US3016430A - Loudspeaker - Google Patents

Description

Jan. 9, 1962 l.. s. HooDwlN 3,016,430

LOUDSPEAKER Filed Nov. 14, 1958 FEE -l 3,016,430 LGUDSPEAKER Louis Hoods/in, Bridgznan, Mich., assigner to Electro- Voice, Incorporated, Buchanan, Mich., a corporation of Indiana Filed Nov. 14, 1958, Ser. No. 773,877 7 Claims. (Cl. 179-1155) The present invention relates to loudspeakers, and particularly to loudspeakers which employ a driver unit and horn.

Most loudspeakers employ either some means for converting electrical energy into acoustical energy, which may be referred to as a driver unit, and a horn, or a cone attached to the driver unit. The present invention is preferably utilized with loudspeakers employing a horn and driver unit, although it may also be practiced with loudspeakers employing cones.

Most driver units exhibit an undesirable response peak at some frequency within their responsive range. Usually a loudspeaker will havea response peak at a frequency corresponding7 to the mechanical resonant frequency of its diaphragm. n

It is one of the objects of the present invention to provide a loudspeaker having a driver unit with a response peak within the responsive range of the speaker and a horn coupled to the driver unit which is provided with anti-resonance means tuned to the frequency of the response peak for the purpose of reducing the acoustic response of the loudspeaker at this frequency.

A further object of the present invention is to provide a loudspeaker with a driver unit having a response peak within the responsive range of the driver unit and a horn acoustically coupled to the driver unit with a cavity opening into the mouth of the horn and forming an antiresonant circuit at the frequency of the response peak.

These and further objects of the present invention will become morefully understood by a further reading of this disclosure, particularly when viewed in the light of the drawings, in which:

FIGURE l is a sectional View of a high frequency loudspeaker constructed according to the teachings of the present invention;

FIGURE 2 is a sectional view taken along the line Z-Z of FIGURE l;

FIGURE 3 is an enlarged fragmentary sectional view of a portion of FIGURE l;

FIGURE 4 is a sectional view taken on line 4-4 of PrGURE 1;

FIGURE 5 is a sectional view taken on line 5-5 of FIGURE 4; and

FIGURE 6 is a view, partly in section and partly in elevation, of a low frequency speaker constructed according to the teachings of the present invention.

FIGURE l illustrates a loudspeaker designed for reproducing high frequencies, commonly referred to as a tweeter, and constructed according to the teachings of the present invention. This speaker has a driver unit 10 having a housing 12 which contains a permanent magnet 14. The housing 12 has a back plate 16 and a front plate 18 provided with an axial opening 20. A diaphragm 22 is mounted on the side of the top plate 18 opposite the magnet 14 and carries a voice coil 24. The diaphragm 22 is clamped between a housing cover 26 and the top plate 18, acushioning ring 28 abutting the cover 26 and diaphragm 22. A pole piece 30 abuts the magnet and extends into the region within the voice coil 24. The

entire assembly forming the driver unit 10is secured in position by four screws 32.

It will be seen from the foregoing description that the driver unit 10 is similar to the one disclosed in the patent 'ice application of Robert C. Avedon, Serial No. 682,234, tiled September 5, 1957. The driver unit 10, however, is coupled to a horn 34 which is of novel construction.

The horn 34 has a flange 36 which mounts in a recess 38 in the cover 26, and the horn flares outwardly to provide the proper acoustical impedance match between the diaphragm 22 and the ambient atmosphere. The end of the horn 34 secured to the frange 36 is referred to herein as the throat of the horn and is designated 39, while the frared end of the horn opposite the throat is referred to as the outer end and designated 40.

The cover 26 has a concave surface 42 confronting the diaphragm 22, and the diaphragm 22 has a convex surface 44 confronting the concave surface 42 of the cover. Further, arcuate slots 46 extend about the periphery of the concave surface 42 to permit sound to pass from the diaphragm 22 to the horn, and an axial bore 48 extends through the concave surface 42.

The fiange 36 of the horn 34 has a pair of arcuate channels S0 which extend therethrough from a chamber S1 located between the cover 26 and a loading plug 52 mounted coaxially within the throat of the horn 34. The surface of the cover 26 confronting the chamber 51 and the loading plug 52 is flat, and is designated 54. The loading plug 52 has a smaller diameter than the throat 39 of the horn 34, and is secured in position by a pair of ribs S6 extending between opposite sides of the loading plug S2 and the flange 36, thereby forming the pair of arcuate channels 50 for transmitting sound into the horn 34. The loading plug S2 tapers from the flange 36 to a point 58, and is provided with a cavity 60 therein. The cavity 60 is formed by a bore 62 extending into the loading plug S2 from the flange 36, and a ilat slug 64 disposed in the mouth of the bore62 confronting the flange 36. The slug 64 has an aperture 66 therein, and the cavity formed by the bore 62 and aperture 66 forms an anti-resonant device at the frequency of mechanical resonance of the diaphragm 22. In this manner, the response peak which would normally occur at the frequency of mechanical resonance of the diaphragm 22 is substantially eliminated to provide an essentially flat frequency response. It is, of course, understood that the cavity 60 and aperture 66 may be selected to reduce a response peak caused by other mechanisms than the resonance of the diaphragm.

