JPH01241296A - Acoustic equipment - Google Patents

Abstract

PURPOSE:To prevent undesired open tube resonance sound at driving and to reduce noise or radiation sound distortion by providing a 2nd Helmholtz resonance tube resonated to the open tube resonance frequency and providing a servo part to a diaphragm driver. CONSTITUTION:An open tube port 12 of a Helmholtz resonator 10 has an open tube port 18 and a cavity 17 and a 2nd helmholtz resonator 15 is provided opened to the center of the port 12 by the open port 18 of the port 16. Moreover, a vibrator 20 comprising a diaphragm 21 and a transducer 22 is fitted to the resonator 10 and the transducer 22 is connected to the diaphragm driver 30. The driver 30 is provided with a servo part 31 applying electric servo so as to cancel air reaction from the resonator side at the drive of the resonator 10. Thus, since the volume of the cavity of the resonator 10 is reduced more than that of the bass reflex speaker system, up to a low sound is reproduced even with miniaturization and the undesired open tube resonance sound caused at the drive of the resonator 10 is prevented by the provision of the resonator 16 thereby reducing noise or radiation sound distortion.

Description

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

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

FIG. 7 is a perspective view and a sectional view showing an example of the configuration of a bass reflex speaker system. In the speaker system shown in the figure, a hole is 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 tube boat 8 having a sound path 7 is provided below the vibrator. There is. Here, in a bass reflex type speaker system that follows normal basic settings, the co-located frequency (resonance frequency) for due to the air spring of the box body 6 and the air mass of the sound path 7 is incorporated into the bass reflex type box body. It is set lower than the lowest resonant frequency fO of the vibrator (speaker). At a frequency higher than the resonance frequency caused by 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. The direct radiation sound from the boat and the sound from the open boat 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 can be extended to below the resonant frequency f0 of the vibrator, and as shown by the two-dot chain line in FIG. The playback range can be wider than that of an infinite plane baffle or a closed bubble.

[Problems to be Solved by the Invention] However, in such a bass reflex type speaker system, open tube resonance occurs in the open tube boat section, and this resonance sound is radiated as is as an acoustic distortion component or noise. was there.

In order to eliminate such distortion or noise, it has been proposed to form a narrow diameter section in the center of the boat to eliminate boat resonance (see Japanese Utility Model Publication No. 35068/1983). However, in this case, the narrower the diameter of the narrow diameter section is made in an attempt to increase the filter effect, the more the acoustic resistance of the boat increases, the Q of the Helmholtz resonance decreases, and the speaker system behaves as a closed-loop. There is a problem in that as the frequency approaches , the frequency characteristics approach the characteristics shown by the dashed line in FIG.

In view of the above-mentioned problems with the conventional type, the present invention provides an acoustic apparatus using a Helmholtz resonator having an open tube boat. The purpose of this invention is to reduce noise or radiated sound distortion by preventing unnecessary open tube resonance sound that occurs when driving this Helmholtz resonator, without sacrificing as much as possible.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a method for resonating with the open-tube resonance frequency in the vicinity of a portion of the open-tube boat of the Helmholtz resonator that generates the velocity node of the open-tube resonance. Equipped with a resonator.

As another resonator that resonates with the open tube resonance frequency, a Helmholtz resonator or a closed tube resonator tuned to the open tube resonance frequency of the open tube boat can be used.

[Function] On the other hand, a resonator is also an absorber of resonant frequency sound, so
In this invention configured as described above, unnecessary resonance sound generated independently of Helmholt resonance at the open tube port of the Helmholtz resonator, that is, open tube resonance sound determined by the port length, is absorbed by the other resonator. , is canceled out.

This resonance sound canceling effect is greater as the attachment position of the another resonator is closer to the velocity node position of the open tube resonance.

[Effects] According to the present invention, unnecessary resonance sounds are absorbed and canceled as described above, and as a result, the emission of open tube resonance sounds, which are noise or distortion components of the acoustic device using the Helmholtz resonator, is reduced or Prevented.

Further, the other resonator can be tuned to only a specific frequency, and only unnecessary imaging (unnecessary resonance sound) can be removed. Therefore, if the unnecessary imaging frequency is sufficiently far from the Helmholtz resonance frequency, the unnecessary imaging can be removed without adversely affecting the Helmholtz resonance.

Furthermore, since there is no need to make the open tube boat extremely narrow,
Also from this point of view, there is little influence on Helmholtz resonance.

[Example] Hereinafter, the present invention will be described in detail with reference to the attached FIGS. 1 to 6. In addition, in the description of the drawings, the same elements are given the same reference numerals, and redundant description will be omitted.

