JPH04233899A - Bass-reflex type loudspeaker - Google Patents

Abstract

PURPOSE:To obtain the flat characteristic in a wide frequency range by preventing generation of a standing wave generated in an acoustic port. CONSTITUTION:In the bass-reflex type loudspeaker formed by providing a loudspeaker unit 1 for radiating a sound to the outside, and an acoustic port 2 for radiating the sound of a low frequency in a cabinet 3, the acoustic port 2 is constituted of a sound absorbing material which can fix the shape.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a bass reflex device configured to combine a part of the sound emitted from the rear side of the speaker unit with the sound emitted from the front side of the speaker unit to enhance bass characteristics. This relates to type speakers.

0002

2. Description of the Related Art Bass reflex speakers have been known as speakers that reproduce rich bass sounds even in small cabinets.

FIG. 6 is a sectional view showing a conventional bass reflex type speaker. In the figure, 1 is a speaker unit that radiates sound to the outside, 21 is an acoustic port that radiates low-frequency sound to the outside, and 3 is the speaker unit 1 and the acoustic port 21.
4 is the speaker unit 1
, 5 is sound radiated from the back of the speaker unit 1 , and 6 is sound radiated from the acoustic port 21 .

[0004] Next, the operation of the above configuration will be explained. The sound 5 emitted from the rear surface of the speaker unit 1 is transmitted through the acoustic port 21, where the low-frequency sound is intensified, and the sound 5 is emitted from the acoustic port 21 to the front surface as the sound 6. Since the sound 6 emitted from this acoustic port 21 is combined with the sound 4 from the front of the speaker unit 1, the bass reflex type speaker can expand the bass range by the amount of sound 6 from this acoustic port 21. .

[0005]

[Problem to be Solved by the Invention] The conventional bass reflex type speaker is constructed as described above, and the acoustic port 21 forms a kind of open tube, so that within the acoustic port 21, fn=(nc/2L ) However, fn: Resonant frequency [Hz] c: Speed of sound [m/s] L: Port length of acoustic port [m] n: Resonance at the frequency of the standing wave order (m = 1, 2, 3,...) A phenomenon occurs and a standing wave is generated.

FIG. 7 shows the vibration state of standing waves generated in an open tube of length L in terms of wavelength and resonant frequency. Due to these standing waves, the frequency-sound pressure characteristics of the speaker are as shown in FIG. As shown by D in , there are many peaks P1 and dips P2.

The present invention was made to solve the above-mentioned problems, and provides a bass reflex type speaker that can prevent the generation of standing waves and obtain flat characteristics over a wide frequency range. The purpose is to

[0008]

[Means for Solving the Problems] A bass reflex type speaker according to the present invention is characterized in that an acoustic port for radiating low-frequency sound is made of a sound-absorbing material whose shape can be fixed.

[0009]

[Operation] According to the present invention, by configuring the acoustic port with a sound absorbing material whose shape can be fixed, the standing waves generated within the acoustic port are absorbed, and the peak/dip of the frequency-sound pressure characteristics is reduced. becomes possible.

0010

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing a bass reflex type speaker system according to an embodiment of the present invention. In FIG. 1, reference numeral 2 denotes an acoustic port made of a sound-absorbing material whose shape can be fixed, and as clearly shown in FIG. , and a blocking layer 2b that blocks air from passing through. Since the other parts are the same as those of the conventional example shown in FIG. 6, the same reference numerals are given to the corresponding parts and the explanation thereof will be omitted.

Next, the structure and function of each part of the above configuration will be explained. The sound absorbing layer 2a made of a sound absorbing material such as a particulate plastic material constituting the acoustic port 2 is made of 1
It has a structure that resembles an agglomeration of pellet-like particles with a diameter of several millimeters, and has a sound-absorbing effect due to the presence of voids.

FIGS. 3 and 4 are diagrams for explaining changes in the sound absorption properties of particulate plastic materials when the porosity is changed. FIG. 3 shows the change in porosity in the thickness direction of three types of samples. The sample shown in this figure has a structure in which the porosity increases as it progresses in the thickness direction, and the overall porosity decreases in the order of F→G→H.

FIG. 4 shows the sound absorption coefficient of the sample shown in FIG.
These are the results of measurements based on IS A1405 "Measurement method of normal incidence sound absorption coefficient of building materials by in-pipe method". As can be seen from the figure, sound absorption is performed around a specific frequency fp determined by the porosity, etc., and the smaller the overall porosity, the lower the frequency fp.

Furthermore, while conventional sound-absorbing materials such as glass wool cannot be fixed in shape, particle plastic materials can be fixed in various shapes by raising the mold, so they are suitable as materials constituting the acoustic port 2. ing.

[0016] Furthermore, particulate plastic material also has air permeability in its normal state, and when it has such air permeability,
Since it cannot play the role of an acoustic port and the sound absorption properties of the particulate plastic material do not have the required properties (peak properties), the acoustic port 2 has an air penetration layer in addition to the sound absorption layer 2a as shown in Figure 2. A blocking layer 2b is provided for blocking. This barrier layer 2b may be constructed from a particulate plastic material with extremely low porosity, or may be constructed from other materials.

On the other hand, since the first-order standing wave (when n=1 in Equation 1) has the greatest influence on the frequency-sound pressure characteristics of the speaker, its resonance frequency fι and the sound absorption of the particle plastic material If the porosity of the particle plastic material constituting the acoustic port 2 is adjusted so that the frequency fp at which the ratio is maximum is equal, the standing waves generated within the acoustic port 2 will be effectively absorbed, and the speaker The frequency-sound pressure characteristic has fewer peaks and dips, as shown by E in FIG.

In the above embodiment, the acoustic port 2 is made of a particulate plastic material, but it may also be made of other shape-fixable sound-absorbing materials, such as foamed metal. It has a similar effect.

[0019]

As described above, according to the present invention, by configuring the acoustic port with a sound absorbing material whose shape can be fixed and absorbing the standing waves generated within the acoustic port, the frequency - sound pressure can be reduced. The peak and dip of the characteristic can be reduced, and flat characteristics can be obtained over a wide frequency range.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the structure of a bass reflex speaker according to an embodiment of the present invention.

FIG. 2 is an enlarged sectional view of main parts.

FIG. 3 is a diagram for explaining changes in the sound absorption properties of a particulate plastic material when the porosity is changed.

FIG. 4 is a diagram for explaining changes in sound absorption characteristics similarly to FIG. 3;

FIG. 5 is a frequency-sound pressure characteristic diagram of the conventional and the present invention.

FIG. 6 is a sectional view showing the structure of a conventional bass reflex speaker.

FIG. 7 is a diagram showing a state of vibration of a standing wave generated in an open pipe of length L.

[Explanation of symbols]

1 Speaker unit 2. Acoustic port 2a Sound absorption layer 2b Blocking layer 3 Cabinet 4, 5, 6 Emitted sound

Claims (1)

[Claims] Claim 1. A bass reflex speaker comprising a speaker unit that radiates sound to the outside and an acoustic port for radiating low-frequency sound in a cabinet, wherein the acoustic port can be fixed in shape. A bass reflex type speaker characterized by being constructed from wood.