Patent Application
20080137895
This invention relates to microphones and, more particularly, to windguards for hands-free microphones such as those used in automatic speech recognition (ASR) systems.
ASR technology enables microphone-equipped computing devices to interpret speech and thereby provide an alternative to conventional human-to-computer input devices such as keyboards or keypads. For example, vehicle telecommunications devices can be equipped with voice dialing features enabled by an ASR system. The ASR system typically includes a hands-free microphone to receive speech from an occupant of a vehicle. The hands-free microphone is usually located in a forward portion of a passenger compartment of the vehicle, such as in an instrument panel, an A-pillar molding, a rear view mirror assembly, a headliner, overhead console, or the like. Such a forward-positioned microphone is generally satisfactory to enable reliable recognition of speech from a driver.
A forward-mounted microphone may be susceptible to airflow noise due to local pressure variations in an air stream such as from windshield defroster vents, open windows, or open roofs. Accordingly, some ASR systems deploy complex digital signal processing and noise cancellation techniques, or multiple microphone arrays, to reduce the influence of airflow noise. But these approaches add cost and complexity to the ASR system. Therefore, windguards are often provided to ameliorate the effects of rapidly moving air over a microphone.
Many windguards are susceptible to Helmholtz resonance, which is a phenomenon of air resonance in a cavity. When air is forced past an acoustic inlet of a windguard, the air pressure inside tends to cyclically increase and decrease, thereby causing vibration and noise that a microphone can pick up, similar to the sound created when one blows across the top of an empty bottle. Thus, such resonant sound can produce poor signal-to-noise ratios from a microphone, thereby rendering conventional windguards counterproductive.
A windguard for a microphone includes an acoustic inlet at a downstream end and at least one pressure-relief port upstream of the acoustic inlet.
In one embodiment of the invention, the windguard comprises a base, a skirt depending from the base, and a first hood projecting from the base which includes at least one pressure-relief port, a second hood upstream of the port(s) and an acoustic inlet downstream of the pressure-relief port(s). The acoustic inlet is recessed within the first hood at a downstream end of the windguard, and the pressure-relief port(s) is at least partially recessed within the second hood at an upstream end of the windguard.
Preferred exemplary embodiments of the invention will hereinafter be described in conjunction with the appended drawings, wherein like designations denote like elements, and wherein:
With reference to the drawings,
The base 12 interconnects the skirt 14 and the hood 16. The base 12 can be generally planar as shown, but can be of any suitable shape and configuration. The base 12 connects to the skirt 14 at the sides of the windguard 10 as shown in
The skirt 14 generally provides several functions. First, it spaces the base 12 away from another component C (
The microphone M can be any suitable device, such as an electroacoustic device including a transducer to convert sound pressure waves to electrical signals. Common microphones include pressure microphones and pressure-gradient microphones. Also, the microphone M can be part of a larger microphone assembly A, which may include a microphone housing, foam, and the like, in addition to the microphone M. Finally, the microphone M can be positioned within the interior I of the windguard 10 and on an outside surface of the component C as shown, or partially or completely behind the outside surface of the component C such as through an aperture thereof, or anywhere therebetween.
The hood 16 generally provides an inclined structure to protect the microphone M from airflow by directing the airflow over and away therefrom. By diverting airflow over and away from the microphone M, the hood 16 can improve the signal-to-noise ratio capability of the microphone M. The hood 16 can be any suitable shape such as half-cone shape, wedge shape, tapered rectangular shape, arched shape, horn-shaped as shown, or the like. The hood 16 includes an upstream end 24 substantially defining a rear or upstream end of the windguard 10, a downstream end 26 that is elevated with respect to the upstream end 24 and that substantially defines a rear or downstream end of the windguard 10, and a midsection 28 between the upstream and downstream ends 24, 26. The hood 16 extends longitudinally from its relatively narrow and short upstream end 24 to its relatively wide and tall downstream end 26 wherein the hood 16 preferably generally outwardly tapers or flares somewhat like a horn.
