US3781475A

US3781475A - Counterbalanced two speaker rotary tremolo device

Info

Publication number: US3781475A
Application number: US00147023A
Authority: US
Inventors: P Sharp
Original assignee: Columbia Broadcasting System Inc
Current assignee: CBS Broadcasting Inc; Marmon Co
Priority date: 1971-05-26
Filing date: 1971-05-26
Publication date: 1973-12-25
Anticipated expiration: 1990-12-25

Abstract

A rotary tremolo device employs a pair of outwardly facing speakers mounted in counterbalanced relationship on a rotatable support. The speakers are respectively driven by signals derived from the same source but differing in phase, preferably by 90 electrical degrees, so as to provide an asymmetrical sound radiation pattern. As the support is rotated at about five to eight revolutions per second, a tremolo and vibrato effect is produced. The support may also be rotated at slower or faster speeds to produce other effects.

Description

United States Patent [1 1 Sharp 1 COUNTERBALANCED TWO SPEAKER ROTARY TREMOLO DEVICE [75] Inventor: Paul R. Sharp, Sierra Madre, Calif. [73] Assignee: Columbia Broadcasting System, Inc.,

New York, NY.

[22] Filed: May 26, 1971 [21] Appl. No.: 147,023

[52] US. Cl. 179/1 J, 84/125 [51] Int. Cl. Golh l/OZ [58] Field of Search 179/1 .1, 1 D, 1 E, 179/1 GA, 1GY;84/1.25; 181/31 B [5 6] References Cited UNITED STATES PATENTS 2,995,054 8/1961 Leslie 179/1 .1 3,160,695 12/1964 Bonham... 84/].25 2,869,667 1/1959 Leslie 84/125 Dec. 25, 1973 Leslie.... Hare Primary Examiner-William C. Cooper Assistant Examiner-Jon Bradford Leaheey Attorney-Flam & Flam 5 7] ABSTRACT 14 Claims, 5 Drawing Figures 22 i DIFFERENQE NETWORK PATENTED UECZS W5 SHEET 2 BF 2 COUNTERBALANCED TWO SPEAKER ROTARY TREMOLO DEVICE BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to acoustic pulsato apparatus in which a sound radiation pattern is rotated. In general there are two types of such apparatus, one in which the acoustic driver is stationary and one in which the acoustic driver is rotated. In both cases a rotary sound channel is provided that cooperates with the acoustic driver. The acoustic driver is stationary. The rotary sound channel has a mouth that continually registers with the driver at the axis of rotation, there being a sound emanating opening which describes an orbital path. In the other type of such apparatus the sound channel is formed by a speaker cone at the center of which the acoustic driver is located. If desired, the sound channel may be extended by components cooperating with the speaker cone. This invention is concerned particularly with the problem of increasing the acoustic power handling capabilities of such devices without increasing the physical size thereof.

2. Description of the Prior Art In order to increase the acoustic power handling characteristics of rotary pulsato apparatus, it has been proposed to provide a pair of sound channels facing radially outward on diametrically opposite sides of the axis of rotation. A single drum, for example, may mount two speakers. The arrangement is not satisfactory because the sound radiation pattern now repeats twice every revolution rather than only once every revolution. Since characteristic tremolo and vibrato is produced by a recurrence rate of about five to eight revolutions per second, the speed of the two-speaker drum must be halved; otherwise, an effect quite different from characteristic tremolo and vibrato will be produced. If the speed is halved, then the orbital velocity of the speaker openings is correspondingly halved. The Doppler effect is accordingly reduced and the frequency or pitch change is likewise reduced. Inorder to restore deep, rich frequency shift characteristic of vibrato, the orbit must be doubled. The result, of course, is an undesired increase in physical size of the rotary apparatus. In U.S. Pat. No. 3,100,024 to Leslie, a plurality in speakers are mounted upon a common drum in such manner that the combined sound radiation pattern is asymmetrical. Accordingly, the 5 to 8 revolutions per second rate of the drum can be'maintained while yet producing characteristic tremolo and vibrato. In order to accomplish that result however, the Leslie patent required the use of three or more speakers, together with a careful selection of the polarity of drive signals for the speakers. The structure shown in the Leslie patent is not-operable if two, and only two, speakers are used, unless the speakers themselves are asymmetrically mounted. But such an arrangement is undesirable because counter-weights are required. The

most advantageous arrangement is one in which the speakers are equally angularly located so that no counter-weight is required. Two diametrically located speakers cannot create an asymmetrical sound radiation pattern, irrespective of the polarity of drive signals applied to the respective speakers, for the reason that the resulting pattern is either a figure eight, the major axis of which is aligned with the speakers, or a figure eight with the major axis perpendicular to the axis of the speakers. In both cases, the sound radiation pattern repeats twice per revolution. The primary object of this invention is to make it possible to provide two sound channels in diametrically opposed relationship, in which an asymmetrical sound radiation pattern is produced notwithstanding the fact that the same source causes the sound channels to be acoustically driven.

