JP2009055605A - Damped loudspeaker unit and loudspeaker system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve both weight reduction of a loudspeaker system and flattening of a sound pressure in the vicinity of the lowest resonance frequency in conjunction by reducing a magnetic force of a magnet of a dynamic loudspeaker unit. <P>SOLUTION: The loudspeaker system makes up a tightly closed loudspeaker system, characterized in that the rear side of the loudspeaker unit 12 of the tightly closed loudspeaker system 10 is covered with an acoustically resistant member 13 having an acoustic resistance as high as at least dynamic impedance of the loudspeaker unit 12, and yet that the acoustically resistant member 13 is arranged in such a location that a ratio (V1/V2) of a volume V1 of the space enclosed by both the rear face of the diaphragm 14 of the loudspeaker and the acoustically resistant member 13; and a volume V2 of the space enclosed by both the acoustically resistant member 13 and the cabinet 11; is ≤1/2. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

    The present invention relates to a speaker unit and a speaker system used in an audio device, and more specifically to a speaker system equipped with a brake speaker unit and a brake speaker unit.

In a sealed speaker system equipped with a dynamic speaker unit, as shown by a solid line in FIG. 16, a phenomenon in which the sound pressure near the lowest resonance frequency (f ₀ ) generally increases in a mountain shape occurs. Therefore, as shown by a one-dot chain line in FIG. 16, various methods have been proposed in which vibration near the lowest resonance frequency (f ₀ ) is braked to flatten the sound pressure peak. Typical methods include a method of increasing the magnetic force of the magnet of the speaker unit and a method of using a sound absorbing material.

The method of increasing the magnetic force of the magnet has a problem that the size of the magnet is increased, resulting in a large speaker unit and a heavy weight. In particular, it is not suitable for applications requiring small size and light weight, such as portable speaker systems, in-vehicle speaker systems, and speaker systems built in thin television receivers.
On the other hand, a method using a sound-absorbing material is expected as an effective means for reducing the size and weight of a speaker system because a small and lightweight speaker unit having a weak magnetic force of a magnet can be employed.

    For example, a method of damping vibrations near the lowest resonance frequency by filling a space in the cabinet with a sound absorbing material such as open cell type urethane, glass wool, and cotton is well known. However, this method has a problem that the sound pressure level not only in the vicinity of the lowest resonance frequency but also in the midrange (300 Hz to 1 kHz) is significantly reduced. In order to solve this problem, an acoustic adjustment material disclosed in Patent Document 1 has been proposed. Next, this acoustic adjustment material will be described.

    Acoustic adjustment materials include reflective / brake members made of aluminum foil, shape retaining / vibration members made of fiber sheets, etc., porous materials such as urethane, sponge, down, cotton, felt, etc., balloons, air cushions, etc. A sound absorbing / buffer member made of an elastic material is wrapped with a sound wave transmitting member such as cloth. When this acoustic adjustment material is attached to a closed type or bass reflex type cabinet, it is attached at a corner in the cabinet or at a position where the sound pressure becomes high.

Patent Document 2 proposes a cabinet in which a sound wave delay plate is installed at a position that partitions the internal space of the cabinet or a position that occupies a part of the internal space. The sonic delay plate is composed of a plurality of perforated plates having a large number of small holes (hole diameter: 1 mm to 10 mm), in which gaps are provided between each other and the hole positions of the perforated plates are stacked so as not to coincide with each other. Has been. When a sound wave enters the sound wave delay plate, the sound wave propagates around each small hole in a zigzag manner. Thus, the generation of the internal standing wave is suppressed by lengthening the propagation path of the sound wave.
JP-A-7-261767 Reality 2-12789

    However, since the acoustic adjustment material described in Patent Document 1 has a complicated configuration and uses a member having a very high braking resistance, that is, a member having no air permeability such as an aluminum foil, a balloon, and an air cushion, The design and control of braking resistance is extremely difficult. In addition, there is a problem that the braking resistance varies depending on how the acoustic adjustment material is attached to the speaker unit (such as adjusting the distance between the acoustic adjustment material and the speaker unit). Furthermore, when the speaker unit is covered with a non-breathable member, there is a problem that the braking resistance becomes too large and the sound pressure level in the entire reproduction frequency is remarkably lowered.

For the sound wave delay plate described in Patent Document 2, a verification experiment was performed to determine whether or not there is a braking action for braking vibrations near the lowest resonance frequency. As a result, in order to play a role as a sound wave passage, it is necessary to make the hole diameter of the sound wave delay plate 1 mm or more, and when the hole diameter is 1 mm or more, the braking action is not expressed.
Therefore, the sound wave retardation plate disclosed in Patent Document 2 and the porous sheet according to the present invention are completely different in configuration and operation effect.

In the case of a bass reflex type speaker system, as indicated by a one-dot chain line in FIG. 10, the sound pressure near the lowest resonance frequency (f ₀ ) increases in a mountain shape, and also near the resonance frequency (fp) of the acoustic port. There is a problem that the sound pressure frequency characteristics in the low sound range are disturbed due to the generation of the sound pressure peaks and valleys. In order to solve this problem, a method of inserting a sound absorbing material into the acoustic port can be considered. However, this method has a problem that the sound frequency below the lowest resonance frequency (f ₀ ) is lowered, so that the reproduction frequency band in the low sound range is narrowed.

