JP2558978B2 - Bass reproduction device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a bass reproducing apparatus utilizing MFB (motional feedback) for reproducing super bass at a high maximum output sound pressure level in spite of its small size.

[0002]

2. Description of the Related Art In recent years, it has become important to reproduce the super bass sound contained in a music source or an AV source at a sufficient volume even in a general home, and a bass reproduction apparatus capable of reproducing the super bass sound at a high sound pressure level while being small in size. It has been requested.

A conventional bass reproduction apparatus will be described below with reference to the drawings. As shown in FIG. 14, the driver unit 41 is attached to the Kelton type cabinet 42. More specifically, the inside of the cabinet is formed by the cavity dividing member 42b so that the first cavity 42c is formed.
And a second cavity 42d, and the driver unit 41 is attached to the cavity dividing member 42b. That is, the rear part of the driver unit 41 is the first
It is sealed with a cavity 42c. A port 42a is provided on the side of the cavity 2; 42d, and a low tone is radiated from the port 42a (this type of cabinet is commonly called a Kelton type cabinet).

The driver unit 41 is driven by a power amplifier 43, and a low-pass filter 44 is inserted in front of the power amplifier 43.

The operation of this conventional bass reproduction apparatus is shown in FIG.
An equivalent circuit of the Kelton type speaker system shown in FIG.

At a lower frequency f ₁ , resonance occurs such that the phases of Vd and Vp become substantially the same between Md and Mp and Cd, Cc ₁ and Cc ₂ , but at a higher frequency f ₂ , Md and Mp.
Resonance occurs such that the phases of Vd and Vp are opposite to each other between p and Cc _2, and 12 in the band outside these two resonance frequencies.
It is possible to obtain the characteristic that the sound pressure is attenuated at the level of dB / oct or more. Further, at a frequency fr (generally called an anti-resonance frequency) substantially in the middle of f ₁ and f ₂ , resonance occurs between Mp and Cc _2, and at this time, Vd becomes minimum.

Md, Cc₁, Red, Cc₂, Mp are appropriate values
To design (usually Cd << Cc₁, Rmd, Rc₁, Rc₂, Rp
<< Because it is Red, it suffices to focus on the above parameters. In addition,
To make it easy to understand the air mechanical resistance Rp in the port,
The friction resistance between the air that oscillates in the port and the wall of the port pipe
And due to turbulence in the air flow generated at the port outlet
It is resistance. ), That is, Md, Cc₁, C
c₂, Mp values are properly balanced and f₁ , F₂ Resonance
Align the peak heights and make Red sufficiently large (Md,
The larger Mp, the more Cc₁, Cc₂The smaller is the resonance Q
Becomes higher and Red needs a larger value. )Each
By dumping the resonance peak of ₁ , F₂ Between
Flat sound pressure frequency range of 1.5 to 2.5 octaves
The wave number characteristic can be obtained.

[0008] To shift the reproduction frequency band in ultra low frequency side, Mp, Md, by increasing the Cc _1, Cc _2, may be lowered to f _1, f _2. However, if only Md and Mp are increased, the Q of resonance increases, so Cc ₁ and Cc ₂
Also needs to be larger.

Since this Kelton type speaker system utilizes resonance, it is more efficient than the closed type speaker system and has a bandpass characteristic, so that it is suitable for low tone reproduction. Although it is well known in acoustic theory,
Since the rear of the driver unit is sealed, how low
The opposite-phase sound pressure behind the driver unit
It does not wrap around and interfere. Therefore other formats
Resonance type cabinet (bass reflex type or driver unit
Ports on both rear and front cavities
Sound pressure in the ultra-low range, such as that produced by
Very good for shifting the band to the very low end without any reduction
are doing.

By driving this Kelton type speaker system with the power amplifier 43, a low-pitched sound reproducing device for reproducing an ultra-low range is constructed. The frequency is 200 to 30
At around 0 Hz, air column resonance of the air in the port 42a may occur, or standing waves may be placed inside the cabinet to disturb the characteristics. Therefore, a low-pass filter 44 is inserted to sufficiently attenuate unnecessary high frequencies. I am letting you.

The electromagnetic braking resistance Red means an electromagnetic brake due to a back electromotive force of a voice coil generated when the vibration system of the driver unit vibrates, and the electromagnetic braking resistance Red.
ed = (magnetic flux density of magnetic circuit x effective length of voice coil conductor)
² / Voice coil DC resistance, so generally, the stronger the magnetic circuit driver unit, the larger the Red.

