WO1991016798A1

WO1991016798A1 - Audio transducer system

Info

Publication number: WO1991016798A1
Application number: PCT/US1991/002481
Authority: WO
Inventors: Paul W. Paddock; Steven R. Geist
Original assignee: Linaeum Corporation
Priority date: 1990-04-25
Filing date: 1991-04-11
Publication date: 1991-10-31
Also published as: AU7771591A

Abstract

A dual audio transducer system includes a pair of identical audio transducers (10a and 10b), each having a cone style diaphragm. Each transducer is mounted in an acoustic suspension manner at one end of a cylindrical cabinet (26) which is sealed at its opposite end. The cabinets are fixedly mounted to each other by column-like support members (42) such that the two diaphragms are disposed in proximate, axially aligned, spaced apart face-to-face relationship. The two transducers are coupled together in parallel in a common electrical circuit such that they are in phase electrically with one another. This eliminates undesirable movement and vibration due to inertial forces in a cabinet.

Description

AUDIO TRANSDUCER SYSTEM BACKGROUND OF THE INVENTION This invention generally relates to an audio transducer system. More particularly, the invention relates to an audio transducer system having plural audio transducers which cooperate with one another.

Various types of audio transducers, as exemplified by audio loudspeakers, are known in the prior art. One common form of audio transducer comprises a cone shaped diaphragm with an attached electromagnetic motor driving element. The cone diaphragm is mounted to a frame by a flexible expanse which bounds the perimeter of the cone. A wire coil located within a magnetic field responds to alternating current impulses generated by a signal source or amplifier, thereby causing the diaphragm to vibrate. This type of transducer is generally characterized by a relatively high diaphragm and coil mass, which creates high inertial forces in the diaphragm. This characteristic is most pronounced in woofer or subwoofer type transducers which are designed to provide lower frequency responses. Typically, the audio transducer is mounted in a loud speaker cabinet.

These inertial forces cause the cabinet to move and vibrate. Such movement and vibration is undesirable for two reasons. First, any movement or vibration of the cabinet represents lost energy which is unavailable to generate sound waves and therefore decreases the efficiency of the transducer. Second, the movement or vibration of the cabinet is transferred to the floor or other cabinet support surface, thereby causing the floor to act as a secondary membrane radiator which produces destructive interference effects through sound wave reinforcements and cancellations at various points within the room. The foregoing problems are most acute in woofers and subwoofers having relatively large and heavy diaphragms. Consequently, the cabinets used to mount woofers and subwoofers tend to be bulky, heavy and relatively inefficient.

SUMMARY OF THE INVENTION An object of this invention, therefore, is to provide an improved audio transducer system which overcomes the above limitations and disadvantages.

More specifically, an object of the invention is to provide an audio transducer system of improved efficiency. Another object of the invention is to provide a transducer system which reduces deleterious cabinet vibration and movement caused by vibration of the diaphragm.

Still another object of the invention is to provide an acoustically and physically balanced transducer system.

A further object of the invention is to provide a transducer system capable of radiating sound waves over 360 degrees. Yet another object of the invention is to provide a transducer system having improved performance characteristics and acoustic properties.

A further object of the invention is to provide a transducer system which provides excellent low bass performance and yet is relatively compact, light in weight and highly efficient.

To achieve these objects, an improved audio transducer system according to the present invention includes a first audio transducer having a first diaphragm, and a second audio transducer having a second diaphragm. The first and second audio transducers are supported by respective cabinets which are rigidly interconnected such that the first and second diaphragms are disposed in proximate, spaced apart, face-to-face relationship. The performance of the transducers is further improved by electrical coupling means for coupling the first and second audio transducers so that they are operated in phase electrically with one another. Other improvements relate to the characteristics of the transducers, the spacing between the two transducers, damping devices, cabinet construction, and construction for mounting the two transducers and their respective cabinets to one another to form a common unit.

These and other objects and advantages of this invention will become more fully apparent as the description which follows is read in conjunction with the accompanying drawings. DESCRIPTION OF THE DRAWINGS

Fig. 1 is a partially sectional view of a conventional cone-type audio transducer.

Fig. 2 is a perspective view of the present invention. Fig. 3 is a vertical sectional view of the present invention.

Fig. 4 is an electrical schematic in accordance with the present invention.

Fig. 5 is a partial vertical sectional view of a second embodiment of the present invention.

