JPH10339499A - Turbulence shield - Google Patents

Abstract

PROBLEM TO BE SOLVED: To place a microphone close to an extremely turbulent area while maintaining a high coherence level between an input and an error microphone, by placing the microphone in a cavity outside duct lining or the chamber inside the cavity. SOLUTION: A porous material 34 is made of the same material as a duct lining material 11, thus has a facing or case to divide a cavity 32 into chambers 32-1 and 32-2. Therefore, the lining material 11 and a partition which is bordered with the porous material 34 provide the decay of draft and the function is promoted by the facing or the case. The microphone 16 is placed in the chambers 32-1 or 32-2 of the upstream side. A duct 10 is provided with an opening part 10-1 at the discharge hole of a fan 12 or the location near it. This opening part is covered with the duct lining material 11, therefore only this lining material 11 separates the inside of the duct 10 and the cavity 32.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to the art of sound detection in duct active noise control (ANC) systems.

[0002]

BACKGROUND OF THE INVENTION In the art of acoustic detection in duct active noise control (ANC) systems, the blocking of turbulence-caused disturbance pressure at the input or error microphones of the system is critical to the system's ability to cancel noise. It is known that
This so-called "airflow noise" reduces the coherence between the detection and error microphones. The level of coherence is directly related to the achievable level of noise cancellation.

[0003] For example, a feedforward type AN
To achieve a 20 dB cancellation level in the C system, a detection-error microphone coherence of 0.99 is required, and if the coherence value is 0.9, the cancellation level drops to 10 dB. The juxtaposition feedback method (so-called “TCM (tight coupled mon
opole), the airflow noise level at the input microphone limits the performance of the system because it represents the lowest volume level that can be achieved by active noise cancellation when the system is working perfectly. is there.

In addition, large-amplitude, low-frequency airflow fluctuations detected by the microphone cause catastrophic large-amplitude speaker movement and system instability. If turbulence is not blocked by a windshield or shield, the only means is to move the ANC system from a high turbulence region, usually near a fan, to a quieter location. In practice, this method increases the overall system length of the ANC system and / or the cross-sectional area of the duct,
In addition, since the microphone cannot be placed near the outlet of the fan, the integration of products is limited. A typical airflow shielding method in standard ANC and HVAC applications is to use a wall mounted microphone placed behind a standard duct lining material. This arrangement is an inexpensive and effective means of blocking unwanted airflow noise. However, in extreme turbulent conditions such as those encountered near the outlet of a fan, this method is inadequate. Therefore, this solution always comes from the need to keep a distance between the microphone and the fan outlet,
Large system length is required.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to enable the microphone to be located close to areas of extreme turbulence while maintaining a high coherence level between the input and error microphones. is there.

It is another object of the present invention to provide a turbulence shield for a microphone.

It is yet another object of the present invention to provide a turbulence shield for a microphone suitable for placement in the area of the fan outlet. These and other objects which will become apparent hereinafter are achieved by the present invention.

[0008]

In the present invention, the microphone is placed in a space outside the duct lining. This dramatically improves performance and avoids problems associated with turbulence even when the microphone is located near the fan outlet. In addition, the microphone may be placed in a chamber provided inside the cavity. This chamber is divided into several chambers by one or two or more porous partitions, at least one of which includes a microphone.

In principle, the detection microphone is ANC
Placed in a void outside the ducting of the system duct. A baffle of porous material may be provided in the void to reduce internal airflow circulation.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS.
Numeral 0 indicates the outline of the duct, which is used, for example, for blowing air-conditioned air, and is applied by using a standard duct lining material, for example, a 1-inch thick glass fiber sound insulating material. I have. Preferably, the duct lining material is porous, but is resistant to air flow penetration due to the presence of a facing, such as a jacket or coating layer. One such suitable material is the Manville Fiber Glass Grove.
up) is a synthetic resin coated glass fiber mat available under the trade name Linacoustic. The upstream fan 12 generates noise primarily through an aerodynamic noise generating mechanism, such as trailing edge noise, which propagates downstream of the duct.

An effective means of controlling the lowest frequency range of noise recently developed is active noise control. In this manner, the control speaker 14 is used to create an opposing disturbing pressure to "cancele" unwanted noise. This cancellation may be achieved by reflecting the sound back toward the sound source (ie, a purely reactive system), absorbing the energy of the sound by the control speaker 14, or a combination of these mechanisms.