[0012]

However, in the above-mentioned conventional configuration, it is necessary to increase Md, Mp, Cc ₁ , Cc ₂ and Red in order to obtain a flat sound pressure frequency characteristic in the ultra-low frequency range although it is small. Therefore, the effective vibration mass of air in the driver unit and the port is increased to strengthen the magnetic circuit of the driver unit, and Cc ₁ = first cavity 4
1 volume / (air density × air velocity ² × S1 ² ), Cc ₂ = second cavity 42 volume / (air density × air velocity ² ×)
S1 ² ), so Cc ₁ ,
In order to increase Cc ₂ , the effective vibration area S1 of the driver unit must be reduced.

Therefore, although it is easy to realize a power amplifier with a large output these days, the maximum output sound pressure level cannot be increased in the ultra-low range because the effective vibration area of the driver unit is small. The diaphragm of the driver unit has a large amplitude, resulting in a large amount of distortion, and the effective vibrating mass of the driver unit and the magnetic circuit are large, making it difficult to realize the driver unit.

On the contrary, if the effective vibration area of the driver unit is forcibly increased in order to increase the maximum output sound pressure level in the ultra-low range, not only Cc ₁ and Cc ₂ decrease but also the resonance frequency increases. M to prevent
Since it is necessary to increase d and Mp, the Q of the resonance of the above two resonance frequencies f ₁ and f ₂ becomes very high, and R
A large peak occurs that cannot be dumped even if ed is increased a little, and the peak of f ₁ is especially high.
There is also a problem that there is a tendency that a flat sound pressure frequency characteristic cannot be obtained.

FIG. 14 shows an example of a conventional bass reproducing apparatus. The driver unit 41 has an effective vibration radius of 78 mm, an effective vibration mass of 14.5 g, a magnetic circuit magnetic flux density of 0.8 tesla (= 8000 gauss), a voice coil effective conductor length of 8 m, a DC resistance of 5 Ω, and a distortion-free maximum amplitude of ± 4 mm ( In general,
The smaller the aperture, the smaller the maximum distortion-free amplitude. ),
It is a speaker with a minimum resonance frequency of 30 Hz and a diameter of 20 cm, and this driver unit 41 is attached to the cavity dividing member 42 b of the Kelton type cabinet 42. The port 42a has an inner diameter of 80 mm and a length of 150 mm. The first cavity 42c has an internal volume of 35 liters,
The second cavity 42d has an internal volume of 15 liters.

The driver unit 41 is driven by a power amplifier 43 having an output of 100 W, and a low pass filter 44 having a cutoff frequency of 250 Hz is inserted in the preceding stage.

FIG. 12 shows the sound pressure frequency characteristics measured by this conventional low-pitched sound reproducing device. As is clear from FIG.
Although almost flat characteristics are obtained from about 30 Hz to 120 Hz, the distortion-free maximum output sound pressure level at 30 Hz is only about 89 dB. The reason why the maximum output sound pressure level is low is not because the output of the power amplifier is insufficient,
This is because the amplitude is limited by the driver unit.

In order to increase the maximum output sound pressure level, an effective vibration radius of 125 mm, an effective vibration mass of 46 g, a magnetic circuit magnetic flux density of 0.8 Tesla, and a voice coil effective conductor length of 1
FIG. 13 shows the sound pressure frequency characteristics when a speaker having a diameter of 30 cm, a resistance of 0 m, a direct current resistance of 5 Ω, a maximum distortion of ± 6 mm, and a minimum resonance frequency of 30 Hz is attached instead of the speaker having a diameter of 20 cm. Around 30Hz and 140Hz, high peaks occur that cannot be dumped even if the magnetic circuit is slightly powerful, and especially the peaks at 30Hz.
It turns out to be expensive and not practical.

The present invention solves the above-mentioned conventional problems, and an object of the present invention is to provide a low-pitched sound reproducing device that reproduces ultra-low sounds flat at a high maximum output sound pressure level while being compact.

