JPH04301998A - Loudspeaker box - Google Patents

Abstract

PURPOSE:To reduce the sound pressure level or distortion of a useless reproducing band lower than a low cut frequency by the loudspeaker box to reproduce low frequencies. CONSTITUTION:First and second cavities 4 and 5 are provided before and behind the radiation plane of a loudspeaker, at each cavity, a passive radiating means depending on acoustic quantity is provided to be linked with an external area and further, the first and second cavities 4 and 5 are coupled by the acoustic quantity. At a frequency lower than the low cut off frequency lower than the lower resonance frequency of the passive radiating means for resonance, the inertance of the acoustic quantity coupling the first and second cavities 4 and 5 is decreased, the sound pressure is canceled each other, and sound pressure radiation from the passive radiating means is reduced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates primarily to a speaker box for reproducing low frequencies, and more particularly to a speaker box with improved efficiency and distortion in low reproduction frequencies.

0002

2. Description of the Related Art Conventionally, there is a compact speaker system exclusively for reproducing low frequencies, as shown in the schematic diagram of FIG. In this system, cavities 4 and 5 are provided before and after the radiation surface of the speaker unit 3, and ducts 7 and 8 are provided in each cavity 4 and 5 to connect with the outside to cause resonance and efficiently radiate sound. It is published in Japanese Patent Application Publication No. 60-9.
8793.

0003

[Problems to be Solved by the Invention] However, with the above-mentioned prior art, the displacement of the speaker diaphragm can be minimized at the resonant frequency of passive radiation means such as a duct, but at lower frequencies, , the displacement of the diaphragm increases rapidly. Therefore, beyond the line system area of the diaphragm support system, drive system, etc., saturation areas are reached on both the plus side and the minus side, and in particular, odd harmonics such as the third harmonic increase rapidly. Since these odd-order harmonics are not consonant with the fundamental tone, they are easily detected as auditory distortion, which poses a problem in that the permissible input in practice becomes small.

0004

[Means for Solving the Problems] Therefore, in the present invention, first and second cavities are provided before and after the radiation surface of a speaker to surround the speaker, and an external area is provided in each of the cavities. A loudspeaker box having a first passive radiating means provided in a first cavity characterized by an acoustic mass coupled to a second cavity, and a second passive radiating means provided in a second cavity characterized by an acoustic mass coupled to said first and the second cavity are coupled by an acoustic mass.

[0005]

[Operation] Therefore, at a frequency lower than the lower resonance frequency of each of the first passive radiation means and the second passive radiation means, the acoustic mass coupling the first and second cavities is The inertance caused by the noise decreases, forming a bypass circuit, which acts to cancel out the sound pressure within the speaker box, thereby reducing the sound pressure and distortion in the band that does not need to be reproduced.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram showing an embodiment of the present invention. In the figure, a speaker box 1 has a speaker mounting plate 2 that divides its interior, with a first cavity 4 on the front side of the radiation surface of the speaker unit 3 and a second cavity 4 on the rear side. A cavity 5 is formed. Furthermore, a speaker unit 3 and a duct 6 are attached to the speaker mounting plate 2, with the front and rear cavities completely blocked off. The ducts 7 and 8 are installed in the first cavity 4 and the second cavity 5, respectively, so that the center axes of the ducts 7 and 8 do not coincide with the center axis of the speaker unit 3, It has good high-frequency attenuation characteristics.

The operation of the speaker box 1 constructed as described above will be explained with reference to FIGS. 2 to 4. Figure 2 shows the acoustic mass of the duct 7 and the acoustic mass of the duct 6 combined with the acoustic mass of the diaphragm of the speaker unit 3 at a certain moment when the cavity 4 resonates (resonance frequency foa). Each duct 6, 7 at that time with respect to the displacement direction
, 8 is a diagram showing the direction of air flow in the ducts.

As shown in the figure, when the diaphragm of the speaker unit 3 is displaced forward (in the direction of the arrow), the acoustic mass obtained by combining the acoustic mass of the duct 6 and the acoustic mass of the duct 7, The air in the ducts 6 and 7 during resonance (foa) with the cavity 4 acts in the direction in which the air flows into the cavity 4 in the opposite direction to the direction of displacement of the diaphragm. At this time, the inside of the duct 8 is deviated from the resonance frequency (FOB) caused by the acoustic mass obtained by combining the acoustic mass of the duct 6 and the acoustic mass of the duct 8 and the cavity 5, so the diaphragm The air acts in the direction in which air flows into the cavity 5 in the same phase as the direction of displacement.