DETAILED DESCRIPTION Referring to Figs. 2 and 3, an audio transducer system according to the present invention includes a pair of identical audio transducers 10a, 10b which are fixedly coupled together as a common unit so as to provide a symmetrical and balanced system in which the transducers are electrically and mechanically in phase with one another. Audio transducers 10a, 10b are mirror images of one another and have respective sound producing diaphragms 14a, 14b and electromagnetic driving elements 20a, 20b.

Transducers 10a, 10b are conventional cone-style transducers of the type shown in Fig. 1, which has a cone- shaped diaphragm 14.

The present invention also includes cabinet means for supporting audio transducers 10a, 10b in an acoustic suspension manner and electrical coupling means for coupling transducers 10a, 10b in electrically in phase relationship. Transducer positioning means are provided to fixedly position transducers 10a, 10b with respect to one another such that the audio transducers and their respective diaphragms 14a, 14b are disposed in axially aligned, spaced apart, face-to-face relationship with an air space therebetween. A signal source means, such as an amplifier 18, is provided to generate alternating current impulses proportional to audio signals, which impulses shift polarity between 20 and 20,000 times per second. The electrical coupling means supplies the current impulses generated by amplifier 18 to transducers 10a, 10b.

More specifically, in the illustrated embodiment of the present invention, audio transducers 10a, 10b are identical high mass, high compliance audio transducers designed to provide a low resonant frequency in a cabinet means of desired volume. The transducers have good extended low bass performance, a diaphragm diameter of 8 inches, and a maximum excursion limit of 0.75 inch. For reasons apparent below, audio transducers 10a, 10b preferably are identical so that they have the same acoustic and physical characteristics, and are true mirror images of one another. For example, transducers 10a and 10b have the same mass, shape, size and maximum excursion. Transducers 10a, 10b are supported by respective cabinets or enclosures 22a, 22b. Cabinets 22a, 22b each have an identical construction and form part of the cabinet means. Each cabinet 22a, 22b includes a cylindrical member 26 which is constructed from a thirty- four inch long section of polyvinyl chloride (PVC) pipe having a diameter of eight inches and a wall thickness of 1/4 inch. The cabinet has a volume of 1600 cubic inches. The rigidity of the PVC material and cylindrical construction serve to minimize wasted energy, undesirable distortions and extraneous frequency responses caused by cabinet walls which otherwise might flex and vibrate. It will be appreciated that other known cabinet configurations and materials which limit cabinet wall flexure and attendant acoustic loss also will work well. For example, transducers 10a, 10b could easily be mounted in a square cabinet. Each transducer and cabinet combination serves a loud speaker.

Each cylindrical member 26 has a diameter comparable to that of the audio transducer and therefore is suited to receive and mount one of the audio transducers at one end thereof. An internal annular shoulder 30 is provided at such end to seat the audio transducer which is fixedly, but removably mounted in place by fastening screws 34 threaded into either shoulder 30 or an end face of member 26. The opposite end of member 26 is sealed by an end cap or plug 38, which is glued in place to provide an air-tight seal.

As so constructed, cylindrical member 26 is sealed at one end by plug 38 and at its opposite end by audio transducer 10a or 10b, with an internal cavity or chamber defined therebetween. In this sealed cabinet construction, the audio transducer is supported in an acoustic-suspension manner whereby movement of the diaphragm causes the air in the internal cavity to compress or rarify, depending upon whether the movement of the diaphragm is toward or away from plug 38. Stated differently, the air inside the sealed cabinet acts as a mechanical or acoustic spring to facilitate piston-like, back-and-forth motion of the diaphragm, with minimal distortion or undesirable flexing of the diaphragm. Such acoustic suspension is particularly desirable in the case of woofers and subwoofers for which the present invention is particularly well suited, since woofers and subwoofers typically have compliant diaphragms designed for maximum excursion but prone to extraneous distortion and flexing.

A chamber damping means is provided within the internal cavity of each cabinet 22a, 22b to dampen any standing wave reflection which otherwise might be encountered in a long, narrow cabinet enclosure. The damping means includes sections of fiberglass building insulation 40 (R16 or 19) , which are loosely packed in layers to completely fill the cabinet's internal cavity. A screen 41 separates fiberglass insulation 40 from the audio transducer. Other known damping materials, such as polyester fluff, felt, long fiber wool and acoustic foam, and known methods for damping standing waves also will work well.

