JPH04281696A - Acoustic signal reproduction system provided with stiffness reduction device - Google Patents

Abstract

PURPOSE:To realize the small scale system in which ultralow frequency sound is reproduced by providing a stiffness reduction unit detecting a back pressure of an acoustic signal reproduction unit and making the back pressure constant accordingly in an enclosure. CONSTITUTION:An output voltage signal of a pressure sensor S1 installed in an enclosure space at the back of an acoustic signal reproduction unit SP1 is amplified by an amplifier AMP 1 and compared with a reference signal at a differential amplifier AMP 2. The comparison output is amplified by an amplifier AMP 3 to drive the stiffness reduction unit SP 2 in phase with the acoustic signal reproduction unit SP1. When both units SP1, SP2 are driven in phase, even when a back pressure is increased by the drive of the acoustic signal reproduction unit SP1, since the pressure rise is compensated by the stiffness reduction unit SP2, the production of stiffness from the enclosure is suppressed. Thus, the equivalent capacity of the enclosure is increased, the low sound reproduction limit is decreased and the reproduction system able to reproduce an ultralow frequency sound is realized with small size.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acoustic signal reproduction system equipped with a stiffness reduction device.

0002

2. Description of the Related Art When bass sounds are reproduced using an electrodynamic speaker, the lowest resonant frequency (f0) is a measure of the reproduction limit frequency band. For example, the f0 of an electrodynamic speaker (hereinafter referred to as a unit) and its sound pressure vs. frequency characteristics rapidly drop below the lowest resonant frequency.

[0003] When sound is emitted from this unit, the sound coming from the back is in the opposite phase to the front, so the reproduced sound is canceled out, especially in the low range. Therefore, in order to prevent the sound from the back from going around to the front, if the unit is attached to an infinite baffle, the characteristics will be as shown in A in Figure 2, and the low-range reproduction limit frequency will be the same as the low-range reproduction limit frequency of the unit itself. It's decided.

[0004] However, not all speaker systems can actually be made into infinite baffles, and most of them are attached to enclosures. At that time,
Due to the stiffness caused by closing the rear part of the unit in a small space, the lowest resonance frequency increases from f0 to f0' as shown in FIG. 2B, and the low frequency reproduction limit frequency also increases.

[0005]

SUMMARY OF THE INVENTION The present invention provides an audio signal reproducing system that suppresses the increase in the low frequency reproduction limit frequency and obtains a state close to the low frequency reproduction limit frequency f0 of the acoustic signal reproduction unit itself. At the point.

[0006]

SUMMARY OF THE INVENTION The present invention includes a unit for reproducing an acoustic signal and a device for reducing stiffness within the enclosure when the unit is housed in the enclosure.

[0007]

[Embodiment] The present invention includes a unit for reproducing an acoustic signal, and a detection means for detecting the back pressure of this unit.
The sound reproduction system includes a stiffness reducing unit in an enclosure, which is driven by the signal output of the detection means and keeps the back pressure constant.

FIG. 1 shows a block diagram of the acoustic signal reproduction system of the present invention. In this embodiment, a stiffness reduction unit, for example, the same electrodynamic cone speaker SP2 as described above, is arranged behind an acoustic signal reproduction unit, for example, an electrodynamic cone speaker SP1, so as to divide the volume of the enclosure into two. do. S1 is a pressure sensor that detects the back pressure of unit SP1 in the space formed by the units SP1, SP2 and the enclosure. For example, a microphone or the like can be used as the pressure sensor S1.

AMP1 is an amplifier for correcting the gain and phase of the pressure signal voltage detected by the pressure sensor S1,
The output signal of the amplifier AMP1 is input to a comparison circuit, for example, a differential amplifier AMP2, which compares it with a reference level to be described later. The output of the differential amplifier AMP2 is amplified by a stiffness reduction unit driving amplifier AMP3 to drive the stiffness reduction unit SP2.

[0010] The operation of the acoustic signal reproducing system capable of reproducing in a state close to the low frequency reproduction limit frequency of the unit SP1 itself will be explained below. The lowest resonant frequency f0, which is a guideline for the reproduction limit frequency band of the unit itself, is:
It is expressed as f0 = 1/2π (√s0 /√m0). Here, m0: equivalent mass of the vibration system [kg], s0:
This is the equivalent stiffness [N/m] of the vibration system.

