ES2286842T3 - TURBULENCE DISPLAY FOR A MICROPHONE IN A WALL CAVITY. - Google Patents

Abstract

A CAVITY (32) IS EXTERNALLY PROVIDED TO A FAN DUCT OR DISCHARGE (10) IN AN ANC SYSTEM, SO THAT THE COVERING OR POROUS MATERIAL (11) OF THE DUCT SEPARATES THE INSIDE OF THE CAVITY (10) (32) . A MICROPHONE (16) IS LOCATED IN THE CAVITY (32). SOME SCREENS (34) OF POROUS MATERIAL ARE PREFERRED IN THE CAVITY (32) TO DIVIDE THE CAVITY (32) IN VARIOUS CHAMBERS (32-1, 32-2) AND REDUCE THE INTERNAL RECYCLING OF THE FLOW IN THE CAVITY (32) .

Description

Turbulence screen for a microphone in a Cavity of a wall.

In the technique of acoustic capture in Active noise control (ANC) systems in ducts is known that the elimination of pressure fluctuations due to turbulence in the microphone or reference or error microphones System is critical for its ability to cancel noise. He DE-A-4421803 describes a Active noise cancellation system for a fan. The Claim 1 is characterized against this description. He Document W09519075A describes an active silencer for a conduit. This so-called "flow noise" reduces consistency between the sensor and error microphones and the level of consistency is directly related to the attainable level of Noise Cancellation. For example, in an ANC system with control predictive, a level of consistency is needed for microphones 0.99 sensor and error to reach a cancellation level 20 dB and a coherence value of 0.9 reduces the level of 10 dB cancellation. For direct feedback approach (called "TCM", by strong coupling monopole) the level Flow noise in the reference microphone limits the system performance because it represents the lowest level sound that can be achieved through active cancellation if The system is operated perfectly. In addition, fluctuations of low frequency and large amplitude flow picked up by the microphone cause destructive large-scale speaker movements and system instabilities. If a removal is not possible enough of the turbulence with a wind shield or shield determined, the only resource is to move the ANC system away from the area high turbulence, typically near the fan, up to a quieter area This strategy actually increases the total system length, and / or cross section size of the ANC system duct and limits product integration since the microphone cannot be placed in the vicinity of the fan discharge. A typical screening strategy of flow used in ANC applications, standard HVAC is the use of a flush mounted microphone that is located below the material standard inner duct lining. This configuration offers a cheap and effective way to eliminate flow noise not wanted. However, under conditions of extreme turbulence, such like the ones near the fan outlet, this strategy is insufficient. So, intrinsically, this solution requires a longer system length due to the need to Move the microphone away from the fan outlet.

In accordance with the present invention, provides a turbulence screen as claimed in the claim 1.

The present invention places a microphone inside of a cavity outside the inner lining of the duct thereby dramatically improving the performance of such so that the microphone can be placed at the output of the fan while avoiding problems related to the turbulence. In addition, the microphone can be placed in a camera which is located inside a cavity, which is divided into several chambers for one or more porous partitions, at least one of the which contains a microphone.

It is an objective of this invention to allow the placement of pickup microphones adjacent to turbulence zones  extreme while maintaining high levels of consistency between the reference and error microphones.

It is another objective of this invention to provide a turbulence screen for a microphone.

It is an additional objective of this invention provide a suitable turbulence display for microphones to be placed in the outlet area of a fan. These and other objectives, as will be apparent later, are achieved by the present invention.

Basically, a pickup microphone is placed inside a cavity outside the lining of a conduit of an ANC system. Acoustic screens of porous material inside the cavity to reduce recirculation Internal flow

Figure 1 is a schematic representation which shows an ANC system for duct systems that employs an adaptive predictive control strategy;

Figure 2 is a schematic representation which shows an ANC system for duct systems that employs a direct feedback approach;

Figure 3 is a sectional view of a first embodiment of the turbulence screen of the present invention;

Figure 4 is a sectional view taken at along line 4-4 in figure 3;

Figure 5 is a sectional view of the embodiment of figure 3 rotated 90 ° with respect to the duct;

Figure 6 is a sectional view of a second embodiment of the present invention;

Figure 7 is a sectional view of a third embodiment of the present invention;

Figure 8 is a sectional view of a fourth embodiment of the present invention;

Figure 9 is a sectional view of a fifth embodiment of the present invention;

Figure 10 is a graph showing the coherence between two microphones located in the same plane transverse with different flow shielding;

Figure 11 is an equivalent sectional view. to figure 5 but with two microphones;

Figure 12 is an equivalent sectional view. to figure 3, but with two microphones;

Figure 13 is a graph showing the coherence between inner lining of coated duct and not covered;

Figure 14 is a sectional view of a sixth embodiment of the present invention; Y

Figure 15 is a sectional view taken at along lines 15-15 of figure 14.