SUMMARY OF THE INVENTION In accordance with one form of the present invention, a pair of speakers are mounted in diametrically opposed relationship on a rotary support. The speakers are driven by a pair of signals differing in phase, optimally by electrical degrees, so as to produce a sound radiation pattern which occurs only once for each revolution of the support. By rotating the support at from about five to eight revolutions per second, a full, rich tremolo or vibrato effect is produced. The speaker drive signals are derived from a single source, e.g., the output of an electronic organ, by using a phase difference network.

The device has the advantage of producing greater acoustic output than could be provided with a single speaker, while permitting the two speakers to be mounted in counterbalanced relationship on the rotatable support.

In an alternative embodiment, a pair of speakers are mounted in spaced, facing relationship and driven by the appropriately phased signals. A rotary reflector plate or baffle is disposed at an angle to the common axis of the speakers. Opposite faces of the baffle reflect the speaker sounds in diametrically opposite directions. The sound radiation pattern yet repeats only once per revolution due to the quadrature phasing of the speaker signals.

BRIEF DESCRIPTION OF THE DRAWINGS A detailed description of the invention will be made with reference to the accompanying drawings.

FIG. 1 is an elevational view of a rotary tremolo device in accordance with the present invention, portions of the rotary support and speaker housing being shown in section.

FIG. 2 is an electrical schematic diagram of a phase difference network useful in conjunction with the device of FIG. 1.

FIG. 3 is a block diagram of another electrical arrangement for driving the speakers used in the invention.

FIG. 4 is a simplified elevational view of a two speaker tremolo device using a rotating reflector plate.

FIG. 5 is a graph showing a typical sound radiation pattern from the inventive two-speaker rotary tremolo device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The following detailed description is of the best presently contemplated modes of carrying out the invention. This description is not to be taken in a limiting sense, but is made merely for the purpose of illustrating the general principles of the invention since the scope of the invention best is defined by the appended claims.

Structural and operational characteristics attributed to forms of the invention first described also shall be attributed to forms later described unless such characaccordance with the present invention. The device 11 includes a rotatable support comprising, in this instance, a housing 12 having a cylindrical wall 12a and ends 12b, 12c coaxially supported on a shaft 13 by means of flanged collars l4, 15. A pair of

speakers

16, 17 are mounted in diametrically opposed relationship within the housing 12. No counter-weight is necessary, since the speaker 16 counterbalances the speaker 17.

The cones or sound channels of the

speakers

16, 17 face radially outwardly through a respective pair of

openings

18, 19 in the housing wall 12a. The

speakers

16, 17 are driven with a pair of signals appropriately differing in phase, optimally by 90 electrical degrees, so as to produce an asymmetrical sound radiation pattern which repeats only once for each revolution of the speaker housing 12. The cabinet structure is either open or louvered to permit passage of sound produced by the

speakers

16, 17.

In the embodiment of FIG. 1, the speaker drive signals are derived by means of a phase difference network 21 mounted within the housing 12 adjacent the shaft 13. The input to network 21 is a single source signal, typically the output of an electronic organ, supplied via a line 22 and amplified by a power amplifier 23. For convenience, the output of the amplifier 23 is communicated to the network 21 via a pair of conductors 24a, 24b, a slip ring assembly 25, and additional conductors interior of shaft 13. The slip ring assembly advantageously may be of the type described in the US. Pat. No. 3,014,192 to Leslie.

Rotational motion at the five to eight revolutions per second rate appropriate for production of tremolo is imparted to the speaker housing 12 by means of a motor 26 connected by a belt 27 and a pulley 28 to the shaft 13. The shaft 13 itself is mounted for rotation between a pair of

ball bearings

29, 30 accommodatedby

interior partition walls

31, 32 forming part of the cabinet structure 10.

