JP2011166489A - Acoustic reproduction apparatus and method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform acoustic reproduction based on the Wave Field Synthesis, even when an upper limit frequency is high and speakers are large. <P>SOLUTION: When defining N as an integer being &ge;2 and (a) as a real number which is &le;1/2 of wavelength of an upper limit frequency of a sound to be collected of &ge;0 and a sound to be reproduced, N pieces of speakers 2<SB>1</SB>, 2<SB>2</SB>to 2<SB>N</SB>for reproducing sounds collected by N pieces of microphones disposed on a line at intervals (a) based on the Wave Field Synthesis are disposed while being shifted vertically in an extending direction of a line having the same shape as that of the line, to be disposed in the extending direction of the line at the intervals (a). <P>COPYRIGHT: (C)2011,JPO&amp;INPIT

Description

  The present invention relates to a technique for collecting and reproducing sound necessary for communication, broadcasting, and the like.

  If you can pick up the radiated sound as if you were listening directly to the radiated sound and play it in a place different from the place where you picked it up, you can feel the presence of communication, broadcasting, etc. Can be improved. As such a sound pickup and reproduction technique, Non-Patent Document 1 proposes a technique using a plurality of microphones and a plurality of speakers based on the wavefront synthesis method.

  In the technique of Non-Patent Document 1, a plurality of speakers are arranged on the line at intervals a as a real number equal to or less than ½ of the wavelength of the upper limit frequency of the sound to be reproduced.

Toshiyuki Kimura, 3 others, “Wavefront synthesis accuracy in wavefront synthesis using directional microphones”, IEICE Technical Report, September 2005, vol.105, no.289, EA2005-47, p.13-18

  However, when the upper limit frequency of the sound to be reproduced is high, the interval a becomes smaller than the lateral width of the speakers, and there is a problem that a plurality of speakers cannot be arranged on the line with the interval a.

  For example, when the upper limit frequency is 7 kHz, the interval a is a real number of 2.5 cm or less. Since the horizontal width of a speaker having a flat frequency characteristic is usually 2.5 cm or more, in this case, a plurality of speakers cannot be arranged on the line at intervals a.

  In order to solve the above-mentioned problem, N is an integer of 2 or more, a is 0 or more and is a real number less than 1/2 of the wavelength of the upper limit frequency of sound to be collected and reproduced, and is arranged on the line at an interval a. The N speakers that reproduce the sound collected by the N microphones based on the wavefront synthesis method are arranged so as to be shifted in the direction perpendicular to the extending direction of the line having the same shape as the above line, thereby extending the line. Arranged at intervals a in the direction.

  A plurality of speakers can be arranged on the line at intervals a even when the interval a is small by disposing the lines in a direction perpendicular to the extending direction of the line.

The functional block diagram of the example of a sound reproducing device. The figure which shows the example of arrangement | positioning of a speaker. The figure which illustrates the sound pressure level of the sine wave output from the speaker arrange | positioned by this invention.

  Hereinafter, an embodiment of a sound reproducing apparatus according to the present invention will be described in detail.

The sound reproducing device includes N speakers 2 ₁ , 2 ₂ ,..., 2 _N and a low-pass filter 4 as illustrated in FIG. N is an integer of 2 or more, the microphone _{3 1,} 3 2, which will be described later, ..., and the same as the number of _{3 N.} Speakers _{2 1,} 2 2, ..., and the number of channels to be input to play from _{2 N,} microphone _{3 1,} 3 2, ..., number of channels to output the collected sound from _{3 N} are equal.

N microphones 3 ₁ , 3 ₂ ,..., 3 _N are arranged at a distance a on a certain line. The line is a straight line or a curve such as an arc or a circle. Here, the interval means the length of the repetitive pitch when arranging a plurality of objects. Assume that a common reference position is provided for an object. The reference position is, for example, the center and the left end of the object. When the objects are arranged at an interval a, the distance between the reference positions of two adjacent objects is a. Sounds collected by _N microphones 3 ₁ , 3 ₂ ,..., 3 _N are output through N channels. Microphone _{3 1,} 3 2, ..., signal picked-up sound _{3 N,} the speaker _{2 1,} 2 2 respectively, ..., is applied to _{2 N.} Microphone _{3 1,} 3 2, ..., ₃ in the case _{where N} is in the remote location, the microphone _{3 1,} 3 2, ..., _{3 N} and speaker _{2 1,} 2 2, ..., _{2 N} are connected by a network.