Therefore, an object of the present invention is to provide an acoustic resistance member with a simple configuration that solves such problems and brakes vibrations near the lowest resonance frequency. Another object of the present invention is to simultaneously reduce the weight of the speaker unit and the speaker system and flatten the sound pressure near the lowest resonance frequency by reducing the magnetic force of the magnet of the speaker unit. It is another object of the present invention to provide a bass reflex type speaker system that can simultaneously achieve flattening of sound pressure near the lowest resonance frequency and near the resonance frequency of the acoustic port and weight reduction.

In order to solve the above problems and achieve the object, the braking type speaker unit of the present invention includes a speaker unit having a speaker diaphragm, and an acoustic resistance member provided in a back space of the speaker diaphragm, The back space is closed by an acoustic resistance member, and the acoustic resistance member has an acoustic resistance equal to or higher than the dynamic impedance of the speaker unit. The peak frequency of the sound absorption characteristic is 1 kHz or less.
With the above configuration, the braking resistance of the speed unit can be controlled with a simple configuration. Therefore, the magnetic force of the magnet of the speaker unit can be reduced to simultaneously realize the weight reduction of the speaker unit and the flattening of the sound pressure near the lowest resonance frequency.
Furthermore, a back plate for forming an air layer is provided on the back side of the acoustic resistance member (the side opposite to the speaker diaphragm). By adopting such a configuration, it is possible to simultaneously reduce the weight of the speaker system and flatten the sound pressure near the lowest resonance frequency.

The acoustic resistance member used in the brake type speaker unit according to the present invention is a porous body having air permeability. Preferably, the porous body is a foam having air permeability of 10 cc / cm ² / sec or less. With such a configuration, the peak frequency of the sound absorption characteristic can be reduced to 1 kHz or less.
More preferably, the porous body is a porous sheet having a plurality of through holes, and the diameter (diameter) of the through holes is 0.8 mm or less. By configuring as above,
B) The peak frequency characteristic of the sound absorption characteristic is 200 Hz, and the sound absorption frequency bandwidth (bandwidth) can be expanded to 1.4 octaves or more.
B) Since the hole structure is simpler than that of the foam, the acoustic resistance design of the acoustic resistance member is facilitated.
C) The acoustic resistance member can be reduced in weight.

    The acoustic resistance member according to the present invention is characterized by comprising a multi-porous sheet in which a plurality of porous sheets are overlapped with a gap therebetween. By adopting such a configuration, the degree of freedom in designing acoustic resistance can be expanded. That is, the acoustic resistance can be adjusted by changing the number of porous sheets to be overlapped.

    Furthermore, the multi-perforated sheet is characterized in that the diameters of the through holes of the perforated sheets are different from each other. With such a configuration, the degree of freedom in designing the peak frequency of the sound absorption characteristics and the sound absorption frequency bandwidth is expanded. Therefore, it is possible to realize a bass reflex type speaker system that has no sound pressure peaks and valleys in the vicinity of the lowest resonance frequency of the cabinet and in the vicinity of the resonance frequency of the acoustic port and has excellent reproducibility in the low sound range.

The speaker system of the present invention includes a cabinet and the above-described braking speaker unit mounted on the inner wall of the cabinet, and is provided between the back surface of the acoustic resistance member provided in the braking speaker unit and the inner wall of the cabinet. It has an air layer.
Further, the ratio (V1 / V2) between the volume V1 of the space surrounded by the back surface of the speaker diaphragm and the acoustic resistance member and the volume V2 of the space surrounded by the back surface of the acoustic resistance member and the inner wall of the cabinet is 1 / The acoustic resistance member is disposed at a position of 2 or less, preferably 1/5 or less.
With the above configuration, the braking resistance of the speaker system can be controlled. Therefore, since the speaker unit having a weak magnetism, that is, a lightweight speaker unit can be used, the speaker system can be reduced in weight and the sound pressure near the lowest resonance frequency can be flattened at the same time.

    The speaker system of the present invention is characterized in that an acoustic port is provided in a part of the back space. This configuration reduces the magnetic force of the magnet of the speaker unit so that the sound pressure near the lowest resonance frequency and the sound pressure near the acoustic port resonance frequency can be flattened and reduced in weight at the same time. A speaker system can be provided.

    According to the speaker unit of the present invention, since the magnetic force of the magnet can be reduced, an effect of reducing the weight of the speaker unit can be obtained.

    Further, according to the speaker system of the present invention, a lightweight speaker unit having a weak magnetic force of a magnet can be used, so that the speaker system can be reduced in weight and the sound pressure near the lowest resonance frequency can be flattened at the same time. The effect that can be obtained.

    Furthermore, according to the bass reflex type speaker system of the present invention, it is possible to obtain an effect capable of simultaneously improving the reproducibility of the low sound range and reducing the weight.

