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1. (WO2019063070) LOUDSPEAKER ARRANGEMENT
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LOUDSPEAKER ARRANGEMENT

BACKGROUND

1. Technical Field

[0001] The disclosure relates to a loudspeaker arrangement, particularly applicable in a higher temperature environment.

2. Related Art

[0002] Engine order cancellation (EOC) systems and methods are commonly used to reduce noise caused by harmonic disturbances, e.g., in car interiors. Similar systems and methods can also be applied in other environments such as heating, ventilation and air conditioning ( I I VAC ) environments or vehicle exhaust environments. Duct-like arrangements, as they may be used in the environments mentioned above, provide a good basis for the application of active noise control (ANC) including EOC to achieve a global noise reduction. However, these environments may also include obstacles to implementing ANC systems such as, e.g., high ambient temperatures, low ambient temperatures, humidity, moisture and chemically aggressive substances, and, thus, the requirements to sensors and (secondary) sound sources of ANC systems operated in these env ironments are high. While sensor technology has made some progress, the performance of sound sources when operated under harsh environmental conditions such as high temperatures is still not satisfactory.

SUMMARY

[0003] A loudspeaker arrangement includes an air-tight, rigid, thermo-eonductive enclosure with an aperture and an outer surface, and a loudspeaker air-tightly mounted in the aperture to form a locked acoustic volume within the enclosure. The arrangement further includes a multiplicity of thermo-conductivc fins attached to or integrated in the enclosure at the outer surface thereof. The multiplicity of fins is distributed over the outer surface of the enclosure.

[0004] Other arrangements, features and advantages will be, or will become, apparent to one with skill in the art upon examination of the following detailed description and appended figures. It is intended that all such additional arrangements, features and advantages be included within this description, be within the scope of the invention, and be protected by the following claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0005] The arrangements may be better understood with reference to the following drawings and description. The components in the figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the figures, like referenced numerals designate corresponding parts throughout the different views.

[0006] Figure 1 is a schematic top view illustrating a loudspeaker arrangement employing fins for increasing heat dissipation.

[0007] Figure 2 is a schematic diagram illustrating an appl ication of the loudspeaker arrangement shown in Figure 1 with a heat shield in connection with a combustion engine.

[0008] Figure 3 is a schematic diagram illustrating an application of the loudspeaker arrangement with a venting duct in connection with a combustion engine.

[0009] Figure 4 is a side view of an exemplary fin with a rib-like shape.

[0010] Figure 5 is a side view of an exemplary fin with a nob-like shape.

[0011] Figure 6 is a schematic diagram illustrating an exemplary active noise control system with the loudspeaker arrangement shown in Figure 1.

DETAILED DESCRIPTION

[0012] Although some of the weaknesses of sound sources to be operated in harsh environmental conditions could be overcome by. e.g., improving their robustness against weak acids, moisture and humidity, other aspects such as high temperatures are still problematic. For example, most of the sound sources of ANC systems used in connection with exhaust systems of combustion engines in vehicles include a loudspeaker tightly mounted in an aperture of a rigid enclosure to provide a sealed acoustic volume. The air mass locked in the enclosure with the mounted loudspeaker generates therein air pressure that depends on the temperature of the locked air mass; the higher the temperature, the higher the pressure. The loudspeaker commonly includes a, compared to the rigidity of the enclosure, softly suspended membrane so that a pressure increase due to an increase of the air mass temperature within the enclosure with mounted loudspeaker mainly forces the membrane outwards from the enclosure shifting the loudspeaker's operating point away from its neutral position. Such a shift of the operating point of the loudspeaker may lead to undesired effects such as restrictions of the dynamic range and a non-linear behavior of the loudspeaker.

[0013] Another result of reducing the temperature range of the environment in which the loudspeaker forming the secondary sound source operates is that the durability of the loudspeaker will increase, leading also to more durable ANC (EOC) systems since it has been found that severe durabil ity issues with exhaust ANC (EOC) systems can be tracked to the secondary source.

