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DESCRIPTION JP2002159083

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DESCRIPTION JP2002159083
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
low frequency reproduction speaker unit, and more particularly to a low frequency reproduction
speaker unit in which a duct having a port (opening) is formed in a speaker enclosure.
[0002]
2. Description of the Related Art As shown in the cross-sectional views and front views of FIGS. 8
(a) and 8 (b) as a low-frequency reproduction speaker unit, a speaker 4 is mounted in an
enclosure (box) 3 in which a speaker opening 1 is formed. There is known a phase-reversal lowrange reproduction speaker unit in which a duct (tube) 5 having a port (opening) 2 at the front of
the enclosure is provided. The sound absorbing material 6 is appropriately disposed inside the
enclosure. According to such a phase-reversal type low-range reproduction speaker unit, the
enclosure itself (referred to as “Vented Type Enclosure”) can be a so-called Helmholtz
resonator, and the entire low range can be enhanced. The reason is explained below.
[0003]
The speaker vibrates back and forth to create a compressional wave in the space, but moving
forward causes the air on the front of the cone to be dense, the air on the back of the cone to be
rough and the phases are opposite. When the speaker sounds barely without a baffle, the front
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and back coarseness mixes with each other and cancels each other out, resulting in no sound. It
is sufficient to attach a large baffle so that the noises of the front and back phases are not mixed,
but the effective baffles to low frequencies are large and not practical. Therefore, in the phasereversal type low-range reproduction speaker unit, the phase of the sound from behind is
inverted by 1,800 in duct 5, and is emitted from port 2 in the same phase as the front phase of
the cone. That is, the phase-reversal type low-pass reproduction speaker unit actively uses the
sound radiated from the rear face of the speaker and generates so-called "Helmholtz resonance"
action between the internal volume of the enclosure 3 and the duct 5, Sound is emitted from the
port 2 to the outside by the resonance action. Since this emitted sound is in phase with the sound
emitted to the front of the speaker unit, it just works to improve the bass activity rate. The socalled "phase inversion" is called an enclosure that actively uses this in order to invert the
positive phase and increase the effect when sound in antiphase from the rear face of the speaker
unit is emitted from the port at resonance. I'm coming from there.
[0004]
FIG. 9 is a perspective view of another conventional phase-reversal low-pass speaker unit, in
which the speaker holes 1 and the ports 2 are formed in adjacent different surfaces of the
enclosure 3 and the pipe duct 5 having a circular cross-section is used. It is formed inside. FIG.
10 shows the electrical impedance characteristic (f-Z characteristic) of the conventional phase
inversion type low-pass reproduction speaker unit. As apparent from the fZ characteristic, the
speaker unit has a first resonance frequency (resonance frequency of the speaker 4 attached to
the box) f1 and a second resonance frequency (resonance frequency of the port 2) f2, , And the
radiation efficiency is increased near the resonance frequency. FIG. 11 shows an example of
speaker arrangement in a sedan type automobile, in which four full range speakers S1 to S4 are
respectively disposed on the front and rear left and right doors, and the low frequency
reproduction speaker S5 of FIG. 8 or FIG. Are arranged in the trunk as a subwoofer. The lowrange reproduction speaker S5 is disposed at the rear end of the luggage storage in the RV and
minivan type cars.
[0005]
SUMMARY OF THE INVENTION In the phase-reversal type low-range speaker unit, the maximum
sound pressure is obtained centered on the resonance frequency, and conventionally, the first
and second resonance frequencies f1 and f2 (FIG. 10) Are both designed to be appropriate values
within the practical use band (about 20 Hz to 100 Hz). Since the electrical impedance changes
around these first and second resonance frequencies f1 and f2, the frequency phase
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characteristic (f-.theta. Characteristic) does not become a flat characteristic of phase = 0 as shown
by the dotted line in FIG. . That is, in the conventional low-range reproduction speaker unit, the
phase θ is delayed or advanced in the actual use band, and a time delay occurs due to the
frequency f. Essentially, it is desirable that the sound arrive with zero phase delay, and if the
phase is delayed or advanced depending on the frequency, the sound becomes turbid and
distortion increases. In particular, as shown in FIG. 11, the sub-woofer S5 is disposed at a
position farthest from the driver's seat in the vehicle, so the delay is further increased and
distortion occurs due to a phase shift with the main speakers S1 to S4 in sound quality. Also,
there is a problem that the sound image localization of the subwoofer S5 is deteriorated. From
the above, the object of the present invention is to reduce distortion and improve low-range
sound image localization.