At its downstream end 26, the hood 16 includes an airflow separation edge 30. The airflow separation edge 30 can be a curved transition edge between the outer surface of the hood 16 and a downstream lip 32 of the hood 16. More specifically, the airflow separation edge 30 can be semi-circular in shape and can be the apex of an angle α formed by the intersection of the lip 32 and the excurvate outer surface of the hood 16 adjacent the lip 32. The lip 32 extends transversely with respect to the longitudinal axis of the hood 16 and curves toward the base 12 to which the lip 32 is attached on either side of an acoustic inlet 34 defined between the lip 32 and the base 12. Thus, the acoustic inlet 34 is disposed substantially at the downstream end of the windguard 10 and is recessed into hood 16 in a substantially horizontal orientation. The acoustic inlet 34 includes a plurality of openings 36 defined by a grille 38. The openings 36 can be of any suitable quantity and shape. If desired, any suitable type of foam (not shown) can be provided in or behind the grille 38 to protect the microphone M from dust, liquid spills, and the like.
The windguard 10 includes one or more features to relieve pressure fluctuations within the interior I of the windguard 10. More specifically, one or more apertures 40, 42 are substantially disposed at the upstream end 24 of the hood 16 to eliminate or at least reduce Helmholtz resonance. These apertures comprise pressure-relief ports. In contrast to the generally horizontally oriented acoustic inlet 34, the apertures 40, 42 are preferably substantially vertically oriented through the hood 16. Any suitable number of apertures can be provided, such as the two apertures 40, 42, which can be of any suitable shape and size, and can be separated by a bridge portion 44. Instead, a single aperture could be provided if desired. In any case, the apertures 40, 42 are preferably protected from airflow in any suitable manner.
Accordingly, adjacent and upstream of the apertures 40, 42, a fin or a second, smaller, hood 46 is provided to protect the pressure relief apertures 40, 42 from airflow. The second hood 46 can be of any suitable shape, and can include an exemplary excurvate outer surface 48 that defines an excurvate outer surface of the hood 16 upstream of the midsection 28, and can include laterally opposed sides 50 that connect to the excurvate outer surface 48. The second hood 46 includes a small, curved, flow separation edge 52 defined at the apex of its excurvate outer surface 48 and its laterally opposed sides 48. As shown, the pressure-relief port(s) as a group can be at least partially recessed within the second hood 46.
The first hood 16 is preferably contoured and can be of any suitable shape. For example, the hood 16 can be both incurvately shaped and excurvately shaped in longitudinal cross-section as best shown in
The windguard 10 can be composed of any suitable material and can be manufactured in any suitable manner. For example, the windguard 10 can be injection molded from any suitable polymeric material, such as those commonly found in automobile interiors. Some parts of the windguard can be formed as a unitary component, such as base 12, skirt 14, and hood 16; whereas other parts can be separately formed and then integrally attached; for example, the grille 38 which can be glued or welded within acoustic inlet 34. Alternatively, the entire windguard could be formed as a unitary component. The windguard 10 can be of any suitable size. For example, the windguard 10 can be on the order of about one to two inches in diameter.
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It is to be understood that the foregoing description is not a definition of the invention, but is a description of one or more preferred exemplary embodiments of the invention. The invention is not limited to the particular embodiment(s) disclosed herein, but rather is defined solely by the claims below. Furthermore, the statements contained in the foregoing description relate to particular embodiments and are not to be construed as limitations on the scope of the invention or on the definition of terms used in the claims, except where a term or phrase is expressly defined above. Various other embodiments and various changes and modifications to the disclosed embodiment(s) will become apparent to those skilled in the art. All such other embodiments, changes, and modifications are intended to come within the scope of the appended claims.
As used in this specification and claims, the terms “for example,” “for instance,” and “such as,” and the verbs “comprising,” “having,” “including,” and their other verb forms, when used in conjunction with a listing of one or more components or other items, are each to be construed as open-ended, meaning that that the listing is not to be considered as excluding other, additional components or items. Other terms are to be construed using their broadest reasonable meaning unless they are used in a context that requires a different interpretation.
