JP2006208883A - Acoustic filter structure and acoustic chamber using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an acoustic filter structure capable of improving a dip in a low-frequency or intermediate-frequency range due to influence of a floor surface, a structure installed thereupon, etc., on acoustic frequency characteristics at a listening point or sound collection point of a source sound or speaker reproduced sound, and an acoustic chamber using the same. <P>SOLUTION: As an embodiment of the present invention, disclosed is an attenuation type acoustic filter structure installed closer to the listening point than to the intersection of a path, reaching the listening point from a virtual image sound source formed at a position symmetrical with a real sound source at a prescribed height about the floor surface of the acoustic chamber, and the floor point, and an attenuation acoustic boundary surface attenuating a sound wave below 500 Hz is formed to correct a dip in a low-frequency or intermediate-frequency range of acoustic frequency characteristics at the listening point. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an acoustic filter structure and an acoustic room using the acoustic filter structure, and more particularly to a listening point (listening position) in an acoustic room (acoustic space) such as a mixing room, a control room, a listening room, a studio, and a semi-anechoic room. ) The acoustic filter structure that can improve the dip in the low range or mid range due to the influence from the floor surface on the frequency characteristics of the original sound or the reproduced sound of the speaker or the influence from the floor installation structure such as a mixing console The present invention relates to a body and an acoustic room using the body.

The important point in acoustic design in mixing rooms, control rooms, listening rooms, studios, and other acoustic rooms is that the original sound or speaker playback sound is not disturbed at the listening point, that is, it is not affected by unnecessary reflected sound and is more faithful. The sound of the real sound source can be obtained and it has excellent frequency characteristics.
For this reason, the acoustic room as described above is usually designed to absorb as much as possible from the wall surface and ceiling surface so as to eliminate as much as possible the adverse effect on the frequency characteristics at the listening point caused by echoes and standing waves. However, equipment and installations will be provided or constructed on the floor later. Moreover, the floor surface is flat and rigid because a person walks and places them.
The influence of the flat and rigid floor surface and the equipment or installation that will be installed or constructed on the floor surface on the frequency characteristics of the listening point cannot be ignored. The representative is the mixing console placed in the mixing room. This causes a dip that causes a problem in listening in the low frequency range, particularly in the vicinity of 100 Hz, in the acoustic frequency characteristic measured at the listening point in the mixing room or studio.

Normally, the dip viewed from the acoustic frequency characteristics at the listening point is not so problematic when the width is sufficiently narrow and steep, and is not so problematic when it is wide and shallow. However, when a dip having an intermediate size occurs, the sound quality is greatly affected, and the listening at the listening point is greatly affected.
Since sound absorbing plates are often used to absorb sound on the wall surface and ceiling surface, a possible way to eliminate the dip that cannot be ignored for listening is to put a sound absorbing plate on the floor surface. This type of sound absorbing plate is known (Patent Document 1). Moreover, what uses an acoustic tube is known as a soundproofing apparatus, such as a highway, which absorbs sound widely (Patent Document 2).
Japanese Patent Laid-Open No. 5-281976 JP 2004-60176 A