[0020]

To achieve this object, a bass reproducing apparatus of the present invention comprises a driver unit, a Kelton type cabinet for sealing the rear of the driver unit and mounting the same, and driving the driver unit. A power amplifier, a detection circuit inserted between the power amplifier and the driver unit to detect a voltage proportional to the vibration system speed of the driver unit, and a low frequency band fed back from the detection circuit to the power amplifier. Two resonance frequencies
Acceleration type of the amount that makes the peak levels of the numbers f1 and f2 the same
Feedback and the peak when the acceleration type feedback is applied
And a feedback circuit for simultaneously applying a velocity type feedback of an amount by which the noise is flattened .

[0021]

With this configuration, the MFB is installed in the driver unit.
Therefore, the electromagnetic braking resistance of the driver unit and the effective vibration mass can be made extremely large equivalently, so
Not only the _two resonance frequencies f ₁ and f ₂ are lowered, but also f ₁ and f
Ru it is possible to suppress the _second peak equally. Driver
Since the rear of the unit is sealed, how low frequencies
The sound pressure behind the driver unit
Since there is no interference, the sound pressure frequency characteristics that are flat in the ultra-low range can be obtained with a large effective vibration area of the driver unit, that is, with a high maximum output large sound pressure.

[0022]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows a first embodiment of the bass reproduction apparatus of the present invention. Driver unit 1 has an effective vibration radius of 125 m
m, effective vibration mass 46 g, magnetic circuit magnetic flux density 0.8 tesla, voice coil effective conductor length 10 m, DC resistance 5 Ω
(Electromagnetic braking resistance = (magnetic flux density x effective conductor length) ² / DC resistance, so the electromagnetic braking resistance of this driver unit is 12.8 mechanical Ω), distortion-free maximum amplitude ± 6 mm, minimum resonance frequency 30 Hz The speaker unit has a diameter of 30 cm, and the driver unit 1 is attached to the cavity dividing member 2 b of the Kelton type cabinet 2. The port 2a has an inner diameter of 80 mm and a length of 150 mm. The first cavity 2c has an internal volume of 35 liters, and the second cavity 2d has an internal volume of 15 liters.

The driver unit 1 is driven by a power amplifier 3 having an output of 200W. The detection circuit 4 has R1 = 3.9K
Ω, R2 = 220Ω, R3 = 0.33Ω, L = 0.1m
It is a bridge circuit having H and a voice coil of the driver unit as one side, and is inserted between the power amplifier 3 and the driver unit 1.

The output voltage of the bridge circuit, that is, the output voltage of the detection circuit 4 is directly proportional to the speed of the vibration system of the driver unit 1. Although this is well known in electroacoustic theory, it will be explained again with reference to FIGS. 5, 6 and 7.

FIG. 5 shows the impedance characteristic of a general speaker. When the frequency is extremely low, the direct current resistance Re of the voice coil becomes Re, and the peak Zmax at the minimum resonance frequency F ₀ (in a powerful speaker of a magnetic circuit, is shown). Zm
The ax becomes about 100 to 300Ω. ), The curve approaches Re again in the middle and low range and gradually rises in the high range.

FIG. 6 shows the impedance component of the voice coil of the speaker. Ze is called a braking impedance of the voice coil (impedance which the voice coil shows in a state where the vibration system of the speaker is fixed so as not to move), and a direct current resistance Re and an inductance of the voice coil are connected in series. (BL) ² / Zm is called the dynamic impedance of the voice coil, and is the impedance due to the back electromotive force of the voice coil generated when the vibration system vibrates. Since the back electromotive force of the voice coil is E = BL × V (V is the speed of the voice coil), the dynamic impedance is directly proportional to the speed of the vibration system.

That is, the impedance curve shown in FIG. 5 is obtained by superimposing the dynamic impedance on the voice coil DC resistance and the inductance. Fig. 7 shows the impedance curve of the Kelton type speaker system.
This is also the same.

Now, a speaker, that is, a voice coil of a driver unit is connected to one side of a bridge circuit as shown in the detection circuit 4 of FIG. 1, and Re: R3 = R1: R2.
And L = voice coil inductance x (R3 / R
By balancing the bridge according to the relational expression e), the voltage due to the DC resistance component and the inductance component of the voice coil is canceled and does not appear in the output of the bridge circuit.
Then, only the voltage due to the dynamic impedance is output from the output of the bridge circuit. That is, this bridge circuit can detect a voltage that is directly proportional to the speed of the vibration system of the driver unit 1.

