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JPH06153291

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DESCRIPTION JPH06153291
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention converts an
electric signal into an acoustic wave by applying a signal current to a movable coil placed in a
magnetic circuit and driving a diaphragm through the movable coil vibrating at this time. In
particular, the present invention relates to a cone type speaker in which a diaphragm is in a cone
shape.
[0002]
2. Description of the Related Art With respect to a cone type speaker, a reproduction band
characteristic indicating a reproducible frequency range and a transient response characteristic
indicating followability to a signal are considered as objective indicators when evaluating the
speaker ability. . Further, it is known that the two characteristics in relation to the mass of the
diaphragm are opposite to each other in reproduction of the low tone range.
[0003]
That is, a cone type speaker is usually used by attaching to an enclosure of appropriate inner
volume, and a diaphragm of the speaker in use is connected to the enclosure via a spring element
having air equivalent to the volume of the enclosure It is in the state. In addition, the
reproduction limit on the low frequency side of the cone type speaker is determined by the
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1
lowest resonance frequency as a speaker system determined by the spring element of air
confined in the enclosure and the mass of the diaphragm.
[0004]
Therefore, when the strength of the spring element is constant, the lower the resonance
frequency as the speaker system decreases as the mass of the diaphragm vibrating in balance
with the spring element increases, the reproduction band characteristic on the low frequency
side While the driving force determined by the magnetic circuit and the movable coil is constant,
as the mass of the diaphragm acting as a load for the driving force increases, the ability to follow
the signal change is impaired Transient response characteristics are degraded.
[0005]
Here, as a general technique for keeping the lowest resonance frequency low by using a
lightweight diaphragm that is advantageous for transient response characteristics, a support
system that mechanically supports the diaphragm, that is, a damper or an edge is made highly
compliant. Can point out the technology to
Also, as a special technique, a metal weight called mass control ring is fixed to the inside of a
bobbin around which a movable coil is wound, and the overall mass of the vibration system is
increased while using a lightweight diaphragm. The thing can be mentioned.
[0006]
Although the above-mentioned technology for making the support system of the diaphragm
highly compliant is extremely effective for lowering the lowest resonance frequency of a single
speaker, the enclosure of this speaker has a realistic interior volume There is a problem that the
lowest resonance frequency as a speaker system can not be kept low when the speaker system is
mounted. That is, since the lowest resonance frequency of the speaker system is mostly
determined by the inner volume of the enclosure used and the mass of the diaphragm, the lowest
resonance frequency of the single speaker can not be maintained at the time of mounting the
speaker.
[0007]
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In addition, the technology using a mass control ring based on the idea of adding weights to the
vibration system of the speaker is as viewed from the movable coil because the mass control ring
and the diaphragm are completely integrated via the bobbin. Both of these are only loads
equivalent to a single diaphragm having a large mass, and although the lowest resonance
frequency can be lowered, there is a problem that the transient response characteristic can not
be avoided from being deteriorated.
[0008]
The present invention aims at coexistence of the reproduction band characteristic and the
transient response characteristic, and a cone diaphragm which positively drives a mass necessary
for a low frequency range reproduction upper vibration system by a movable coil, and a cone
vibration plate only in the low frequency range. Cone type that can obtain a sufficiently low
minimum resonance frequency even when mounted in a small enclosure while maintaining
excellent transient response characteristics by ensuring both with the additional vibration plate
that vibrates accompanying it. It aims at providing a speaker.
[0009]
SUMMARY OF THE INVENTION In order to achieve the above object, the present invention forms
an air chamber of a fixed volume on the back surface of a cone diaphragm actively driven by a
movable coil via a resilient connecting member. An additional diaphragm is attached in a manner
as described above.
[0010]
A sound absorbing material can be interposed between the cone diaphragm and the additional
diaphragm as required.
[0011]
In addition, vent holes can be provided in the additional diaphragm as required.
[0012]
[Operation] The cone type speaker having such a configuration can share the mass necessary for
the vibration system between the cone diaphragm and the additional diaphragm, so the cone
diaphragm is ideal in pursuit of transient response characteristics. The range can be lightweight.
[0013]
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When a realistic input signal in which high frequency components and low frequency
components are mixed is added to the movable coil, the cone diaphragm responds lightly to the
signal waveform over the entire range by being lightweight and responsive Can play excellent
sound.