FIG. 1 shows the basic configuration of an audio device according to an embodiment of the present invention. The acoustic device shown in the figure uses a Helmholtz resonator 10 having an open tube boat 12 with a frontage boat 11 that forms a resonance emission section. In this Helmholtz resonator 10, an air resonance phenomenon occurs due to the closed air conditioner and the open tube boat. And this resonant frequency fOPI is for+ = C(S+ /, e+ v,)''/2π
・・・・・・(1) It is obtained as follows. Here, C: speed of sound Sl, cross-sectional area 1 of the two-opening boat 11,: length vl of the open tube boat 12, volume of the cavity of the Helmholtz resonator 10.

The open tube boat 12 of this Helmholtz resonator 10 includes:
A second Helmholtz resonator 15 having an open tube port 16 and a cavity 17 and opening into the center of the open tube port 12 by a frontage boat 18 of the open tube boat 16 is attached.

The resonant frequency f of this second Helmholtz resonator 15. P
2 is fop2=C(32/JZ2 V2) ”'/2
π・・・・・・(2) It is obtained as follows. Here, C is the speed of sound, S2 is the cross-sectional area of the open boat 18, °C2 is the length of the open tube boat 16,
is the volume of the cavity 17.

In this example, this resonant frequency f. P2 is the open tube resonance frequency f of the open tube boat 12, T=c/2fL, (3
), i.e., fOP□=e(S2/λ y , ) l/2/2
π= c / 21L + = f or Therefore, (S 2 / 112 V 2 ) ”' = π/i+
......(4) It is set so that it becomes.

In the acoustic device of this embodiment, a vibrator 20 consisting of an imaging plate 21 and a transducer 22 is attached to a Helmholtz resonator 10. Additionally, this transducer 22 is connected to a vibrator drive 30. The vibrator drive device 30 also includes a servo section 31 that performs electrical servo to cancel the atmospheric reaction from the resonator side when the Helmholtz resonator 10 is driven. In such a servo system, a negative impedance component (20
) and the diaphragm 2 that generates negative impedance.
A known circuit such as a motional feedback (MFB) circuit that detects a motion signal corresponding to the motion of 1 by some method and provides negative feedback to the input side 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 applied from the vibrator drive device 30 to the transducer 22 of the vibrator 20, the transducer 22 converts the stiffness into an electrical mechanism and reciprocates the diaphragm 21 back and forth (left and right in the figure).

The diaphragm 21 converts this reciprocating motion into mechanical sound. Here, the front side (the left side in the figure) of the diaphragm 21 constitutes a direct radiation part for directly radiating sound to the outside, and the imaging plate 21
The rear side of 1 (right side in the figure) is the Helmholt resonator 10.
The resonator drive unit is used to drive the resonator. and,
On the rear side of this imaging plate 21, a Helmholtz resonator 10 is provided.
Although an atmospheric reaction from the air in the cavity is added, the vibrator drive device 30 drives the vibrator 20 so as to cancel out this atmospheric reaction.

In this way, since the vibrator 20 is driven so as to cancel out the atmospheric reaction from the resonator 10 when the Helmholtz resonator 10 is driven, the diaphragm 21 of the vibrator 2o is not visible from the side of the Helmholtz resonator 10. It cannot be driven and acts as a rigid body or wall.

Therefore, the resonant frequency and Q of the Helmholtz resonator 1o are independent of the resonant frequency and Q of the vibrator 20, and the driving energy of the resonator 10 from the converter 22 is also applied independently of the direct radiation section. It turns out. This allows the volume of the cavity (for example, a speaker cabinet) of the Helmholtz resonator 10 to be smaller than that of a conventional bass reflex speaker system, and to reduce the resonant frequency f. Even if P is set lower than that of this bass reflex type speaker system, the Q value can be set sufficiently high, and as a result, even if it is made smaller than the bass reflex type speaker system, it is possible to reproduce even lower tones.

In FIG. 1, transducer 22 drives vibrator 21 in response to a drive signal from vibrator driver 30, and independently provides drive energy to Helmholtzian oIWto. As a result, sound is directly radiated from the recording board 21 as shown by the arrow a in FIG. Then, sound with sufficient sound pressure is resonantly radiated from the resonant radiator (open boat 11). Then, by adjusting the air equivalent mass in the open tube boat 12 in the Helmholtz resonator 10, this resonant frequency fQP is adjusted to the vibrator 20.
Set lower than the playback frequency band of, and open pipe port 1
The condition is that an appropriate level of sound pressure is obtained from the open port by setting the Q value to an appropriate level by adjusting the equivalent resistance in step 2, and further increasing or decreasing the human signal level as necessary, e.g. A sound pressure frequency characteristic as shown in FIG. 2 can be obtained.

During this acoustic radiation, the second Helmholtz resonator 15
In the case where the Helmholtz resonator 10 is not attached, the open tube boat 12 causes open tube resonance due to the air flow passing through the open tube boat 12 of the Helmholtz resonator 10, and during this period, the frequency f(,7=c/211 . . . ...(2)
There is a drawback that the sound (indicated by the dashed line in FIG. 3) is mixed into the resonance radiated sound of the Helmholtz resonator 10 as a distortion or noise component. These drawbacks are due to the fact that - the vibrator (speaker) of the numerical bass reflex type speaker system -
This also exists when driven by a numerical power amplifier, but by driving the vibrator 20 so as to cancel out the atmospheric reaction from the Helmholtz resonator 10 side, the Q value of the Helmholtz resonator 10 is improved and resonance radiation is reduced. This is particularly noticeable when the sound pressure is increased.

