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JPH04281696

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DESCRIPTION JPH04281696
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
acoustic signal reproduction system provided with a stiffness reduction device.
[0002]
2. Description of the Related Art When performing bass reproduction using an electrodynamic
speaker, the reference of the reproduction limit frequency band is called the lowest resonance
frequency (f0). For example, an electrodynamic speaker (hereinafter referred to as a unit). In the
case of f0) and its sound pressure versus frequency characteristics, the level below the lowest
resonance frequency drops sharply.
[0003]
[0003] When sound is emitted from this unit, since the sound of the opposite phase to the front
is emitted from the back, the reproduced sound is canceled particularly in the low frequency
range. Therefore, when the unit is attached to the infinite baffle to avoid the sound from the back
to be introduced to the front, the characteristics shown in A of FIG. 2 are obtained, and the low
frequency reproduction limit frequency is the low frequency reproduction limit frequency of the
unit itself. It is decided.
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[0004]
However, in practice, not all speaker systems can be made into an infinite baffle, but most are
attached to an enclosure. At that time, the lowest resonance frequency is raised from f0 to f0 'as
shown in B of FIG. 2 due to the stiffness generated by closing the unit back in a small space, and
the low frequency reproduction limit frequency is also raised.
[0005]
SUMMARY OF THE INVENTION According to the present invention, there is provided an acoustic
signal reproduction system capable of suppressing the increase of the low frequency
reproduction limit frequency and obtaining a state close to the low frequency reproduction limit
frequency f0 of the acoustic signal reproduction unit itself. To provide.
[0006]
SUMMARY OF THE INVENTION The present invention comprises a unit for reproducing an
acoustic signal and a device for reducing the stiffness within the enclosure when the unit is
housed in the enclosure.
[0007]
BEST MODE FOR CARRYING OUT THE INVENTION The present invention relates to a unit for
reproducing an acoustic signal, a detection means for detecting the back pressure of the unit, and
a stiffness reduction driven by the signal output of the detection means to make the back
pressure constant. Sound reproduction system comprising an audio unit in an enclosure.
[0008]
FIG. 1 shows a block diagram of an acoustic signal reproduction system according to the present
invention.
In this embodiment, a stiffness reduction unit, such as the above-described electrodynamic cone
speaker SP2, is disposed behind the acoustic signal reproduction unit, such as the electrodynamic
cone speaker SP1, so as to divide the volume of the enclosure into two. Do.
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S1 is a pressure sensor, which detects the back pressure of the unit SP1 in the space formed by
the units SP1 and SP2 and the enclosure.
For example, a microphone or the like can be used as the pressure sensor S1.
[0009]
AMP1 is an amplifier for gain / phase correction of the pressure signal voltage detected by the
pressure sensor S1, and a comparison circuit for comparing the output signal of the amplifier
AMP1 with a reference level described later, such as a differential amplifier AMP2 Enter in The
output of the differential amplifier AMP2 is amplified by the stiffness reduction unit drive
amplifier AMP3 to drive the stiffness reduction unit SP2.
[0010]
The operation of the acoustic signal reproduction system capable of reproducing in the state
close to the low frequency reproduction limit frequency of the unit SP1 itself will be described
below. The lowest resonance frequency f0, which is an indicator of the reproduction limit
frequency band of the unit itself, is expressed by f0 = 1 / 2.pi. (.Sqroot.s0 / .sqroot.m0). Here, m0:
equivalent mass of the vibration system [kg], s0: equivalent stiffness of the vibration system [N /
m].
[0011]
Further, the lowest resonance frequency f0 'when the unit is attached to the enclosure is
represented by f0' = 1 / 2.pi. (.Sqroot. (S0 + sc) /. Sqroot.m0). Here, sc is equivalent stiffness [N /
m] of the enclosure. Furthermore, the equivalent stiffness sc of the enclosure is expressed by sc =
0 0 c 2 π 2 a 4 / v. Here, ρ 0: density of air [kg / m 3], c: speed of sound [m / sec], a: vibration
effective radius of diaphragm of unit [m], v: volume of enclosure [m 3].