The inventors tried to put a sound absorbing plate on the floor surface between the mixing console and the sound source in the mixing room where the mixing console was placed. However, even in such a case, as shown in FIG. 9, it has been found that the dip generated in the acoustic frequency characteristic of the listening point returns more peaks and dips than before and deteriorates the characteristic.
FIG. 9 is an explanatory diagram of the acoustic frequency characteristics of the listening point when the sound absorbing plate is stretched on the floor and when the sound absorbing plate is not stretched, and the vertical axis indicates the sound pressure level of the listening point normalized by the level of the direct sound ( NORMALIZED SPL [dB]), and the horizontal axis represents frequency.
As shown in the characteristic 20, peaks are generated in the vicinity of 150 Hz and 320 Hz, a dip is generated in the vicinity of 550 Hz, and a dip in a relative meaning is also generated before and after the peak. Characteristic 21 is a case where no sound absorbing plate or the like is stretched on the floor, and problematic dip occurs in the vicinity of 100 Hz and in the vicinity of 400 Hz and 600 Hz.
Next, a sound absorbing plate was put on the bottom of the mixing console (Characteristic 22). As shown in FIG. 9, the characteristic is that only the peak and dip positions of the low and middle bands change. The acoustic frequency characteristics on the listening point were not improved.
Here, β is the acoustic admittance where the sound absorbing material is stretched, ρ is the air density, and c is the speed of sound.
As a result, it was found that the technique of absorbing sound on the wall surface and ceiling surface using a sound absorbing plate cannot be applied to the floor surface.
An object of the present invention is to provide a low frequency band due to an influence from a floor surface or a structure installed on an acoustic frequency characteristic on a listening point or a sound collecting point of an original sound or a speaker reproduction sound in an acoustic room (acoustic space). Or it is providing the acoustic filter structure which can improve the dip in a mid range, and the acoustic chamber which uses this.
The sound room in the present invention and claims includes a mixing room, a control room, a listening room, a studio, a semi-anechoic room, etc., as well as a home viewing room, a concert hall, a movie theater, a public hall, etc. Includes rooms with space. Moreover, the low frequency in this invention is a thing with an acoustic frequency of 250 Hz or less, and a middle range is a thing of the range of 250 Hz-1 kHz.

  The acoustic filter structure of the present invention for achieving the above object and the characteristics of the acoustic chamber using the acoustic filter structure are as follows. An attenuation type acoustic filter structure installed on the listening point side from the intersection of the path from the virtual image sound source (image sound source) formed at a symmetric position to the listening point and the floor surface, and attenuates sound waves at 500 Hz or less Attenuating acoustic boundary surface is formed to correct the dip in the low or middle frequency range of the acoustic frequency characteristic at the listening point.

In the characteristic 20 of FIG. 9 mentioned above, peaks occur near 150 Hz and 320 Hz, dip occurs near 550 Hz, and dip in a relative sense occurs before and after the peak. The sound absorbing plate stretched on the floor surface has a sound absorbing effect on the sound from the actual sound source, and the reflected sound from the mixing console also has a considerable effect on the actual sound source. Thought.
This is because a low-frequency 100 Hz dip on the acoustic frequency characteristic measured at the listening point usually disappears, but peaks occur near 150 Hz and 320 Hz, and deep dip occurs near 550 Hz. In other words, the phase of the sound from the virtual image source (reflected sound from the floor surface) is enhanced and peaked when added at the listening point at the positive phase, becomes a dip when added at the opposite phase, and directly from the real sound source. FIG. 9 shows the result of partial absorption of the noise.
The acoustic frequency characteristics of the listening point are due to the interference sound due to the amplitude and phase of the direct sound and reflected sound of the actual sound source when the listening point arrives, and the reflected sound at the mixing console is greatly at the listening point. The effect is that the listening point is behind the mixing console.
From the characteristic results of FIG. 9, it was found that the sound absorbing member affects the sound from the real sound source, and the influence of unnecessary reflected sound cannot be eliminated, so it was thought that the sound tube would absorb the sound corresponding to the 100 Hz dip. . However, there was a problem in what form and where to place it without affecting the sound from the actual sound source. Since sound diffuses three-dimensionally, if the acoustic filter is a single structure, it becomes a sound scattering structure (original sound reflector) with respect to the listening point, and conversely disturbs the sound field. Because there is a possibility. In addition, when an acoustic tube is used to absorb sound corresponding to a dip of 100 Hz in the acoustic frequency characteristics, the length to the bottom of one acoustic tube is as much as 86 cm. It is a problem to install several very long acoustic tubes in the acoustic chamber.
In order to solve this problem, the inventors replaced the mechanical acoustic filter with an electrical filter, analyzed the state of the sound field in the mixing room as an equivalent circuit of the electrical circuit, and placed the structure of the acoustic filter. Considered the location.