[0006]
SUMMARY OF THE INVENTION In order to achieve the above object, according to the present
invention, the phase characteristic in the actual use band is made substantially flat (= zero). In
particular, in order to achieve the above object, the low frequency reproduction speaker unit of
the present invention includes a speaker enclosure, a duct formed in the speaker enclosure, and a
duct provided with a port on the speaker enclosure, and a speaker attached to the speaker
enclosure. The speaker has a first resonant frequency set higher than the upper frequency of the
actual use band, and the port has a second resonant frequency set lower than the lower
frequency of the actual use band. Preferably, the speaker has a vibration system which makes the
first resonance frequency higher than the upper frequency of the actual use band by weight
reduction. Alternatively, the first resonance frequency is made higher than the upper frequency
in the actual use band by lowering the compliance of the speaker. Preferably, the second
resonance frequency is made lower than the lower frequency in the actual use band by
increasing the duct length. Alternatively, the second resonance frequency is made lower than the
lower frequency in the actual use band by controlling the cross-sectional area of the duct.
According to the above speaker unit for low-frequency reproduction of the present invention, by
bringing the first and second resonance frequencies of the speaker unit to the outside of the
actual use band, it is possible to flatten the phase characteristics in the actual use band,・ There
is no time delay. For this reason, not only distortion due to phase shift between other speaker
units is reduced, but also time lag for each frequency is eliminated so that sound image
localization in the low band is significantly improved, and a clear sense of localization can be
obtained. . Furthermore, according to the low-frequency reproduction speaker unit of the present
invention, both phase characteristics and frequency characteristics can be made flat in the actual
use band, and therefore, a small speaker can output high-power sound. Further, according to the
low-frequency reproduction speaker unit of the present invention, the low-compliance (small
amplitude) speaker unit may be used for the realization, so that the speaker unit is not damaged
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due to the low-frequency excessive amplitude. It is possible to improve the reliability.
[0007]
DESCRIPTION OF THE PREFERRED EMBODIMENTS (A) Schematic of the Present Invention FIG. 1
is a schematic explanatory view of a speaker unit for low frequency reproduction according to
the present invention. The low-range reproduction speaker unit has an enclosure 10 in which
speaker openings 11 and ports (openings) 12 are formed on adjacent surfaces. A speaker 13 is
attached to the inside of the enclosure 10 so as to be fitted into the speaker opening 11, and a
duct (tube) 14 forming the port 12 is provided so as to extend in a substantially L shape inside
the enclosure 10. ing.
[0008]
In the low-frequency reproduction speaker unit shown in FIG. 1 of the present invention, the
resonance frequency (first resonance frequency) f1 of the speaker 13 when attached to the
enclosure 10 is higher than the upper frequency of the practical use band (about 20 Hz to 100
Hz) The speaker 13 and the duct 14 are designed so that the resonance frequency (second
resonance frequency) f2 of the port 12 is higher than the lower frequency of the actual use band.
When the first and second resonance frequencies f1 and f2 are designed to be outside the
practical use band (about 20 Hz to 100 Hz) as described above, the electrical impedance
characteristic (f-Z characteristic) is as shown by the solid line in FIG. The phase characteristic (f.theta. Characteristic) becomes substantially flat (= zero) in the actual use band as indicated by
the dotted line in FIG.