Referring still to Figs. 2 and 3, the transducer positioning means preferably includes a plurality of rigid column-like support members or spacer bars 42, which rigidly mount and interconnect cabinet 22a to cabinet 22b such that diaphragm 14a and diaphragm 14b are disposed in proximate spaced-apart, axially-aligned, face-to-face relationship with respect to each other. Four support members 42 are equally spaced around the central circumference of the stacked transducer arrangement. Each support member 42 is fastened at one end by suitable fastening means 44a to cabinet 22a and at its opposite end by suitable fastening means 44b to cabinet 22b. Support members 42 are made of metal or comparable material to provide a rigid interconnection between cabinets 22a and 22b, and have sufficient strength to support the upper cabinet when disposed in an upright "stacked" position on a floor F (Fig. 3) . The support members are sufficiently thin to provide a spacious, largely unobstructed central air space between the pair of face-to-face audio transducers, thereby permitting sound waves emanating from such central air space to travel unencumbered radially outwardly in a 360 degree arc.

The close proximity of diaphragm 14a to diaphragm 14b is important. It is preferable to make the spacing between the two diaphragms as close as possible, leaving just enough room to allow for maximum diaphragm excursion. For example, in the case of transducers having a maximum excursion limit of 0.75 inch, the optimum spacing between the diaphragms is approximately equal to the sum of the maximum excursions of each diaphragm, or about 1-1/2 inches. As so spaced, in normal operation diaphragms 14a and 14b will rarely, if ever, contact one another. The closest feasible spacing optimizes the operating efficiency of the system at the lowest frequencies in the range of about 20 to 30 Hertz. However, for reasons apparent below, improved efficiency also can be attained at greater spacings which preferably are no greater than the maximum transverse dimension (i.e., diameter) of the diaphragms. In the case of cone style diaphragms having a diameter of 8 inches, the maximum spacing necessary for at least some level of improved efficiency is believed to be no greater than about 8 inches. Notably, however, it will be apparent from the theory of operation discussion below, that the preferred range of spacings available to improve the efficiency of tandem face-to-face transducers having various parameters and properties can be readily determined empirically by experimentation. Furthermore, the advantages associated with a mechanically balanced system can be obtained regardless of the spacing between the diaphragms.

As shown in Fig. 4, the electrical coupling means preferably includes a common electrical circuit 50 having leads 51a, 51b, in which audio transducers 10a, 10b are coupled together to operate in electrical parallel with amplifier 18. The audio transducers are in phase electrically and, therefore, simultaneously receive the same alternating current impulses generated by amplifier 18.

In an alternate embodiment shown in Fig. 5, a central damping means is provided between diaphragms 14a and 14b to dampen extraneous frequency responses, especially higher frequency irregularities, caused by sound waves bouncing between the diaphragms. The central damping means preferably includes a damping disc 46 made of high-density fiberglass (preferably about 6 to 8 pounds per cubic foot), felt, or other suitable material. Damping disc 46 is supported by wires 52 or other suitable fastening means attached at one end to disc 46 and at their other end to respective support members 42. A damping disc 46 having a thickness of about one-half to one inch and a diameter of about 3 inches works well when positioned centrally between 8-inch cone-style woofers to absorb energy in the upper frequency regions above the useful range of the woofers. Of course, disc 46 can have various sizes and shapes depending upon the acoustic properties of the material. Disc 46 does not interfere with the vibrating motion of diaphragms 14a, 14b because it is axially aligned with recessed portions of the diaphragms where the spacing or gap between the diaphragms is relatively large. OPERATION AND THEORY

It will be apparent from the foregoing that the present invention provides a balanced self-actively loaded, dual transducer system in which both transducers are in phase electrically and mechanically, and operate in mirror image fashion. In response to signals from amplifier 18, diaphragms 14a, 14b move simultaneously either toward or away from each other. Moreover, the diaphragms travel toward and away from each other the same amount with respect to a neutral "at rest" reference base line.

The dual transducer system provides a near- perfect mechanical balance which virtually eliminates deleterious cabinet movement and vibration. One diaphragm's electromagnetically-induced inertia causes forces to be exerted on its supporting cabinet. In the present system, such forces are offset by equal and opposite in phase forces resulting from the second diaphragms's electromagnetically-induced inertia. These offsetting forces virtually eliminate cabinet movement and vibration and the attendant energy loss accompanying same, thereby significantly improving the over all efficiency of the system. In addition, the problematic tendency of a single unbalanced transducer to excite the floor or other cabinet support surface into a secondary membrane radiator is greatly reduced, thereby virtually eliminating the resultant destructive interference effects particularly common in conventional subwoofer and woofer systems. In sum, the present system greatly reduces energy loss, destructive harmonic distortions and peaks and valleys in the response curve caused by cabinet movement and vibration or flexing of the cabinet walls. It will be apparent that a rigid connection between the opposed transducers and their cabinets is necessary to permit the forces generated by the two diaphragms to counteract and offset one another. It will also be apparent that the foregoing advantages of a mechanically balanced system are not dependent upon the spacing of the two diaphragms, but rather on a physical arrangement of the diaphragms which is mechanically balanced. Thus, for example, a pair of face-to-face loud speakers separated by one to two feet or more can still be mechanically balanced.

