US2869668A

US2869668A - Plural drive loudspeaker

Info

Publication number: US2869668A
Application number: US635630A
Authority: US
Inventors: Sidney E Levy
Original assignee: Individual
Current assignee: Individual
Priority date: 1957-01-23
Filing date: 1957-01-23
Publication date: 1959-01-20
Anticipated expiration: 1976-01-20

Description

Jan. 20, 1959 s LEVY PLURAL DRIVE LOUDSPEJAKER 2 SheetsSheei-. 1

Filed Jan. 25, 1957 FIG. la.

INVENTOR. SIDNEY E. LEVY WWW ATTORNEYS.

Jan. 20, 1959 5 LEVY PLURAL DRIVE LOUDSPEAKER 2 Sheets-Sheet 2 Filed Jan. 23, 1957 INVENTOR. SIDNEY E. LEVY A TTOR/VEYS.

United States Patent PLU RAL DRIVE LOUDSPEAKER Sidney E. Levy, White Plains, N. Y., assignor of one-half to Arthur Blumenfeld, New York, N. Y.

Application January 23, 1957, Serial No. 635,630

7 Claims. (Cl. 181-27) This invention has to do with a horn-type loudspeaker having a plurality of driving units and in which the individual sound passages of the driving units expand outwardly and merge intoa common sound passage or horn having the form of an annulus wherein further expansion of the combined sound takes place.

In United States Patent No. 2,550,359, issued April 7.4, 1951, there is shown a loudspeaker wherein a plurality or sound-driving units are mounted near the periphery of a flat circular element in which are formed sound passageways extending radially inward from each driving unit to a common central chamber where the sound waves merge. The merged or mixed sound waves emerge from the central mixing chamber through a conical or megaphone-type horn.

The present invention is an improvement over such a device and provides a multi-driver unit loudspeaker having an increased sound output capacity and improved directional control of the sound pattern without impairing the frequency response characteristics of the loudspeaker.

In the preferred embodiment of this invention, a plurality of driver units are mounted on a fiat ring-shaped member in which are formed sound passages each extending radially outward from the driving units and each expanding at the same time at the same predetermined rate. The inner end of each passageway is connected by an orifice to a driver unit and the outer ends of the passageways merge smoothly into an annular common sound passage or horn of an area equal to the combined areas of the ends of the individual passages where the sound waves from such passages are united in phase. The merged sound waves are further expanded at some predetermined rate in the annular-shaped horn. The horn axis may be disposed in the same plane as the flat ring member, i. e. at an angle of 90 degrees to the axis of the ring, or at any other angle of the quadrant depending on the directional pattern one desires to establish. Regardless of the directional pattern selected, a loudspeaker results having exceptional high-power output capabilities and good frequency response characteristics.

It is a feature of this invention that a rather well defined cylindrically shaped sound beam emerging in the general form of an annulus is producible by providing an annular-shaped horn whose outer surface is generally cylindrical and whose inner surface is determined by a generally frusto-conical shaped plug member which tapers from the outer ends of the plurality of sound passageways towards the mouth of the horn into a circular plane substantially parallel although not necessarily coincident to the plane of the mouth. The beam becomes even more sharply defined by having the diameter of the surface plane of the plug member at least twice the distance across the annulus portion of the mouth opening.

In the drawings, Fig. 1 is an end view, with

elements

16 and 18 re moved, of a fiat ring-shaped member arranged for a ice plurality of sound-driver units connected through sound passageways or tone arms within the member to an annular-type horn;

Fig. 1a is a perspective of one of the tone arms;

Fig. 2 is a section taken along the line 22 of Fig. l, omitting allbut two oppositely disposed driver units in which an annular cylindrically disposed horn is shown;

Fig. 3 shows in sectional view a loudspeaker having a flat ring-shaped member similar to that of Fig. 2 but in which the axis of the annular horn is disposed along the surface of a cone; and

Fig. 4 shows in sectional view a loudspeaker having a flat ring-shaped member similar to that of Fig. 2 but in which the axis of the annular horn is disposed along the plane of the ring member.