[0009]
(B) The resonance frequency (first resonance frequency) f1 of the speaker 13 when attached to
the adjustment enclosure 10 of the first and second resonance frequencies is f1 = (1 / 2π) / (M
× C) 1/1 2 Determined by (1). Here, M is the mass of the vibration system of the speaker, and C
is the compliance of the speaker. Therefore, the resonance frequency f1 of the speaker unit can
be made higher than the upper frequency of the practical use band (about 20 Hz to 100 Hz) by
reducing the mass M or the compliance C of the vibration system. Here, compliance is an
antonym of stiffness (rigidity) and is a value indicating ease of amplitude (vibration).
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[0010]
Further, the resonant frequency (second resonant frequency) f2 of the port 12 can be obtained
by the following equation f2 = (Vs / 2π) × {S / (L × VI)} 1/2 (2). Where Vs is the speed of
sound, S is the cross-sectional area of the duct 14, L is the length of the duct, and VI is the
volume of the enclosure 10. Therefore, by making the length L of the duct 14 integrally formed
in the enclosure longer than usual, or reducing the cross-sectional area S of the duct 14, the
resonance frequency f2 can be used in the practical use band (about 20 Hz to 100 Hz) Can be
lower than the lower frequency. In this case, if the duct cross-sectional area S is reduced, the
acoustic resistance is increased and the sound pressure is insufficient. Also, if the duct length L is
increased, the sound pressure is also reduced. For this reason, it is desirable to adjust the duct
length L and the cross-sectional area S so that the sound pressure does not become so small and
the resonance frequency f2 becomes lower than the actual use band.
[0011]
(C) Loudspeaker Configuration FIG. 3 is a schematic diagram of the most common cone-type
loudspeaker, which is mainly divided into three parts. The first is a vibration system, the second
is a magnetic circuit, and the third is a main body portion supporting these. The vibration system
comprises a diaphragm (cone paper) 21, an edge 22, a voice coil 23, a damper 24, a center cap
25 and the like, and a magnetic circuit comprises a magnet 26, a center pole / yoke 27, and a
plate 28 The portion is composed of a frame 29, a gasket 30, an input terminal 31, and the like.
When current is supplied to the voice coil 23 based on the voice signal, the cone paper 21
vibrates in the directions of arrows A and B according to the positive and negative of the current
according to the left-hand rule of flumming, and sound is emitted.
[0012]
Cone diaphragm The cone diaphragm 21 is characterized by being conical in shape, and is an
important part that affects the speaker performance, and various shapes, materials, and
manufacturing methods for its purpose and performance There is something different from The
cone diaphragm 21 is generally driven by fixing the voice coil 23 to the neck and supported by
the edge 22 at its periphery, and has a conical shape so that the periphery away from the drive
point can withstand the air load. Requires angled slopes and mechanical strength. As the material
of the corn, there is a paper pulp treated with a phenol resin to aluminum or silk fibers, for
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example. Recently, new materials such as aluminum single plate, sandwich structure or
honeycomb sandwich using CFRP have been developed. Paper cones, which are currently widely
used as cones, have physical properties as diaphragms, ie stiffness, density and internal loss close
to the appropriate values, moreover, they are easy to manufacture and other materials have
unappealable characteristics . The paper cones have features such as laminated cones, non-press
cones, wet press cones, and dry press cones. There are many corn materials in addition to the
above, and in view of their combinations and blending ratios, the types of materials are very
large.
[0013]
Damper Damper 24 suspends the voice coil 23 in the magnetic pole gap G and has a function to
maintain the center so as not to hit the magnetic pole at the time of vibration and a position to
hold the entire vibration system. It becomes a factor that governs the bass resonance frequency
of the system. Therefore, it is necessary to have a structure and a material having a property that
it is soft in the axial direction which is the vibration direction and is hard to move in the lateral
vibration perpendicular to this. In general, the outer damper containing corrugation called spider
is mainly made of linen, cotton, silk or nylon fiber material, and is often heat-formed by
impregnating with a phenol resin. It is because the roughness of the eyes of these fabrics is
breathable and has the effect of preventing internal resonance and sound radiation.
