JPH01241297A - Acoustic equipment - Google Patents

Abstract

PURPOSE:To prevent undesired open tube resonance sound generated at the drive of a resonator and to reduce noise or radiation sound distortion by providing a pressure buffer means to a speed node position of tube resonance of an open tube port of a Helmholtz resonator or its vicinity. CONSTITUTION:As the open tube port 8, the tube formed by a felt is used and dense and thin air density at resonance repeats at the resonance frequency at the part of the node of the velocity of the open tube resonance, that is, the loop of pressure, but the resonance hardly takes place due to the porosity of the felt. Since the inner face of the felt-made open tube port 8 has a large resistance with respect to the movement of air, the resonance energy is absorbed therein into heat and the resonance level is lowered. Moreover, the inner face of the port 8 becomes a passive diaphragm due to the flexibility of the felt and absorbs the sound due to the tube resonance. Thus, the air reaction is cancelled via a transducer 3 and a servo part 31 or the like to prevent the undesired open tube resonance sound caused at the drive of the Helmholtz resonator without sacrificing the low sound radiation capability to the utmost thereby reducing or eliminating noise or radiated sound distortion.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention provides a Helmholtz resonator having an open tube port with a vibrator, and drives the vibrator to radiate resonant sound. The present invention relates to an acoustic device, and particularly to an acoustic device that removes unnecessary resonance sounds other than the Helmholtz resonance generated when the Helmholtz resonator is driven, thereby eliminating noise from radiated sound and improving distortion characteristics.

[Prior Art] A phase inversion type (bass reflex type) speaker system is known as an acoustic device that solely utilizes Helmholtz resonance.

FIG. 9 is a perspective view and a sectional view showing an example of the configuration of a bass reflex speaker system. The speaker system shown in the figure has a hole made in the front of a box body 6 to which a vibrator consisting of a diaphragm 2 and an electrodynamic speaker 3 is attached, and an open pipe port 8 with a sound path 7 provided below. There is. Here, in a bass reflex type speaker system that follows normal basic settings, the resonance frequency (resonance frequency) fo due to the air spring of the box body 6 and the air mass of the sound path 7.

is set lower than the lowest resonant frequency f0 of the camera (speaker) when it is assembled in a bass reflex box.

At a frequency higher than the resonance frequency due to the air spring and air mass, the sound pressure from the rear surface of the diaphragm 2 has an opposite phase at the sound path 7, and therefore, at the front of the box body 6,
The sound radiated directly from the front surface of the diaphragm 2 and the sound from the open port end up being in phase, increasing the sound pressure. As a result, according to the optimally designed bass reflex speaker system, the frequency characteristics of the output sound pressure are changed to the resonant frequency f0 of the vibrator.
As shown by the two-dot head line in FIG. 10, the −-like regeneration range can be made wider than that of an infinite plane baffle or a closed baffle.

[Problems to be Solved by the Invention] However, in such a bass reflex type speaker system, open tube resonance occurs at the open tube port portion, and this resonance sound is radiated directly as noise or acoustic distortion components, which is a disadvantage. was there.

In order to eliminate such distortion or noise, it has been proposed to form a narrow-diameter portion in the center of the port and eliminate port No. 1 (see Japanese Utility Model Publication No. 54-35068). However, in this case, the narrower the diameter of the narrow diameter part is made in an attempt to increase the filter effect, the more the acoustic resistance of the port increases, the Q of the Helmholtz resonance decreases, and the speaker system behaves as a closed-loop. , the frequency characteristics approach the characteristics shown by the dashed-dotted line in FIG. 10, resulting in a problem in that the bass radiation ability decreases.

In view of the above-mentioned problems with the conventional type, the present invention provides an acoustic device using a Helmholtz resonator having an open tube port, in which the Ql of the Helmholtz resonator and therefore the bass radiation ability of the acoustic device equipped with the Helmholtz resonator are improved. The purpose of this invention is to reduce noise or radiated sound distortion by preventing unnecessary open tube resonance sound generated when driving the Helmholtz resonator with as little sacrifice as possible.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a method for making it difficult to generate tube resonance at or near a portion of an open tube port of a Helmholtz resonator where a velocity node of open tube resonance occurs. A pressure relief means is provided.

The method for providing the pressure relief means is as follows: (1) The velocity streak generating portion of the open pipe port is formed of an acoustically resistant breathable material, such as felt, sponge, nonwoven fabric, or woven fabric, or is pasted on the inner surface.

(2) The velocity streak generating portion of the open tube port is made of a flexible material having viscoelasticity, such as rubber.

(2) A fine gap or a fine opening having acoustic resistance is formed in the velocity streak generating portion of the opening tube port.

■Combine these methods from ■ to ■.

(2) The entire open pipe port is made of the material (2) or (2) above.

etc.

[Function] Since the nodes of velocity are the antinodes of pressure, in this invention having the above-described configuration, the pressure due to open tube resonance is absorbed by the resistance of the inner surface of the pressure relief means, leaked due to air permeability,
or relaxed for flexibility. As a result, pressure changes (air density) at the open tube port of the Helmholtz resonator are alleviated, and the pressure amplitude of open tube resonance is suppressed. That is, the Q of open tube resonance decreases. Therefore, the level of open tube resonance determined by the port length is reduced or eliminated.