[0014]
At this time, the additional diaphragm is separated from the vibration system by not operating
when the cone diaphragm reacts to a high frequency range component having a small amplitude
due to the air layer being interposed between the additional diaphragm and the cone diaphragm.
ing.
[0015]
On the other hand, when the cone diaphragm operates in response to a large amplitude bass
component, a pressure change occurs in the air in the air layer, so the additional diaphragm
vibrates accompanying the cone diaphragm.
Therefore, for the bass component, the mass of the vibration system increases, and the lowest
resonance frequency of the speaker system can be kept low even when mounted in a small
enclosure.
[0016]
By interposing a sound absorbing material between the cone diaphragm and the additional
diaphragm, the sound wave emitted from the back surface of the cone diaphragm is reflected by
the additional diaphragm and the linearity of the cone diaphragm is determined. In addition to
preventing harm, it is possible to attenuate harmful standing waves etc. parasitic between the
two.
[0017]
In addition, by providing a vent hole in the additional diaphragm, the air in the air layer can be
made to enter and exit at that limit, and the sensitivity of the additional diaphragm to changes in
air pressure in the air layer can be lowered. It is possible to adjust the frequency at which the
additional diaphragm starts to operate by changing the opening ratio of the vent while making
the behavior at the start slow.
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[0018]
Embodiments of the present invention will be described below with reference to the drawings.
[0019]
The cone type speaker is mainly composed of the magnetic unit 10, the vibration system 20, and
the frame 30 (FIG. 1).
[0020]
In the magnetic unit 10, the ring magnet 11 is sandwiched from the front and back by a high
purity iron top plate 11a and a bottom plate 11b, and the columnar pole piece 11c is protruded
from the center of the bottom plate 11b toward the top plate 11a. It is an external magnet type
magnetic circuit provided.
In addition, even if it is an internal magnet type, there is no difference in the magnetic circuit.
[0021]
The frame 30 is a casting of nonmagnetic metal formed in a hollow truncated cone shape that
spreads forward from the magnetic unit 10 and is fixed to the top plate 11 a side of the magnetic
unit 10.
The side portions of the frame 30 are maximally lightened so as not to block the back side of the
vibration system 20 as much as possible.
[0022]
The vibration system 20 includes a cone diaphragm 21, an additional diaphragm 22, a movable
coil 25 and the like.
[0023]
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The cone diaphragm 21 is a general diaphragm formed by forming a pulp-based material into a
cone shape through ordinary processing steps, but is extremely light in weight and tough
compared to diaphragms of the same diameter. .
The top of the cone diaphragm 21 is removed at a position where a central opening equivalent to
the diameter of the bobbin 24 is generated, and one end of the bobbin 24 is adhesively fixed so
as to be inserted into the central opening.
A predetermined amount of conducting wire is wound around the other end of the povin 24 to
form a movable coil 25.
Therefore, the movable coil 25 and the cone diaphragm 21 are in a state of being mechanically
coupled via the bobbin 24.
A center cap 21 c is attached to the cone diaphragm 21, and the center cap 21 c is bonded to the
center of the cone diaphragm 21 so as to cover the front end of the bobbin 24.
[0024]
The cone diaphragm 21 is vibratably fixed to the frame 30 via the edge 27 and the damper 26 so
that the movable coil 25 is accommodated in a predetermined position of the magnetic unit 10.
[0025]
The edge 27 is a free edge formed by forming a sheet of elastic foam material into an arc shape
in cross section, and the entire peripheral portion of the cone diaphragm 21 is elastic on the
inner peripheral portion of the flange 31 on the front side of the frame 30 It is fixed fixedly (Fig.
1, Fig. 3).
The damper 26 is a twill weave fabric base impregnated with a resin, and the whole is formed
into a wave shape that describes concentric circles (FIG. 1), and between the flange 32 on the
base side of the frame 30 and the bobbin 24 It is interspersed.
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Therefore, the top side of the cone diaphragm 21 is resiliently supported via the bobbin 24.
The bobbin 24 is fitted to the outside of the pole piece 11c in this state, and the movable coil 25
is positioned to cut the magnetic flux passing between the pole piece 11c and the top plate 11a.
[0026]
The additional diaphragm 22 is attached to the back surface of the cone diaphragm 21 so as to
form an air layer R while maintaining a constant distance between the additional diaphragm 22
and the cone diaphragm 21.