    Hereinafter, embodiments of the present invention will be described with reference to the drawings of FIGS.

(First embodiment)
FIG. 1 is a schematic cross-sectional view showing a configuration example of a sealed speaker system according to the present invention. FIG. 2 is an electroacoustic equivalent circuit diagram of the braking speaker unit shown in FIG. FIG. 3 is an electroacoustic equivalent circuit diagram of the sealed speaker system shown in FIG. FIG. 4 is a sound pressure frequency characteristic diagram in which the relationship between sound pressure and frequency is obtained by calculation simulation using the electroacoustic equivalent circuit diagram shown in FIG. FIG. 5 is a diagram showing the relationship between the sound absorption characteristics of the acoustic resistance member and the braking action. 6, 7 and 8 are schematic views showing one configuration example of the acoustic resistance member according to the present invention.

[Configuration of sealed speaker system]
As shown in FIG. 1, the sealed speaker system 10 includes a cabinet 11, a speaker unit 12 mounted on the wall surface of the cabinet 11, and an acoustic resistance member 13 provided on the back side of the speaker unit 12. The speaker unit 12 is a generally well-known dynamic speaker unit, which includes a speaker diaphragm 14 (hereinafter referred to as a diaphragm for short), a support system 15 for the diaphragm 14, a voice coil 16, and a magnet 17. And a frame 18. In the present embodiment, the back surface of the frame 18 is covered with the acoustic resistance member 13. Hereinafter, the speaker unit 12 carrying the acoustic resistance member 13 will be referred to as a braking speaker unit 19 (portion surrounded by a dotted line). V <b> 1 is a space surrounded by the back surface of the diaphragm 14 and the acoustic resistance member 13.

The acoustic resistance member 13 is made of a porous body having acoustic resistance equal to or higher than the dynamic impedance R2 (see FIG. 2) of the speaker unit 12 and having air permeability. Preferably, a porous body having sound absorption characteristics with a sound absorption peak frequency of the acoustic resistance member 13 of 1 kHz or less is preferable. The reason is that if the sound absorption peak frequency of the acoustic resistance member 13 is higher than 1 kHz, the resistance component of the acoustic resistance member 13 near the desired frequency at which braking is expected, for example, near the lowest resonance frequency, becomes small, and the sound pressure near the lowest resonance frequency. This is because the effect of flattening is reduced. Further, if the speaker unit 12 is covered with a non-breathable acoustic resistance member, the braking resistance becomes too large, causing a problem that the sound pressure level in the entire reproduction frequency is significantly reduced.
Here, the sound absorption peak frequency is, for example, the sound absorption coefficient having the highest sound absorption coefficient in the sound absorption coefficient frequency characteristic obtained by a generally well-known measurement method such as a normal incidence sound absorption coefficient measurement method or a reverberation room sound absorption coefficient measurement method. Is the frequency. Next, the configuration of the brake speaker unit 19 will be described in detail.

[Configuration of braking type speaker unit]
In FIG. 2, a portion 21 surrounded by a dotted line is an electroacoustic equivalent circuit of the speaker unit 12 portion, a portion 22 surrounded by a one-dot chain line is an electroacoustic equivalent circuit of the space V1, and a portion 23 surrounded by a two-dot chain line is an acoustic resistance member. 13 is an electroacoustic equivalent circuit of 13 parts.
Vac is the alternating driving force, L1 is the mass of the speaker vibration system, C1 is the compliance of the support system 15 of the diaphragm 14, R1 is the resistance of the support system 15, R2 is the dynamic impedance, C3 is the acoustic compliance of the space V1, and R4 is the acoustic The acoustic resistance of the resistance member 13, C 4 is the acoustic compliance of the acoustic resistance member 13, and L 4 is the acoustic inductance of the acoustic resistance member 13. Next, the operation of the braking speaker unit 19 will be described with reference to FIG.

At a frequency sufficiently away from the parallel resonance frequency of the acoustic compliance C4 of the acoustic resistance member 13 and the acoustic inductance L4, the electroacoustic equivalent circuit 23 of the acoustic resistance member 13 is substantially equivalent to the acoustic resistance R4 of the acoustic resistance member 13. Further, in the low frequency region sufficiently away from the parallel resonance frequency, the impedance of the acoustic compliance C3 in the space V1 becomes extremely large. Therefore, only the acoustic resistance R4 is added to the electroacoustic equivalent circuit 21 of the speaker unit 12, and the braking resistance of the speaker unit 12 increases from (R1 + R2) to (R1 + R2 + R4). In particular, the braking resistance R2 related to the magnetic strength B of the magnet 17 has increased to (R2 + R4). Therefore, as can be seen from the equation (1), the braking type speaker unit 19 has a braking ability equivalent to that of the speaker unit in which the magnetic force B of the magnet 17 is square root times (1 + R4 / R2). The peaks and valleys of the sound pressure near the lowest resonance frequency are flattened.
For example, in order to achieve a braking force equivalent to that of a speaker unit in which the magnetic force B of the magnet 17 is twice, the acoustic resistance R4 may be set to three times or more the dynamic impedance R3 of the speaker unit.
Dynamic impedance R2 = (Bl) ² / R (1)
Where B is the magnetic flux density of the magnetic flux crossing the voice coil 16, l is the length of the voice coil 16, and R is the electrical resistance of the voice coil 16.

