Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
1998-09-24
2003-04-15
Barnie, Rexford (Department: 2643)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S412000, C381S419000, C381S420000, C181S160000, C181S166000, C181S185000, C181S196000
Reexamination Certificate
active
06549637
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to a loudspeaker system, and in particular to using differential flow vents within a loudspeaker enclosure and within the backplate of a loudspeaker magnet structure to provide preferential airflow to cool and ventilate the system and to compensate for non-linear effects created by dynamic loudspeaker offset such as that found in a woofer.
Reference is made to
FIG. 1
which illustrates a conventional loudspeaker
10
using a cone-shaped diaphragm
12
and a voice coil
14
formed by having wire wound around an annular coil form
16
made from a heat resistant material which may be metallic or plastic-based. The diaphragm
12
, otherwise known as a speaker cone, vibrates through an electro-mechanical drive. The wire used in forming the voice coil has a coating for insulation purposes. The material of such coating may include shellac, an epoxy material, or varnish, wherein the coil windings are cemented onto the coil form. The voice coil defines a voice coil chamber
18
therein. The coil form is attached to a spider element
20
. The spider element is fabricated from a resin impregnated clothlike material and has circular corrugations formed therein. The spider element resiliently supports the coil form from a loudspeaker frame, also known as a basket
22
which typically comprises a metal material. In certain situations, the spider may be integrally formed with the coil form. The basket may be attached to the speaker enclosure by, a gasket
24
. The cone
12
may be fabricated from well-known materials and is attached to the coil form
16
at one end, while attached to a speaker surround
26
at the other, possibly with the use of gasket
24
. The surround is attached to the basket. The voice coil operates in a conventional manner in an annular gap
28
, which is positioned between a center pole piece
30
and an annular magnet
32
. The pole piece and magnet causes the mechanical actuation of the voice coil and the coil form about the voice coil chamber in response to electrical signals received at the coil. This in turn causes the speaker cone diaphragm to vibrate with acoustical energy. A backplate
34
and top plate
36
help secure the above mentioned components in place and direct the magnetic field from the magnet. A protective dust cap
38
is placed over the voice coil chamber.
When the electrical signal or current is supplied to the voice coil, the speaker cone vibrates in accordance with the audio frequency and polarity of the electrical signal. The winding used to form the coil has an electrical resistance to the flow of current and generates heat. This heat increases the temperature within the loudspeaker and the corresponding enclosure. As heat is generated in the voice coil, it is conducted away from the coil by means of both the thermally conductive voice coil form and the front plate. These function to dissipate the heat energy. Thus, a portion of electrical power input towards driving the speaker is converted into heat as opposed to acoustic energy. For high power loudspeaker systems, the temperature of the voice coil and the loudspeaker enclosure correspondingly increases. Accordingly, the components used in the loudspeaker control the ability of the loudspeaker to tolerate heat. When the capacity of heat dissipation of the loudspeaker components is exceeded, overheating occurs.
To prevent overheating and to provide loudspeaker cooling, methods to remove heat energy have been suggested since the operation and performance of the loudspeaker is directly affected by the heat tolerance level. For example, it is well known to cool a loudspeaker by using a heat sink. U.S. Pat. No. 4,138,593 to Hasselbach et al. discloses an extended heatsink in contact with the loudspeaker magnet structure for dissipating heat across the enclosure housing. However, the hot air remains in the interior of the enclosure. U.S. Pat. No. 4,210,778 to Sakurai et al. discloses a heat pipe device for transferring heat over a distance to be vented out of the cabinet. The heat pipe is attached to the magnet structure and draws heat from the magnet structure, and the terminus of the heat pipe is centered within the vent of the enclosure. Yet, this appears to be unsatisfactory because any airflow pertaining to the action of the vent is not a continuous motion, but encompasses air in the vent which is merely oscillating back and forth with no net travel. What is needed is a manner of exhausting the heated air out of the enclosure.
The prior art attempts to exhaust this heated air through the use of vents positioned within the loudspeaker enclosure. U.S. Pat. No. 4,196,792 to Grieves et al. discloses a V-slot or V-shaped vent installed in the back wall of the enclosure of a speaker assembly and suggests that the vent prevents pressure build-up and whistling. U.S. Pat. No. 4,284,166 to Gale discloses a port opening in a speaker enclosure for free movement of air outwardly and inwardly. U.S. Pat. No. 3,778,551 to Grodinsky discloses holes in the speaker cabinet which open to the outside and lead via an air passage to the power transistors. Using the speaker cone as an air pump, air is forced into and out of the cabinet for cooling the transistors. Japanese Patent Application No. 6-141396 discloses a series of passages through the front plate of a speaker to allow air circulation. U.S. Pat. No. 5,533,132 to Button discloses air movement within the loudspeaker to aid in heat dissipation, and in particular, the embodiment comprises a symmetrical pair of air vents in the enclosure in which the air moves in and out at high velocity so as to act as a fan on a vaned heat sink. But with all of these techniques, the problem with providing simple holes or vents in a speaker enclosure is that air only moves back and forth in the vent, even with the use of the speaker cone as an air pump. Moreover, small openings or holes do not act preferentially by themselves and tend to be acoustically resistive, constituting an acoustical leak which lowers the quality factor or efficiency of the enclosure.
The difficulty with using these vents of the prior art may be better recognized through an understanding of the hole or vent being idealized. In an idealized or theoretically perfect vent, the same slug of air moves back and forth within the vent. The more this slug of air is disturbed or broken up, the less efficient the vent acts as an acoustical element. If the slug of air is never changed, it would heat up and reach thermal equilibrium with the surroundings. Due to turbulence and any net air motion outside of the enclosure, a portion of the slug of air will be very slowly exchanged over a period of time for different “fresh” air. As a result, the slug of air will continue to heat up and reach thermal equilibrium with the surroundings. The net effect is only a small amount of cooling.
Likewise, in another attempt to provide loudspeaker cooling, U.S. Pat. No. 4,928,788 to Erickson discloses a ported reflex speaker enclosure and a method which is somewhat similar to convection cooling techniques that capitalizes on the natural tendency of heated air to rise. Although it is suggested that heated air is exhausted from the enclosure via the port, under principles of convection cooling, hot air tends to rise and thus, any air flowing from the hole residing on the bottom of the speaker housing would consequently not aid in the cooling of the speaker. Additionally, notches or openings near mounting holes in the speaker system are discussed to complement cooling; however, they appear to function as resistive vents, or some sort of pressure relief and with the presence of a larger bass reflex vent, these openings will be effectively short-circuited acoustically and see little or no pressure. Accordingly, what is needed is an improvement over the conventional vent of the prior art, and in particular, a vent that provides airflow in a preferred direction. It is desirable to overcome the drawback of the conventional vent having a slug of air moving back and forth by
Barnie Rexford
Dykema Gossett PLLC
Harvey Dionne
Peavey Electronics Corp.
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