The effect of this pressure relief means is greater as the position of the pressure relief means is closer to the velocity node position of the open tube resonance, that is, the pressure antinode.

[Effect] According to the present invention, as described above, open tube resonance, which is unnecessary for a Helmholtz resonator, is suppressed, and as a result, open tube resonance, which is a noise or distortion component of an acoustic device using this Helmholtz resonator, is suppressed. Radiation is reduced or prevented.

Furthermore, there is no need to extremely narrow the opening pipe port.
The effect on Helmholtz resonance is small.

[Example] Hereinafter, the present invention will be described in detail with reference to the attached FIGS. 1 to 8. Note that elements common or corresponding to those of the conventional example shown in FIG. 9 are given the same reference numerals.

FIG. 1 shows the basic configuration of an audio device according to an embodiment of the present invention. The audio equipment (speaker system) in the same figure is
A hole is made in the front of the box body 6 to attach a vibrator consisting of a diaphragm 2 and an electrodynamic electroacoustic transducer (speaker) 3, and a sound path 7 is provided below which opens to the outside of the box body 6. An open pipe port 8 is provided, and this open pipe port 8 and the box body 6
This forms a Helmholtz resonator. In this Helmholtz resonator, the air spring in the box body 6 which is a closed cavity and the air Xt in the sound path 7 of the open tube port 8
This causes the air Ime 1 phenomenon. And this resonance frequency f. P is determined as for=c (s/pv)""/2i"...(1). Here, C is the speed of sound, S is the cross-sectional area of the sound ln7, is the length of the open pipe port 8, and ■ is This is the volume of the box body 6.

In the acoustic device of this embodiment, the transducer 3 is connected to a vibrator drive device 30. This vibrator drive device 30 is equipped with a servo section 31 that performs electrical servo to cancel the atmospheric reaction from the resonator side when driving a Helmholtz resonator consisting of a box body 6, an open tube port 8, etc. Such a servo system uses a negative impedance generation circuit that equivalently generates a negative impedance component (-20) in the output impedance, or a motional signal that detects and inputs a motion signal corresponding to the movement of the diaphragm 2 by some method. A known circuit such as a motional feedback (MFB) circuit that provides negative feedback at the end can be applied.

Next, the operation of the acoustic device having the configuration shown in FIG. 1 will be explained.

When a drive signal is given to the transducer 3 from the vibrator drive device 30, the transducer 3 converts it into an electromechanical converter to reciprocate the diaphragm 2 back and forth (left and right in the figure). The diaphragm 2 converts this reciprocating motion into mechanical sound. Here, the front side of the diaphragm 2 (
The right side in the figure) constitutes a direct radiating part for directly radiating sound to the outside, and the rear side of the diaphragm 2 (left side in the figure) is a Helmholtz resonance consisting of a box body 6 and an open tube port 8. It serves as a resonator driver for driving the resonator. Although an atmospheric reaction from the air inside the box 6 is applied to the rear side of the diaphragm 2, the vibrator driving device 30 drives the converter 3 so as to cancel this atmospheric reaction.

In this way, when the converter 3 is driven so as to cancel out the atmospheric reaction from the Helmholtz resonator when the Helmholtz resonator is driven, fJA! The II plate 2 cannot be driven from the side of the resonator, but acts as a rigid body or wall when viewed from the side of the resonator. Therefore, the resonant frequency and Q as a Helmholtz resonator are independent of the resonant frequency and Q as a direct radiation part by the diaphragm 2 and the converter 3, and the resonator driving energy from the converter 3 is also It will be given independently from the department. Also, converter 3
is driven in a so-called dead state, unaffected by atmospheric reaction from the resonator, that is, from the box 6 side, so the frequency characteristics of the directly radiated sound are not affected by the volume of the box 6. Therefore, according to the configuration of this embodiment, the volume of the box 6, which is the cavity of the Helmholtz resonator, can be made smaller than that of the conventional bass reflex speaker system, and in this case, the resonance frequency f. Even if P is set lower than that of this bass reflex type speaker system, the Q value can be set to a sufficiently large value. As a result, in the acoustic device shown in Fig. 1,
Even if the box body 6 is made smaller than a conventional bass reflex speaker system, it is possible to reproduce even lower frequencies.

In FIG. 1, a transducer 3 drives a diaphragm 2 in response to a drive signal from a vibrator drive device 30, and is independent of a Helmholtz resonator composed of a box body 6 and an open tube port 8. gives driving energy to. As a result, sound is directly radiated from the diaphragm 2 as shown by arrow a in FIG.
As indicated by the arrows in the figure, sound with sufficient sound pressure is resonantly radiated from the resonant radiator (open port 9 of open tube port 8). Then, by adjusting the air equivalent mass in the open tube port 8 in the Helmholtz resonator, this resonance frequency f'op is set lower than the reproduction frequency band of the converter 3, and the equivalent resistance of the open tube port 8 is adjusted. By setting the Q value to an appropriate level, it is possible to obtain the frequency characteristic of the sound pressure as shown in FIG. 2, for example, on the condition that an appropriate level of sound pressure is obtained from the opening port 9. In the figure, the solid line indicates the frequency characteristic of the resonance radiated acoustic sound pressure from the frontage port 9, and the broken line indicates the frequency characteristic of the directly radiated acoustic sound pressure from the transducer (speaker).