    The acoustic resistance member 13 is provided at a position set based on the acoustic characteristics of the speaker unit 12 and the sound absorption characteristics of the acoustic resistance member 13. Next, the arrangement of the acoustic resistance member 13 will be described in detail.

[Disposition of acoustic resistance members]
In FIG. 1, the volume of the space surrounded by the back surface of the diaphragm 14 and the acoustic resistance member 13 is V1, and the volume of the space surrounded by the acoustic resistance member 13 and the inner wall of the cabinet 11 is V2. Usually, the acoustic resistance member 13 is provided at a position where the ratio of V1 and V2 (V1 / V2) is 1/2 or less, preferably 1/5 or less. If the acoustic resistance member 13 is arranged at such a position, the acoustic resistance member 13 exerts a braking action on the entire speaker system, and the disturbance of the sound pressure frequency characteristic (sound pressure peak) near the lowest resonance frequency is reduced. Is preferable. Next, the expression of the braking resistance will be described in detail with reference to the electroacoustic equivalent circuit diagram 30 shown in FIG.

    In FIG. 3, a portion 31 surrounded by a dotted line has the same basic configuration as the electroacoustic equivalent circuit 20 of the braking speaker unit 19 described in FIG. Therefore, the same components as those shown in FIG. Here, a configuration different from FIG. 2 will be described.

A portion 32 surrounded by an alternate long and short dash line is an electroacoustic equivalent circuit of the cabinet 11 part. C2 is the acoustic compliance of the space V2 surrounded by the acoustic resistance member 13 and the inner wall of the cabinet 11, R3 is the radiation resistance, and L2 is the ineffective component of the radiation impedance. As shown in FIG. 2, the electroacoustic equivalent circuit of the acoustic resistance member 13 is at a frequency that is sufficiently away from the parallel resonance frequency of the capacitance C4 and the inductance L4, that is, a frequency that exhibits the effect of the present invention (near the lowest resonance frequency). The acoustic resistance is R4. Therefore, hereinafter, the electroacoustic equivalent circuit of the acoustic resistance member 13 will be described in a simplified manner as the acoustic resistance R4.

FIG. 3 shows the sound pressure frequency characteristics obtained by calculating the relationship between the sound pressure and the frequency by the calculation simulation using the ratio C3 / C2 (corresponding to V1 / V2) of the sound compliance C3 and the sound compliance C2 shown in FIG. FIG. The calculation simulation was performed by an electric CAD after converting mechanical parameters to electric parameters. The numerical values of each parameter used for the calculation are as follows.
Characteristics of speaker unit 12: Vac = 1V, L1 = 2780 μH, C1 = 426 μF, R1 = 0.683Ω, R2 = 1.38Ω
Acoustic resistance R4 of the acoustic resistance member 13: Five types of 0.2Ω, 0.4Ω, 0.6Ω, 0.8Ω, and 1.0Ω

    FIG. 4A is a sound pressure frequency characteristic diagram when the acoustic resistance member 13 is arranged at a position where C3 / C2 is 1/30 (corresponding to V1 / V2 = 1/30). Similarly, in FIG. 4b, C3 / C2 is 1/5 (corresponding to V1 / V2 = 1/5), FIG. 4c is C3 / C2 is 1/2 (corresponding to V1 / V2 = 1/2), and FIG. It is a sound pressure frequency characteristic figure at the time of arrange | positioning the acoustic resistance member 13 in the position where C3 / C2 becomes 1/1 (equivalent to V1 / V2 = 1/1). In addition, the direction of the arrow in the drawing indicates the direction in which the acoustic resistance R4 of the acoustic resistance member 13 increases in order from top to bottom. For example, referring to FIG. 4a, the uppermost sound pressure frequency characteristic is when R4 is 0.2Ω, and the lowermost sound pressure frequency characteristic is when R4 is 1.0Ω.

    As can be seen from FIG. 4, when the acoustic resistance member 13 is arranged at a position where V1 / V2 (C3 / C2) is 1/2 or less, the braking resistance is increased in proportion to the acoustic resistance R4 of the acoustic resistance member 13, The effect of flattening the peak of the sound pressure near the lowest resonance frequency appears. However, if the acoustic resistance member 13 is disposed at a position where V1 / V2 (C3 / C2) is greater than 1/2, the braking resistance is reduced, and the acoustic is detected at a position where V1 / V2 (C3 / C2) is 1/1 or more. It can be seen that when the resistance member 13 is disposed, the braking action does not appear even if the acoustic resistance R4 is increased.