Referring to the drawing Figs. 1 and 2, there is shown a generally fiat ring-shaped member 10 having therein a plurality of sound-conducting passageways or tone arms 11. In the interest of clarity,

elements

16 and 18 to be described hereinafter have been omitted in the end view of Fig. 1. The inner end of each tone arm 11 terminates in a hole or orifice 12, adjacent tone arms alternatively terminating on opposite faces of the member 10.

A sound-driving

unit

13 or 13a, which performs the function of translating electric signal energy into sound waves, is afiixed to the member 10 at each of the orifices 12. Only two of these units are shown for the sake of simplification.

The central portion of member 10 is cut out at 15, thereby providing a lighter unit and allowing access to driver units 13 mounted on the left side of member 10 as viewed in Fig. 2. The enclosure plate 21 is remov ably mounted to a flange of the member 10, the flange being of sufficient length to provide accommodation for the driver units 13a mounted on the right side of member 10 as seen in Fig. 2.

Each of the tone arms 11 is generally of circular cross-section at the point of attachment of the driving units 13 and, after a smooth turn into the plane of the member 10, extends radially outward towards the periphery of the member 10. As the tone arms progress, they become narrower in the thickness dimension of the member 10 and expand in the plane of the member 10 until they terminate with a turn towards the common sound passage 14. The change in configuration of the walls of each tone arm is so proportioned that the crosssectional area of each tone arm expands at a predeter-' mined rate from the driver unit orifice to the point of confluence of the tone arms with the common sound passage 14. A tone arm in a plan view is shown in the cut-out section 11 of Fig. 1, and is seen in a perspective view, to be discussed in more detail later, in Fig. 1a.

.The common sound passage 14 is smoothly formed by the merging of all of the tone arms 11. The combined area of the ends of each tone arm 11 is equal to the area of the annular-shaped common sound passage 14. The common sound passageway then expands at some predetermined rate from the ends of the tone arms to the mouth 19 of the annular horn. The outer surface of the annular horn is determined by a hollow cylinder 16 which is joined to a lip of the ring member 10 at a recess 17. The inner surface of the annular horn is determined by a plug member 18. The plug member is in the form of a hollow bell, being joined to a lip of ring member 10 at a recess 20.

The plug member 18 tapers from the junction 20 at a predetermined rate, terminating smoothly into a fiat circular surface in a plane parallel to the plane of the month end 19 of the cylinder 16. The circular surface of the 3 end plane of the cylinder 16. As seen in Fig. 2, the surface of plug 18 is slightly recessed with respect to the end plane of the cylinder 16.

The annular sound passage formed by the cylinder 16 and plug member 18 increases in cross-sectional area from the common sound passage 14 formed at the end of tone arms 11 to the mouth portion 19.

It is well known that the expansion rate of a horn determines the frequency response characteristic of the horn. For example, if the expansion rate is gradual, the frequency response would be such as to have a low frequency cut-off point, and, if the expansion rate is more rapid, the frequency cut-otf point is shifted upward'in the sound frequency spectrum. It is also known that the shapes of the cross-sectional areas taken normal to the sound path need not be similar provided that, for optimum operation, the transition between dissimilar crosssections is smooth.

The perspective view of a tone arm 11 for the driver units 13 mounted on the left side of member as seen in Fig. 2 is shown in Fig. 1a. The tone arms for driver units 13a mounted on the right side of member 10 would be substantially the same except that the turn at the expanded end 14 would be in the opposite direction.

It is known that a turn in a sound wave path tends to produce energy cancellation of the instantaneous sound wave fronts due to the unequal path lengths created by the turn. This phenomenon of energycancellation may be called phase distortion. practice of this invention, this phase distortion etfect is minimized by providing two turns in the wave path from the sound-driver units 13a to the common sound passage 14'. The first turn of tone arm 11, starting at the orifices 12 opening on the right side of member 10, as seen in Fig. 2, is in the opposite sense of the second turn in tone arm 11 into passage 14. By thus providing each of the two turns in an opposite sense, the unequal path length differentials are minimized, thereby minimizing the phase distortion effect.