FIGS. 1 and 2 show two basic ways of achieving duct ANC (active noise control). FIG.
2 and the juxtaposed feedback system of FIG. In the adaptive control feed-forward system of FIG. 1, the detection microphone 16 detects the noise that is propagating, and converts this signal to the adaptive control DSP.
(Digital signal processor) It supplies to the front through the controller 18. The controller compensates for the signal in time delay, sound amplitude decay, duct condition, speaker dynamics, etc., and provides the signal to the control speaker 14, which provides noise cancellation.

A downstream error microphone 20 detects residual noise. The signal from the downstream microphone 20 is used to adjust the coefficients of the DSP 18 to minimize the residual noise signal at the error microphone 20. The co-located feedback system of FIG. 2 uses a microphone 2 that measures the sum of fan noise and speaker noise.
2, an analog controller 24 and a control speaker 14 are used. The signal from the microphone 22 is input to an analog controller 24, which continuously adjusts the output of the control speaker 14 so that the signal detected by the microphone 22 is minimized. In general, the adaptive control feedforward scheme of FIG. 1 can obtain higher performance than the feedback scheme of FIG. 2, but on the other hand, the system length is large and the cost is high.

In either duct ANC system, the system should be located as close as possible to the outlet of the fan (ie, to minimize the distance D between the fan outlet 12 and the nearest microphone 16 or 22). It is beneficial to minimize the space requirements of the system. However, the turbulence T near the fan discharge port is extreme and prevents such a policy from being applied completely. Such turbulent fluctuations can exceed 50% of the average flow velocity in the duct 10. Microphone 1
The disturbance pressure caused by the turbulent structures impinging on 6 and 22 generates an "airflow noise" signal, which is added to the acoustic disturbance pressure.

[0015] Airflow noise limits the amount of noise cancellation that can be achieved by the ANC system. For example, if the airflow noise is lower than the acoustic noise, the attenuation will be limited to the portion of the audio signal detected above the airflow noise floor. Further, when the airflow noise is larger than the acoustic noise, A
NC systems dissipate airflow noise through control speakers. Then the system becomes a noise generator rather than a noise attenuator. ANC
There are four options to increase the damping capability of the system:

(1) Move the ANC system downstream to a quieter airflow region.

(2) The airflow noise from the microphone 16 is electronically filtered before being input to the controller 18 or, similarly, the airflow noise from the microphone 22 is input to the controller 24.

(3) Using a series of detection microphones with appropriate signal conditioning, electronically separate noise due to airflow from noise propagating through the duct 10.

(4) The turbulence energy at the microphone surface relative to the intensity of the acoustic noise signal propagating in the duct 10 is provided using a shield that suppresses turbulence around the microphones 16, 20, and 22. Selectively reduces strength.

The use of option (4), a turbulence suppression shield around the detection microphone, is a preferred option and the concept of novel and high performance shielding is the subject of the present invention.

The present invention allows the microphone 16 to be located in the region of the turbulence T associated with the outlet of the fan 12. Also provides additional shielding when used with microphones 20 and 22. Referring to FIGS. 3 and 4, it can be seen that the cover member 30 defines a three-dimensional cavity 32 having one open side. The cavity is oriented longitudinally in the direction of air flow indicated by the arrows in FIG. 3, and in one embodiment has dimensions of 20 inches long, 10 inches wide and 3 inches deep. In another embodiment,
The dimensions are 10 inches, 5 inches and 3 inches, respectively. The cover member 30 has a peripheral flange 30-1 so that the cover 30 can be attached to the duct 10.

The porous material 34 is usually made of the adhesive material 1 in a duct.
1 and thus has an overlay or jacket, but this allows the cavity 32 to be in the chamber 32-1.
And 32-2. Thus, the liner 11 and the partition defined by the porous material 34 provide airflow attenuation, the action of which is facilitated by the overlay or jacket.

Although the microphone 16 is shown as being located in the upstream chamber 32-1, it may also be located in the chamber 32-2. Duct 1
0 has an opening 10-1 at or near the discharge port of the fan 12, the size of which corresponds to the size of the open side surface of the cover 30. This opening is covered with the ducting material 11, and
Only the interior of the duct 10 and the cavity 32 are separated. The cover 30 is fixed to the outside of the duct 10 by screws 38 or any other suitable attachment means. If necessary or desired, cover 30
A gasket or seal may be placed between the flange 10 and the duct 10. Air leaks can be a source of airflow noise and the cover must be airtight to contain the noise.