The present system is particularly well-suited for use in subwoofers and woofers having relatively high diaphragm/coil mass and, hence, high inertial forces. The illustrated embodiment described herein is designed for use as a subwoofer primarily in the frequency range of 20 to 120 Hertz. Woofers and subwoofers are particularly susceptible to the problems overcome by the present invention, as evidenced by the common personal experience of feeling the floor vibrate when a woofer or subwoofer is operated at a moderate to loud volume. The present system works best for frequencies below about 400 to 500 Hertz, depending upon the size of the diaphragm, because the diaphragm behaves as a point source for large sound waves. Ideally, the diameter of the diaphragm should exceed the wave length of the highest frequency produced by a factor of about two. At higher frequencies the diaphragm no longer functions as a point source, causing phase cancellations and aberrations in the response curve.

It is believed that the present system produces a net gain in efficiency of about 2 to 3 decibels when compared to a pair of identical audio transducers arranged in a different physical relationship. Such gain equates to a two-fold increase in efficiency. Some of the efficiency gain undoubtedly is attributable to the virtual elimination of extraneous cabinet motion and vibration. However, it is believed that the in phase operation of face-to-face diaphragms in close proximity to one another causes the air space therebetween to rarify and compress, depending upon whether the diaphragms are moving away from or toward one another, thereby causing the diaphragm pair to behave in combination as a larger diaphragm of greater surface area. It is theorized that the air space between the two diaphragms is excited enough to cause a more efficient coupling of acoustic power falling somewhere between conventional baffle loading and horn loading. It is possible that the two audio transducers load each other acoustically. It is also possible that the compression/rarefication effect creates a ring of excited air surrounding such air space which behaves like a large diaphragm. This would explain the present invention's ability to pressurize a very large area relative to the relative small size of the transducer diaphragms. As the spacing between the diaphragms increases, the rarefication and compression effect is expected to drop off to the point where normal efficiency is reached once the spacing between the diaphragms roughly corresponds to the magnitude of the diaphragm diameter (the benefits of reduced cabinet motion aside) . Thus, in the preferred embodiment it is expected that the rarefication and compression effect will drop off at a spacing of about 8 inches for cone style diaphragms having a maximum transverse dimension or diameter of 8 inches. The tightly coupled acoustic, physical and electrical relationship of the two transducers is believed to create a self-controlling symbiotic relationship in which the transducers strive to correct any imbalances between the two. The foregoing advantages enable the present invention to be relatively compact and light in weight, since a large cabinet mass is not necessary to offset diaphragm inertial forces, and yet behave performance- wise like a much larger transducer because of its highly efficient operation. It is estimated that a horn type enclosure would have to be several times as large and much heavier than the present system to achieve the same output and effect. These features lend themselves well to automobile loud speaker applications, although for such applications the various parameters, such as transducer type and cabinet size, would be modified using well-known criteria to suit the more compact environment of an automobile.

Although the present audio transducer system is particularly well suited to stand upright, it retains its inherent mechanical and acoustic balance regardless of its orientation. Notably, cone-style diaphragms commonly used in woofers and subwoofers tend to settle somewhat because of their large mass. The present audio transducer system, with its symmetry in all three directions, can be periodically flipped upside down to counteract any such settling of the diaphragm. It will be apparent that the present audio transducer is suited for more than just loud speaker applications including, for example, microphone applications.

Having illustrated and described the principles of the invention in a preferred embodiment, it should be apparent to those skilled in the art that the invention can be modified in arrangement and detail without departing from such principles. I claim all modifications coming within the spirit and scope of the following claims.

Claims

CLAIMS 1. An audio transducer system comprising: a first audio transducer having a first diaphragm; a second audio transducer having a second diaphragm; the first and second audio transducers being positioned with respect to one another such that the first and second diaphragms are disposed in proximate substantially face-to-face relationship; and electrical coupling means for coupling the first and second audio transducers to be in phase electrically with one another.

2. The audio transducer system of claim 1 wherein the electrical coupling means includes a common electrical circuit containing the first and second transducers together in electrical parallel.