[0014] In an exemplary loudspeaker arrangement shown in Figure 1 , a loudspeaker 101 is air-tightly mounted in or at an aperture 102 of rigid, air-tight enclosure 103 so that an air volume 104 with a corresponding air mass is locked within the enclosure 103 when the loudspeaker 1 01 is mounted thereto. The loudspeaker 101 has a rigid, air-permeable basket 105 as a basic structure to which a magnet system 1 06 is fixedly mounted and to which a membrane 107 is movably attached via a resil ient spider 108 and a resilient suspension 109 to allow for an inward and outward movement of the membrane 107 relative to the basket 105. The basket 105 may be mounted at an edge of the aperture 1 02 to connect the loudspeaker to the enclosure 103 and the membrane 107 in connection with the suspension 109 seals the aperture 102 so that the volume 104

within the enclosure 103 is locked. The membrane 107 is rigidly and air-tight (e.g., using a dust cap) connected to a voice coil 1 1 0 that dips into an air-gap of the magnet system 106.

[0015] In the exemplary loudspeaker arrangement shown in Figure 1 , the enclosure 1 03 may have a shape identical or similar to a cup, semi-spherical shell, spherical shell , box or any other shape suitable to provide in connection with a loudspeaker a sealed acoustic volume. The enclosure 103 includes a thermo-conductive shell 1 1 1 , e.g., a shell made from or including thermo-conductive material such as metal, metal alloy, ceramics, etc., and a multiplicity of thermo-conductive fins 1 12 attached to or integrated in the shell 1 1 1 at its outer surface. Integrated includes that the fins and the enclosure are one piece. The fins 1 12 may have a shape identical or similar to gills, ribs, nubs, strips, or any other shape suitable to enlarge the outer surface area of the shel l 1 11 for an improved thermal coupling between the shel l 1 1 1 and the ambient air. The fins 1 1 2 may be made from the same material as the shel l 1 1 1 or from any other thermo-conductive material. For example the shell 1 1 1 and the fins 1 1 2 may be one piece (not shown in Figure 1 ) or separate parts may be thermally connected to each other (shown in Figure 1). The air volume 104 may be fil led with acoustically damping material such as rock wool, foam, etc.

[0016] Heat may be input into the air volume 104 by one or more internal heat sources, e.g., the voice coil 1 10 (via the magnet system 106), and one or more external heat sources, e.g., exhaust pipes, mufflers, combustion engines that are thermally coupled to the loudspeaker arrangement (via air gaps or thermo-conductive elements such as pipes, couplers etc. ). Heat input into the air volume 1 04 heats up the air volume 1 04, which thus tries to expand but, due to the dimensional restrictions set by the enclosure 103 in connection with the loudspeaker 101 , the air volume is prevented from significantly expanding and the pressure within enclosure 1 03 with mounted loudspeaker 1 01 increases, forcing the membrane 1 07 of the loudspeaker 1 01 outwards of the enclosure 103 and thereby causing the undesired effects described above. In order to cool the air volume 104, the enclosure 1 03 is made from or includes thermo-conductive material, and the area of the outer surface of the enclosure 103 is enlarged by way of the fins 1 1 2 that are made from or include thermo-conductive material . For example, thermo-conductive material may be considered to be materia! that has a thermal conductivity of more than 1 W (k m).The fins 112 may be of different shape and size, and may be distributed over the outer surface of the enclosure 103 with different distribution densities, but in the present exemplary arrangement the fins 112 are designed so that the resulting area of the outer surface of the enclosure 103 together with the fins 1 12 is more than 1 .5 times (e.g., 2, 3, 4 times etc.) of the surface area of the outer surface of the enclosure 103 without fins 112.