In operation, the noise generated by the fan easily passes through the adhesive material 11 in the duct, enters the chambers 32-1 and 32-2 of the cavity 32, and is detected by the microphone 16. The in-duct adhesive 11 restricts the turbulence T from flowing into the cavity 32. In addition, the porous material 34 that divides the cavity 32 into chambers 32-1 and 32-2,
And the internal airflow circulation between and 32-2. Since the opening 10-1 is considerably large, the noise generated near the inner lining due to the turbulent flow is averaged. Thereby, the internal airflow circulation is attenuated. On the other hand, the large opening facilitates passage of turbulent flow through the duct inner covering 11 covering the opening 10-1. In addition, the porous material 34 acting as a partition effectively acts on the airflow circulation in the cavity 32 so as to negate the effect of the opening 10-1 being considerably large. That is, the opening 10
When -1 is large, airflow circulation is promoted, but by providing the porous material 34, this airflow circulation is suppressed.

FIG. 5 is similar to the apparatus of FIGS. 3 and 4 except that the cover 30 has been rotated 90 °. The meaning of repositioning in such a position is that the requirement for the length of the duct 10 is smaller for installing the cover 30,
The opening 10-1 occupies a shorter distance in the flow direction, and the two chambers 32-1 and 32-2 are at the same position in the length direction of the duct 10. The operation of the device in the position as in FIG. 5 is the same as in FIGS.

In the embodiment of FIG.
Is a partition made of a porous material.
-1, 134-2. Therefore, the cavity 32 has the chambers 132-1, 132-2, 1
32-3, which are smaller than the corresponding chambers 32-1 and 32-2. The microphone 16 has chambers 132-1, 132-2, 132-
Although satisfactory results can be obtained by placing them in any of 3 above, it is better to place them in the chamber 132-2. Chamber 13
Three of the six surfaces 2-2 are made of a porous material, whereas only two of the six surfaces are made of a porous material in the chambers 132-1 and 132-3. is there. The added porous material aspect of the chamber 132-2 provides additional means to counteract the effects of airflow circulation, as described above. The same applies to chambers smaller than the chambers 32-1 and 32-2.
Otherwise, the operation of the device of FIG. 6 is similar to that of FIGS.

In the embodiment of FIG. 7, the duct 10 is not bonded, so that the opening 10-1 provides free communication between the duct 10 and the cavity 32. Therefore, the porous material 111 is placed in the cover 30. It is embedded in the cavity 32, covers the open side of the cover 30, and forms a surface flush with the inside of the duct wall 10. The cavity 32 is divided into chambers 232-1 and 232-2 by a porous material 234 forming a partition. Microphone 16 is completely in chamber 232
Instead of being placed inside -1, it protrudes from one side, specifically the bottom, of the cover 30 so that the microphone surface is flush with the cover.

However, this is possible in any of the other embodiments of the present invention where the microphone has penetrated the interior of the cavity. Furthermore, since the microphone need only respond to sound pressure in the cavity 32, it may be placed outside the cavity 32 to provide fluid communication through a tube or the like. Assuming that the dimensions of the cover 30 are the same, since the porous material 111 is placed inside the cover 30,
Chambers 232-1 and 232-2 are in chamber 3
The operation of the device of FIG. 7 is similar to that of FIGS. 3 and 4, except that it is smaller than 2-1 and 32-2. If desired, porous material 111, either by itself or in combination with porous material 234, may fill most or all of cavity 32. This option is facilitated by flush placement of the microphone 16.

In the embodiment shown in FIG.
4 is located in the cavity 32 in parallel with and spaced from the duct lining 11 and divides the cavity 32 into chambers 332-1 and 332-2. A chamber 332-1 and a porous material partition 334 are located intermediate the chamber 332-2 of the cavity and the interior of the duct 10, thereby providing additional means for reducing airflow circulation with respect to the chamber 332-2. doing. Therefore, the microphone 16
Is preferably located in chamber 332-2. The operation of the embodiment of FIG. 8 is basically the same as that of the embodiment of FIGS.