[0027]
The additional diaphragm 22 is finished in a cone shape having the same aperture, mass, and
apex angle as the cone diaphragm 21.
However, the additional vibration plate 22 is finished to have a large internal loss by setting a
low pressure in the process of forming a pulp-based material.
The top portion of the additional diaphragm 22 is deleted at a position where a central opening
with a diameter larger than that of the povin 24 is generated, and is evenly distributed over the
whole to form a plurality of vent holes 22h, 22h.
[0028]
The additional diaphragm 22 is attached to the cone diaphragm 21 via a plurality of resilient
connection members 23, 23..., And within the range of elastic deformation of the connection
members 23, 23. Is able to behave differently.
[0029]
However, the additional diaphragm 22 moves well along the amplitude direction of the cone
diaphragm 21 and does not easily move in the other direction due to the shape and the
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arrangement of the connecting members 23.
That is, each connecting member 23 is formed by molding a resilient foam material into a thin,
short pipe shape (FIGS. 1 and 2). Therefore, it is easily deformed in the radial direction and is not
easily deformed in the axial direction. .
Furthermore, the plurality of connecting members 23, 23 ... are radially disposed centering on
the bobbin 24, and the additional diaphragm 22 is a cone diaphragm 21 with the radial
deformation of all the connecting members 23, 23 .... It can be displaced along the amplitude
direction of
[0030]
The basic operation when the cone type speaker of such a configuration is mounted in a closed
type enclosure E having a suitable internal volume is as follows (FIG. 3).
[0031]
At this time, when the mass of the cone diaphragm 21 is M1, the mass of the additional
diaphragm 22 is M2, and the mass of the vibration system 20 is Mo, it is assumed that M11M2
and Mo = M1 + M2 in non-operation.
That is, the mass of the bobbin 24, the movable coil 25, the edge 27, etc. is ignored.
When the spring element of air in air layer R is S1 and the spring element of air in enclosure E is
S2, the spring action of air is smaller as the volume is larger, so naturally S1 >> S2 Also, the
compliance of the connecting members 23, 23 ... is sufficiently high within the elastic
deformation range.
[0032]
Here, when an input signal to be reproduced by the speaker is f3 (FIG. 4), generally, the input
signal f3 has a high frequency range component f1 having a short period T and a small
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amplitude d1, and a low period T and a large amplitude d2 A range component f2 is included,
and the input signal f3 has a complex waveform obtained by combining the two.
Further, the amplitude d3 of the input signal f3 is substantially determined by the bass range
component f2, so that the amplitude d3 2 d2. In addition, f4 has shown the output signal of the
speaker.
[0033]
When an input signal f3 is applied to the movable coil 25, a driving force is generated in the
movable coil 25 accordingly, and the movable coil 25 can vibrate the cone diaphragm 21 via the
bobbin 24. At this time, since the amplitude of the cone diaphragm 21 is small with respect to
the high frequency range component f1 included in the input signal f3, the cone diaphragm 21
vibrates independently regardless of the spring elements S1 and S2. That is, the spring elements
S1 and S2 acting by the change in air pressure do not constrain the operation of the cone
diaphragm 21 in reproducing the high frequency range component f1, and the cone diaphragm
21 secures the air layer R of a fixed volume As long as it operates, it receives only the constraint
of its mass M1. Therefore, the mass Mo of the vibrating system 20 in operation with respect to
the high tone range component f1 is Mo = M1. Here, by making the mass M1 of the cone
diaphragm 21 lightweight, it is possible to improve the followability to the high frequency range
component f1, that is, the transient response characteristic. In addition, the point of the volume
of air layer R is mentioned later.
[0034]
On the other hand, for the low frequency range component f2 included in the input signal f3, the
amplitude of the cone diaphragm 21 becomes relatively large, and the spring elements S1 and S2
due to the pressure change are not ignored. Here, according to S1 >> S2, first, the spring element
S1 acts, and the cone diaphragm 21 and the additional diaphragm 22 are integrally oscillated in
phase at a boundary of a constant frequency. This is because the spring element S1 changes in
the positive and negative directions, and drives the additional diaphragm 22 to follow the cone
diaphragm 21 at a frequency exceeding the inertia inertia of the additional diaphragm 22.