Since only half of the plurality of tone arms are ar ranged, in a preferred form of the invention, with the oppositely disposed turns just described, it is appreciated that the tone arms not so arranged produce, in fact, an aggravation of the total phase distortion manifested at the common sound passage 14 since the two turns thereof are in the same sense. However, in order to further minimize the phase distortion produced by unequal path lengths, there is provided, as a feature of this invention,

a tone arm which expands at a desired rate and yet a path and to the member It diminishes along the sound I path. This dimension at common sound passage 14 is then very much smaller than the corresponding dimension at the orifice 12. The opening of the tone arm 11 at portion 14 is substantially a slit whose wide dimension, i. e. the dimension along the periphery of member 10, is produced by the flaring of the tone arm 11 in the plane of member 10 and is better seen by the sectional view of tone arm 11a in Fig. l. The perspective view of Fig. 1a illustrates the entire form of the tone arm. Thus, the effect of such a formed tone arm minimizes the differential path length produced by the first turn and further allows for a turn in either the same or opposite sense as that of the first turn into the common sound passage portion 14 whereby the phase distortion efiect is minimized.

If by choice, for example, it is desired to have a loudspeaker of the invention with a constant exponential expansion characteristic, the shape of the tone arm 11 would be made such that sectional area A would be larger than A .in accordance with the relation Advantageo-usly, in the p where e is the constant epsilon 2.718

m is the horn flare constant, and v Z is the incremental distance between areas A and A along the axis Z of the sound passageway.

The areas of each of the tone arms merge smoothly into the common sound passage 14 and their combined areas are equal to the area of the portion 14 shown also in Fig. la as A The subsequent sectional areas of the common sound passage now in the form of an annular horn are arranged to expand at a constant exponential rate defined by Equation 1.

1n the operation of the loudspeaker of the invention, electrical signals from a common source are applied to each of the

driver units

13 and 13a in any manner known in the art whereby sound wave energy is produced at the beginning, that is, at the throat of each of the tone arms 11 simultaneously and at substantially the same average intensity. The sound waves in each of the tone arms expand in accordance with a desired rate, e. g. that specified in Equation 1, combining at a greater amplitude and substantially in phase at the common sound passage portion 14. The combined sound wave then expands at the same rate in the annular horn sound passage and is projected into the atmosphere after passing through the mouth portion of the horn 19.

The sound pattern projected by the loudspeaker of the invention has greater power levels than loudspeakers 0f the prior art of comparable size. Further, the sound pattern is more sharply defined and can be projected, for example, in accordance with the structure of Figs. 1 and 2 as a cylindrical beam. 1 have found that this beam is more sharply defined than the patterns produced by horns known heretofore flared at the same rate, especially at frequencies near the low frequency cut-off determined by the rate of flare. This directional action is most effective when certain relations are maintained between the dimension y shown in Fig. 2 representing the distance across the annular portion of the mouth and the diameter of the fiat circular portion of the plug member 18 represented by the distance x. For best results the dimension y should be less than onehalf of distance x.

A cylindrical sound pattern is produced by the structure shown in Figs. 1 and 2 since the central axis c of the member 10 is substantially parallel to the axis z of the horn portion of the loadspeaker. Various sound patterns by choice may be determined by varying the angle between the central axis c and the horn axis 2 as required.

The structure shown in Fig. 3, for example, is sub stantially identical to the structure of Fig. 2 and the corresponding portions which are identical are correspondingly labeled. The difference resides in the common sound passageway or horn being of a different form. The inner and outer surface members for determining the horn portion of the loudspeaker are shown as

members

38 and 36 respectively. The sound beam produced by such an arrangement is in the general form of an expanding annulus and may be used, for example, to radiate a sound pattern extending in a large ring-like pattern which is located above the surface to be radiated upon.

The embodiment shown in Fig. 4 has the axis of the horn z substantially perpendicular to the central axis c. Such a form of the invention radiates a circular planar sound pattern.

