Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
1998-04-16
2001-07-10
Mei, Xu (Department: 2644)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S335000, C381S111000, C381S182000, C381S402000
Reexamination Certificate
active
06259799
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a speaker system having a plurality of double-voice-coil speaker units, a closed type cabinet, and an impedance compensating circuit for making the resistance of an input impedance constant.
2. Description of the Related Art
FIG. 5
shows a structural example of a conventional speaker disclosed by Watkins (W. H. Watkins, “New Loudspeaker with Extended Bass,” Audio, Dec. 1974, pp.38-46) which is designed to improve a sound radiation efficiency in a low sound region by using double voice coils. In
FIG. 5
, reference numeral
100
denotes a signal input terminal to a speaker;
10
, an impedance compensating circuit made up of a series circuit consisting of an inductance L and a capacitance C for making the resistance of an electric impedance of the speaker constant;
20
, a double-voice-coil speaker unit;
21
, a first voice coil;
22
, a second voice coil; and
25
, a bobbin for fixing those voice coils
21
and
22
.
In general, in the case where there is no impedance compensating circuit
10
, that is, in the case where only the first voice coil
21
is used, the electric impedance of the speaker unit
20
forms a parallel resonance circuit so that a characteristic peak occurs in the vicinity of a minimum resonance frequency f
0
of the speaker unit as shown in FIG.
6
. For that reason, a current that flows in the first voice coil
21
is reduced in the vicinity of the resonance frequency f
0
, to thereby reduce the efficiency of a sound radiated from the speaker.
Therefore, in
FIG. 5
, an impedance compensating circuit
10
made up of a series circuit consisting of an inductance L and a capacitance C is added in series to the second voice coil
22
in such a manner that a series resonance circuit having a resistance provided by the second voice coil
22
is connected in parallel with the first voice coil
21
, thereby making the electric impedance constant at all times (making the resistance constant) to improve the sound radiation efficiency.
FIG. 7
shows a change in sound pressure level in a low sound region due to the presence/absence of the impedance compensating circuit
10
.
As is apparent from
FIG. 7
, a rise of the sound pressure level, that is, a rise of the sound radiation efficiency is found in the vicinity of the minimum resonance frequency f
0
with making the resistance of the impedance constant using the impedance compensating circuit
10
. The effect reaches to the extent that the sound pressure level reaches several dB, depending on the conditions.
FIG. 8
shows a system extended from the conventional speaker structure shown in
FIG. 5
, in which a plurality of double-voice-coil units are used.
In
FIG. 8
, reference numeral
10
-
1
, . . . ,
10
-i, . . . ,
10
-n denote impedance compensating circuits;
20
-
1
, . . . ,
20
-i, . . . ,
20
-n, double-voice-coil speaker units;
21
-
1
, . . . ,
21
-i, . . . ,
21
-n, first voice coils;
22
-
1
, . . . ,
22
-i, . . . ,
22
-n, second voice coils; and
25
-
1
, . . . ,
25
-i, . . . ,
25
-n, bobbins for fixing the voice coils. The same or like parts as those in
FIG. 5
are indicated by the identical references.
By the way, in order to realize the low resistance in the conventional speaker structure, there is required one impedance compensating circuit for each double-voice-coil unit. To satisfy the above requirement, an impedance compensating circuit corresponding to each speaker unit is required in FIG.
8
.
As shown in
FIG. 8
, in the case where a plurality of speaker units are used, an impedance compensating circuit is required in correspondence with each unit in the conventional speaker structure. Therefore, in the speaker system using a plurality of units, there are required a plurality of impedance compensating circuits. As a result, such a speaker unit is generally expensive, and an interior of the cabinet is occupied by those plural impedance compensating circuits from the spacial viewpoint, resulting in a problem that a volume necessary for low-sound reproduction cannot sufficiently be ensured.
SUMMARY OF THE INVENTION
The present invention has been made to solve the above drawbacks in the conventional example, and therefore an object of the present invention is to provide a closed type speaker system which is capable of making a resistance of an electric impedance constant with one impedance compensating circuit, even in the case where a plurality of double coil units are used.
In order to achieve the above object, according to the present invention, there is provided a speaker system comprising: a closed type cabinet in which a rear space with respect to a speaker disposed face is closed; a plurality of double-voice-coil speaker units of the same specification each having a first and a second voice coils and being fixed to said closed type cabinet; and an impedance compensating circuit that makes the resistance of an electric impedance of the speaker system constant; wherein the first voice coils are connected in parallel to each other so that the respective same polarities are connected to each other, the second voice coils are connected in parallel to each other so that the respective same polarities are connected to each other, an input signal is directly applied to the respective first voice coils, and the input signal is applied to the respective second voice coils through the impedance compensating circuit.
Also, the impedance compensating circuit is made up of a series circuit that includes an inductance and a capacitance.
Further, the double-voice-coil speaker unit is characterized in that a resistance R
v2
of the second voice coils and element constants L, C of the impedance compensating circuit satisfy the following expressions, assuming that a resonance angular frequency viewed from the first voice coil is &ohgr;
0
, an equivalent mass is m
0
, a compliance is C
0
, an electric sharpness is Q
0
, a mechanical sharpness is Q
m
, a ratio of the force factor of the second voice coil to the first voice coil is &agr;, an air compliance due to a volume within the closed type cabinet viewed from a single unit as disposed is C
b
, a mechanical resistance is r
b
, an inductance of the impedance compensating circuit is L, a capacitance is C, the resistances of the first and second voice coils are R
v1
and R
v2
, respectively, and the number of the double-voice-coil speaker units as used is n, under the condition where the second voice coils are opened:
R
V2
=
R
V1
(
Q
0
Q
m
Q
m
-
Q
0
)
{
(
1
Q
0
+
n
Q
b
)
-
2
α
(
Q
m
-
Q
0
Q
m
Q
0
)
}
;
L
=
R
V1
ω
0
(
Q
0
Q
m
Q
m
-
Q
0
)
;
and
C
=
1
R
V1
ω
0
(
Q
m
-
Q
0
Q
0
Q
m
)
γ
b
n
+
γ
b
,
where
γ
b
=
C
b
C
0
and
Q
b
=
ω
0
m
0
r
b
.
REFERENCES:
patent: 3665124 (1972-05-01), Sotome
patent: 3838216 (1974-09-01), Watkins
patent: 3984635 (1976-10-01), Nsetorovic et al.
patent: 4504704 (1985-03-01), Ohyaba et al.
patent: 5117459 (1992-05-01), McShane
patent: 5828767 (1998-10-01), Button
patent: 56-54195 (1981-05-01), None
Dickson, Vance “Loudspeaker Design Cookbook”, p.30, 1991.
Kyouno Noboru
Suzuki Seiki
Mei Xu
Mitsubishi Denki & Kabushiki Kaisha
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