[0012]
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In view of the above equation, it can be seen that the increase in f o is due to the equivalent
stiffness sc of the enclosure, and that the increase in sc is due to the decrease of the volume v of
the enclosure. That is, the low range reproduction limit of the unit is basically a problem due to
the small v.
[0013]
Increasing the volume of the enclosure can lower the low frequency reproduction frequency,
which is inconsistent with the miniaturization of the acoustic signal reproduction system.
Therefore, according to the present invention, the volume of the space behind the unit is changed
due to the vibration of the unit for reproducing an acoustic signal, and the pressure in the space
is also changed. Is equivalent to that in a large enclosure if controlled to be 0), and the low
frequency reproduction limit frequency of the acoustic signal reproduction system is
approximately close to the low frequency reproduction limit frequency of the acoustic signal
reproduction unit itself It is what makes it a state.
[0014]
The present invention will be described based on the following examples to achieve the abovementioned state. In the acoustic signal reproduction system shown in FIG. 1, an output voltage
signal of a pressure sensor S1 disposed in an enclosure space behind the acoustic signal
reproduction unit SP1 is amplified by a gain / phase correction amplifier AMP1 and a
comparator, for example, The differential amplifier AMP2 compares it with the reference signal
set to the ground level. The output signal of the comparator is amplified by the stiffness
reduction unit drive amplifier AMP3 to drive the stiffness reduction unit SP2 in phase with the
signal for driving the acoustic signal reproduction unit.
[0015]
When both units SP1 and SP2 are driven in the same phase, even if the volume of the space
behind the acoustic signal reproduction unit SP1 decreases and the pressure rises, the pressure
rise also causes the stiffness reduction unit SP2 to also As it is driven through the space of the
enclosure behind the unit SP1, it compensates for the reduction in volume and does not change
volume, so that the pressure is also kept constant without rising. As a result, the occurrence of
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stiffness of the enclosure is suppressed, and the low frequency region of the audio signal is
reproduced in a state close to the lowest resonance frequency f0 determined only by the
equivalent stiffness of the acoustic signal reproduction unit SP1.
[0016]
In the embodiment described above, the reference signal is set to the ground level, but in this
case, if the servo system is greatly utilized, the phase margin is lost, and the residual pressure
due to the drive of the unit SP1 for reproducing the acoustic signal enters the space of the
enclosure. There is an increase in the second and third harmonic levels around 300 Hz.
Therefore, the level of the harmonics can be suppressed by applying an acoustic signal for
driving the acoustic signal reproduction unit SP1 as a reference signal to the comparison
amplifier AMP2 at a constant ratio.
[0017]
Here, one measurement example of the latter embodiment to which the present invention is
applied will be described. An enclosure with a total volume of 18 liters is divided by a stiffness
reduction unit SP2 and divided into two to form the volume behind the two units to
approximately 9 liters. First, when only the acoustic signal reproduction unit SP1 (16 cm, 4 Ω) is
attached to the enclosure, the lowest resonance frequency rises from 32, 4 Hz to about 49 Hz,
but with the stiffness reduction unit SP2 (16 cm, 4 Ω) When the system was driven by
partitioning as described above, the lowest resonance frequency dropped to about 34, 7 Hz. This
is equivalent to an enclosure having a volume of 18 liters converted to an enclosure having an
equivalent volume of about 170 liters, which can greatly reduce the equivalent stiffness of the
enclosure.
[0018]
FIG. 3 shows the frequency characteristics of this embodiment, in which the lowest resonance
frequency is lowered from 49 Hz to 34.7 Hz, and the sound pressure level is also raised, and the
effect of improvement is remarkable.
[0019]
According to the present invention, since the equivalent volume of the enclosure can be
increased, the bass reproduction limit can be lowered, and a small-sized, capable of reproducing
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a deep bass can be realized. .
[0020]
Brief description of the drawings
[0021]
1 is a block diagram of the present invention acoustic signal reproduction system.
[0022]
2 is a sound pressure level versus frequency characteristic diagram.
[0023]
3 is a measurement of the frequency characteristics of the present invention.
[0024]
Explanation of sign
[0025]
SP1 · · · · · · · · · · · · · · · · · · · · · · · · · SP1 · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · ·
· · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · · pressure sensor AMP1 · · · ·
amplifier for gain and phase correction AMP · · · differential amplifier
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