However, the result of an electrical equivalent circuit is not always a mechanical acoustic filter. The electric circuit is free by active filters and calculations, but the mechanical acoustic filter is a physical structure. On the other hand, in the acoustic filter characteristics, the current situation is that simple frequency exclusion like electrical characteristics cannot be performed. The acoustic tube does not necessarily correspond to the tube length and the frequency at which the sound wave is attenuated.
FIG. 7 shows the conclusion obtained as a result. The vertical axis is the voltage output level [dB] of the equivalent circuit, and the horizontal axis is the same as in FIG. FIG. 7 shows the relationship between the reflected sound components H1 (f) and H2 (f) other than the direct sound Hd (f) at the listening point LP.
When attention is paid to the low and middle range of the acoustic frequency of 1 kHz or less in FIG. The dotted line 8 is a characteristic of the transfer function H2 (f) due to the reflected sound of the floor surface F. The solid line 9 is the frequency characteristic at the listening point.
As a result, when only the solid line 9 was seen, and when this was seen in a wide band, it was not clear what kind of characteristic the acoustic frequency characteristic of the listening point was synthesized. However, the result of synthesizing the characteristics of the lines 7 and 8 by the analysis focusing on the low and middle range of the acoustic frequency of 1 kHz or less and the actual calculation result by the boundary element method (BEM) in FIG.
Therefore, paying attention to the dotted line 8 which is a characteristic of the transfer function H2 (f) due to the reflected sound of the floor surface F, a frequency-dependent soft boundary surface is formed in a bandwidth of 500 Hz or less by an acoustic tube. An acoustic filter that attenuates sound waves of a specific frequency is provided. In the case of the sound absorbing plate, the absorption of sound waves is determined by the air density ρ and the sound velocity c, and the sound absorption coefficient α is α = 1. At this time, the admittance β = 1 / ρ · c. According to the acoustic tube, the attenuation absorptivity becomes admittance β >> 1 / ρ · c and can be selected, and the structure enables large attenuation of sound waves in a specific band with reference to the center frequency. . That is, this is the concept of an acoustic filter.
In the example described later, FIG. 8 shows a case where an attenuation acoustic boundary surface that attenuates sound waves is not formed by the acoustic filter structure, and when the distance between the actual sound source S and the listening point is 3.0 m, FIG. As shown in FIG. 2, even when the mixing console is changed to A, B, and S, a dip that causes a problem occurs in the low and middle range of 1 kHz or less as in the case where the mixing console is not provided.
Considering the problematic dips D1, D2, and D3 that occur at 150 Hz, 450 Hz, and 750 Hz when no mixing console is provided, the problematic dips D1, D2 as described in the section of the prior art. , D3 is when a dip of an intermediate size occurs, and the dip is not within the range of ± 6 dB at the 1/3 octave band level as a whole in the low-mid range of 1 kHz or less.

On the other hand, even if the reflected sound when reaching the listening point is added in the opposite phase and the sound of the actual sound source is somewhat canceled, if the sound falls within the above range, the effect of improving the sound characteristics of the listening point is high. FIG. 7 shows the analysis result of the electrical equivalent circuit described above with the idea of correcting the dip on the acoustic frequency characteristics of the listening point to a range of ± 6 dB at the 1/3 octave band level. Then, it can be seen that correction is possible by forming a plurality of attenuation type acoustic filter structures that individually attenuate the characteristic of the dotted line 8 at a specific frequency of 500 Hz or less.
Therefore, the sound corresponding to the dip of 100 Hz is not directly attenuated by the acoustic tube, but this neighborhood is smoothed by paying attention to the dip D1 to D3 that cause problems at 150 Hz, 450 Hz, and 750 Hz in FIG. Attenuation type acoustic filter structure that forms an attenuation acoustic boundary surface is provided to correct the characteristics so that the dip and peak in the low and middle range are within the level where there is no problem and the sound quality from the actual sound source is greatly affected . That is the present invention. In particular, if an acoustic tube that dampens at 100 Hz or higher is provided, the acoustic filter structure can be made smaller. Even if it is provided in the acoustic room, the provided acoustic filter structure is reduced by that amount, so that it becomes difficult to become a new sound source reflector, and no sound field is found. Further, the vibration of the sound wave of 500 Hz to 1 kHz can be suppressed by absorbing the harmonic sound component three times.
Considering these points, a listening point in an acoustic room (acoustic space) is provided by correcting the characteristics by providing an attenuation acoustic filter structure that forms an attenuation acoustic boundary surface for attenuating sound waves at 500 Hz or less as described above. This reduces the influence of the floor surface or the structure installed on the frequency characteristics of the original sound or the reproduced sound of the speaker, and improves the sound quality.
In addition, in the embodiment described below, a plurality of acoustic tubes or a plurality of acoustic grooves are laminated to form an attenuation type acoustic filter structure, thereby forming an attenuation acoustic boundary surface for attenuating sound waves with a wide band. The interface is soft.