Actually, there is a direct current resistance of the lead wire for connecting the driver unit, and since the voice coil braking impedance contains a slight capacitance component, fine adjustment is made from the value of each element according to the above relational expression. is necessary. For that reason, the value of each element of the bridge circuit of the detection circuit 4 of the present embodiment is not exactly the same as that obtained by the above relational expression.

As described above, the output voltage of the detection circuit 4 is a voltage proportional to the speed of the vibration system of the driver unit 1.
However, by passing this through a differentiation circuit,
A voltage proportional to speed is obtained. Feedback circuit 5 of this embodiment
Is equivalent to the effective vibration mass of the driver unit 1 being 76
g to become like, that the two resonance frequencies f _1, f ₂
Acceleration type feedback is applied in the same amount as the peak level.
Differentiating circuit with gain and electromagnetic control of driver unit 1
So that the dynamic resistance is equivalently 51.2 mechanical Ω,
The peaks of f ₁ and f ₂ when the above acceleration type feedback is applied
A gain adjustment circuit that gives velocity-type feedback of the amount to be flattened.
It is a combination of the road and the road. And the output of the detection circuit 4
The voltage is fed back to the power amplifier 3 by the above feedback circuit 5.
It Note that the feedback amount is attenuated so as not to become unstable at approximately 200 Hz or higher.

Further, a low-pass filter 6 having a cutoff frequency of 200 Hz is inserted before the power amplifier 3 to attenuate an unnecessary band.

The effects of MFB will be described in detail below with reference to FIGS. 8, 9 and 15.

The speed of the vibration system of the driver unit is shown in FIG.
It is represented by Vd of the equivalent circuit of, but when the frequency is very low, the reactance component of Cc ₁ of the equivalent circuit becomes dominant,
When the frequency is halved, Vd is halved, and the characteristic is that it is attenuated at 6 dB / oct. On the contrary, when the frequency is very high, the reactance component of Md of the equivalent circuit becomes dominant, and when the frequency is doubled, Vd becomes 1
The relationship is that it becomes / 2, and this also has the characteristic of attenuating at 6 dB / oct.

On the other hand, at frequencies near f ₁ and f ₂ , Vd is also f ₁ and f when the sound pressure frequency characteristic has a peak.
_It has a peak at ₂ and has a minimum at the anti-resonance frequency fr. That is, when the sound pressure frequency characteristic is as shown in FIG. 8A, the speed Vd of the vibration system of the driver unit is as shown in FIG. 8B.

Here, when the voltage proportional to the speed of the vibration system of the driver unit is detected and speed type feedback (negative feedback) is applied as in the above configuration, the speed of the vibration system of the driver unit becomes constant. Since servo is applied, f ₁ , f
_When the levels of the _two peaks are the same, the speed of the vibration system of the driver unit becomes as shown in FIG. 8D when the peaks of f ₁ and f ₂ are flattened equally . That is, the sound pressure frequency characteristic becomes accordingly as shown in FIG. 8C, and f ₁ ,
It becomes flat with the peak of f ₂ . This is just equivalent to increasing the electromagnetic braking resistance Red of the driver unit in the equivalent circuit of FIG. 15, and corresponds to strengthening the magnetic circuit of the driver unit. By increasing the feedback amount, the electromagnetic braking resistance Red of the driver unit can be equivalently increased to a very large value.

Further, when acceleration type feedback (negative feedback) is applied, servo is applied in a direction to keep the vibration system acceleration of the driver unit constant. Since the acceleration is the velocity obtained by differentiating the velocity with the angular frequency, the entire characteristic of FIG. 8B is 6 dB / oct.
The more you move to the left. That is, the vibration system acceleration has a characteristic such as (E) which is flat above f ₂ and attenuates at 12 dB / oct below f ₁ . Since the servo is applied in the direction in which this becomes constant, the flat band of the vibration system acceleration spreads to a lower frequency, which is just the effective vibration mass Md of the driver unit of the equivalent circuit in FIG.
Is equivalent to increasing, and corresponds to increasing the vibration system of the driver unit. By increasing the feedback amount, the effective vibration mass Md of the driver unit can be equivalently increased to a very large value. However, the Q of resonance is high.
Therefore , the peak levels of f ₁ and f ₂ become high, especially
The peak of f ₂ is higher because the amount of feedback is larger.
It

Therefore, by simultaneously applying the velocity type feedback and the acceleration type feedback as described above, it is possible to equivalently increase the electromagnetic braking resistance of the driver unit and the effective vibration mass very much.

