Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Having acoustic wave modifying structure
Reexamination Certificate
1999-05-07
2001-03-20
Le, Huyen (Department: 2743)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Having acoustic wave modifying structure
C381S399000, C381S343000
Reexamination Certificate
active
06205228
ABSTRACT:
TECHNICAL FIELD OF THE INVENTION
The present invention relates generally to electro-dynamic acoustic transducers, and more particularly to a transducer having a pleated diaphragm in which an accordion-like alternating movement of the adjacent pleats is perpendicular to the radiation (acoustic) axis of the transducer.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 3,832,499 (Oscar Heil) discloses an electro-acoustic transducer in which a conductor is arranged in a meander pattern on at least one side of a flexible diaphragm. The flexible diaphragm is pleated or corrugated such that when the diaphragm is placed in a magnetic field oriented in a front to rear axis, with electrical current flowing perpendicular to the magnetic field in one direction in a given fold and in an opposite direction in an adjacent fold, the adjacent folds are alternately displaced to the right and to the left along a third axis perpendicular to both the front to rear axis and to the direction of the electrical current. The air spaces between adjacent folds facing one side of the diaphragm are expanded while the air spaces on the other side are contracted, thereby causing acoustic radiation to be propagated along the front to rear axis.
A two-part article in Speaker Builder (March and April 1982) by Kenneth Rauen discloses alternate designs for the diaphragm of a horn loaded “Heil Air Motion Transformer” (“AMT”), based in part on techniques previously published by Neil Davis (Audio Amateur, February 1977)
Another design for a horn loaded AMT is disclosed in U.S. Pat. No. 5,325,439 (Smiley) and was incorporated in a coaxial speaker marketed by Cerwin Vega (applicant's assignee) as model CATA-15.
However, none of the known prior art designs for a pleated diaphragm transducer provide for both substantially uniform acoustical coupling of the entire effective area of the diaphragm and substantially uniform magnetic flux through that same effective area. Furthermore, no previously known prior art design provides sufficient acoustical loading to match the mechanical impedance of the diaphragm and therefore such prior art designs are unable to maximize the efficiency of the transducer. Accordingly, the known prior art pleated diaphragm transducers are not readily adaptable for high power and high sound pressure level applications such as sound systems for concerts and motion picture theaters.
SUMMARY OF THE INVENTION
Accordingly, it is an overall object of the present invention to overcome the limitations of the prior art.
In accordance with one aspect of the invention, the front pole plate is a “magnetic throat” constructed from a unitary casting of a ferrous magnetic material (such as an iron silicon alloy), with a number of apertures extending from the front surface of the diaphragm to the inlet of an external loading horn. In an exemplary embodiment, the open area at the rear of the pole plate may be approximately ⅓ the active area of the diaphragm, thereby providing a compression ratio of 3:1.
In an alternate embodiment, the “magnetic throat” is constructed by stacking plates of a suitable cast or machined ferrous magnetic material, perpendicular to the radiation axis of the diaphragm, with each aperture formed by opposing recesses in two adjacent plates.
Yet another embodiment may be constructed by the layering of laminations of perforated steel, with each wafer being oriented perpendicular to the radiation axis of the diaphragm. Each consecutive wafer contains circular perforations of an increasing diameter, such that when the wafers are lined up in sequence the apertures register and form a stepped flare that opens outwards from the pole plate to the external horn.
In accordance with another aspect of the invention, the apertures are substantially uniformly distributed over the effective area of the diaphragm, to provide uniform acoustical coupling and prevent the occurrence of acoustical resonances and standing waves along the diaphragm's length.
In accordance with yet another aspect of the invention, each aperture opens up towards the front of the magnetic throat, such that the corresponding area at the inlet of the loading horn is substantially open, thereby providing a smooth transition through the magnetic pole plate to the external horn, with the apertures preferably designed with an exponential flare. These apertures may be tapered as part of the magnetic pole plate or the tapered portions may be formed separately from magnetic or non-magnetic materials, such as plastic or aluminum, and joined to a pole plate having corresponding apertures.
In a preferred embodiment, each aperture is in the form of a horizontal slit extending across the active width of the diaphragm, and the apertures are arranged in a vertical array to cover this entire active area. Each slit increases in width as it tapers towards the front pole plate, providing the smoothest possible acoustical transition to the external horn.
In other embodiments, the magnetic throat may comprise a plurality of apertures arranged in a planar array comprising several rows and several columns. In such cases, each aperture may open up in either the horizontal or vertical plane, or preferably in both.
REFERENCES:
patent: 3832499 (1974-08-01), Heil
patent: 5325439 (1994-06-01), Smiley
Armstrong Kirk
Czerwinski Eugene J.
Karstensen Terry
Megyeri Laszlo M.
Voishvillo Alexander
Cerwin-Vega, Inc.
Fulbright & Jaworski L.L.P.
Le Huyen
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