In Figures 1 and 2, the number 10 designates from general manner to a conduit such as that used in the air conditioning distribution and that is coated with a standard inner lining material for ducts such as an insulating fiberglass one inch (25.4 mm) thick. Preferably, the inner lining material of the duct It is porous but resistant to flow through it due to the presence of a coating such as a wrap or a paint. A Suitable material is a fiberglass coated blanket, with plastic paint, marketed by Manville Fiber Glass Group under the commercial name of Linacoustic. The fan 12 located waters above produces noise, mainly due to sound mechanisms aerodynamically operated, such as edge noise from exit, which spread along the duct. An effective means of control the lower frequencies of this noise, developed in the recent years, it is the active noise control, by which use a control speaker 14 to create a disturbance of counter sign pressure to "cancel" the noise no wanted. This cancellation is made by reflecting the sound of back to the source (i.e. a purely reactive system), at absorb sound energy through control speaker 14, or by A combination of both mechanisms. Figures 1 and 2 show the two main means to achieve ANC (active control of noise) in ducts, adaptive predictive control in Figure 1 and direct feedback in figure 2. For the control strategy predictive of figure 1, a sensor 16 sensor detects the noise that propagates and sends this signal directly through a 18 adaptive DSP (digital signal processor) controller that compensates for the signal in terms of time delay, attenuation of The amplitude of the sound, duct modes, speaker dynamics, etc. and sends a signal to the control speaker 14 that cancels the noise. An error microphone 20 downstream detects the noise residual. The signal from the microphone 20 located downstream It is used to adapt the coefficients of DSP 18 in such a way that minimize this residual noise signal in microphone 20 of error. The direct feedback approach of Figure 2 employs a microphone 22 that measures the sum of fan noises and of the speaker, an analog controller 24 and a speaker 14 of control. The signal from microphone 22 is input to the analog controller 24, which continuously adjusts the control speaker output 14 to minimize the detected signal by microphone 22. In general, the predictive control strategy adaptive of figure 1 allows higher yields than the feedback strategy of figure 2, but at the expense of System length and cost.

For any ANC duct system, it is advantageous to place the system as close as possible to the fan discharge (i.e. minimize length D, the distance between discharge of fan 12 and microphone 16 or 22 closest), to minimize space needs for the system. However, the turbulence T in the vicinity of the Fan discharge is extreme and prevents total utilization of This strategy Such turbulence fluctuations can overcome 50% of the average flow rate inside the duct 10. Pressure oscillations caused by structures turbulent that impact on microphones 16 and 22 generate a "flow noise" signal that adds to the oscillations of acoustic pressure Flow noise will limit the amount of noise cancellation that can be achieved with the ANC system. By For example, if the flow noise is less than the acoustic noise, the attenuation will be limited to that fraction of the acoustic signal that It can be detected above the minimum flow noise limit. Also, if the flow noise is greater than the acoustic noise, then the ANC system will emit the flow noise through the control speaker, thereby being a noise generator in Place of a noise attenuator. To increase the capacity of ANC system attenuation can be considered four options: (1) move the ANC system downstream to one more flow zone quiet, (2) electronically filter the flow noise of the signal from microphone 16 before input to controller 18, or the one coming from microphone 22 before it convert input to controller 24, (3) use an array of pick-up microphones with adequate signal conditioning to electronically separate the noise induced by the flow of the noise that propagates through conduit 10, and (4) use a turbulence elimination screen around microphones 16, 20 and 22 to selectively reduce the energy force of turbulence on the microphone surface in relation to force of the acoustic noise signal that propagates through conduit 10. The option (4), the use of a turbulence elimination screen around the pickup microphone, is the desired option and a Unique concept of high performance display is the object of this invention.