    As described above, the braking resistance of the entire speaker system 10 can be controlled by adjusting the acoustic resistance R4 of the acoustic resistance member 13 and the arrangement of the acoustic resistance member 13, that is, C3 / C2. For example, when the dynamic impedance R2 (braking resistance) of the speaker unit 12 is small, the speaker unit 12 is disposed in the vicinity of the speaker unit 12 and the speaker unit 12 is covered with the acoustic resistor member 13 having a large acoustic resistance. The braking resistance of the entire system 10 can be increased. This can be considered that the apparent dynamic impedance of the speaker unit is increased by the acoustic resistance member 13. Therefore, it is possible to flatten the sound pressure near the lowest resonance frequency of a speaker system using an inexpensive speaker unit having a low dynamic impedance, that is, a speaker unit having a weak magnet magnetic force.

    As described above, the acoustic resistance member 13 exhibiting the braking action is preferably a porous body having a sound absorption peak frequency of 1 kHz or less and air permeability. The basis for this will be described below.

    FIG. 5 shows the results of experiments on the relationship between the sound absorption characteristics and braking action of each urethane foam using five types of urethane foam (open cell urethane) as the porous body. The presence / absence of the braking action was determined using the sealed speaker system shown in FIG. 1 based on whether or not the peak of the sound pressure generated near the lowest resonance frequency was low. The sound absorption peak frequency of the urethane foam was determined by measuring with a normal incidence sound absorption rate measuring device.

As can be seen from FIG. 5, samples A and B having a sound absorption peak frequency of 1 kHz or less have a braking action, but samples C, D, and E having a sound absorption peak frequency of 1 kHz or more have no braking action. Further, when the samples A and B were compared, the braking effect of the sample A was greater than that of the sample B. When this difference was examined in detail, the sound absorption frequency bandwidth (150 Hz to 850 Hz) of sample A was wider than the sound absorption frequency bandwidth (300 Hz to 1.2 kHz) of sample B, and sample A had the lowest resonance frequency than sample B. The sound absorption rate in the vicinity was high. Further, there is a correlation between the air permeability of the urethane foam and the braking effect, and the samples A and B having an air permeability of 10 cc / cm ² / sec or less, preferably about 1 cc / cm ² / sec, have a braking effect. I understood.

    From the above experimental results, it has been found that the required performance required for the acoustic resistance member 13 is preferably a sound absorption peak frequency of 1 kHz or less, a wide sound absorption frequency bandwidth, and a sound absorption characteristic near the lowest resonance frequency. .

[Configuration of acoustic resistance member]
As the acoustic resistance member 13 applicable to the present invention, any member may be used as long as it has a sound absorption peak wavelength of 1 kHz or less and air permeability. As for those having such characteristics, there are open-cell foams made of resin, synthetic rubber, metal, etc., semi-closed-cell foams in which closed cells and open cells are mixed, fine pores with a diameter of 0.8 mm or less. And a multi-perforated sheet in which a plurality of perforated sheets are stacked with a gap therebetween.

Open cell foam or semi-closed cell foam includes elastomers such as thermoplastic polyurethane, thermoplastic polyolefin, and thermoplastic polystyrene, synthetic rubber such as NBR, SBR, silicon rubber, and ethylene propylene rubber, polypropylene resin, and polyethylene resin. And foamed with a resin such as aluminum and a metal such as aluminum. These foams have an air permeability of 10 cc / cm ² / sec or less, preferably about 1 cc / cm ² / sec, but the sound absorption peak frequency is 1 kHz or less, and a large acoustic resistance can be obtained in a small amount. Is preferable.

    As the porous sheet 50, as shown in FIG. 6, a plurality of holes 52 (a plurality of holes 52 () are formed in a base plate 51 made of a metal plate such as stainless steel, copper, iron, or nickel, a plastic sheet such as PET or aramid, or a ceramic sheet such as zirconia. The thing which opened the through-hole) can be used. By appropriately selecting the thickness of the substrate 51 (the length of the hole), the hole diameter of the hole 52, the opening ratio of the hole 52, and the shape of the hole 52, the sound absorption peak frequency, the sound absorption frequency bandwidth, the acoustic resistance, etc. The characteristics can be adjusted.

    Widening the sound absorption frequency bandwidth is desirable in that the frequency bandwidth that can be braked is widened. For example, in order to make the sound absorption frequency bandwidth 1.4 octave or more, the thickness of the base material 51 is 0.1 to 1 mm, the hole diameter of the hole 52 is 0.1 to 0.8 mm, and the hole area ratio of the hole 52 is Of 0.1 to 2%.

    The acoustic resistance of the porous sheet 50 can be adjusted by the thickness of the substrate 51 (the length of the holes 52) and the opening ratio of the holes 52. That is, the acoustic resistance increases in proportion to the length of the hole 52 and increases in inverse proportion to the opening ratio of the hole 52. Therefore, the drilling method is important in that it has a great influence on the acoustic characteristics, manufacturing cost, and processing accuracy of the porous sheet. Next, the drilling method will be described.

When desired acoustic resistance is obtained within a range (L ≦ R) in which the length (L) of the hole 52 is not longer than the hole diameter (R) of the hole 52, drilling such as chemical etching, electrical discharge machining, punching, etc. The hole 52 can be formed with high accuracy by the construction method.
The porous sheet prepared by the above-described construction method is excellent in that the manufacturing cost is low. However, when the acoustic resistance is too small with one porous sheet described above, it is preferable to use a multi-porous sheet described later.