By the way, in such an acoustic device, when the open tube port 8 is formed using a rigid body such as plastic or wood, the open tube port 8 is caused to undergo open tube resonance due to the air flow passing through the open tube port 8 due to Helmholtz resonance. During this time, the frequency f, we/2. due to tube resonance. Q...
...(2) f2 = C/4 J2 +
There was a drawback that the sound (3) was radiated as shown by the dashed line in FIG. 2, and this was mixed into the resonant radiated sound of the Helmholtz resonator as a distortion or noise component. Such drawbacks also exist when the vibrator (speaker) of a numerical bass reflex speaker system is driven by a numerical power amplifier, but as mentioned above,
This is particularly noticeable when the Q value of the Helmholtz resonator is improved by driving the transducer 3 so as to cancel out the atmospheric reaction from the Helmholtz resonator, thereby increasing the sound pressure of the resonant radiation.

In the embodiment shown in FIG. 1, the open pipe port 8 is made entirely of felt. Therefore, at the speed node of open tube resonance shown in Figure 3, that is, the pressure antinode, the air density during resonance repeats sparse and dense at the resonance frequency, but due to the air permeability of the felt, it becomes sufficiently sparse and dense. Furthermore, since the inner surface of the felt fissure tube port has a large resistance to air movement, the resonance energy is absorbed and becomes heat, which lowers the level of resonance. Furthermore, due to the flexibility of the felt, the inner surface of the open tube port is no longer a fixed wall and becomes a passive vibrator to absorb sound due to tube resonance of the open tube port.

As a result of the above, the open tube resonance frequency, that is, the noise or distortion component due to open tube resonance, which appeared as peaks at frequencies f1 and f2 in FIG. 2, is reduced or eliminated.

Note that other breathable and acoustically resistant materials such as sponge, non-woven fabric, woven fabric, etc. can also be used instead of the felt. In the following, felt, sponge, nonwoven fabric, woven fabric, etc. are collectively referred to as felt, etc.

[Other Embodiments] FIGS. 4 to 8 are views showing other embodiments of the open tube port of FIG. 1, respectively.

In the open pipe port shown in Fig. 4, only the velocity node in the fundamental wave of open pipe resonance, that is, the central part of the open pipe port is made of felt or the like 41, and the other parts are made of the same hard material (rigid material) as before. It is composed of

The open tube port shown in FIG. 5 has a central portion cut out from the outside, an opening 51 provided in the central portion, and the opening 51 covered with a cylindrical felt 52 or the like. In addition,
When using non-woven fabrics or woven fabrics as felt etc., these materials are not formed into a cylindrical shape as described above;
It may be made into a band shape and wrapped around the aperture 51 portion by a considerable amount.

The open pipe port in FIG. 6 consists of two open pipes 8a of the same length.
, 8b are connected by a connecting support member 62 with a minute gap 61 therebetween.

The open tube port shown in FIG. 7 has a fine hole 71 in the center.

The open tube port shown in FIG. 8 has a central portion made of a flexible and viscoelastic material, such as rubber. Due to its flexibility, such a material exhibits a pressure-relieving effect that is substantially equivalent to the breathability of the felt or the like. Also, due to its viscoelasticity, it acts as a resistance that consumes energy when it bends.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of the basic configuration of an acoustic device according to an embodiment of the present invention, FIG. 2 is a frequency characteristic diagram of the sound pressure of the sound emitted from the acoustic device of FIG. 1, and FIG. , an explanatory diagram showing the state of open tube resonance in an open tube port, FIGS. 4 to 8 are diagrams showing modifications of the open tube port in FIG. 1, and FIG. 9 is a diagram showing the configuration of a conventional bass reflex speaker system. The perspective view and sectional view shown in FIG. 10 are explanatory diagrams of the sound pressure characteristics of the speaker system of FIG. 9. 2: Vibration plate, 3: Converter, 8: Open pipe port, 302 Stationary device driving device, 31: Servo section, 41: Felt, etc., 5
2: Ring of felt, etc., 61 Fine gap, 71: Fine hole, 8
1: Rubber etc.

Claims (2)

[Claims] (1) In an acoustic device in which a vibrator is disposed in a Helmholtz resonator having an open tube port, and the vibrator is driven to radiate resonant sound, the open tube port has at least one of the tube ports. 1. An acoustic device comprising a pressure relief means at or near a velocity node position of tube resonance. (2) The acoustic device according to claim 1, wherein the vibrator is driven by electrical servo so as to cancel out an atmospheric reaction from the resonator side when the resonator is driven.