In the embodiment of FIG. 1, the open tube resonance sound of f 0T=C/2λ1 as shown by the dashed line in FIG. The sound is absorbed by the device 15 as shown by the dotted line in FIG. 3, and a comprehensive characteristic with the open tube resonance sound removed as shown by the solid line in FIG. 3 is obtained.

Such an open tube resonance acoustic removal effect is achieved by changing the attachment point of the second Helmholtz resonator 15, that is, the opening position of the open boat 18, to the position where the velocity node of the open tube resonance is formed and the pressure is maximum, i.e. The maximum value is obtained when the distance l from the open boat 11 is set at a position where the distance is =1□/2.

[Other Examples] Note that the present invention is not limited to the above-mentioned embodiments, and can be implemented with appropriate modifications. For example, open tube resonance can occur at each harmonic with f6T=C/2℃1 as the fundamental wave, but when the level and frequency of these open tube resonances are non-negligible, each harmonic The third harmonic resonates at that velocity node position for each. 4th. It is sufficient to arrange a Helmholtz resonator of... For example, in the case of the second harmonic, as shown in FIG.
It is placed in either or both positions with s-311/4, and the dimensional relationship is (S s / JZ 6 V 3)
”' Just set wx 2π/11.Here,
S is the cross-sectional area of the open tube boat 42, and 16 is the open tube boat 4.
The length of 3, ■, is the volume of the cavity 44.

Also, the open tube boat 1 of the second Helmholt resonator 15
Open-tube resonance can also occur at magnitude 6. If the level and frequency of these open tube resonances cannot be ignored, measures similar to those described above may be taken sequentially for these open tube boats 16 and the like.

Furthermore, as a resonator for open tube resonance absorption, it is also possible to use a closed tube resonator, as shown in FIG. In this case, the resonant frequency f OT3 of the closed tube resonator is the closed tube 51
If the length of is flos, fo dings = C/4fLo
s, a closed tube 51 with a length of 2°3=It l/2 may be attached to the open tube boat 12. The distance from the open boat 11 for this closed tube resonator and the Helmholtz resonator is ℃.

The unnecessary resonance absorption effect can be maximized when attached at a location of -4, /2.

Even when using this closed tube resonator, open tube resonance is used.

2nd. Third. It is also possible to absorb each harmonic of .... For example, in the case of the second harmonic, as shown in FIG. Closed tube resonator 61. ... may be attached. In this case, the third closed tube resonator 61 has a length of j2oa"'J2+/4, and λ, s=
, xr/4 and/or at the position λ,=342+/4.

In addition, these closed tube resonators utilize the closed tube resonance of the fundamental wave to absorb the open tube resonance of the open tube port, but the closed tube resonance sound of the harmonics of these closed tube resonators may become a new problem. . In order to absorb this, measures similar to those described above may be sequentially applied to these closed tube resonators. However, in that case, it should be noted that the position of the velocity node of the harmonic closed-tube resonance is generated somewhat differently from the case of the open-tube resonance described above. For example, the velocity node of the second harmonic of the closed tube resonance occurs at the M end between the tubes and at a position 2/3 of the tube length from this point back to the C2-1 open end side.

It goes without saying that the above-mentioned Helmholtz resonator and closed-tube resonator may be used in combination as a sound-absorbing resonator, and sound-absorbing material can be appropriately filled into these resonators to improve the sound-absorbing effect. You can do it like this.

[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. , a sound pressure frequency characteristic diagram for explaining the absorption effect of unnecessary resonance sound in the acoustic device shown in FIG. 1, FIG. 4 is a diagram showing a modification of the embodiment shown in FIG. 1, and FIG. 6 is a diagram illustrating a modification of the embodiment shown in FIG. 5, and FIG. 7 is a perspective view and a cross-sectional view showing the configuration of a conventional bass reflex speaker system. FIG. 8 is an explanatory diagram of the sound pressure characteristics of the speaker system of FIG. 7. 10: Helmholt resonator, 12: Open tube bow) -, 1
5: Second Helmholtz resonator, 20; Stationary device, 21:
diaphragm, 22: converter, 30: camera driving device, 31:
Servo section, 41: Third Helmholtz resonator, 51: Closed tube common mouth, 1 unit.

Claims (2)

[Claims] (1) In an acoustic device in which a vibrator is disposed in a Helmholtz resonator having an open tube port, and resonance sound is emitted by driving the vibrator, the velocity node of the open tube resonance of the open tube port is provided. An acoustic device characterized in that another resonator that resonates at the open tube resonance frequency is attached near the position. (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.