FIG. 1 is an explanatory diagram of a relationship between an actual sound source and a listening point in a mixing room to which the acoustic filter structure of the present invention is applied, FIG. 2 is an explanatory diagram of a structure of an attenuation type acoustic filter structure, and FIG. 3 is a mixing room. FIG. 4 is an explanatory diagram of the state of the sound field relative to the listening point, FIG. 5 is an explanatory diagram in which the sound field is expanded into an electrical equivalent circuit, and FIG. 6 is an acoustic filter. It is characteristic explanatory drawing which shows the sound quality improvement of a structure.
In addition, the same component is shown with the same code | symbol in each figure, and the description is omitted.
First, the sound field and its electrical equivalent circuit, which are the premise for obtaining an attenuation type acoustic filter structure, will be described.
Describing from the sound field, in FIG. 4, S is an actual sound source using the original sound or the position of the speaker as a sound source. LP is a listening point, F is a floor surface of the mixing room 1, and MC is a mixing console.

The virtual image sound source Sra is set with the surface of the mixing console MC as a mirror surface CS (see FIG. 4) as a reflected sound from the mixing console MC with respect to the real original sound S. Further, a virtual image sound source Srb for the real original sound S is set as a sound source for the reflected sound from the floor surface F at a symmetrical position with the floor surface F of the mixing room 1 as a mirror surface.
The position of the virtual image sound source Sra is determined by the relationship between the listening point LP and the structure on the floor surface F. In order to simplify the description, here, the virtual image source Sra is the surface of the mixing console MC. The virtual image sound source is provided on a straight line connecting the real original sound S and the virtual image sound source Srb.
Therefore, the sound obtained at the listening point LP is a sound resulting from interference of sounds from these three sound sources.
Assuming that the sound from each sound source is transmitted to the listening point LP, the transfer function of the direct sound obtained from the real original sound S is Hd (f), and the transfer function from the virtual image sound sources Sra and Srb is H1 (f). , H2 (f). Then, it is assumed that the sound from the real sound source S is transmitted without direct attenuation with Hd (f) = 1. Further, the distances from the respective sound sources to the listening point LP are assumed to be r, r1, and r2, as shown in the figure.

When the sound field of FIG. 4 is expressed as an electrical equivalent circuit in terms of correcting the dip on the acoustic frequency characteristic of the listening point LP within a range of ± 6 dB at the 1/3 octave band level, the transfer function H1 (f) , H2 (f) can be represented electrically by an attenuation type filter.
As the filter, the reflected sound from the structure such as the mixing console MC is higher in the mid-high range than the low range of the actual original sound S, so the HPF (high bass filter) 4a is used. Since the low frequency of the original sound S increases, it is considered as an LPF (low-pass filter) 4b. The sound of the virtual image sound source Sra and the virtual image sound source Srb has a longer distance to the listening point LP with respect to the real original sound S, and there is also a phase difference, so that the attenuation circuits 2a and 2b are assumed to be attenuated and delayed. And delay circuits 3a and 3b are required. Further, an adder circuit 5 is provided for synthesizing the finally obtained sound as an interference sound at the listening point LP.
That is, in FIG. 5, the transfer function H1 (f) of FIG. 4 is replaced with a series circuit of an attenuation circuit 2a, a delay circuit 3a, and an HPF 4a having the characteristics of HHPF (f). Similarly, the transfer function H2 (f) is replaced with a series circuit of an attenuation circuit 2b, a delay circuit 3b, and an LPF 4b having the characteristics of HLPF (f). Here, it is assumed that the signals of the virtual image sound sources Sra and Srb obtained from these series circuits and the signal obtained directly from the actual original sound S are added by the adder circuit 5 to be a sound signal obtained at the listening point LP.
The transfer function HHPF (f) of the HPF 4a and the transfer function HLPF (f) of the LPF 4b are
HHPF (f) = 1 / {1- (f0 / f) ² −j / Q × (f0 / f)} (1)
HLPF (f) = 1 / {1- (f / f0) ² −j / Q × (f / f0)} (2)
It is.
As a result, the equivalent circuit 6 shown in FIG. 5 can be obtained.