[0014]
The edge 22 serves as an acoustic end of the diaphragm 21 as well as holding the diaphragm in
the correct position and preventing acoustic shorting between the baffle and the outer periphery
of the diaphragm. Therefore, the edge 22 is required to have mechanical linearity with respect to
the vibration of the diaphragm 21. In addition, it works as a stiffness of the vibration system
together with the damper 24 and controls the bass resonance frequency, so that it is required to
be flexible in the axial direction which is the vibration direction and hard to move in the lateral
vibration. A device is necessary. There are various types of structures of the edge, which are
classified into three types of fixed edge, free edge and edgeless which are roughly classified. In
addition, materials include dumped edges coated with damping paint on paper or cloth, leather
(deer, goat, rattan, etc.), felt, urethane foam, rubber molded products, etc. It is desirable to have
resistance.
[0015]
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(D) Specific Adjustment Method of First Resonance Frequency According to the equation (1), to
adjust the resonance frequency (first resonance frequency) f1 of the speaker 13, the mass M of
the vibration system is reduced or the compliance C is lowered. Just do it. In order to reduce the
mass M of the vibration system, the material such as the diaphragm (corn paper) 21, the edge
22, the voice coil 23, the damper 24, the center cap 25 and the like and the impregnated
material are devised to reduce the weight. Also, as described above, the damper and the edge
operate to provide stiffness of the vibration system and dominate the aforementioned bass
resonance frequency. Therefore, the compliance C can be lowered by devising the material and
structure of these dampers and edges. For example, the stiffness (spring coefficient) is increased
by using a thick linen cloth as the damper 24 or by performing a treatment such as hardening
after being impregnated. (E) Comparison of the configuration and characteristics of the speaker
unit according to the present invention and the prior art FIG. 4 is a configuration diagram of the
low frequency reproduction speaker unit of the present invention, and FIG. 5 is a configuration
diagram of the conventional low frequency reproduction speaker unit a) is a perspective view
and (b) and (c) are diagrams showing the shape of a duct in the enclosure. In the inventive
loudspeaker unit of FIG. 4, the duct 14 is substantially L-shaped and is longer than the duct of
the conventional loudspeaker unit of FIG. FIG. 6 is a characteristic diagram of the low-frequency
reproduction speaker unit according to the present invention, and FIG. 7 is a characteristic
diagram of the conventional low-frequency reproduction speaker unit, wherein (a) shows f-Z
characteristics and (b) shows f-.theta. It is a characteristic. As apparent from FIGS. 6 (a) and 6 (b),
according to the speaker unit for low band reproduction of the present invention, the first and
second resonance frequencies f1 and f2 are set outside the practical use band (subwoofer band)
FU. And the f-.theta. Characteristic can be made substantially flat (= zero) within the actual use
band. On the other hand, in the conventional low frequency reproduction speaker unit, the first
and second resonance frequencies f1 and f2 are both in the actual use band (subwoofer band)
FU, so the f-θ characteristic is the actual use band It does not flatten and changes significantly.
Although the present invention has been described above by way of examples, the present
invention can be variously modified in accordance with the spirit of the present invention
described in the claims, and the present invention does not exclude these.
[0016]
As described above, according to the present invention, by bringing the first and second
resonance frequencies of the speaker unit to the outside of the actual use band, the phase
characteristics in the actual use band can be made flat, and phase delay / time delay is realized.
There is no For this reason, not only distortion due to phase shift between other speaker units is
reduced, but also time lag for each frequency is eliminated so that sound image localization in
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the low band is significantly improved, and a clear sense of localization can be obtained. .
Further, according to the present invention, both phase characteristics and frequency
characteristics can be made flat in the actual use band, so that high-power sound can be output
with a small speaker. Further, according to the present invention, the speaker unit for realization
can be of low compliance (small in amplitude), so breakage of the speaker unit due to excessive
amplitude in the low range can be eliminated and reliability can be improved. .
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