In the embodiment of FIG. 9, the cover 430 has a three-dimensional parabolic shape in the cross section shown. Due to the parabolic shape, noise of small wavelength (that is, turbulence generated by the wall surface) reaching the cavity 432 is reflected toward the focal point of the parabola by the inner surface of the cover 430. Focusing on such small wavelength turbulent disturbance pressure fluctuations allows for greater averaging, thereby minimizing its effect. Large wavelength acoustic energy (ie, fan noise) is essentially unaffected by the presence of the reflective surface. The microphone 16 is located at the focus of the parabola, and preferably in the partition that defines the sound insulating material 434.

This partition divides the cavity 432 into chambers 432-1 and 432-2. Although illustrated here as a parabolic shape, there are other shapes having a focal point toward which noise should be reflected, such as a part of a three-dimensional ellipse. Except for focusing the turbulent noise and focusing the microphone 16, the embodiment of FIG. 9 operates similarly to the apparatus of FIGS. 3 and 4 with respect to attenuation of the internal airflow circulation.

FIG. 10 shows the performance in the same transverse plane when mounted flush and according to the wall cavity turbulence shield concept of the present invention as the coherence between two similarly shielded microphones. ing. This is a 25-ton vertical package air conditioner (VPAC)
In the unit, obtained just downstream of the fan outlet and at a 90 ° bend (turbulence levels reach 25-30% of the bulk average flow velocity). The addition of the lining dramatically increases coherence above 20 Hz, but has little effect below 20 Hz. It can be seen that adding a cover (20 inches × 10 inches × 3 inches) significantly improves coherence in all frequency bands. The coherence is further improved, especially at low frequencies, by an internal baffle or partition of three vertically arranged porous materials to attenuate internal circulation.

One or more additional microphones can be added to cavity 32 and added together to improve the coherent sound energy measured from fan 12. For example, for every doubling of the number of microphones / sensors, the coherent sound energy increases at a rate of 6 dB, whereas for non-coherent sounds, ie turbulent noise, for every doubling of the number of microphones / sensors. Increases by 3 dB. The distance between each microphone / sensor will be taken greater than the coherent length of the turbulence. Referring to FIG. 11, this includes the addition of microphone 16-1 and cavity 32.
5 corresponds to FIG. Since microphones 16 and 16-1 are at the same distance from fan 12, they are directly connected to adder 50. Referring also to FIG. 12, this means that cover 30 is turned clockwise 90 degrees.
゜ Except for rotation, this corresponds to FIG. As a result, the microphone 16-1 and the chamber 32-
2 is downstream of the microphone 16 and the chamber 32-1 with respect to the fan 12. Therefore, there is a time delay Δτ between the microphones 16 and 16-1. The microphone 16 is then connected to the adder 50 via a time delay 60. On the other hand, the microphone 16-1 is the adder 5
Directly connected to 0.

As mentioned above, the duct lining 11 and the partitions 34, 134-1, 134-2, 234, 334, and 434 are preferably of the same material, ie, glass fiber.

It is porous and has an overlay or jacket to improve its resistance to air flow penetration. FIG. 13 shows the increase in coherence due to the presence of the glass fiber overlay. Referring to FIGS. 14 and 15, the housing or protrusion 110-1 that defines the cavity 532 may be integral with the duct or fan outlet 110. A major advantage of such an embodiment is air tightness. That is, the only opening required for the housing 110-1 is the chamber 532-
Microphones 16 and 1 in 1 and 532-2
Only for electrical connection to 6-1. In addition, the housing 110-1 is a duct or fan outlet 1
It is of the same material as 10 and therefore has the same ability to confine sound / noise. The embodiments of FIGS. 14 and 15 correspond directly to the embodiment of FIG. 12, and a 90 ° rotation directly corresponds to the embodiment of FIG. However, also in the embodiments of FIGS. 3 to 9, the cover can be integrated with the duct without changing its basic function.
Accordingly, illustrations of variations of the apparatus of the embodiments of FIGS. 3-9 with the cover integrated with the duct or fan outlet need not be provided as they provide no additional information or teaching.

While the preferred embodiment of the invention has been illustrated and illustrated, other modifications will occur to those skilled in the art. For example, the number of chambers may be greater, unequal in size, and / or unequal in direction. Also, since the microphone only needs to react to the sound pressure in the cavity, it is not necessary to physically install the microphone in the cavity. This may be useful when the dimensions of the cavity are relatively small relative to the microphone and baffle. Therefore, the scope of the present invention should be limited only by the scope of the appended claims.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing an ANC system for a duct system using an adaptive control feedforward scheme.