By setting various parameters in this equivalent circuit 6 and collating them with the results calculated by the boundary element method (BEM) indicating the current state, appropriate parameter values of f0 and Q in equations (1) and (2) are obtained. To decide.
By the way, the listening point LP of the mixing room 1 is a viewing position of the mixing engineer. According to various standards, the distance between the listening position of the mixing engineer and the speaker is recommended to be 1.7 m to 3.0 m, but NHK (Japan Broadcasting Corporation) is 3.0 m to 6.0 m. Therefore, here, as shown in FIGS. 1 and 2, the distance r is set to 3.0 m. The height of the mixing console MC is set to 0.7 m, the depth width is set to 1.0 m, and the actual sound source S is set at an elevation angle of 10 ° at the listening point LP. The height of the real sound source S is about 1.7 m. In FIGS. 1 and 2, the intersection of the vertical line passing through the listening point LP and the floor surface F, that is, the foot portion of the vertical line is the origin (0, 0, 0), and the direction of the vertical line is z. An axis, a direction along the floor surface F is a y-axis, and a direction perpendicular to the paper surface is an x-axis. The coordinates of the listening point LP in FIGS. 1 and 2 are (0, 1.2) because x = 0 is omitted, the listening point LP is at the position of y = 0 m, Z = 1.2 m, and left and right This means that the speaker is located at the center (x = 0) of the speakers 13R, 13.
As a result, when r = 3.0 m, r 1 = 3.3 m, and r 2 = 4.2 m, the optimum values for f 0 and Q are obtained by calculation, for example, f 0 = 30 Hz of HHPF (f), Q = 0 .1 and HLPF (f) f0 = 500 Hz, Q = 0.5, a substantial correspondence between the calculation result by the boundary element method and the calculation result by the equivalent circuit 6 could be seen.

The conclusion obtained as a result is FIG. 7 described above. As described above, FIG. 7 shows the relationship between the reflected sound components H1 (f) and H2 (f) other than the direct sound Hd (f) at the listening point LP.
Therefore, correction of the acoustic frequency characteristic of the listening point LP by the attenuation type acoustic filter structure obtained according to FIG. 7 will be described.
The attenuation type acoustic filter structure was studied as a structure that is as small as possible and does not become a sound scatterer. Therefore, an acoustic tube having a damping space that suppresses vibrations of sound of 100 Hz or higher has been studied.
In FIG. 3, reference numeral 10 denotes a studio facility, and a main studio 12 is located in front of the mixing room 1. The left and right speakers 13R, 13L are arranged on the main studio 12 side of the mixing room 1. Behind the main studio 12 is a booth 14 where musical instruments are placed.
Reference numeral 1 denotes a mixing room, and an attenuation-type acoustic filter structure 11 shown in FIG. 2 is provided as a part of the mixing console MC at a lower portion of the mixing console MC. The physical relationship between the real sound source S and the listening point LP is shown in FIGS. 1 and 2, as described above.
There are three reasons for providing the attenuation type acoustic filter structure 11 at this position. First, the first is because it is in the vicinity of the reflection point of the virtual image sound source Srb and is located on the listening point LP side where the reflected sound is received. Secondly, since the acoustic filter is a single structure, it is a position where it is difficult to become a sound scattering structure (original sound reflector) with respect to the listening point LP. Thirdly, a plurality of acoustic grooves (corresponding to acoustic tubes) constituting the attenuation-type acoustic filter structure 11 are laminated, and each of the vibration control center frequencies exceeds 100 Hz and has a sound of about 500 Hz. This is because it was shortened.