Although the

driver units

13 and 13a are shown connected to the channel arms along an axis perpendicular to the plane of the member 10, they may be connected at any angle other than the perpendicular, provided there is not established thereby physical interference from adjacent units.

It will be obvious to those skilled in the art that my invention is capable of various modifications and I do not desireto be restricted therefore to the particular details shown and described but only within the scope of the appended claims.

I claim:

1. A loudspeaker system for amplifying the sound emanating from a plurality of separate driver units, comprising a plurality of sound conducting and expanding channels arranged in a plate-like member, each of said sound channels being connected at its inner end to a driver unit and extending outwardly therefrom, a common sound passageway or horn in the general form of an annulus into the throat of which the sound channels merge in a confluent manner, said driver units being mounted on at least one face of said plate-like member at a point intermediate the center and periphery thereof, said sound conducting passages being formed within said member and extending outwardly from the driver units to the periphery of said member where they merge int the annular horn, and the dimension of each of said sound channels diminishing in a plane perpendicular to the plane of the plate-like member and expanding in the plane of the member as the passages extend outwardly to the periphery thereof.

2. A loudspeaker as in claim 1 in which the annular horn includes an outer skirt-like member and an inner plug-like member, both members extending from the plate-like member in a direction substantially perpendicular to said plate-like member and being suitably flared to cause the desired expansion of the sound waves in the annular horn, said inner member terminating in a substantially circular fiat plane substantially parallel to the plane of the plate-like member, the said circular flat plane being at least equal to the radial opening of the mouth of said horn.

3. A loudspeaker as in claim 1, in which the axis of the horn lies in the same palne as the plane of the passageways whereby the emerging expanded sound waves are directed in a circular planular pattern.

4. A loudspeaker as in claim 1, in which the axis of the horn is disposed at an acute angle to the plane of the passageways whereby the loudspeaker produces a sound beam in the general form of an expanding annulus.

5. A loudspeaker as in claim 1, in which the axis of the horn is disposed at substantially a right angle to the plane of the passageways whereby the amplified sound waves emerge in the general shape of an annulus.

6. A loudspeaker system for amplifying sound emanating from a plurality of separate sound sources, the combination comprising a substantially planar member hav ing a plurality of sound-conducting channels radially extending and gradually expanding in area from a central portion of said planar member and merging into a common annular horn formed at the peripheral portion of said planar member, a plurality of closely-spaced sound driver units, alternate driving units of said plurality of driver units being mounted on opposite faces of said planar member, each of said plurality of driver units being connected to the inner end of a respective one of said plurality of tone arms, each of said tone arms flaring in the plane of said planar member and diminishing in a plane perpendicular to said planar member whereby the expanding sound waves from each of said tone arms are combined substantially in phase in said annular horn, said annular horn including an outer skirtlike member and an inner plug-like member, both members extending from the planar member in a direction substantially perpendicular to said planar member and being suitably flared to cause the desired expansion of the sound Waves in the annular born, the radius of said inner plug being at least equal to the radial opening of the mouth of said horn.

7. A loudspeaker system for amplifying the sound emanating from a plurality of separate drive units, comprising a plurality of sound conducting and expanding channels arranged in a plate-like member, each of said sound channels being connected at its inner end to a driver unit and extending outwardly therefrom, a common sound passageway or horn in the general form of an annulus into the throat of which the sound channels merge in a confluent manner, said driver units being mounted on at least one face of said plate-like member at a point intermediate the center and periphery thereof, said sound conducting passages being formed within said member and extending outwardly from the driver units to the periphery of said member where they merge into the annular h rn, the cross-sectional area of said sound conducting channels expanding continuously from said driver units to the common passageway to combine the sound waves from each of the sound conducting channels substantially in phase.

References Cited in the tile of this patent UNITED STATES PATENTS 1,943,499 Williams Ian. 16, 1934 2,550,359 Levy Apr. 24, 1951 2,622,692 Leslie Dec. 23, 1952