[0017] The enclosure 103 may be acoustically coupled to a coupling device 113 with a housing 114 having two opposite apertures 115 and 116. The coupling device 1 13 may have, for example, a shape identical or similar to a cup with two opposite apertures, a shell or box with two opposite apertures, or any other shape suitable to provide a type of funnel to which, at one aperture, a hose, tube, pipe, channel, or the like can be connected, and to which, at the other aperture, the enclosure 103 can be connected. The coupling device 1 13 may be coupled to the enclosure 103 by way of a thermo-insulating plate 1 1 7 which may reduce heat transmission from the coupling device 1 13 to the enclosure 103. The thermo-insulating plate 1 1 7 has an aperture 118 that corresponds to the aperture 102 of the enclosure 103, and may also serve to mount the loudspeaker 101 to the enclosure 103 (as shown). Alternatively or additionally, the coupling device 1 13 may be made from or include thermo-insulating material. The position of aperture 118 may correspond to the position of aperture 115 of the coupling device 1 13. Aperture 1 16 may provide a connection to a hose, tube, pipe, channel, etc.

[0018] Referring to Figure 2, an exemplary application of the loudspeaker arrangement may include a combustion engine 201. to which an exhaust pipe 202 is attached so that hot exhaust gas from the combustion engine 201 is deflected via the exhaust pipe 202. The exhaust gas carries noise 203 that originates from the combustion engine 201 and from gas flow in the exhaust pipe 202. A loudspeaker arrangement 204, which may be identical or similar to that described above in connection with Figure 1 , is acoustically coupled to the exhaust pipe 202 via a Y-pipe 205 having two inputs and an output. One input is coupled to the exhaust pipe 202 and the other input is coupled to an output aperture of the loudspeaker arrangement 204 (e.g., aperture 1 16 in the loudspeaker arrangement shown in Figure 1). At the output of the Y-pipe 205 the

exhaust gas from the combustion engine 201 is further deflected, however, in the Y-pipe 205 the noise 203 is reduced or even cancelled by cancelling sound 206 generated by the loudspeaker arrangement 204. The cancel l ing sound 206 destructively interferes with the noise 203 so that little or even no residual noise or sound occurs at the output of Y-pipe 205.

[0019] In the example shown in Figure 2, the loudspeaker arrangement 204 may be exposed to heat according to the following scenarios: (a) Heat may be generated internally in the loudspeaker arrangement 204, e.g., by the loudspeaker enclosed therein; (b) heat generated by the combustion engine 20 1 may be transferred via an air path directly to the loudspeaker arrangement 204; (c) heat generated by the combustion engine 201 may be transferred to the loudspeaker arrangement 204 via the exhaust pipe 202 and an air path between the exhaust pipe the loudspeaker arrangement 204; and (d) heat generated by the combustion engine 201 may be transferred to the loudspeaker arrangement 204 v ia the exhaust pipe 202 and the Y-pipe 205.

[0020] In view of the heat quantity released by the respective heat source and the thermal conductivity of the path between the source and the loudspeaker arrangement, scenario (d) may input the most heat into the loudspeaker arrangement 204. This heat is dissipated by the enlarged surface of the loudspeaker arrangement 204. To further improve the heat dissipation, the loudspeaker arrangement 204 may be exposed to a relatively cool airstrcam 207 due to movement of a vehicle (not shown ) carrying the loudspeaker arrangement 204. Further, as already described above in connection with Figure 1 , the Y-pipe 205 may be thermal ly decoupled from the loudspeaker arrangement 204 by way of thermally insulating material, e.g.. disposed between Y-pipe 205 and the output of loudspeaker arrangement 204 (such as in the loudspeaker arrangement shown in Figure 1 , around 1 1 5 ) and/or between two parts of the loudspeaker arrangement 204 (such as in the loudspeaker arrangement shown in Figure 1 , enclosure 103 and coupling device 1 1 3 ). In order to also reduce the heat transmission according to scenario (b) and/or scenario (c), a heat shield 208 may be disposed between the combustion engine 201 and/or the exhaust pipe 202 on one side, and the loudspeaker arrangement 204 on the other side. The heat shield 208 is designed to block heat transmission via air path to the loudspeaker arrangement 204. The heat from the

loudspeaker in the loudspeaker arrangement 204 according to scenario (a) is dev iated so that the loudspeaker's environment within the loudspeaker arrangement 204 is kept cool by the enlarged outer surface of the loudspeaker arrangement 204.