[0011] Furthermore, the lowest resonant frequency f0' when the unit is installed in the enclosure is f0'=1/2π(
It is expressed as √(s0 +sc)/√m0). Here, sc: Equivalent stiffness of enclosure [N/m
]. Furthermore, the equivalent stiffness sc of the enclosure is expressed as sc = ρ0 c2 π2 a4 /v. Here, ρ0: Density of air [kg/m3]
, c: Sound velocity [m/sec], a: Vibration effective radius of unit diaphragm [m], v: Enclosure volume [m3
].

Considering the above equation, it can be seen that the increase in f0 is due to the equivalent stiffness sc of the enclosure, and the increase in sc is due to the decrease in the volume v of the enclosure. In other words,
The problem with the low frequency reproduction limit of the unit is basically that v is small.

[0013] Although it is possible to lower the low frequency reproduction frequency by increasing the volume of the enclosure, this is inconsistent with miniaturizing the acoustic signal reproduction system. Therefore, the present invention detects the change in pressure to keep the pressure constant (typically If it is controlled so that it becomes 0), it is essentially equivalent to putting it in a large enclosure, and the low-frequency reproduction limit frequency of the acoustic signal reproduction system is almost close to the low-frequency reproduction limit frequency of the acoustic signal reproduction unit itself. It is something that makes a state.

In order to achieve the above-mentioned state, the present invention will be explained below based on embodiments. In the configuration diagram of the acoustic signal reproduction system shown in FIG. 1, the acoustic signal reproduction unit SP
The output voltage signal of the pressure sensor S1 arranged in the enclosure space behind the
1 and compared with a reference signal set to ground level using a comparator, for example, a differential amplifier AMP2. The output signal of the comparator is connected to a stiffness reduction unit driving amplifier A.
Amplify with MP3 and use stiffness reduction unit SP2
is driven in phase with the signal that drives 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 reproducing unit SP1 decreases and the pressure increases, the increase in pressure is
Since the stiffness reducing unit SP2 is also driven through the enclosure space provided behind the unit SP1, the volume does not change by compensating for the decrease in volume, and therefore the pressure is kept constant without increasing. . As a result, the occurrence of stiffness in 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 audio signal reproduction unit SP1.

In the above embodiment, the reference signal is set at the ground level, but in reality, if the servo system is used to a large extent, there will be no phase margin, and the acoustic signal reproducing unit S
Residual pressure due to the drive of P1 exists in the enclosure space, and the second and third harmonic levels increase around 300 Hz. Therefore, by applying the acoustic signal that drives the acoustic signal reproduction unit SP1 as a reference signal to the comparison amplifier AMP2 at a constant ratio, it was possible to suppress the level of the harmonics.

Here, one of the latter embodiments to which the present invention is applied
An actual measurement example will be explained. An enclosure with a total volume of 18 liters is divided into two by stiffness reduction unit SP2.
The volume behind the two units is approximately 9 liters. First, the acoustic signal reproducing unit SP1 (16c
When only the stiffness reduction unit SP2 (16c
When the system was driven as described above, the lowest resonant frequency was reduced to about 34.7 Hz. This is equivalent to converting an enclosure with a volume of 18 liters into an enclosure with an equivalent volume of approximately 170 liters, which can significantly reduce the equivalent stiffness of the enclosure.

FIG. 3 shows the frequency characteristics of this example. The lowest resonant frequency is lowered from 49 Hz to 34.7 Hz, and the sound pressure level is also increased, which is a significant improvement.

[0019]

According to the present invention, since the equivalent volume of the enclosure can be increased, the bass reproduction limit can be lowered, and it is possible to realize a compact acoustic signal reproduction system capable of reproducing deep bass sounds.

[Brief explanation of the drawing]

FIG. 1 is a configuration diagram of an audio signal reproduction system of the present invention.

FIG. 2 is a sound pressure level versus frequency characteristic diagram.

FIG. 3 is an actual measurement diagram of frequency characteristics of the present invention.

[Explanation of symbols]

SP1...Unit for acoustic signal reproduction SP2...Unit for stiffness reduction S1...Pressure sensor AMP1...Amplifier for gain/phase correction AMP2...Differential amplifier AMP3...
Unit drive amplifier for stiffness reduction

Claims (1)

[Claims] 1. An acoustic signal reproducing unit, a pressure sensor that detects the back pressure of the acoustic signal reproducing unit, a servo loop electric circuit that applies an output signal of the pressure sensor, and the acoustic signal reproducing unit. and a stiffness reducing unit disposed behind the servo loop electric circuit and driven by the output of the servo loop electric circuit, the acoustic signal reproduction system characterized in that the back pressure is kept constant.