JPS5829295A - Loudspeaker driving device - Google Patents

Abstract

PURPOSE:To expand a low-pitched sound reproducing area, by connecting a negative resistance circuit in series to a loudspeaker, making the circuit concerned have negative resistance at less than prescribed frequency, and also adding an impedance circuit. CONSTITUTION:A negative resistance circuit 3 has negative resistance at less than the lowest resonance frequency. That is to say, it is constituted of a voltage inverted type transistor circuit, and to this circuit, a low-pass filter 4 having cut-off frequency fc is connected. This circuit 3 has negative resistace in an area which is less than the frequency fc as shown in the figure, therefore, Dc resistance Re of a moving coil becomes as a dotted line shown in the same figure, and in an area being less than the lowest resonance frequency fo, acoustic pressure drops by 6dB/oct, and also in an area exceeding the frequency fo, the negative resistance circuit 3 has no negative resistance, therefore, a peak in an acoustic pressure characteristic is not generated in a series resonance point omega1 of electric inductance Le of the moving coil, and momentum impedance Zm.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a speaker driving device for improving bass characteristics.

Conventionally, a method of expanding the bass reproduction range by making the output impedance of a speaker driving amplifier negative is known, but since the drive target is a specific speaker system, there are problems in terms of the usability of the amplifier. Furthermore, it has the disadvantage that it is not possible to achieve sufficient improvement in bass characteristics.

The present invention provides a novel speaker driving device that overcomes these conventional drawbacks, and will be described below with reference to the drawings.

First, we will consider the electro-mechanical acoustic conversion system in an electrodynamic speaker.

The equivalent circuit of the electrical-mechanical acoustic conversion system is shown in Figure 1 (electrical system).
, as shown in Fig. 2 (mechanical acoustic system), but in such a system, generally, EO= (Zo+Zl) Q0m・! F = (z
o + zl)) - mu - q = .

holds true, and from both equations, the vibration speed of the diaphragm is l.

However, EO: Input voltage F: Driving force: Re product: Output impedance of the driving source zl: Electrical impedance of the moving coil 12: Kinetic electrical impedance zO: Acoustic impedance of the medium zl: Vibratory electrical impedance zm: Kinetic mechanical impedance In the figure, Le: inductance of the moving coil Re: DC resistance of the moving coil Pm: mechanical resistance of the vibration system Mo: equivalent mass of the vibration system CO: equivalent cosipliance of the vibration system; There is a relationship of 10zt.

In both equations, the first term is the inflow current q from the power supply voltage,
The second term is the operation of converting the input current q into the driving force F, and the eighth term is
The terms each indicate the operation of converting the driving force F into r dynamic speed).

In other words, when considering the electrical/mechanical acoustic conversion system, it is necessary to consider the electrical system and the mechanical acoustic system in conjunction with each other, and in the electrical system, the kinetic mechanical impedance Zm is This shows that there is no need to take it into consideration, and conversely, there is no need to take the kinetic-electrical impedance Zm into account in a mechanical acoustic system.

Since such an electro-mechanical acoustic conversion system is normally driven at a constant voltage, the case of constant voltage driving will be discussed below.

In the case of constant voltage drive, the output impedance ZoI of the drive source
/iZl, ZmK ratio is sufficiently small, (1), (2
) Ni′hatona,ru.

Next, the bass range near the lowest resonance frequency fo will be considered.

Below the lowest resonant frequency fo, in the equivalent circuit of Fig. 2, the vibration velocity 5 is approximately 0 9 = −−A, jωC0 le from equation (4), and therefore 1 sound pressure (acceleration) 1=-・A・・-c.

It becomes Re. That is, below the lowest resonant frequency fo, the vibration velocity is elastically controlled, and the sound pressure decreases by 12 dB10Ct, as shown by the solid line a in FIG.

The present invention was developed by further considering the bass range near the lowest resonance frequency fO (=J) as described above, and will be detailed below.

In explaining the present invention, its technical background will be explained.

(I) In equation (4) or Fig. 79, when the DC resistance Re of the moving coil is made a variable and this Re is decreased, below the lowest resonance frequency IO, the DC resistance pe of the i'+J moving coil is Since the 2 Re involved is sufficiently large compared to the other elements, the vibration velocity) is approximately E, R.

Chi-1・A・- (constant) ′EIe A2 Also, the sound pressure becomes Eo 1 sound pressure (acceleration) 1-1・ω hm2, and as the DC resistance Re of the moving coil decreases, the vibration speed) is constant due to resistance control, and the sound pressure is 6 dB/o as shown by the dotted line in Figure 8.
Descending at ct.

(It) On the other hand, from the perspective of the electrical system (equivalent circuit in Figure 1), the electrical inductance of the moving coil]1. The relationship between +e and kinetic electrical impedance Zm is shown in FIG. In the figure, (1;O(2π10) is the parallel resonance point of Zm, c
a lC2z f 1 )keZ m (-j term) and Le
(+j term) is the series resonance point.

Therefore, above the lowest resonance frequency fo, as the DC resistance R, of the moving coil is decreased, the resonance Q at the series resonance point ωl increases, and the sound pressure peaks near the series resonance point Product 1. , as shown by the dotted line in Figure 8.

As is clear from the above considerations, the DC resistance R of the moving coil
By decreasing e, the sound pressure can be lowered by 6 dB10 ct in the bass range below the lowest resonant frequency fO, but on the other hand, the electric inductance Le of the moving coil
A peak occurs on the sound pressure characteristics at the series resonance point ω1 of the kinetic electrical impedance Zm.