Hereinafter, it will be described with reference to FIG. 9 that even when the effective vibration area of the driver unit is large, the velocity-type and acceleration-type feedback are used together to obtain a flat sound pressure frequency characteristic in the ultra-low range. FIG. 9A shows the sound pressure frequency characteristics without feedback in the state where the effective vibration area of the driver unit is large, but the frequencies of f ₁ and f ₂ are high and also have peaks.
In general, the peak of f ₁ has a higher level. If acceleration feedback is applied to this, the effective vibration mass of the driver unit is equivalently increased. Further, by increasing the effective air vibration mass Mp in the port, the two resonance frequencies f ₁ and f _{2 in} (A) are lowered, and the peak level of f ₂ is
Becomes larger, and as shown in (B), the peaks of f ₁ and f ₂ are
The characteristic is that the level of the peak is uniform .

In practice, if feedback is applied to a frequency that is too high, the operation becomes unstable and may oscillate.
Above a certain frequency fc, the amount of feedback is reduced. Therefore,
The characteristic is such that the gain increases above fc as in (B).

[0041] By applying a further speed-type feedback thereto, the electromagnetic damping resistance of the driver unit is equivalently increased, the peak of f _1, f ₂ to have all the levels of the peak of f _1, f ₂ It can be suppressed in the same way .
Furthermore, by attenuating unnecessary fc or more by the low-pass filter, a flat sound pressure frequency characteristic in the ultra low frequency range can be finally obtained as shown in (C).

The low-pitched sound reproducing device configured as described above is
MFB is applied to the driver unit, so that the electromagnetic braking resistance of the driver unit and the effective vibration mass can be made extremely large equivalently (for example, the electromagnetic braking resistance is 12.8).
To 51.2 mechanical Ω is equivalent to doubling the magnetic flux density of the magnetic circuit, and it is extremely difficult to realize this with the magnetic circuit itself as in the conventional case, which causes a tremendous increase in cost. . ), The two resonance frequencies f
Not only can ₁ and f ₂ be lowered, but also the peak can be suppressed, and flat sound pressure frequency characteristics in the ultra-low frequency range can be obtained with a large effective vibration area of the driver unit.

FIG. 10 shows the measured sound pressure frequency characteristics of the low-pitched sound reproducing device configured as described above. As is clear from FIG. 10, not only the flat characteristics are obtained from about 30 Hz to 120 Hz, but the total volume inside the cabinet is as small as 50 liters, but the distortion-free maximum output sound pressure level of about 100 dB at 30 Hz is obtained. Can be obtained.

Although L is inserted in the detection circuit 4 in this embodiment, the same effect as if there is L can be obtained even if L is removed and a capacitor is placed in parallel with R2 instead. Alternatively, if the voice coil has a small diameter or the magnetic circuit yoke has a copper short ring, and the inductance of the voice coil is so small as to be negligible, L may be omitted.

Next, a second embodiment of the present invention will be described with reference to FIG. Driver unit 1
1 is effective vibration radius 176 mm, effective vibration mass 85 g, magnetic circuit magnetic flux density 1 Tesla, voice coil effective conductor length 14 m, DC resistance 5 Ω (electromagnetic braking resistance = (magnetic flux density × effective conductor length) ² / DC resistance) Therefore, the electromagnetic braking resistance of this driver unit is 39.2 mechanical Ω), distortion-free maximum amplitude ± 8 mm, and minimum resonance frequency of 20 Hz.
This speaker unit 11 is attached to the cavity dividing member 12b of the Kelton type cabinet 12 as a speaker of cm. The port 12a has an inner diameter of 100 mm,
The length is 580 mm, and bellmouth-shaped flanges are provided at both ends of the port in order to suppress wind noise generated at the end of the port due to violent movement of air. Since the port 12a is long, it is attached to the side surface of the second cavity 12d. The first cavity 12c has an internal volume 60
The second cavity 12d has an internal volume of 16 liters.

The driver unit 11 is driven by the power amplifier 13 having an output of 600W. In addition, the driver unit 1
A resistor R having a small value is inserted as a detection circuit 14 between 1 and the power amplifier 13. In this embodiment, R =
It is 0.1Ω.

The voltage across the resistor R is inversely proportional to the voice coil impedance curve of the driver unit 11 (see FIG. 7). That is, the two resonance frequencies f ₁ and f ₂ have a minimum value and the anti-resonance frequency fr has a maximum value.

