applied) provided from the low-pass filter 6 and signal components of high-frequency ranges, to which the weighting means 8-1 to 8-15 impart weights based on the Bessel function, together, thus supplying addition results to the speaker units 1-1 to 1-15 respectively. Herein, the same cutoff frequency is set for the low-pass filter 6 and the high-pass filter 7, for example; hence, input signals are divided into signal components of low-frequency ranges and signal components of high-frequency ranges. Incidentally, the low-pass filter 6 and the high-pass filter 7 can be each constituted using an analog filter or a digital filter.
In the aforementioned fourth embodiment, input signals are divided into signal components of low-frequency ranges and signal components of high-frequency ranges by use of the frequency corresponding to the wavelength identical to the width of the speaker unit string; the corresponding speaker units are subjected to weighting using a gain of 1 with respect to signal components of low-frequency ranges; they are subjected to weighting using weight coefficients based on the Bessel function with respect to signal components of high-frequency ranges; and thereafter, these signals components are added together and output. Thus, similarly to in the foregoing embodiments using the all-pass filters, it is possible to secure a sufficiently high gain in low-frequency ranges, and it is possible to avoid the occurrence of beams and comb shapes in audio emission characteristics with respect to high-frequency ranges.
The aforementioned embodiments are each constituted using fifteen speaker units; however, this invention effectively works in any array speaker system having five speaker units or more. In addition, weight coefficients based on the Bessel function are not necessarily limited to the aforementioned values.
As described heretofore, in the array speaker system of this invention, speaker units are each driven with positive phases with respect to low-frequency ranges; hence, it is possible to prevent audio emission characteristics from deteriorating irrespective of inverse phase components, which occur due to negative values of weight coefficients based on the Bessel function; and with respect to high-frequency ranges, speaker units are each driven with weighting using weight coefficients based on the Bessel function; hence, it is possible to avoid the occurrence of beams and comb shapes in sound. Therefore, it is possible to avoid the occurrence of beams and comb shapes in audio emission characteristics in a broad range of frequencies ranging from low-frequency ranges to high-frequency ranges, and it is possible to realize efficient audio emission in which a sound field is formed in a spherical manner.
Incidentally, this invention is not necessarily limited to the aforementioned embodiments; hence, it may embrace design changes within the scope of the invention.
Number | Date | Country | Kind |
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2003-131538 | May 2003 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/JP04/06423 | 5/6/2004 | WO | 11/7/2005 |