Therefore, the operational mass Mo of the vibration system 20 at this time can be represented by
Mo = M1 + M2. That is, by M1MoM2, it is possible to double the mass Mo of the reproduction
system of the low frequency range component f2 upon reproduction.
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[0035]
As the frequency to be reproduced is further reduced, the amplitude of the cone diaphragm 21 is
relatively increased and the spring element S2 of the enclosure E acts to determine the lowest
resonant frequency of the loudspeaker system. Here, according to S1 >> S2, at a low frequency at
which the spring element S2 acts, the spring element S1 of the air layer R naturally acts first.
Therefore, the lowest resonance frequency is determined by the spring element S2 and the mass
Mo of the vibration system 20 represented by Mo = M1 + M2. That is, this indicates that even
when the mass M1 of the cone diaphragm 21 is small, the reproduction band characteristic can
be expanded to the bass range side by increasing the mass M2 of the additional diaphragm 22.
[0036]
In operation of the cone diaphragm 21 and the additional diaphragm 22, a phase delay occurs on
the side of the additional diaphragm 22 due to the integration of the both via the spring element
S1. The phase delay of the additional diaphragm 22 corresponds to the input signal f3, and the
additional diaphragm 22 operates in the direction to drive the stopped cone diaphragm 21 and in
the direction to stop the accelerating cone diaphragm 21. It acts as a problem of However, the
disadvantage of the phase delay occurs later in time with respect to the operation of the cone
diaphragm 21, so that the magnetic unit 10 can be reinforced and suppressed by increasing the
electromagnetic braking force of the cone diaphragm 21. . Further, since the front and rear sides
of the additional diaphragm 22 are isolated by the cone diaphragm 21 and the enclosure E, the
operation of the additional diaphragm 22 is limited as long as the cone diaphragm 21 responds
correctly to the input signal f3. The influence on the reproduced sound can be neglected on
hearing. The phase delay of the additional diaphragm 22 becomes a problem only in a narrow
band near the frequency at which the additional diaphragm 22 starts to operate.
[0037]
The frequency characteristics of such a cone-shaped speaker (FIG. 5) are the general frequency
characteristic F1 of a speaker having a light single diaphragm and the general frequency
characteristic F2 of a speaker having a heavy single diaphragm. The characteristic is seamed at
the crossover frequency fc. However, the frequency characteristic F1 is a characteristic having a
diaphragm of the same diameter as the cone diaphragm 21 and having an equivalent mass Mo ≒
M1, and the frequency characteristic F2 is a mass Mo equivalent to twice the diameter of the
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cone diaphragm 21. It is a characteristic of one having a diaphragm of 22M1.
[0038]
That is, generally, the high frequency limit of the reproduction band characteristic of the
dynamic speaker is limited by the mass Mo of the diaphragm, so the frequency characteristic F1
of the light speaker of the diaphragm is a characteristic relatively extended to the high frequency
side . On the other hand, since the lowest resonance frequency does not decrease, the low band
side has a falling characteristic from a relatively high frequency. On the other hand, the
frequency characteristic F2 of the speaker having a heavy diaphragm is relatively extended to the
low frequency side, and the high frequency side is not sufficiently extended. In addition, when
the mass ratio of the two diaphragms is 1: 2, an efficiency difference of 6 dB on average occurs
in the frequency characteristics F1 and F2.
[0039]
Therefore, the frequency characteristic of the cone type speaker in which the mass Mo of the
vibration system 20 changes in the range of Mo = M1 and Mo = M1 + M2 ≒ 2M1 on the high
band side and the low band side is from the low band part of the frequency characteristic F2. The
characteristic is such that the characteristic is continuous to the high frequency side of the
frequency characteristic F1. The cross frequency fc is a frequency at which the additional
diaphragm 22 starts to vibrate accompanying the cone diaphragm 21. That is, the frequency
characteristics of the cone-type speaker are structurally accompanied by a level difference at the
crossover frequency fc, and the output signal f4 of the cone-type speaker with respect to the
input signal f3 (FIG. 4) is for the high frequency range component f1. The low frequency range
component f2 has a relatively compressed waveform. However, the level difference of 6 dB is
within the control range of a general acoustic amplifier, and can be easily restored to an
approximate waveform as the input signal f3 by enhancing the bass range. The level difference
increases as the mass M2 of the additional diaphragm 22 with respect to the mass M1 of the
cone diaphragm 21 increases, and decreases in the opposite case, and can be freely adjusted.