As in this embodiment, the magnetic flux density B of the magnetic circuit is
When the voice coil effective conductor length L is large and the product BL is sufficiently large, the voice coil impedance is dominated by the dynamic impedance in the low tone range, and the braking impedance can be ignored. That is, the resistance R
It can be considered that the voltage across both ends, that is, the detection voltage of the detection circuit 14, is inversely proportional to the dynamic impedance, that is, the speed of the vibration system of the driver unit 11.

Therefore, the detected voltage is directly phased.
Speed feedback by performing positive feedback without inverting
Light To explain clearly, two resonance frequencies f
₁ , F ₂ , The detected voltage becomes minimum and positive feedback
However, the output of the power amplifier 13 remains almost unchanged. When
The anti-resonance frequency Fr or f₁ , F₂ Frequencies outside
In this case, the detection voltage becomes large and the power is increased due to the positive feedback.
The output of the width device 13 increases. That is, relatively f₁ , F₂ 
Since feedback is applied in the direction of suppressing the peak of
It operates in the same way as speed feedback.

By passing this detected voltage through a differentiation circuit, a voltage inversely proportional to the acceleration of the vibration system of the driver unit 11 can be obtained. Therefore, the voltage is directly fed back without inverting the phase, and the acceleration type feedback is performed. Takes.

As described above, the driver unit 11
Of the effective vibration mass of 370 g
The two resonance frequencies f ₁ and f ₂ have the same peak level.
Differentiating circuit with a gain to which the amount of acceleration feedback is applied
And the electromagnetic braking resistance of the driver unit 11 is equivalently 1
80 mechanical Ω, that is, the above acceleration type feedback
Velocity type that flattens the peaks of f ₁ and f ₂ when applied
Feedback is provided to the power amplifier 13 by a feedback circuit 15 including a gain adjusting circuit that provides feedback. About 200H
The feedback amount is attenuated so as not to become unstable above z.

Further, a low-pass filter 16 having a cutoff frequency of 200 Hz is inserted in front of the power amplifier 13 to attenuate unnecessary bands.

The low-pitched sound reproducing device configured as described above is
The driver unit takes MFB, since the electromagnetic damping resistance and effective vibration mass of the driver unit <br/> can be equivalently very large, two well reduce the two resonance frequencies f _1, f ₂ that-out <br/> in it is suppressed equal peaks. Also, the rear of the driver unit is sealed
And no matter how low the frequency is, behind the driver unit
Since the sound pressure of the driver unit does not wrap around to the front and interfere with it , the flat sound pressure frequency characteristics in the ultra-low frequency range can be achieved with a large effective vibration area of the driver unit , that is, a high maximum output large sound pressure.
Obtained by.

FIG. 11 shows the measured sound pressure frequency characteristics of the low-pitched sound reproducing device configured as described above. As is clear from FIG. 11, not only a flat characteristic is obtained from an ultra-low sound of 20 Hz to about 100 Hz, but also the cabinet has a small total volume of 76 liters and a maximum distortion-free output of about 100 dB at 20 Hz. Sound pressure level is about 111 dB at 30 Hz
You can get a powerful undistorted maximum output sound pressure level.

Next, a third embodiment of the present invention will be described with reference to FIG. Driver unit 2
Reference numeral 1 is a speaker having a diameter of 30 cm, which is the same as that described in the first embodiment. The same applies to the Kelton type cabinet 22. The port 22a has an inner diameter of 80 mm, a length of 150 mm, the first cavity 22c has an internal volume of 35 liters, and the second cavity 22d has an internal volume of 15 liters.

The driver unit 21 is driven by a power amplifier 23 having an output of 200W. In addition, the driver unit 2
A piezoelectric sensor 24 is attached to the center of the vibration plate 1 to detect the vibration of the vibration system of the driver unit 21.
In the case of the piezoelectric sensor, this detected voltage is a voltage proportional to the acceleration of the vibration system of the driver unit 21 . Again
When the detection voltage of the sensor 24 is passed through an integrating circuit, it is compared with the speed of the vibration system.
An example voltage is obtained. Therefore, the detection voltage of the sensor 24
The gain of the driver unit 21
The oscillating mass is equivalent to 76g, that is, two
Amount to make the peak levels of resonance frequencies f ₁ and f ₂ the same
The gain adjustment circuit that gives the acceleration feedback of
The electromagnetic braking resistance of the IVA unit 21 is equivalent to 51.2 units.
It becomes mechanical Ω, that is, the above acceleration type feedback is applied
The velocity type feedback of the amount that flattens the peaks of f ₁ and f ₂
Combining the gain-adjusted integration circuit in this way,
The feedback circuit 25 feeds back to the power amplifier 23. In addition,
The feedback amount is attenuated so as not to become unstable at about 200 Hz or higher.