In order to reproduce sound based on the wavefront synthesis method, N speakers 2 ₁ , 2 ₂ ,..., 2 _N are connected to a line 1 having the same shape as _N microphones 3 ₁ , 3 ₂ ,. It is necessary to arrange them at the same interval a. For this purpose, N speakers 2 ₁ , 2 ₂ ,..., 2 _N are arranged so as to be shifted in the direction perpendicular to the extending direction of the line 1. For example, as shown in FIG. 2, the speakers 2 ₁ , 2 ₂ ,..., 2 _N are stacked in three stages while being shifted by a distance a in the direction perpendicular to the extending direction of the line 1 (upward with respect to the plane of FIG. 2). Speakers 2 ₁ , 2 ₂ ,..., 2 _{N in} FIG. 2 are cubes having a side length of 3a. By arranging in this way, the speakers 2 ₁ , 2 ₂ ,..., 2 _N having a width equal to or larger than the interval a can be arranged at the interval a in the extending direction of the line 1 and based on the wavefront synthesis method. Sound can be reproduced.

  The wave field synthesis method (WFS) reproduces a sound field by controlling the sound pressure on an infinite plane based on, for example, the first integration of Rayleigh expressed by the following equation (1).

Here, k = ω / c is the wave number, and c is the sound propagation speed. r is a point in the region S, and P (r _s , ω) is a sound pressure distribution on the region S formed by the main sound source existing outside the region S. n is the normal vector of the plane _{S 1.} In the expression (1), the region S is enlarged to the infinite plane z = z ₁ and cut out by the plane S ₁ . Therefore, it is possible to calculate the sound pressure at the listening area from the only sound pressure distribution in the plane S _1.

Specifically, the microphone 3 _1, 3 2, which are arranged on a straight line on a plane S _{1, ...,} 3 signals picked-up sound _N, speakers 2 ₁ disposed on straight _lines, 2 ₂ ,..., _2N , it is possible to reproduce sound based on the wavefront synthesis method, and to reproduce the sound pressure in the space on the listening point side.

Incidentally, the microphone _{3 1,} 3 2, ..., _{3 N} is regardless of the shape of the line is arranged, the microphone _{3 1,} 3 2, ..., ₃ signals picked-up sound _N, in each above By applying to the appropriately arranged speakers 2 ₁ , 2 ₂ ,..., 2 _N , it is possible to reproduce sound based on the wavefront synthesis method.

  FIG. 3 shows the sound pressure level of a sine wave measured at a position 3 m away from the speaker arranged as shown in FIG. The line (1) represents the sound pressure (A) measured when 64 speakers are arranged and reproduced, and the line ◆ represents the sound pressure (B) measured when reproduced from one speaker. And the ▲ line represents the difference obtained by subtracting B from A. The vertical axis represents the sound pressure level (dB), and the horizontal axis represents the frequency of the reproduced sine wave in logarithm. As can be seen from the difference, when the number of speakers is increased to 64, the sound pressure does not increase uniformly at each frequency, but the low frequency increases more. In the case of FIG. 3, the frequency rises by about 3 dB on average every octave as the frequency becomes lower. From this result, the high-pass filter 4 in FIG. 1 performs filtering so as to decrease the level as the frequency becomes lower in accordance with the number of speakers to be reproduced.

  In this way, when speakers are placed close to each other, out of the sound reproduced from multiple speakers, the phase is matched at a low frequency, and the low frequency range of the reproduced sound is emphasized compared to the collected sound, It becomes a muffled sound. By using the high-pass filter 4, it is possible to prevent this sound accumulation.

In the above embodiment, the microphone _{3 1,} 3 2 to the sound reproducing apparatus, ..., _{3 N} are not included, the microphone _{3 1,} 3 2 to the sound reproducing apparatus, ..., be contained _{3 N} Good.

  The present invention is not limited to the above-described embodiment, and can be modified as appropriate without departing from the spirit of the present invention.

2 ₁ , 2 ₂ ,..., 2 _N speaker 3 ₁ , 3 ₂ ,..., 3 _N microphone 4 High pass filter

Claims (2)

Sound was collected by N microphones arranged at intervals a on the line, where N is an integer of 2 or more, a is 0 or more, and is a real number less than 1/2 of the wavelength of the upper limit frequency of the sound to be reproduced. Including N speakers that reproduce sound based on wavefront synthesis,
The sound reproducing apparatus, wherein the N speakers are arranged so as to be shifted in a direction perpendicular to the extending direction of a line having the same shape as the line, and are arranged at an interval a in the extending direction of the line. The sound reproducing device according to claim 1,
A high-pass filter for filtering sound signals applied to the N speakers;
A sound reproducing apparatus further comprising:

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