[0021] Referring to Figure 3, instead of the heat shield 208 used in connection with the loudspeaker arrangement 204 described above in connection with Figure 2, a duct

301 such as a pipe, channel, etc. may be employed to guide an airstream 302, e.g., from the front of a vehicle (not shown) to the loudspeaker arrangement 204. The airstream

302 may be intensified by way of a funnel-shaped air inlet 303 of the duct 301 . As shown in Figures 4 and 5, exemplary fins 401 and 501 applicable as fins 1 12 to the loudspeaker arrangements described in connection with Figure 1 may have the shape of a rib (see Figure 4) or a nob (see Figure 5). The enlargement of the outer surface of the enclosure 103 depends on the dimensions of the fins and their number. The fins 401 and 501 may be one piece with enclosure 103 which allows for an optimum temperature transmission between the enclosure and the fins due to the absence of any boundaries between them.

[0022] The loudspeaker arrangements shown in Figures 2 and 3 may be used in connection with an engine order control (EOC) system as il lustrated in Figure 6 or any-other active noise control (ANC ) system. The EOC system shown in Figure 6 additionally includes a reference microphone 60 1 and an error microphone 602, which are connected to a noise controller 603, e.g. an EOC controller. The noise controller 603 drives the loudspeaker arrangement 204. The reference microphone 601 is located between the noise source, i .e., the combustion engine 201 , and the loudspeaker arrangement 204. The error signal 602 may be disposed downstream of the loudspeaker arrangement and the exhaust pipe 202, e.g., at the output of the Y-pipe 205. Signals (reference signals) from the reference microphone 601 are processed by the noise controller 603 along with (error) signals from the error microphone 602 to generate a drive signal for the loudspeaker arrangement 204. The acoustic path that extends from the combustion engine 201 to the Y-pipe 205 is referred to as the acoustic primary path. The path between loudspeaker arrangement 204 and Y-pipe 205 is referred to as the acoustic secondary path. Since acoustic feedback from the secondary speaker, e.g., speaker arrangement 204, to the reference sensor, e.g., reference microphone 601 . is known to cause robustness problems in practical ANC systems it is more reliable to use a non-acoustical reference sensor instead. In the case of machines and engines that predominantly produce periodic signals, a pure reference signal without any interferences can be generated using a non-acoustic sensor system 604, e.g., a rotational speed signal generator in connection with a synthesizer. Suitable algorithms applied in the noise controller 603 are, for example, the least mean square (LMS) algorithm, the filtered U-recursive least mean square (FUR LMS ) algorithm or the hybrid filtered-X least mean square ( H FX LMS ) algorithm. Robustness, e.g., stabil ity, of the control algorithm employed can be enhanced by reducing the dynamic of temperature fluctuations in the secondary path. Since the secondary sound source (loudspeaker) is an important part of the secondary path, stabilizing the temperature of the second source increases the robustness of the control algorithm.

[0023] The description of embodiments has been presented for purposes of il lustration and description. Suitable modifications and variations to the embodiments may be performed in l ight of the above description or may be acquired from pract icing the methods. The described arrangements are exemplary in nature, and may incl ude additional elements and/or omit elements. As used in this application, an element recited in the singular and proceeded with the word "a" or "an" should be understood as not excluding plural of said elements, unless such exclusion is stated. Furthermore, references to "one embodiment" or "one example" of the present disclosure are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features.

[0024] While various embodiments of the invention have been described, it will be apparent to those of ordinary skilled in the art that many more embodiments and implementations arc possible within the scope of the invention. In particular, the skilled person will recognize the interchangeability of various features from di fferent embodiments. Although these techniques and systems have been disclosed in the context of certain embodiments and examples, it will be understood that these techniques and systems may be extended beyond the specifical ly disclosed embodiments to other embodiments and/or uses and obvious modifications thereof.