The present invention allows the placement of the microphone 16 in the turbulence zone T, associated with the discharge from fan 12 while providing shielding additional when used with microphones 20 and 22. Making now reference to figures 3 and 4 it is evident that piece 30 of cover delimits a three-dimensional cavity 32 with one side open. The cavity is lengthened in the direction of flow, indicated by arrows in figure 3, and in one embodiment it has the dimensions twenty inches (508 mm) in length, ten inches (254 mm) wide and three inches (76.2 mm) deep. Other realization is ten by five by three inches (254 by 127 per 76.2 mm). The cover piece 30 has a tab 30-1 peripheral to allow fixing of the cover 30 to the duct 10. The porous material 34, which is normally of the same material as the inner lining 11 of the duct, and therefore is coated or lined, divides the cavity 32 in chambers 32-1 and 32-2. Accordingly, the coating 11 and the 34 porous material that defines the partition provide attenuation of flow that is increased by the coating or the envelope. He microphone 16 is illustrated as located inside the camera 32-1 located upstream but may also be located inside chamber 32-2. The opening 10-1 is located in conduit 10, at the exit of the fan 12 or near it, and is sized to match the open side of cover 30 and is covered by the lining 11 of the conduit such that only the duct liner 11 separates the inside of duct 10 from the cavity 32. The cover 30 is fixed to the outer face of the conduit 10 by screws 38, or by any other means of proper fixing. If needed or desired, a gasket or seal between cover tabs 30 and conduit 10 since air leakage can result in flow noise and it is necessary that the cover be air tight and act containing the sound

During operation, the noise generated by the fan easily passes through the lining 11 of the conduit into chambers 32-1 and 32-2 of cavity 32 where it is captured by the microphone 16. The lining 11 of the conduit provides a restriction to the turbulence T flowing into the interior of the cavity 32. In addition, the porous material 34 that divides the cavity 32 in cameras 32-1 and 32-2 attenuates the recirculation of the internal flow between the chambers 32-1 and 32-2. The attenuation of the internal flow recirculation is a result of the relationship of significant opening size 10-1 for calculate the average noise generated in the cladding by the turbulence, which also facilitates the flow of turbulence through the lining 11 of the lining duct the opening 10-1. The porous material 34, acting like a partition, it effectively counteracts the effects of significant opening size 10-1 with with respect to the flow in recirculation inside the cavity 32

Figure 5 is the same as the device Figures 3 and 4 except that the cover 30 is rotated 90 °. The consequence of repositioning is that cover 30 needs less duct length 10 for placement, the opening 10-1 extends a shorter distance in the flow direction and both chambers 32-1 and 32-2 are in the same position with respect to the duct length 10. The operation of the device in the position of figure 5 would be the same as that of figures 3 and Four.

In the embodiment of Figure 6, the partition defined by the porous material 34 has been replaced by partitions 134-1 and 134-2 of porous material of such that the cavity 32 is divided into chambers 132-1, 132-2 and 132-3, which are smaller than corresponding cameras 32-1 and 32-2. The microphone 16 can be placed successfully in any of the cameras 132-1, 132-2 and 132-3 but by placing it in chamber 132-2 three of the six sides of chamber 132-2 are constituted by porous material while only two of the six sides of the cameras 132-2 and 132-3 are constituted by porous material. The extra side of porous material on camera 132-2 it provides an extra measure against the effects of recirculation flow, as described previously, like the smaller camera, in comparison with cameras 32-1 and 32-2. Apart from this the operation of the device of Figure 6 is the same as in figures 3 and 4.