In one particular construction of the present invention, the loudspeaker is designed with a response range extending from 2,000 to 21,000 cycles per second. This speaker has a horn with a rectangular open end 40 measuring 3 inches by 9.54 inches, and the open end is spaced from the throat 39 of the horn by a distance of 6.57 inches. The loading plug 52 has a length of 1.30 inches' and a diameter at the end of the flange of 5%4 inch. Ilhe bore 62 has a diameter of .56 inch and extends a distance of .9 inch. The opening 66 in the slug 64 has a diameter of 0.17 inch, andthe slug 64 is spaced from the surface 54 of the cover by a distance of approximately 1/16 inch. The response peak of the loudspeaker corresponding to the mechanical frequency of resonance of the diaphragm would occur in the lower portion of the response range of the speaker, namely approximately 3500 cycles per second. The anti-resonance device here disclosed reduces this re sponse peak to approximately the value of the response throughout the rest of the response range of the speaker.

rl`he loading plug "52 provides in addition to the conventional vfunctions of reducing the throat area to increase the air particle velocity and phase equalization, the additional function of providing an anti-resonance device at the throat of the horn which is effective to reduce an unwanted response peak. The anti-resonance device here disclosed is a resonator which includes a cavity and a connecting neck or aperture in which the natural frequency o Ts" f aan nro where S is the cross sectional area of the neck, V the volume of the cavity, l the length of the neck, and C the velocity of sound. Where the neck is merely an aperture,

the effective length of the neck l is given by the following equation,

where a is the radius ofthe aperture.

This structure forms an anti-resonant network at the resonant frequency of the resonator since the sound waves from the aperture 66 are out of phase with those from the diaphragm. Further, since the aperture of the resonator is at the throat of the horn, the resonator produces its optimum effect in reducing the magnitude of the response peak.

While the embodiment of the invention described above concerns a high frequency or tweeter loudspeaker, the present invention may also be practiced with a low frequency horn speaker. In low frequency speakers, it is generally more convenient to construct the anti-resonant cavity in the Walls of the horn, ratherV than in a loading plug as disclosed above, although it is to be understood that a loading plug cf sufficient size to produce anti-resonance at the desired frequency can be employed. FIG- URE 6 illustrates a low frequency speaker which employs a driver unit 68 coupled to a horn 7) in which the throat of the horn is provided with openings 72, and housings 74 delining cavities 76 are secured within the openings 72. Each of the housings 74 has a neck 7S extending from the opening 72` to the cavity 76.

This embodiment of the invention employs two cavities as anti-resonant devices in order to decrease the unwanted responseV peak to a greater extent than can be accomplished by a single cavity and neck. Further, in a low frequency or woofer speaker', the frequency response peak generally occurs at a lower frequency than in a high frequency speaker, and generally atthe frequency of resonance of the speaker diaphragm, requiring a relatively large cavity 76 to form the anti-resonant device.

The present invention may also be practiced with loudspeakers having a cone and means attached to the apex of the cone for driving the cone. However, since a resonator can neither be attached to nor built into the cone of the speaker, it must be a separate unit mounted to the support structure of the cone, and preferably confronting the cone.

Those skilled in the art will readily devise modifications and-irnprovements on the foregoing invention from a reading of the present disclosure. 1t is therefore intended that the scope of the present invention be not limited to the foregoing disclosure, but rather only by the appended claims,

The invention claimed is:

1. A loudspeakercomprising, in combination, .means estense for converting electrical energy into acoustical energy having an output at one frequency greater than at another frequency, a sound propagating means acoustically l coupled to the energy converting means, and means defining a resonator having a vcavity and a neck extending from the cavity to the propagating means, the air in said cavity and neck resonating at the frequency of greater output of the energy converting means whereby the resonator forms an anti-resonant circuit at that frequency.

2. A loudspeaker having a driver unit and a horn with a throat and a portion flaring outwardly from the throat, said driver unit having a rst output frequency of greater amplitude than a second output frequency, in combination with a resonator having means defining a cavity and a neck extending between the throat of the horn and the cavity, the air in said cavity and neck resonating at the first frequency of the driver unit, whereby the resonator forms an anti-resonant circuit.

3. A loudspeaker comprising the elements of claim 2 wherein a plurality of resonators are acoustically coupled to the throat of the horn.

4. A loudspeaker comprising a driver unit having an output at a first frequency greater than the output of the driver unit at a second frequency, a horn mounted on the driver unit having a phasing member disposed on the axis ofthe throat of the horn, said phasing member havl ing a cavity therein and an aperture between the cavity and the throat of the horn, the natural resonance of the air in the cavity and aperture approximately equaling .y

ing member mounted von. the axis of the horn adjacent to the diaphragm having a cavity therein and an opening between the cavity and the diaphragm, the natural frequency of resonance of the air within the cavity and opening approximately equaling the mechanical frequency of resonance ofthe diaphragm.

6. A loudspeaker comprising a driver unit having a diaphragm with a mechanical resonance at a particular frequency, means defining a chamber confronting the diaphragm, a horn secured to the chamber defining means with thhe throat of the horn confronting the chamber, a phasing member mounted on the axis of the throat of the horn having a cavity extending therein and an aperture between the cavity and the chamber, the natural frequency of the air within the cavity and aperture approximately equaling the frequency of mechanical resonance of the diaphragm.

7. A loudspeaker comprising the elements of claim 6 in combination with a member disposed in the chamber adjacent to the diaphragm having aplurality of channels extending therethrough between the diaphragm and the throat of the horn.

References Cited in the file of this patentY UNITED STATES PATENTS 1,995,071 Mackenzie et a1.' Y Mar. 19, 1935 2,124,933 Starkweather July 26, 1938 2,873,812 v Avedon Feb. 17, 1959 FOREIGN PATENTS l 495,784 Great Britain NovA 18, 1938

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