    When the acoustic resistance is increased by making the length (L) of the hole 52 of the porous sheet 50 longer than the hole diameter (R) (L> R), it can be achieved by punching with picosecond laser processing. The perforated sheet produced by this method is excellent in that the structure is simple and the acoustic resistance can be freely controlled.

    In FIG. 6, the shape of the hole 52 is circular. However, the shape of the hole 52 is not limited to this, and may be a shape according to the purpose such as a square shape or a star shape. Further, by providing the hole 52 with a taper, the sound absorption frequency bandwidth can be expanded. Specifically, the hole diameter on the side where the sound wave enters the porous sheet is reduced, and the hole diameter on the side where the sound wave is emitted from the porous sheet is increased.

    Another method for adjusting the acoustic resistance can be achieved by using a multi-porous sheet 60 as shown in FIG. The multi-porous sheet 60 is composed of a plurality of the porous sheets described in FIG. The positions of the holes in the porous sheets 62 and 62 'may or may not coincide. Although FIG. 7 shows an example in which two porous sheets 62 are stacked, the acoustic resistance can be increased in proportion to the number of stacked sheets.

    By adjusting the distance (D) between the perforated sheets 62 and 62 ', the frequency bandwidth for absorbing sound can be controlled. The sound absorption frequency bandwidth becomes wider in proportion to the interval (D). Usually, the interval is set to 20 to 100 mm.

    As another method for widening the sound absorption frequency bandwidth, as shown in FIG. 8, a multi-porous sheet in which a porous sheet 71 (hole diameter: r1) and a porous sheet 72 (hole diameter: r2) having different hole diameters are overlapped is used. It can be achieved by using. That is, the sound absorption frequency bandwidth can be widened by overlapping the porous sheets having different sound absorption peak frequencies. Although FIG. 8 shows an example in which two porous sheets 71 and 72 are stacked, the acoustic resistance can be increased in proportion to the number of stacked sheets.

(Second embodiment)
[Configuration of bass reflex type speaker system]
FIG. 9 is a schematic cross-sectional view showing a configuration example of a bass reflex speaker system according to the present invention. FIG. 10 is an explanatory diagram for explaining the sound pressure frequency characteristics of the bass reflex type speaker system according to the present invention.
As shown in FIG. 9, the bass-reflex speaker system 80 has the same configuration as the sealed speaker system 10 shown in FIG. 1 except that an acoustic port 81 is attached to a part of the cabinet 11. Accordingly, the same components as those of the sealed speaker system 10 are denoted by the same reference numerals as those in FIG. Here, only a configuration different from FIG. 1 will be described.

    The arrangement of the acoustic resistance member 13 is calculated by including the volume of the acoustic port 81 in the volume V2 of the space surrounded by the acoustic resistance member 13 and the inner wall of the cabinet 11 described in the configuration of the sealed speaker system 10. Should be provided. When the acoustic resistance member 13 is arranged under such conditions, the sound pressure peak generated near the lowest resonance frequency (f0) of the cabinet 11 and the resonance frequency of the acoustic port as in the sound pressure frequency characteristic indicated by the solid line in FIG. The peaks and valleys of the sound pressure generated near (fp) are flattened. In addition, the dashed-dotted line of FIG. 10 is a sound pressure frequency characteristic when the acoustic resistance member 13 is not inserted.

(Third embodiment)
[Configuration of braking type speaker unit]
FIG. 11 is a schematic cross-sectional view showing a configuration example of a braking speaker unit according to the present invention. FIG. 12 is a schematic cross-sectional view showing another configuration example of the braking speaker unit according to the present invention. The braking type speaker unit shown in FIG. 11 is the same as the braking type speaker system described in FIG. Therefore, the same components as those in the braking speaker unit shown in FIG. 1 are denoted by the same reference numerals as those in FIG. Here, only the configuration different from the braking type speaker unit shown in FIG. 1 will be described.
As shown in FIG. 11, the braking speaker unit 19 has a configuration in which the back space of the diaphragm 14 of the speaker unit 12 (vibration space of the diaphragm 14) is closed by the acoustic resistance member 13.

    FIG. 11 a is a configuration example of a speaker unit suitable for the case where the acoustic resistance member 13 is an open-cell foam or a semi-closed-cell foam. A cap-type acoustic resistance member 13 obtained by molding the acoustic resistance member 13 made of such a foam according to the shape of the frame 18 is put on the frame 18 and joined. The shape and volume of the cap may be optimized according to the acoustic resistance of the acoustic resistance member 13, and is not limited to the form shown in the figure.

    FIG. 11 b shows an example of a configuration of a braking speaker unit suitable for the case where the acoustic resistance member 13 is a porous sheet or a multi-porous sheet having a narrow interval between the porous sheets, for example, 10 mm or less. Such a sheet-like acoustic resistance member 13 is joined to an opening window 101 (dotted line portion) provided in a frame 18 through which a back acoustic wave from the diaphragm 14 passes. When the acoustic resistance of the acoustic resistance member 13 may be small, the above-described foam may be joined to the opening window 101.