In view of the above considerations, the first aspect of the present invention is to connect an electrodynamic speaker (
2) and a negative resistance circuit (8) is connected in series with the electrodynamic speaker (2), the negative resistance circuit (3) becomes as shown in Fig. 6. Predetermined frequency (
It is designed to have negative resistance below the lowest resonant frequency (at or near the lowest resonant frequency fO). That is, the negative resistance circuit (3) is constituted by, for example, a well-known voltage inversion type transistor circuit, that is, a common base type transistor circuit that combines positive voltage feedback and negative current feedback, and in this embodiment, a predetermined frequency is set in the feedback loop. The configuration is such that a low-pass filter (4) having a cutoff frequency fa is inserted and connected.

As shown in FIG. 6, this negative resistance circuit (3) has a characteristic of having negative resistance in the region below the cutoff frequency fC of the low-pass filter (4), and therefore the DC resistance Re of the moving coil is the same. As shown by the dotted line (Re) in the figure, the lowest resonance frequency f.

In the vicinity and below, the sound pressure decreases by 6 dB10 ct as shown in Figure 7, and in the region above a predetermined frequency, the negative resistance circuit (3) has no negative resistance, so the above A peak in the sound pressure characteristics does not occur at the series resonance point ωl of the electric inductance Le of the moving coil and the kinetic electrical impedance Zm.

Next, in the first invention described above, as shown in FIG. 8, an impedance circuit (5) consisting of a capacitor C and a resistor R is provided between the electrodynamic speaker (2) and the negative resistance circuit (8). Let's consider the case where .

In the case of constant voltage drive, assuming that the output impedance zo of the drive source is sufficiently small, the equivalent circuits of the mechanical acoustic system are as shown in FIGS. 2 to 9.

In the same figure, in the region O below the lowest resonance frequency fo, the impedance (jωLe) of the moving coil is sufficiently small, and the DC resistance Be of the IIJ moving coil is controlled sufficiently small by the negative resistance circuit (3). ,
The equimedullary mass M O' of the diaphragm in this system is MO' = M,
+ OA" and the apparent potency increases, so the lowest resonant frequency fO' becomes, which is the conventional lowest resonant frequency i.

fo = 2.Ji Punishment decreases relative to

FIG. 10 shows the change in the lowest resonant frequency when the value of the capacitor C of the impedance circuit (5) is changed. The figure shows that the capacitor C is
The value of 200μF, 1500μF, 1000μF, 200
A specific example will be shown in which the values are increased in the order of 0 μF 18011 00 μF.

Furthermore, since the resonance Q at the lowest resonance frequency fo' is given by, the resonance Q can be controlled by adjusting the value of the resistor R of the impedance circuit (5).

FIG. 11 shows a specific example where the value of the resistor R is gradually increased in the order of 20Ω, 35Ω, and 65Ω in the case where the lowest resonant frequency fo=70Hz and the capacitor c of the impedance circuit (5)=500μF.

That is, in the present invention, as the value of capacitor C of the impedance circuit increases, the lowest resonant frequency decreases.
In addition, as the value of resistor R decreases, the resonance Q at the lowest resonant frequency decreases, and by appropriately setting the value of capacitor C1 resistor R, the lowest resonant frequency can be lowered and this region can be controlled by critical damping or It is possible to achieve ideal characteristics close to this, and to expand the sound reproduction range.

Note that the negative resistance circuit (3) is not limited to the embodiments shown in FIGS. 5 and 8, and the load of the negative resistance circuit (8) as shown in FIG. A modified circuit that combines the impedance of 2) in the figure and the electrodynamic speaker (2) may be used.

As described above, the present invention provides a configuration in which an electrodynamic speaker is connected to the output of an amplifier, and a negative resistance circuit is connected in series with the electrodynamic speaker. Since the area has a negative resistance, the sound pressure drops by 6dB10at in the area below the lowest resonant frequency, and the lowest resonant frequency can be lowered by adding an impedance circuit in series with the negative resistance circuit. , has an excellent use of being able to expand the bass reproduction range.

[Brief explanation of the drawing]

1 and 2 are diagrams showing the equivalent circuit of the electro-mechanical acoustic system, FIGS. 3 and 4 are diagrams showing the characteristics, and FIG. 5 is a diagram showing the configuration of the speaker driving device of the present invention. Figure 6 shows the characteristics of the negative resistance circuit, Figure 7 shows the characteristics of the negative resistance circuit.
8 is a diagram showing the configuration of another speaker driving device of the present invention, FIG. 9 is a diagram showing the equivalent circuit, FIGS. 10 and 11 are the same, and FIG. A diagram showing frequency characteristics, and FIG. 12 are diagrams showing another embodiment of the same. (1) is an amplifier, (2) is a speaker, (3) is a negative resistance circuit, and (5) is an impedance circuit. Patent Applicant Onkyo Co., Ltd. Agent Patent Attorney Sato Yatabe No. 1 VIj No. 20 No. 4 Closing No. 5 No. 60 Liquid Collection No. 7 No. 811i6 □□----" 487- Figure 10 circumference number 11th concave

Claims (1)

[Claims] 1. A speaker (2) is connected to the output of the amplifier (1),
A speaker driving device 2 characterized in that a negative resistance circuit (8) having a negative resistance at a frequency below a predetermined frequency is connected in series with the speaker (2), the speaker (2) being connected to the output of the amplifier (1). A negative resistance circuit (
3) and an impedance circuit (5) connected in series with the negative resistance circuit (8). 3. The speaker driving device according to claim 2, wherein the impedance circuit (5) is a capacitor C. 4. The speaker drive device according to claim 2, wherein the impedance circuit (5) is a parallel circuit of a capacitor C and a resistor R.