In the embodiment of Figure 7, the conduit 10 it is uncoated so that the opening 10-1 would provide free communication between the inside of the duct 10 and cavity 32. Accordingly, porous material 111 is located inside cover 30 and extends into the cavity 32 so that it closes the side that otherwise would be open from deck 30 and provide a surface flush with the inside face of the wall 10 of the duct. The cavity 32 is then divided into cameras 232-1 and 232-2 by the porous material 234 forming a partition. Instead of placing microphone 16 completely inside the Camera 232-1, this extends through one side, specifically the bottom side, of the cover 30, so that it is flush with her, but this is possible in any of the other embodiments of the present invention such as extending more the microphone into the cavity. In addition, it is only necessary that the microphone is sensitive to the acoustic pressure inside the cavity 32 and can be placed outside the cavity 32 but in fluid communication by means of a tube or the like. Because the porous material 111 is located inside the cover 30, assuming the same dimensions of the cover 30, cameras 232-1 and 232-2 will be more smaller than cameras 32-1 and 32-2 but on the contrary the operation of the device of the Figure 7 would be the same as in Figures 3 and 4. If desired, the porous material 111 in combination with porous material 234 can fill most of cavity 32. This option is favored by flush positioning of the microphone 16.

In the embodiment of Figure 8, the material Porous 334 is located inside the cavity 32 parallel to the lining 11 of the duct and separated from it so that it forms a partition within the cavity 32 that divides it into the chambers 332-1 and 332-2. The camera 332-1 and partition 334 of porous material are located between chamber 332-2 of the cavity and the inside the conduit 10 thereby providing an extra measure  to reduce the recirculation of the internal flow in relation to the camera 332-2. Accordingly, microphone 16 is preferably placed inside chamber 332-2. He operation of the embodiment of figure 8 is basically the same as the embodiment of figures 3 and 4.

In the embodiment of Figure 9, the cover 430 is of a three-dimensional parabolic shape in the section illustrated. Due to the parabolic shape, the noise of small wavelength (i.e. turbulence generated on the wall) which reaches cavity 432 is reflected by the inner surface from deck 430 towards the focus of the parabola. This approach of turbulent pressure fluctuations of small wavelength  it allows a greater average minimizing in this way its effects. The longest wavelength sound energy (i.e. the noise of the fan) remains essentially unaffected by the presence of the reflective surface. The microphone 16 is placed in the focus of the parabola and, preferably, inside the 434 insulating material that defines the partition and divides the cavity 432 in chambers 432-1 and 432-2 Although one way is illustrated in particular parabolic, there are other forms such as a portion of a three-dimensional ellipse that has a focus towards which it would be reflected the noise. Except for the turbulence noise approach and placing the microphone 16 in the focus, performing the Figure 9 will work essentially the same way as the device of figures 3 and 4 with respect to the reduction of recirculation of the internal flow.

Figure 10 shows the performance of the concept of wall cavity turbulence screen of the present invention and that is flush mounted in terms of consistency between two Identically shielded microphones located in the same plane cross section obtained in a compact air conditioner vertical, VPAC, twenty-five tons, placed just waters below the fan discharge and with a 90º turn (the Turbulence levels are equal to 25-30% based in the average volumetric velocity). The coating addition interior dramatically increases consistency above 20 Hz, with little effect below 20 Hz. It is noted that the addition of the cover (20 x 10 x 3 inches, 508 x 254 x 76.2 mm) ago considerably improve consistency across the band and that with three acoustic screens or internal partitions of porous material vertically oriented to attenuate flow recirculation internal, coherence improves even more, especially at low frequency.

One or more additional microphones can be added to cavity 32 and combine to improve sound energy consistent that is measured from the fan 12. For example, the coherent sound energy will increase at the rate of 6 dB each time double the number of microphones / pickups while the sound Incoherent, that is, turbulent noise, will increase by 3 dB each once the number of microphones / sensors is doubled. The microphones / sensors would be separated more than the consistent length of the turbulence. Referring now to figure 11, this is equivalent to figure 5 except that has added the 16-1 microphone and that said microphone It is located in cavity 32-2. Because the 16 and 16-1 microphones are the same distance from the fan 12, join directly to adder 50. Doing now reference to figure 12, this is equivalent to figure 11 except that the cover 30 is rotated 90 ° in the direction of the clock hands This results in the microphone 16-1 and camera 32-2 are located downstream of microphone 16 and camera 32-1 in relation to the fan 12. Therefore, there is a delay temporal,? Delta, between microphones 16 and 16-1 and microphone 16 is connected to adder 50 by means of a 60 relay while the microphone 16-1 is connected directly to adder 50.