Further, a low-pass filter 26 having a cutoff frequency of 200 Hz is inserted in front of the power amplifier 23 to attenuate unnecessary bands.

The low-pitched sound reproducing device configured as described above is
Since MFB is applied to the driver unit and the electromagnetic braking resistance of the driver unit and the effective vibration mass can be made extremely large equivalently, not only the _two resonance frequencies f ₁ and f ₂ are lowered but also the two peaks are suppressed to be equal. it that-out is in <br/>. Also, the rear of the driver unit is sealed
And no matter how low the frequency is, behind the driver unit
Since the sound pressure of the driver unit does not wrap around to the front and interfere with it , the flat sound pressure frequency characteristics in the ultra-low frequency range can be achieved with a large effective vibration area of the driver unit, that is, a high maximum output large sound pressure.
Obtained by.

The measured sound pressure frequency characteristics of the low-pitched sound reproducing device configured as described above are the same as those shown in FIG. As is clear from FIG. 10, 30 Hz to 1
Not only is a flat characteristic obtained over approximately 20 Hz, but the total internal volume of the cabinet is as small as 50 liters, but it is approximately 100 at 30 Hz.
It is possible to obtain a distortion-free maximum output sound pressure level of dB.

Although the sensor is of the piezoelectric type in this embodiment, it goes without saying that it may be of the moving coil type, the light amount detecting type, the electrostatic type or the like. For example, in the case of a moving coil type sensor, a voltage proportional to the speed of the driver unit vibration system is obtained, so that a voltage proportional to the acceleration of the vibration system can be obtained by passing the differential circuit through the feedback circuit. Alternatively, in the case of a light amount detection type or electrostatic type sensor, a voltage proportional to the displacement of the vibration system can be obtained,
A voltage proportional to the acceleration can be obtained by passing the differential circuit once through the feedback circuit, and by passing the differential circuit once again. Further, although the sensor is attached to the center of the diaphragm of the driver unit, it may be attached to an arbitrary portion of the vibration system such as an outer peripheral portion of the diaphragm or a voice bobbin.

Next, a fourth embodiment of the present invention will be described with reference to FIG. The configuration is the same as that of the third embodiment shown in FIG. 3, except that the sensor attached to the diaphragm is the microphone 34 and is provided inside the first cavity 32c.

The microphone 34 has the first cavity 32.
c The sound pressure inside, that is, the rear of the driver unit 31 is sealed
The sound pressure inside the cavity is detected, but the sound pressure inside the first cavity 32c has a sound wavelength of the first cavity 32c.
In a range that is sufficiently larger than the length of each side of c, that is, in the low sound range, it is proportional to the displacement of the vibration system of the driver unit. The voltage detected by the microphone 34 is passed through the differentiating circuit once by the feedback circuit 35, and the voltage is proportional to the acceleration by passing through the differentiating circuit once more. Then, these are adjusted in gain and fed back. The electromagnetic braking resistance and the effective vibration mass are equivalently set to the same values as in the third embodiment.

Therefore, the operation and effect are exactly the same as those of the third embodiment, and the same sound pressure frequency characteristics as those shown in FIG. 10 can be obtained. However, by using the microphone as the sensor, this is used as the vibration system of the driver unit 31. It is not necessary to attach it to the sensor, which makes it easier to handle the lead wire from the sensor.
This has the effect of facilitating the assembly of the bass reproduction device.