The attenuation type acoustic filter structure 11 is basically composed of a laminated structure of a plurality (four) of acoustic grooves 11a, 11b, 11c, and 11d. As shown in the partial cross-sectional view in FIG. 2, by adopting a tube configuration having a plurality of vibration control center frequencies, a wide soft boundary surface is formed, and the acoustic frequencies near 150 Hz and 350 Hz are attenuated and a problem occurs. It has a characteristic to correct the dip.
Since the actual mixing room 1 is a stereo sound source, the plurality of acoustic grooves are formed by overlapping tubes in the x-axis direction or as grooves, and the mixing console MC shown in FIG. 3 has a width of 4 m in the x-axis direction. And has a width exceeding the distance between the two speakers 13R and 13L in the depth direction of FIG.
In this way, by arranging a plurality of acoustic tubes stacked on the lower side of the mixing console MC, a sound attenuation type soft acoustic boundary surface can be formed with respect to the admittance β at the lower part of the mixing console MC.

In the prior art, it has been described that a dip that cannot be ignored occurs in the vicinity of 100 Hz in the low frequency range in the frequency characteristics. Therefore, when acoustic tubes that attenuate a frequency that is an odd multiple of 100 Hz are arranged, the tube length L of the sound wave to be attenuated at a frequency of 100 Hz is set to λ / 4 or an odd multiple of that. Therefore, in order to form a soft acoustic boundary surface with respect to the dip frequency of 100 Hz and attenuate and absorb, it is necessary to set the tube length of the frequency of the sound wave to be attenuated and absorbed to a tube length in the vicinity thereof and to provide a plurality Become advantageous.
However, as the length L of the acoustic tube becomes longer, the dip showing the steep attenuation of characteristics shifts to a lower range and does not necessarily correspond to the expected effect and the tube length. However, it is possible to attenuate and absorb the sound of the harmonic component three times that of the fundamental wave.
The attenuation-type acoustic filter structure 11 performs attenuation absorption that reduces dip due to mutual interference between a plurality of acoustic tubes set in the vicinity, on a soft acoustic boundary surface.
Therefore, the four acoustic grooves 11a, 11b, 11c, and 11d having different damping center frequencies have dimensions as shown in FIG. 2A, and the damping center frequencies are 340 Hz, 245 Hz, and 215 Hz from the bottom. 190Hz. The absorption of the input sound wave is 1/4 of the wavelength of the sound wave, and the sound wave having a phase difference of 180 ° with respect to the input sound wave is reflected by inverting the phase of the sound wave of a specific frequency with an acoustic tube having a closed end. It is made by a cavity damping box with a damping space that suppresses the vibration of the sound structure.
Here, since the vibration suppression minimum center frequency is 190 Hz, the length to the bottom surface of the acoustic groove is 45 cm. Moreover, the effect of improving the characteristics extends from 100 Hz to a lower frequency due to the laminated form of the four acoustic grooves.

The structure will be described more specifically. The attenuation type acoustic filter structure 11 shown in FIG. 2A has a height of 35 cm, and the groove widths (opening heights) of the acoustic grooves 11a, 11b, 11c, and 11d. ) Is 7.6 cm, the length L of the acoustic groove 11a is 25 cm, the length L of the acoustic groove 11b is 35 cm, the length L of the acoustic groove 11c is 40 cm, and the length L of the acoustic groove 11d is 45 cm. It is. The entire length of the groove covers the distance between the two speakers 13R and 13L, and is 4 m as described above. The height 7.6 cm of the acoustic grooves 11a, 11b, 11c, and 11d is selected in relation to the attenuation of the harmonics, and here, the harmonics can be attenuated three times. The unit of length in FIG. 2 is [m].
FIG. 6 is an explanatory diagram of acoustic frequency characteristics at the listening point LP of the type S mixing console MC shown in FIG. The vertical axis is the sound pressure level (dB) of the listening point normalized with the direct sound, and the horizontal axis is the frequency.
The bar graph 15 is the acoustic frequency characteristic of the listening point LP of the mixing room 1 according to the embodiment of FIG. 1 in which the attenuation type acoustic filter structure 11 is provided, and the bar graph 16 of □ does not have the attenuation type acoustic filter structure 11. It is an acoustic frequency characteristic of the listening point LP of the mixing room 1.
In the type S mixing console MC shown in FIG. 8, there are dips at 95 Hz, 350 Hz, and 550 Hz. According to FIG. 6, they are corrected to dip around 80 Hz and 500 Hz, and 1/3. It is within the range of ± 6 dB at the octave band level. Thereby, it turns out that the sound quality improvement effect of the attenuation | damping type | mold acoustic filter structure 11 is high.