As indicated above, the lining 11 of the duct and partitions 34, 134-1, 134-2, 234, 334 and 434 are preferably of the same material, fiberglass, which is porous, with a coating or wrap that makes it more resistant to flow through it. Figure 13 shows the increase in coherence due to the presence of a coating on the fiber of glass.

Referring now to figures 14 and 15, the casing or projection 110-1 that delimits the cavity 532 can be integral with the fan duct or outlet 110. A great advantage of this embodiment is the degree of tightness since the only necessary opening in the housing 110-1 is for the electrical connection to the 16 and 16-1 microphones that are inside the cameras 532-1 and 532-2, respectively. In addition, the 110-1 housing is the same material as the duct or outlet 110 of the fan and will have the same capacity to contain the sound / noise. The embodiment of figures 14 and 15 is directly equivalent to the embodiment of Figure 12 and, if it is turned 90º, to the realization of figure 11, but the embodiments of figures 3-9 could also have its integral covers with the duct without changing its basic operation. Therefore, the illustration of the modified embodiments of the devices Figures 3-9 to show the covers integrals with the duct or fan outlet, since no Provide additional information or explanation.

Although they have been described and illustrated the preferred embodiments of the present invention, other changes may  occur to those with experience in the technique. For example, more cameras can be formed, and the cameras can be Different size and / or have different orientations. Also they microphones only need to be sensitive to the acoustic pressure of the inside the said cavity so that it is not necessary to place physically the microphone (s) inside the cavity. This will be useful where the dimensions of the cavity are small in relation to to a microphone and an acoustic shield. It is intended for so long as the scope of the present invention is limited only by the scope of the appended claims.

Claims (13)

1. An active noise cancellation system in ducts that includes a fan (12) noise generator and a discharge of the fan with flow turbulence inside, air distribution means including the said discharge of the fan and that are defined at least in part by a duct (10), which has a wall and an interior, and a screen of turbulence that includes: means defining a cavity (32; 432; 532) with an open end; said means defining a cavity that is located adjacent to said conduit so that said end open coincides with an opening in said wall; flow attenuation means (11; 111) located between said interior and said cavity; Y at least one means (16; 16-1) of sound pick-up positioned so as to be sensitive to the acoustic pressure inside said cavity such that said sound pick-up means is separated from said interior by said attenuation means of flow, characterized in that said cavity is divided into a plurality of chambers and because flow attenuation means comprising a porous material are used to divide said cavity into a plurality of chambers. 2. The active noise cancellation system in conduits of claim 1, wherein said means of flow attenuation are the only physical barrier between the aforementioned interior and said at least one means of sound capture. 3. The active noise cancellation system in conduits of claim 1, wherein said means of flow attenuation at least partially fill the cited cavity. 4. The active noise cancellation system in ducts of claim 1, 2 or 3, wherein said least one means of sound pickup is located at least partially inside a first (332-2) chamber of the mentioned plurality of them and a second (332-1) chamber of said plurality of them is  located between said first chamber of said plurality of them and the aforementioned interior. 5. The active noise cancellation system in ducts of claim 1, 2 or 3, wherein said minus one means (16) of sound pickup is located within a chamber of said plurality of them. 6. The active noise cancellation system in ducts of claim 5, further including a second means (16-2) of sound capture, which is at less partially located within a second chamber of the cited plurality of them. 7. The active noise cancellation system in ducts of claim 6, wherein said first chamber of the said plurality of them is located upstream of said second chamber of said plurality of them. 8. The active noise cancellation system in ducts of claim 1, 2 or 3, wherein said cavity It has a three-dimensional parabolic shape. 9. The active noise cancellation system in conduits of any preceding claim, wherein said at least one sound pickup means is located within the said flow attenuation means dividing said cavity into a plurality of cameras. 10. The active noise cancellation system in ducts of claim 1, wherein said means which defines the cavity comprises a cover, said cover having A parabolic shape 11. The active noise cancellation system in ducts of claim 10, wherein said at least one half sound sensor is located within said means of flow attenuation that divides said cavity into a plurality of cameras 12. The active noise cancellation system in ducts of claim 1, wherein said means which defines the cavity comprises a cover, said cover being and the aforementioned cavity formed by it configured so that Reflect the sound to a focus. 13. The active noise cancellation system in ducts of claim 12, wherein said at least one Half sound sensor is located in the aforementioned focus.