[0064]

As is apparent from the above description, according to the present invention, the power amplifier and the rear of the driver unit are hermetically sealed.
The detection circuit inserted between the driver unit stored in the Kelton type cabinet detects the voltage proportional to the vibration speed of the driver unit, and the detected output is fed back to the power amplifier to reduce the low frequency range. Two resonances
Acceleration of an amount that makes the peak levels of frequencies f1 and f2 the same
Degree-type feedback and the above when the acceleration-type feedback is applied
By adopting the configuration in which the velocity type feedback of the amount for flattening the peak is applied at the same time , the electromagnetic braking resistance of the driver unit and the effective vibration mass can be made extremely large equivalently, and the two resonance frequencies f ₁ , f ₂ Not only lowering f
Runode can be suppressed equal to _1, the peak of f _2, or
The rear of the driver unit is sealed, so
Even if the frequency is very low, the sound pressure behind the driver unit
Since it does not wrap around to the front and interfere with it , flat sound pressure frequency characteristics in the ultra low frequency range can be obtained with a large effective vibration area of the driver unit. It is possible to realize a low-pitched sound reproducing device capable of reproducing flatly.

Further, the same structure can be adopted in which the sensor detects the vibration of the vibration system of the driver unit to generate a voltage, and the output voltage of the sensor is fed back to the power amplifier by the feedback circuit to perform the velocity type feedback and the acceleration type feedback. The effect is obtained.

Furthermore, by using a microphone as the sensor, it is not necessary to attach it to the vibration system of the driver unit, and it is possible to realize a bass reproduction apparatus in which the lead wire from the sensor can be easily processed and the assembly is easy. it can.

[Brief description of drawings]

FIG. 1 is a block diagram showing a configuration of a bass reproduction device according to a first embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a bass reproduction device according to a second embodiment of the present invention.

FIG. 3 is a block diagram showing a configuration of a bass reproduction device according to a third embodiment of the present invention.

FIG. 4 is a block diagram showing a configuration of a bass reproduction device according to a fourth embodiment of the present invention.

FIG. 5 is a characteristic diagram showing impedance characteristics of a voice coil of the speaker in the example.

FIG. 6 is an equivalent circuit diagram showing an impedance component of a voice coil of the speaker in the example.

FIG. 7 is a characteristic diagram showing impedance characteristics of a Kelton type speaker system for explaining the embodiment.

FIG. 8 is a characteristic diagram for explaining the effect of MFB in the first embodiment.

FIG. 9 is a characteristic diagram for explaining the effect of MFB in the first embodiment.

FIG. 10 is a characteristic diagram showing actually measured sound pressure frequency characteristics in the first embodiment of the present invention.

FIG. 11 is a characteristic diagram showing actually measured sound pressure frequency characteristics in the second embodiment of the present invention.

FIG. 12 is a characteristic diagram showing sound pressure frequency characteristics measured by a conventional bass reproduction device.

FIG. 13 is a characteristic diagram showing sound pressure frequency characteristics measured by a conventional bass reproduction device.

FIG. 14 is a block diagram showing a configuration of a conventional bass reproduction device.

15 is an equivalent circuit diagram of the Kelton type speaker system in FIG.

[Explanation of symbols]

 1 Driver unit 2 Kelton type cabinet 3 Power amplifier 4 Detection circuit 5 Feedback circuit 6 Low pass filter

Claims (3)

(57) [Claims] 1. A driver unit, a Kelton type cabinet that seals the rear of the driver unit and attaches the driver unit, a power amplifier for driving the driver unit, and a power amplifier inserted between the power amplifier and the driver unit. A detection circuit for detecting a voltage proportional to the speed of the vibration system of the driver unit, and two low frequency bands fed back from the detection circuit to the power amplifier.
Amount to make the peak levels of the resonance frequencies f1 and f2 of the
Acceleration type feedback and when the above acceleration type feedback is applied
And a feedback circuit for simultaneously applying a speed type feedback in an amount such that the peak is flattened . 2. A driver unit, a Kelton-type cabinet for sealing the rear of the driver unit and mounting the same, a power amplifier for driving the driver unit, and detecting a vibration of a vibration system of the driver unit to generate a voltage. The sensor that is generated and the two low frequency bands that are fed back from the sensor to the power amplifier .
The amount of equalizing the peak levels of the resonance frequencies f1 and f2
Acceleration type feedback, and further when applying the acceleration type feedback
A low-pitched sound reproducing device comprising: a feedback circuit that simultaneously receives the speed-type feedback in an amount that flattens the peak . 3. A microphone is used as a sensor for detecting the vibration of the vibration system of the driver unit, and the microphone is used as a microphone.
Cabinet behind the driver unit of the Luton cabinet
The bass reproduction device according to claim 2, wherein the bass reproduction device is provided in a tee .