    Further, when the acoustic resistance member 13 is constituted by a single porous sheet, it may be a frame 102 having a plurality of holes as shown in FIG. 11c.

    FIG. 11d is a configuration example of a brake type speaker unit suitable for the case where the acoustic resistance member 13 is a multi-perforated sheet having a wide interval (10 mm or more) between the perforated sheets. This brake type speaker unit is provided with a pedestal 103 at a part of a flat portion of the frame 18 (a flat portion provided for mounting the speaker unit to a cabinet with screws or the like), and a multi-perforated sheet 104 is bonded onto the pedestal 103. It has a configuration.

    For example, when the lowest resonance frequency of the speaker unit is 80 to 200 Hz, the thickness of the substrate 51 is 0.1 to 1 mm, the diameter of the hole 52 is 0.1 to 0.8 mm, and the aperture ratio of the hole 52 is 0.1. A 1-2% porous sheet (see FIG. 6) is used. Such a porous sheet has an action of braking a sound pressure of 50 to 500 Hz, but has no action of braking the sound pressure for other frequencies. Therefore, the sound pressure frequency characteristic in the vicinity of the lowest resonance frequency is flattened, and the sound pressure frequency characteristic in which the sound pressure at a frequency of 500 Hz or higher is not reduced is obtained.

In addition, when using the braking type speaker unit to which the perforated sheet or the multi perforated sheet is attached to an open type speaker system such as a flat baffle type speaker system, as shown in FIG. 12, the perforated sheet 102 (see FIG. 12a) or a back plate 112 for forming an air layer on the back side of the multi-porous sheet 104 (FIG. 12b). Here, the side surface of the support frame 111 is open.

(Specific Example 1)
A dynamic speaker unit “EAS8P170A” (manufactured by Panasonic Corporation) shown below was installed in a closed cabinet (110 × 100 × 60 mm) having an internal volume of 0.66 liters.
● Standard dynamic impedance of speaker unit: 1.38Ω
Minimum resonance frequency (f0): 155 Hz
Reproduction frequency band: f0-32kHz
Output sound pressure level: 83.5dB / W (1m)
m0: 2.4 g
Q0: 1.2
Next, what was molded into a cap shape (volume: 0.5 liter) using “urethane foam DOX” (sample A shown in FIG. 5, acoustic resistance: 4.5Ω) manufactured by Bridgestone Corporation as an acoustic resistance member, As shown in FIG. 11a, the sealed speaker system 10 as shown in FIG. The ratio V1 / V2 (see FIG. 1) between V1 and V2 is about 1/30. The normal incidence sound absorption characteristic of “urethane foam DOX” is shown by a solid line in FIG.

The sound pressure frequency characteristic measured by putting the above-described sealed speaker system in an anechoic chamber is shown by a solid line in FIG. Note that the sound pressure frequency characteristic indicated by the dotted line in FIG. 14 uses the sample D (acoustic resistance: 0.2Ω) shown in FIG. 5 as the acoustic resistance member. As can be seen from FIG. 14, by providing the acoustic resistance member of Sample A in the cabinet under the above-described conditions, the sound pressure near the lowest resonance frequency was flattened. On the other hand, with the acoustic resistance member of Sample D, no braking effect was obtained.

(Specific Example 2)
A speaker unit to which a cap-like urethane foam similar to that of Example 1 (the volume of “urethane foam DOX”: about 1.2 liters) is attached to a bass-reflex cabinet having the following specifications, as shown in FIG. A bass-reflex speaker system was created. The ratio V1 / V2 (see FIG. 9) between V1 and V2 is about 1/70.
● Specifications of bass reflex type cabinet: Approximately 4.9 liters (length 220 x width 140 x depth 160 mm)
Acoustic port: inner diameter (diameter) 54mm, length 120mm

The sound pressure frequency characteristic measured by putting the above-described bass reflex type speaker system in an anechoic chamber is shown by a solid line in FIG. In addition, the sound pressure frequency characteristic shown with the dotted line of FIG. 15 uses the sample D shown in FIG. 5 as an acoustic resistance member. As can be seen from FIG. 15, the sound pressure near the resonance frequency (about 85 Hz) and the lowest resonance frequency (about 180 Hz) of the acoustic port is flattened, and the reproducibility of the low sound range is improved. On the other hand, with the acoustic resistance member of Sample D, no braking effect was obtained.