Next, by lowering the frequency, the frequency (fo
The direction of air flow in each duct with respect to the displacement direction of the diaphragm of the speaker unit 3 in b) will be explained with reference to FIG. As shown in the figure, the acoustic mass of duct 8 and the duct 6
acoustic mass synthesized with the acoustic mass of cavity 5
The air within the ducts 6 and 8 at the time of resonance (FOB) acts in the direction in which the air flows out from the cavity 5 in the opposite direction to the direction of displacement of the diaphragm. Since the air within the duct 7 at this time is out of the resonance frequency (FOA), the air acts in the outflow direction from the cavity 4 in the same phase as the direction of displacement of the diaphragm.

Next, FIG. 4 shows the relationship when the frequency is further lowered. When the diaphragm of the speaker unit 3 is displaced forward, the cavity 4 is compressed, and the air within the ducts 6 and 7 acts in the direction of flowing out from the cavity 4 according to the amount of compression. On the contrary, the ducts 6 and 8 connected to the reduced pressure cavity 5 act so that air flows into the ducts.

[0011] As described above, in the frequency range lower than the resonant frequency (FOB), the inertance of the duct 6 decreases and it operates as a bypass circuit that connects the cavities 4 and 5. It acts to cancel out the sound pressure, reducing the sound pressure from the ducts 7 and 8, and also reducing the distortion level. Then, the resonant frequency (f
oa) In higher frequency bands, the inertance of the duct 6 increases and has no effect on the sound pressure radiation or distortion of the duct 6 to the speaker box 1.

Next, a prototype example will be shown. 12cm diameter speed
The resonance frequency (FOA) that resonates by the acoustic circuit of the cavity unit 3, the first cavity 4 having a volume of 1900 cubic centimeters, and the ducts 6 and 7 is set to 240Hz.
shall be. The second cavity 5 having a volume of 12,100 cubic centimeters and the acoustic circuit of the ducts 6 and 8 have a resonance frequency (FOB) of 60H.
z, opening area 2.54 square centimeters, length 1
The sound pressure characteristics when a 3 cm duct 6 is provided are shown by a solid line 9 in FIG. The sound pressure characteristics when the duct 6 is not provided at this time are shown by the broken line 10 in FIG.

As shown in the figure, the degree of attenuation of the sound pressure level is increased by providing the duct 6 below the resonance frequency (FOB). FIG. 6 shows a comparison of the third harmonic distortion characteristics during the sound pressure characteristics in FIG. 5. A solid line 11 shows the distortion characteristics in the example, and it can be seen that the distortion level is lower than in the case where the duct 6 is not provided, as shown by the broken line 12.

[0014] The first and second passive radiation means and the means for coupling the cavities 4 and 5 are not limited to ducts, but can also be used as long as they can provide acoustic mass, such as passive radiators. can.

[0015]

As described above, according to the present invention, it is possible to reduce the sound pressure level and distortion in the unnecessary reproduction band below the low cutoff frequency.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing one embodiment of the present invention.

[Figure 2]

[Figure 3]

FIG. 4 is an explanatory diagram for explaining the above embodiment.

[Figure 5]

FIG. 6 is a characteristic diagram of the above embodiment.

FIG. 7 is a schematic configuration diagram showing a conventional example.

[Explanation of symbols]

1 Speaker box 2
Speaker mounting plate 3 Speaker unit 4 First cavity 5 Second cavity 6, 7, 8
Ducts 9, 10 Sound pressure characteristics 11, 12 Distortion characteristics

Claims (1)

[Claims] 1. A device characterized by: enclosing means for enclosing the speaker by providing first and second cavities before and after a radiation surface of the speaker; and an acoustic mass coupled to each of the cavities with an external region. In a speaker box having a first passive radiating means provided in a first cavity and a second passive radiating means provided in a second cavity, the first and second cavities are acoustically A speaker box characterized by being connected by mass.