Bass reproduction speaker apparatus

Details Bass reproduction speaker apparatus Bass reproduction speaker apparatus

2000-04-24

2003-06-03

Ramakrishnaiah, Melur (Department: 2643)

Electrical audio signal processing systems and devices

Electro-acoustic audio transducer

Electromagnetic

C381S413000

Reexamination Certificate

active

06574346

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to a bass reproduction speaker apparatus that provides improved bass reproduction performance even if the cabinet is small.
BACKGROUND OF THE INVENTION
Regarding the bass reproduction of a typical speaker, there is an inverse proportional relationship between the cabinet internal volume V, bass reproduction limit frequency fc, and efficiency &mgr;. Therefore, as commonly known, it is very difficult to reproduce lower frequencies efficiently in a small cabinet.
It has been also known that bass reproduction performance can be improved without concern for these constraints if negative stiffness is used to decrease air stiffness in the cabinet and increase equivalently the internal volume of the cabinet. Actually, however, there have been no suitable methods to achieve this purpose.
The following are conventional techniques disclosed to realize the concept in U.S. Pat. No. 2,810,021 patented on Oct. 15, 1957 (Low Frequency Loudspeaker), and in U.S. Pat. No. 4,607,382 patented on Aug. 19, 1986 (Electroacoustic Transducer Unit With Reduced Resonant Frequency And Mechanical Spring With Negative Spring Stiffness, Preferably Used In Such A Transducer Unit).
FIG. 17
shows a configuration of a conventional bass reproduction speaker apparatus disclosed in U.S. Pat. No. 2,810, 021.
In
FIG. 17
,
351
denotes a speaker unit, and the speaker unit
351
includes a field magnetic portion
351
a
, a frame
351
b
, a voice coil
351
c
, a damper
351
d
, an edge
351
e
and a diaphragm
351
f
. Numeral
352
denotes an airtight cabinet to which the speaker unit
351
is attached.
Numeral
358
denotes a supporter that is fixed to the cabinet
352
. Springs
359
b
disposed on the inner wall of the supporter
358
press levers
359
c
in an inward direction. The levers
359
c
are supported by fulcrum grooves
359
d
. A rod
359
a
is attached to the upper part of the voice coil
351
c
of the speaker unit
351
, and toggle pins
359
f
are entrapped between grooves
359
g
of the rod
359
a
and grooves
359
e
of the levers
359
c.
A movable electrical contact
360
a
is provided at the upper part of the rod
359
a
, and the contact
360
a
is flexibly supported by a spring
360
c
. And a fixed electrical contact
360
b
is arranged to sandwich the movable electrical contact
360
a
. To these electrical contacts, an exhaust pump
360
d
and an intake pump
360
e
are connected.
A conventional bass reproduction speaker apparatus thus configured operates as follows.
The springs
359
b
press the toggle pins
359
f
in the inward direction through the levers
359
c
. Therefore, when the voice coil
351
c
is displaced and the toggle pins
359
f
lose the equilibrium, the toggle pins
359
f
are tilted further and press the rod
359
a
in the displacement direction.
When a vibration system including the voice coil
351
c
and the diaphragm
351
f
is displaced, the stiffness of a supporting system (the damper
351
d
and the edge
351
e
) and the stiffness of air in the cabinet
352
act to pull the vibration system back to the central position. However, the toggle mechanism including
359
a
-
359
g
generates a force in the reverse direction, more specifically, the toggle mechanism acts to further push out the vibration system of the speaker unit
351
in the displacement direction.
In other words, the toggle mechanism including
359
a
-
359
g
provides negative stiffness to the vibration system of the speaker unit
351
. Since the toggle mechanism cancels and reduces the stiffness provided by the supporting system of the speaker unit
351
and of the air in the cabinet
352
, the internal volume of the cabinet
352
is increased equivalently. This results in improvement of the bass reproduction performance. The principle of the equivalent increase of the cabinet internal volume due to negative stiffness and improvement in the bass reproduction performance will be described later in detail.
When this negative stiffness is greater than the stiffness of the supporting system of the speaker unit
351
, the vibration system cannot stay at the inherent displacement central position due to a slight air leak from the cabinet
352
or the like, but it is offset in either displacement direction. The electrical contacts (
360
a
,
360
b
) and the pumps (
360
d
,
360
e
) serve to correct the offset.
More specifically, when the vibration system of the speaker unit
351
is offset forward, the movable electrical contact
360
a
contacts with the upper part of the stationary electrical contact
360
b
, and the exhaust pump
360
d
activates. As a result, air in the cabinet
352
is exhausted and the vibration system of the speaker unit
351
is pulled back to the inherent displacement central position. On the contrary, when the vibration system is offset backward, the movable electrical contact
360
a
contacts with the lower part of the stationary electrical contact
360
b
, and the intake pump
360
e
activates. As a result, air flows into the cabinet
352
, and the vibration system of the speaker unit
351
is pushed back to the inherent displacement central position.
Sequentially, an offset in the displacement direction of the vibration system of the speaker unit
351
is corrected even when the negative stiffness is great.
However, the springs
359
b
in the above-mentioned configuration will have a mechanical fatigue since the negative stiffness is generated by the mechanical toggle mechanism including
359
a
-
359
g
. Operation with large amplitude for a long time can cause a rupture. This will deteriorate the reliability. Moreover, the portions at which the toggle pins
359
f
and the levers
359
c
contact with each other generate abnormal noises. In addition, increased numbers of components make the apparatus complicated.
The apparatus inevitably will be more complicated and large-scaled since it requires pumps (
360
d
,
360
e
) to correct an offset in the displacement direction of the vibration system, and the pumps cause noises in a case that negative stiffness is great.
Configurations of other conventional bass reproduction speaker apparatuses disclosed in U.S. Pat. No. 4,607,382 are shown in
FIGS. 18 and 19
. These speaker apparatuses are further developed though the basic principles thereof are identical to the first speaker apparatus.
In
FIGS. 18 and 19
,
451
denotes an electrodynamic speaker unit, and it includes a field magnetic portion
451
a
, a frame
451
b
, a voice coil
451
c
, a damper
451
d
, an edge
451
e
, and a diaphragm
451
f
. Numeral
452
denotes an airtight cabinet to which the speaker unit
451
is attached.
Numeral
451
i
denotes a ring to reinforce the diaphragm
451
f
, and the ring is attached to the outer rim of the diaphragm
451
f
. Numeral
454
denotes pairs of springs respectively composed of two warped plate springs opposing each other. While being compressed in the longitudinal direction, one end of each spring
454
is attached to a movable part supporting member
451
g
on the reinforcement ring
451
i
, and the other end is attached to the stationary part supporting member
452
a
that is fixed to the frame
451
b
. Two springs
454
are arranged longitudinally in a line centering the movable part supporting member
451
g
. In this example, three sets of spring pairs
454
arranged in a line are provided to be substantially rotationally symmetric about the central axis of the diaphragm
451
f.
Two springs
454
should be arranged in a line on both sides of the movable part supporting member
451
g
. If there is only one pair of springs
454
, a rotational force about the central axis will act on the reinforcement ring
451
i
(i.e., the diaphragm
451
f
, and thus, the supporting systems of the speaker unit
451
are subjected to stress and can be damaged.
Numeral
458
denotes a means to detect displacement of the diaphragm
451
f
from the central position of the vibration. U.S. Pat. No. 4,607,382 refers to detection methods including capacitive detection, inductive detection, optoelectrical detectio

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