(Specific Example 3)
First, two porous sheets each having a plurality of holes formed in a lattice shape in a circular stainless steel sheet were prepared, and a multi-porous sheet as shown in FIG.
● Multi-porous sheet specifications Stainless steel sheet: 0.4mm thickness, 86mm diameter
Hole diameter: 0.4mm diameter
Hole opening rate: 1%
Pitch between holes: 3.3 mm
Spacer: Acrylic pipe with an inner diameter (diameter) of 80 mm, an outer diameter (diameter) of 86 mm, and a length (corresponding to D in FIG. 6) of 88 mm

Next, the above-mentioned multi-perforated sheet was attached to the speaker unit used in the specific example 1 through a pedestal to produce a multi-perforated sheet-attached speaker unit as shown in FIG. 11d. For the pedestal 103, the same acrylic pipe (22 mm in length) as the above spacer was used.
Next, this multi-perforated sheet-attached speaker unit was mounted on a bass reflex type cabinet similar to the specific example 2, and a bass reflex type speaker system as shown in FIG. 9 was produced. The ratio (V1 / V2) between V1 and V2 shown in FIG. 9 is about 1/10.

When the above-described bass reflex type speaker system was placed in an anechoic chamber and the sound pressure frequency characteristics were measured, characteristics substantially equivalent to those of the specific example 2 (see the solid line in FIG. 15) were obtained.

    The speaker unit and the speaker system according to the present invention are useful in the field of acoustic equipment.

Schematic cross-sectional view showing one configuration example of a sealed speaker system according to the present invention. Electroacoustic equivalent circuit diagram of a braking speaker unit according to the present invention Electroacoustic equivalent circuit diagram of the sealed speaker system shown in FIG. FIG. 1 is a diagram of sound pressure frequency characteristics simulated for the sealed speaker system shown in FIG. 1 using the arrangement of acoustic resistance members as parameters. The figure which shows the relationship between the sound absorption characteristic of an acoustic resistance member, and a braking effect Schematic which shows one structural example of the acoustic resistance member which concerns on this invention Schematic which shows the other structural example of the acoustic resistance member which concerns on this invention. Schematic which shows the other structural example of the acoustic resistance member which concerns on this invention. Schematic cross-sectional view showing a configuration example of a bass reflex speaker system according to the present invention. Sound pressure frequency characteristic diagram for explaining the sound pressure frequency characteristics of a conventional sealed speaker system Schematic cross-sectional view showing a configuration example of a speaker unit according to the present invention. Schematic cross-sectional view showing another configuration example of the speaker unit according to the present invention. Normal incidence sound absorption coefficient characteristic diagram showing an example of normal incidence sound absorption coefficient of the acoustic resistance member according to the present invention Sound pressure frequency characteristic diagram showing an example of sound pressure frequency characteristics of the sealed speaker system according to the present invention. Sound pressure frequency characteristic diagram showing an example of the sound pressure frequency characteristic of the bass reflex type speaker system according to the present invention. Sound pressure frequency characteristic diagram for explaining the sound pressure frequency characteristics of a conventional sealed speaker system

Explanation of symbols

10 Sealed speaker system 11 Cabinet 12 Speaker unit 13 Acoustic resistance member
19 Braking Speaker Unit 20 Electroacoustic Equivalent Circuit of Braking Speaker Unit 30 Electroacoustic Equivalent Circuit of Sealed Speaker System 50, 102 Perforated Sheet 60, 104 Multiple Perforated Sheet 80 Bass Reflex Speaker System 112 Back Plate

Claims (12)

  A speaker unit having a speaker diaphragm; and an acoustic resistance member provided in a back space of the speaker diaphragm, the back space being closed by the acoustic resistance member, and the acoustic resistance member being the speaker A braking type speaker unit having an acoustic resistance equal to or higher than the dynamic impedance of the unit.   The braking speaker unit according to claim 1, wherein a sound absorption peak frequency of the acoustic resistance member is 1 kHz or less.   The braking type speaker unit according to claim 1, further comprising a back plate for forming an air layer on a back side of the acoustic resistance member (a side opposite to the speaker diaphragm).   The brake type speaker unit according to claim 1, wherein the acoustic resistance member is a porous body having air permeability. The braking type speaker unit according to claim 4, wherein the porous body is an open-cell foam or a semi-closed-cell foam having an air permeability of 10 cc / cm ² / sec or less.   The braking speaker unit according to claim 4, wherein the porous body is a porous sheet having a plurality of through holes, and the diameter of the through holes is 0.8 mm or less.   The braking type speaker unit according to claim 6, wherein the porous body is a multi-perforated sheet in which a plurality of the porous sheets are opposed to each other with a gap therebetween.   The braking speaker unit according to claim 7, wherein the through holes of the plurality of perforated sheets have different diameters for each sheet.   A cabinet and a braking speaker unit according to any one of claims 1 to 8 mounted on an inner wall of the cabinet, and a back surface of an acoustic resistance member provided in the braking speaker unit; A speaker system comprising an air layer between an inner wall of a cabinet.   At a position where the ratio (V1 / V2) of the volume V1 of the space surrounded by the back surface of the speaker diaphragm of the braking type speaker unit and the acoustic resistance member to the volume V2 of the air layer is 1/2 or less. The speaker system according to claim 9, wherein the acoustic resistance member is disposed.   The speaker system according to claim 10, wherein the (V1 / V2) is 1/5 or less.   The speaker system according to any one of claims 9 to 11, wherein an acoustic port is provided in a part of the cabinet.

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