FIG. 2 is a conceptual diagram illustrating an ANC system for a duct system using a collocated feedback scheme.

FIG. 3 is a sectional view of a first embodiment of a turbulence shield according to the present invention.

FIG. 4 is a sectional view taken along line 4-4 in FIG. 3;

FIG. 5 is a cross-sectional view of the embodiment of FIG. 3 rotated by 90 ° with respect to a duct.

FIG. 6 is a sectional view of a second embodiment of the present invention.

FIG. 7 is a sectional view of a third embodiment of the present invention.

FIG. 8 is a sectional view of a fourth embodiment of the present invention.

FIG. 9 is a sectional view of a fifth embodiment of the present invention.

FIG. 10 is a graph showing coherence between two microphones when different airflow shielding is performed on the same transverse plane.

FIG. 11 is a sectional view corresponding to FIG. 5, but with two microphones.

FIG. 12 is a sectional view corresponding to FIG. 3, but with two microphones.

FIG. 13 is a graph showing coherence with and without an overlay applied in a duct.

FIG. 14 is a sectional view of a sixth embodiment of the present invention.

FIG. 15 is a cross-sectional view taken along line 15-15 of FIG. 14;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Duct 10-1 Opening 11 Internal adhesive material 16 Microphone 30 Cover member 30 32 Cavity 32-1 Chamber 32-2 Chamber 34 Porous material 38 Screw

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Mark A. Daniels United States, New York, Manlius, Shadowlock 8040 (72) Inventor Duane Cie. M.C.Cormick Middletown Road, Colchester, Connecticut, United States of America 190 (72) Inventor Shaw-Takul. Butterfly United States, New York, Riverpool, Ingleside Lane 87

Claims (15)

[Claims] 1. A fan (12) for generating noise, a fan outlet having a turbulent flow therein, and at least a portion of a duct (10) including the fan outlet and having a wall and an interior. Air distribution means; and a turbulence shield of an active noise cancellation system for a duct used in a system having means for defining a cavity (32, 432, 532) having an open end, said means comprising: , A cavity defined to be located adjacent to the duct, the open end being an opening in the wall surface, and an air flow attenuating means (11, 111) disposed between the interior and the cavity. ) And at least one acoustic detection means (16, 16-1) positioned to respond to sound pressure in the cavity, wherein the acoustic detection means A turbulence shield separated by the airflow damping means. 2. The turbulence shield according to claim 1, wherein said airflow attenuation means is the only physical barrier between said interior and said at least one acoustic detection means. 3. The turbulence shield of claim 1 wherein said airflow damping means at least partially fills said cavity. 4. The turbulence shield according to claim 1, wherein said cavity is partitioned into a plurality of chambers. 5. The at least one acoustic detection means is at least partially disposed in a first chamber (332-2) of the plurality of chambers, and a second of the plurality of chambers. Chamber (332-1)
5. The turbulence shield according to claim 4, wherein is disposed between a first chamber of said plurality of chambers and said interior. 6. The at least one sound detecting means (1)
The turbulence shield of claim 4, wherein 6) is located in one of the plurality of chambers. 7. The turbulence shield according to claim 6, further comprising a second acoustic detection means (16-2) at least partially disposed in a second chamber of the plurality of chambers. 8. The turbulence shield of claim 7, wherein a first of said plurality of chambers is located upstream of a second of said plurality of chambers. 9. The turbulence shield according to claim 4, wherein said cavity has a three-dimensional parabolic shape. 10. The turbulence shield according to claim 10, wherein airflow attenuation means is used to divide said cavity into a plurality of chambers. 11. The turbulence shield according to claim 10, wherein said at least one acoustic detection means is located in said airflow attenuation means dividing said cavity into a plurality of chambers. 12. The turbulence shield according to claim 1, wherein the cover has a parabolic shape. 13. The turbulence shield of claim 12, wherein said at least one acoustic detection means is located in airflow attenuation means dividing said cavity into a plurality of chambers. 14. The turbulence shield of claim 1, wherein the cover and the cavity formed by the cover are shaped to reflect sound toward a focal point. 15. The turbulence shield according to claim 14, wherein said at least one acoustic detection means is located at said focal point.