By the way, the acoustic groove in the embodiment may be configured by arranging a plurality of acoustic tubes individually corresponding to the interval width of the two speakers, and the opening structure of the acoustic tube structure is limited to a circle or a rectangle. Is not to be done. In particular, a sound absorbing material may be attached to the bottom surface or the inner wall surface of the acoustic groove or acoustic tube to absorb the sound. In this case, the sound absorption rate can be adjusted according to the attenuation sound absorption characteristic, and the acoustic frequency characteristic of the listening point LP can be corrected in accordance with the state of the acoustic room.
In the embodiment, two speakers are described. However, in the 5.1 channel speaker system, since two speakers are arranged on the back side, an attenuation type acoustic filter is also provided on the side surface or the back side. Of course, a structure may be constructed.
In the present invention, the listening point of the embodiment may of course be a sound collection point where a microphone or the like is installed.

As described above, in the embodiment, the attenuation type acoustic filter structure is a laminated tube type. However, the acoustic tube stand which does not become a sound scattering structure (original sound reflector) or has little scattering is independent from the mixing console MC. Of course, the structure may be installed before the listening point or before the structure such as the mixing console MC.
In the embodiment, an attenuation type acoustic filter structure is provided on the front side of the bottom of the sound scattering structure such as a mixing console. However, the attenuation type acoustic filter structure is adjacent to the sound scattering structure. It may be provided.
Furthermore, the present invention is not limited to the acoustic groove or the acoustic tube shown in the embodiments, and any structure may be used as long as it is an acoustic filter that attenuates sound waves.
Furthermore, although the embodiments have been described mainly with respect to the mixing room, the present invention is not limited to an acoustic room such as a control room, listening room, studio, semi-anechoic room, or a facility such as a concert hall, a movie theater, or a public hall. Even so, it is applicable. In particular, in facilities such as public halls, it is possible to install an attenuation type acoustic filter structure corresponding to the physical positional relationship between a speaker (sound source) and a chair that is individually installed at the bottom of the chair where the audience sits. .

FIG. 1 is an explanatory diagram of the relationship between an actual sound source and a listening point in a mixing room to which the acoustic filter structure of the present invention is applied. FIG. 2 is an explanatory diagram of the structure of the attenuation-type acoustic filter structure. FIG. 3 is a plan view of a studio facility with a mixing room. FIG. 4 is an explanatory diagram of the state of the sound field with respect to the listening point. FIG. 5 is an explanatory diagram in which the sound field of FIG. 4 is developed into an electrical equivalent circuit. FIG. 6 is a characteristic explanatory diagram showing sound quality improvement of the acoustic filter structure. FIG. 7 is an explanatory diagram of the acoustic frequency characteristics other than the direct sound at the listening point analyzed by an equivalent circuit focusing on the mid-low range of an acoustic frequency of 1 kHz or less. FIG. 8 is an explanatory diagram of the acoustic frequency characteristic of the listening point subjected to numerical analysis. FIG. 9 is an explanatory diagram of the acoustic frequency characteristics of the listening point when the sound absorbing plate is stretched on the floor and when it is not stretched.