[0040]
The crossover frequency fc is almost determined by three factors of the volume of the air layer R,
the mass M2 of the additional diaphragm 22, and the vent holes 22h, 22h. Each of the three
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elements is in the relation of increasing the cross frequency fc by increasing and decreasing the
cross frequency fc by decreasing the other two elements. Therefore, when one element, for
example, the mass M2 of the additional diaphragm 22 is increased and the other element, for
example, the volume of the air layer R is decreased, the two elements are changed in opposite
directions, The crossover frequency fc does not always change. In other words, it is possible to
change the mass M2 or the like of the additional diaphragm 22 while maintaining the crossover
frequency fc constant. Also, conversely, by changing two or more elements in the same direction,
the crossover frequency fc can be changed in an additive manner. That is, this indicates that the
design freedom by the combination of three elements is very large. Note that the vents 22h,
22h,... Not only contribute to the determination of the crossover frequency fc, but also reduce the
sensitivity of the additional diaphragm 22 to changes in air pressure in the air layer R, and flatten
the frequency characteristics near the crossover frequency fc. Work to do.
[0041]
Another Embodiment A sound absorbing material 22d can be interposed between the cone
diaphragm 21 and the additional diaphragm 22 (FIG. 6). The sound absorbing material 22 d is
uniformly attached to the front surface side of the additional diaphragm 22 avoiding the
connecting members 23, 23, and has an additional mass of the additional diaphragm 22. That is,
the mass M2 of the additional diaphragm 22 may be considered to include the sound absorbing
material 22d, and therefore, the sound absorbing material 22d does not have to be light.
However, as the sound absorbing material 22d, it is preferable to use a flexible material which
has a large porosity so as not to reduce the substantial volume of the air layer R, and which does
not emit unnecessary noise even when coming into contact with the cone diaphragm 21 . In this
case, since the sound wave radiated from the back surface side of the cone diaphragm 21 can be
absorbed by the sound absorbing material 22 d, it is not necessary to require the additional
diaphragm 22 to have a large internal loss, and the additional diaphragm 22 is strengthened.
Can.
[0042]
The additional vibration plate 22 can be integrally molded from a foamable resin material (FIG.
7). The materials of the cone diaphragm 21 and the additional diaphragm 22 need not be limited
to pulp-based ones, and in particular, the additional diaphragm 22 does not directly contribute to
the sound quality, so the degree of freedom in material and shape is high. In this case, the
additional diaphragm 22 is formed in a cross-sectional profile in which the middle portion is
thick and the thickness decreases toward both ends, so that structurally high strength can be
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exhibited and resonance at a specific frequency is suppressed. It can be done.
[0043]
The additional diaphragm 22 can be attached via the connecting members 23, 23 having the
same structure as the edge 27 and the damper 26 (FIG. 8). The connection member 23
equivalent to the edge 27 connects the peripheral edge of the additional diaphragm 22 to the
back surface side of the peripheral edge of the cone diaphragm 21. The connection member 23
equivalent to the damper 26 is the top peripheral edge of the additional diaphragm 22 The part
is connected to the bobbin 24. Further, the additional vibration plate 22 is provided with a large
number of vent holes 22h, 22h... So that the air in the air layer R is not sealed. Such support by
the connection members 23, 23 is conventionally employed as a support structure of the
diaphragm, has good linearity, and can ensure a sufficient stroke. In this case, the connecting
member 23 corresponding to the edge 27 does not have to be continuously provided over the
entire circumference of the additional diaphragm 22, but may be partially attached. The
connecting member 23 may have any other structure as long as the required linearity and stroke
are secured.
[0044]
As described above, in the cone type loudspeaker according to the present invention, the
additional diaphragm is attached so as to form an air layer on the back surface side of the cone
diaphragm actively driven by the movable coil. For the high frequency range component included
in the input signal, only the cone diaphragm is driven, and for the low frequency range
component of the input signal, the cone diaphragm and the additional diaphragm are controlled
via the pressure change of the air layer. Since the system can be driven integrally, the mass of the
vibration system is light for high frequency range components and changes so as to be heavy for
low frequency range components, and the excellent transient response characteristics and the
extension of reproduction band characteristics And can be realized.
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