The phase difference network 21 may comprise any type of conventional circuitry accepts accpets a 'single source signal and provides a pair of output signals of mutually different phase, but corresponding in amplitude and frequency to the source signal. By way of example only, FIG. 2 shows a pair of conventional lattice filters 21a, 21b which may be employed advantageously to form the phase difference network 21. The stop band of each lattice filter 21a, 21b is selected to be above the highest frequency of the amplified source signal supplied via lines 24a, 24b, so that each

speakers

16, 17 receives via the respective pair of lines 35, 36 a drive signal substantially duplicating the source signal. However, each lattice filter 21a, 21b is designed, in a manner well known to those skilled in the filter network art, to provide a phase shift which is linear with frequency. Moreover, the filter 21a is designed to introduce a phase shift which is greater or less than that introduced by the filter 21b. Accordingly, the speaker signal on the lines 35 will differ in phase by a constant phase angle from the other speaker drive signal on the lines 36. I

Optimally, the drive signals to the

speakers

16, 17 should differ in phase by 90 electrical degrees, as this results; in a completely asymmetrical sound radiation patterns which repeats only once for each revolution of thespeaker housing 12. However, acceptable pulsato still is obtained with a phase difference in the range of from about 45to about l35this also producing an asymmetrical radiation pattern. Of course, the phase difference could be an integral number of cycles plus 40 to Further, either of

speakers

16, 17 may lead or lag the other. A phase difference of 0 or is not acceptable, as this would result in a figure-eight sound radiation pattern, as disclosed herein.

An alternative arrangement for providing the speaker drive signals is shown in FIG. 3. Referring thereto, the source-signal supplied via the line 22 is provided directly to a phase difference network 21'. The two speaker drive signals produced by network 21 then are individually amplified by

amplifiers

38, 39 and provided via the lines 35'36' to the respective speakers l6, 17.

An alternative embodiment of the inventive rotary tremolo device is shown in FIG. 4. In this embodiment, a pair of speakers 41, 42 are fixedly mounted in spaced, facing relationship in a cabinet structure 43. The sound channels of the speakers 41, 42 project vertically through a respective pair of openings 44, 45 provided in the horizontal partition walls 46, 47 interior of the cabinet 43. The speakers 41, 42 respectively receive via the lines 35a, 35b a pair of drive signals differing'in phase, optimally by 90as described above. i i

A rotary reflector plate or baffle 49 supported on a vertical shaft 51 is used to reflect the sound from the speakers 41, 42 outwardly through the open front of the cabinet structure 43. The reflector plate 49 is dis posed at an acute angle, preferably 45with respect to the shaft 51. Preferably, the shaft 51 is aligned coaxially with the speakers 41, 42. Rotational motion is imparted to the reflector plate 49 by means of a motor 52, a belt 53 and a pulley 54 attached to the shaft 51.

It will be appreciated that the sound produced by the speakers 41, 42 and reflected by the baffle 49 will exhibit an asymmetrical radiation pattern like that produced by the-

speakers

16, 17 shown in FIGS. 1 through 3. When the reflector plate 49 is rotated at between about five and eight revolutions per second, the asymmetrical sound radiation pattern correspondingly will rotate about a vertical axis, producing a full, rich pulsato effect.

The asymmetrical sound radiation pattern produced by the diagonally opposed

speakers

16, 17 when driven out of phase by 90 electrical degrees is typified by the curve 60 of FIG. 5. The curve 60 is shown superimposed on circular coordinates centered at the speaker axis of rotation. Although the exact shape will differ from frequency to frequency, the radiation pattern is characterized by a region 60a of minimum intensity in one direction and a region 60b of minimum intensity in the opposite direction. As the housing 12 isrotated about the shaft 13, a listener situated at a fixed location will sense only one maximum 60b for each revolution of the housing. That is, the sound radiation pattern repeats only once per revolution of the speaker support.

Intending to claim all novel, useful and unobvious features shown or described,

I claim:

1. An apparatus for producing pulsato by acoustic means, comprising:

a. a support;

b. means for rotating said support about an axis;

0. first and second speakers mounted on said support on diametrically opposite sides of said axis to be mutually counterbalanced;

d. means for supplying to the respective speakers, drive signals derived from the same source signal, but differing in phase by a value other than either zero, 180 or a multiple of l80said drive signals producing from said speakers a sound radiation pattern which repeats only once per revolution of said support.

2. The apparatus according to claim 1 in which said support is a drum, said speakers facing radially outwardly.

3. The apparatus according to claim 1 in which said rotating means imparts rotation to said support at a rate of about five to eight revolutions per second.

4. The apparatus according to claim 1 in which said drive signals differ in phase by about 45 to 135 or by such amount plus a multiple of 180.

