Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
1999-10-29
2001-04-17
Le, Huyen (Department: 2743)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S433000, C381S412000
Reexamination Certificate
active
06219431
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to loudspeakers, and, more particularly, to structure associated with the frame and top plate of a loudspeaker which is effective to direct a flow of cooling air along the surface of the top plate and at least a portion of the voice coil of the loudspeaker.
BACKGROUND OF THE INVENTION
Loudspeakers generally comprise a frame, motor structure, a diaphragm, a lower suspension or spider and a surround. In one common type of speaker, the motor structure includes a top plate spaced from a back plate with a permanent magnet mounted therebetween. The magnet and top plate define an air gap within which a hollow, cylindrical-shaped voice coil is axially movable with respect to a fixed pole piece which is centrally mounted atop the back plate.
The voice coil generally comprises a cylindrical former which receives a winding of wire. The diaphragm extends between the voice coil and the surround, which, in turn, is mounted to the upper end of the frame. The spider is connected at one end to the voice coil, and at its opposite end to a point between the upper and lower ends of the frame. In this construction, one cavity or space is formed in the area between the diaphragm and spider, and a second cavity is formed in the area between the spider and the top plate of the motor structure. Many speaker designs include a dust cap mounted to the diaphragm in position to overlie and cover the voice coil and pole piece.
In the course of operation of a speaker of the type described above, electrical energy is supplied to the voice coil causing it to axially move relative to the pole piece and within the air gap formed by the top plate and magnet. The diaphragm, spider and the surround, move with the excursion of the voice coil. A pervasive problem associated with speaker operation involves the build up of heat produced by the voice coil and radiated to surrounding surfaces. Both the voice coil and top plate become quite hot during speaker operation which can reduce the power handling of the speaker, and increase power compression, i.e. a reduction in acoustic output due to temperature-related voice coil resistance.
A variety of designs have been employed in the prior art to address the problems associated with heat build up in speakers. Much of the design effort has been devoted to creating a flow of cooling air over the voice coil itself, such as disclosed, for example, in U.S. Pat. Nos. 5,042,072 to Button; 5,081,684 to House; and 5,357,586 to Nordschow et al. A typical construction in speaker designs of this type involves the formation of passages in or along the voice coil which form a flow path for the transfer of cooling air from the cavity between the voice coil and the dust cap and/or diaphragm, and vent openings usually formed in the back plate of the motor structure. An air flow through these passages is created in response to movement of the diaphragm with the excursion of the voice coil. When the diaphragm moves in one direction, air is drawn from outside of the speaker, through the vent opening in the back plate, along the passages in or along the voice coil and then into the cavity. Movement of the diaphragm in the opposite direction creates a flow out of the cavity along the reverse flow path.
One problem with the approach described above is that the design and construction of the flow passages often do little more than provide venting of the area or cavity between the diaphragm and voice coil. The actual air flow generated by movement of the diaphragm is typically relatively low volume. As a result, very little cooler ambient air from outside of the speaker actually flows along the voice coil to provide effective cooling. Additionally, little or no air flow is directed along the top plate, which remains hot.
Alternative designs depend upon thermal conduction and convection to cool the voice coil and/or top plate. Typically, structure associated with the frame is positioned in engagement with or proximate the top plate of the motor to provide a heat sink or thermally conductive path along which heat can move from the relatively hot top plate to the relatively cool frame. See, for example, U.S. Pat No. 4,933,975 to Button and French Application FR 2667212-A.
Constructions of the type described above provide some benefit, but reliance on conduction and convection alone to remove heat from the top plate and voice coil is of limited effectiveness with today's high performance, high excursion speakers. This is particularly true in applications such as vehicle speakers where space is at a premium and the speaker frame must be as compact as possible. In such designs, it is often not feasible to incorporate additional frame structure whose purpose is primarily or exclusively intended for the conduction of heat away from the voice coil and top plate.
SUMMARY OF THE INVENTION
It is therefore among the objectives of this invention to provide a loudspeaker construction which provides a comparatively high velocity, high volume flow of cooling air over the top plate and at least a portion of voice coil of the motor structure, which increases power handling of the speaker, which reduces power compression and which is efficient and economical to manufacture.
These objectives are accomplished in a loudspeaker including a frame mounted to a motor structure, a diaphragm connected between the voice coil of the motor structure and a surround carried by the frame, and, a spider extending from the voice coil to the frame in position to form a cavity between the top plate of the motor and the spider. An air flow path is formed at the juncture of the frame and top plate of the motor through which a comparatively high volume of cooling air is circulated at relatively high velocity in and out of the cavity between the spider and top plate in response to excursion of the voice coil during operation of the speaker. The air flow path is positioned to direct such cooling air over the top plate and at least along a portion of the voice coil to aid in cooling of these elements.
This invention is predicated upon the concept of using the “pumping” action of the diaphragm and spider created by excursion of the voice coil to obtain a high volume, high velocity flow of cooling air in and out of the cavity formed between the spider and top plate, along a flow path which is thermally adjacent to the top plate and voice coil. A stand-off is located between the bottom of the frame and the top plate of the motor to form the flow path for the cooling air moving in and out of the cavity. In some embodiments, the cooling air is made to flow directly into contact with the voice coil in the course of movement in and out of the cavity. Alternatively, the frame is formed with an inner ring which encircles the voice coil and directs the air flow in and out of the cavity through bores formed in the bottom of the frame.
In one group of presently preferred embodiments, the frame is fabricated from comparatively thin sheet metal in a stamping operation which forms a bottom surface. In one particular embodiment, a series of circumferentially spaced inserts or spacers are located between the bottom surface of the frame and the top plate of the motor to create a flow path for the cooling air entering and leaving the cavity. Alternatively, the stand-offs comprise extrusions or detents formed either in the top plate or the bottom surface of the frame, which are circumferentially spaced from one another to create the spacing between the frame and top plate. In all of these embodiments, the space formed between the bottom of the frame and the top plate defines the flow path for cooling air moving in and out of the speaker. When the voice coil axially moves in one direction, a flow of comparatively cool, ambient air from outside of the speaker is drawn into the speaker, over the top plate and against at least a portion of the voice coil into the cavity between the lower suspension and the top plate. Upon movement of the voice coil in the opposite direction, the air within such cavity is forced out
Harvey Dionne N.
Holland & Knight LLP
Le Huyen
LandOfFree
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