Explanation of symbols

1 ... mixing room, 2a, 2b ... attenuation circuit,
3a, 3b ... delay circuit, 4a ... HPF (high pass filter),
4b ... LPF (low pass filter), 5 ... adder circuit,
6 ... Equivalent circuit, 10 ... Studio facility,
11 ... Attenuating acoustic filter structure, 11a, 11b, 11c, 11d ... acoustic groove,
12 ... Main studio, 13R, 13L ... Speaker,
14 ... Booth, S ... Real sound source, Sra ... Virtual image sound source,
Srb ... virtual image source, LP ... listening point,
F ... floor of mixing room, MC ... mixing console,
CS: Surface including the surface of the mixing console.

Claims (10)

  Installed on the listening point side from the intersection of the path from the virtual image sound source to the listening point, which is formed in a symmetrical position with the floor surface of the acoustic room as a mirror surface with respect to the real sound source at a predetermined height, and the floor surface An acoustic filter structure that is an attenuation type acoustic filter structure, and forms an attenuation acoustic boundary surface that attenuates a sound wave at 500 Hz or less to correct a low-frequency or middle-frequency dip of an acoustic frequency characteristic at the listening point.   The acoustic filter structure according to claim 1, wherein the attenuation type acoustic filter structure includes a plurality of acoustic tubes or a plurality of acoustic grooves, and attenuates at a plurality of predetermined center frequencies in a range of 100 Hz to 500 Hz.   The acoustic chamber has a sound scattering structure, and the attenuation type acoustic filter structure is provided integrally with or adjacent to the sound scattering structure, and the attenuation acoustic boundary surface is a gentle boundary surface. The acoustic filter structure according to claim 2, wherein the number of the acoustic filter structures is three or more, and the listening point is set behind the sound scattering structure.   The acoustic chamber is a mixing room, the sound scattering structure is a mixing console, the listening point corresponds to a listening position in the mixing console, and the plurality of acoustic tubes or the plurality of acoustic grooves are Each acoustic tube or each acoustic groove that is laminated forms a damping space that suppresses vibration of sound whose depth to the bottom surface corresponds to λ / 4 of the predetermined center frequency, and each of the predetermined acoustic channels. 4. The acoustic filter structure according to claim 3, wherein the center frequency of the mixing console is over 100 Hz and is integrally formed with the bottom of the mixing console.   The acoustic filter structure according to claim 1, wherein the listening point is a sound collection point. An actual sound source at a predetermined height,
Listening point,
Attenuation type acoustic filter provided on the listening point side from the intersection of the path from the virtual image sound source, which is formed in a symmetrical position with the floor surface of the acoustic room as a mirror surface to the real sound source, to the listening point and the floor surface With a structure,
An acoustic chamber for correcting a dip in a low frequency range or a mid frequency range of an acoustic frequency characteristic at the listening point by forming an attenuated acoustic boundary surface that attenuates a sound wave at 500 Hz or less by the attenuation acoustic filter structure.   The acoustic chamber according to claim 6, wherein the attenuation type acoustic filter structure includes a plurality of acoustic tubes or a plurality of acoustic grooves, and attenuates at a plurality of predetermined center frequencies in a range of 100 Hz to 500 Hz.   The acoustic chamber has a sound scattering structure, and the attenuation type acoustic filter structure is provided integrally with or adjacent to the sound scattering structure, and the attenuation acoustic boundary surface is a gentle boundary surface. The acoustic chamber according to claim 7, wherein the number of the acoustic chambers is three or more, and the listening point is set behind the sound scattering structure.   The acoustic chamber is a mixing room, the sound scattering structure is a mixing console, the listening point corresponds to a listening position in the mixing console, and the plurality of acoustic tubes or the plurality of acoustic grooves are Each acoustic tube or each acoustic groove that is laminated forms a damping space that suppresses vibration of sound whose depth to the bottom surface corresponds to λ / 4 of the predetermined center frequency, and each of the predetermined acoustic channels. 9. The acoustic chamber according to claim 8, wherein the center frequency of the mixing console exceeds 100 Hz and is integrally formed with the bottom of the mixing console.   An acoustic chamber provided with the acoustic filter structure according to any one of claims 1 to 6.

Images