5. Apparatus according to claim 1 wherein .said means for driving comprises a phase difference network receiving said source signal and providing said phase differing speaker drive signals.

6. Apparatus according to claim 5 further comprising means for amplifying said source signal.

7. Apparatus according to claim 5 further comprising means for separately amplifying each of said speaker drive signals.

8. Apparatus according to claim 5 wherein said phase difference network comprises first and second lattice filters each receiving said source signal, said source signal being substantially within the pass band of said filters, said pair of speaker drive signals being provided respectively by said first and second filters.

9. Apparatus according to claim 1 wherein said speaker drive signals differ in phase by 90 or 90 plus a multiple of 180.

10. Apparatus according to claim 9 wherein said support includes a generally cylindrical housing carried by a coaxial shaft, said speakers being mounted adjacent the periphery of said housing in counterbalanced relationship.

ll. A'rotary tremolo device comprising a. a support;

b. means for rotating said support about an axis at between about flve and eight revolutions per second;

c. a pair of oppositely facing sound channels mounted in counterbalanced relationship on said support; and

d. means for driving said sound channels with a pair of signals differing in phase by an angle of between about 45 and 135or by an integral number of cycles plus said angle, to produce from said channels an asymmetrical sound radiation pattern which repeats only once per revolution of said support.

12. A rotary tremolo device according to claim 9 wherein said angle is 13. Apparatus for producing tremolo acoustically,

comprising:

a. first and second speakers mounted in spaced, facing relationship along a vertical axis;

b. planar reflecting means disposed between said speakers and mounted for rotation about said vertical axis at a rate of between about five and eight revolutions per second, said planar reflecting means being situated at other than a right angle with respect to said vertical axis; and

0. electrical signal source means for driving said speakers with a pair of signals differing in phase by between approximately 45 and to produce from said apparatus a sound radiation pattern which repeats only once per revolution of said pla nar reflecting means.

14. A rotary tremolo device comprising:

a. two speakers;

b. means for driving said speakers with a pair of signals derived from the same source signal but differ ing in phase to produce an asymmetrical sound radiation pattern having a single major lobe; and

c. rotary means for effectively causing said asymmetrical sound radiation pattern to rotate about an axis at a slow speed, said sound radiation pattern repeating only once per revolution of said rotary means.

Claims

1. An apparatus for producing pulsato by acoustic means, comprising: a. a support; b. means for rotating said support about an axis; c. first and second speakers mounted on said support on diametrically opposite sides of said axis to be mutually counterbalanced; d. means for supplying to the respective speakers, drive signals derived from the same source signal, but differing in phase by a value other than either zero, 180* or a multiple of 180said drive signals producing from said speakers a sound radiation pattern which repeats only once per revolution of said support.

4. The apparatus according to claim 1 in which said drive signals differ in phase by about 45* to 135* or by such amount plus a multiple of 180*.

5. Apparatus according to claim 1 wherein said means for driving comprises a phase difference network receiving said source signal and providing said phase differing speaker drive signals.

9. Apparatus according to claim 1 wherein said speaker drive signals differ in phase by 90* or 90* plus a multiple of 180*.

11. A rotary tremolo device comprising a. a support; b. means for rotating said support about an axis at between about five and eight revolutions per second; c. a pair of oppositely facing sound channels mounted in counterbalanced relationship on said support; and d. means for driving said sound channels with a pair of signals differing in phase by an angle of between about 45* and 135or by an integral number of cycles plus said angle, to produce from said channels an asymmetrical sound radiation pattern which repeats only once per revolution of said support.

12. A rotary tremolo device according to claim 9 wherein said angle is 90*.

13. Apparatus for producing tremolo acoustically, comprising: a. first and second speakers mounted in spaced, facing relationship along a vertical axis; b. planar reflecting means disposed between said speakers and mounted for rotation about said vertical axis at a rate of between about five and eight revolutions per second, said planar reflecting means being situated at other than a right angle with respect to said vertical axis; and c. electrical signal source means for driving said speakers with a pair of signals differing in phase by between approximately 45* and 135* to produce from said apparatus a sound radiation pattern which repeats only once per revolution of said planar reflecting means.

14. A rotary tremolo device comprising: a. two speakers; b. means for driving said speakers with a pair of signals derived from the same source signal but differing in phase to produce an asymmetrical sound radiation pattern having a single major lobe; and c. rotary means for effectively causing said asymmetrical sound radiation pattern to rotate about an axis at a slow speed, said sound radiation pattern repeating only once per revolution of said rotary means.