3. The audio transducer system of claim 1 further including signal source means for generating alternating current impulses in proportion to audio signals and supplying the current impulses to the first and second audio transducers through the electrical coupling means.

4. The audio transducer system of claim 1 wherein the first and second diaphragms are disposed in axial alignment with one another and each have substantially the same maximum transverse dimension, the first and second diaphragms being spaced apart a distance substantially no greater than the maximum transverse dimension.

5. The audio transducer system of claim 4 wherein the first and second diaphragms each have a maximum excursion limit, the first and second diaphragms being spaced apart a distance about equal to the sum of the maximum excursion limits of the first and second diaphragms, whereby in normal operation the first and second diaphragms rarely if ever contact one another.

6. The audio transducer system of claim 1 wherein the first and second audio transducers have substantially the same physical and acoustic characteristics.

7. The audio transducer system of claim 1 wherein the first and second audio transducers have substantially the same mass, shape, size and maximum excursion characteristics.

8. The audio transducer system of claim 7 wherein the first and second audio transducers are each cone-type transducers having substantially the same diameter.

9. The audio transducer system of claim 8 wherein the first and second audio transducers are woofers.

10. The audio transducer system of claim 8 wherein the first and second audio transducers are subwoofers.

11. The audio transducer system of claim 1 further including cabinet means for supporting the first and second diaphragms in an acoustic suspension manner.

12. The audio transducer system of claim 11 wherein said cabinet means includes a first substantially cylindrical cabinet for supporting the first diaphragm at one end thereof and having a first plug at an opposite end thereof, and a second substantially cylindrical cabinet for supporting the second diaphragm at one end thereof and having a second plug at an opposed end thereof, the first and second cabinets having substantially equal diameters.

13. The audio transducer system of claim 11 wherein the first and second cabinets are constructed of a rigid material.

14. The audio transducer system of claim 13 wherein the first and second cabinets are constructed of a polyvinyl chloride material.

15. The audio transducer system of claim 13 wherein the first and second cabinets each define respective internal cavities, and further including chamber damping means disposed inside both the first and second cabinets to dampen sound waves in the cavities.

16. The audio transducer system of claim 15 wherein the chamber damping means includes fiberglass insulation.

17. The audio transducer system of claim 1 further including central damping means located substantially centrally between the first and second audio transducers for damping undesirable frequencies.

18. The audio transducer system of claim 17 wherein the central damping means includes a pad made of high density fiberglass material.

19. In an audio transducer system having a first audio transducer with a first diaphragm and a second audio transducer with a second diaphragm, the improvement comprising: transducer positioning means for fixedly positioning the first and second transducers such that the first and second diaphragms are disposed in proximate, substantially face-to-face relationship with respect to one another; and electrical coupling means for coupling the first and second audio transducers to be in phase electrically with one another.

20. An audio transducer comprising: a first audio transducer having a first diaphragm supported in an acoustic suspension manner by a first cabinet; a second audio transducer having a second diaphragm supported in an acoustic suspension manner by a second cabinet; transducer positioning means for fixedly positioning the first and second audio transducers with respect to one another such that the first and second diaphragms are disposed in proximate, spaced apart face- to-face relationship; and electrical coupling means for coupling the first and second audio transducers to be in phase electrically with one another.

21. The audio transducer system of claim 20 wherein the electrical coupling means includes a common electrical circuit containing the first and second audio transducers together in electrical parallel.

22. The audio transducer system of claim 20 wherein the first and second diaphragms are disposed in axial alignment with one another and each have substantially the same maximum transverse dimension, the first and second diaphragms being spaced apart a distance substantially no greater than the maximum transverse dimension.

23. The audio transducer system of claim 22 wherein the first and second diaphragms each have maximum excursion limits, the first and second diaphragms being spaced apart a distance about equal to the sum of the maximum excursion limits of the first and second diaphragms, whereby in normal operation the first and second diaphragms rarely if ever contact one another.

24. The audio transducer system of claim 20 wherein the first and second audio transducers have substantially the same physical and acoustic characteristics.

25. The audio transducer system of claim 20 wherein the first and second audio transducers are each cone-type transducers having the substantially the same diameter.

26. The audio transducer system of claim 20 wherein the first and second audio transducers are woofers.

27. The audio transducer system of claim 20 wherein the first and second cabinets are each substantially cylindrical, each support one of the first and second audio transducers respectively at one end thereof and each are sealed at an opposite end thereof, the first and second cabinets having substantially equal diameters.

28. The audio transducer system of claim 20 wherein the first and second cabinets each define respective internal cavities, and further including chamber damping means disposed inside both the first and second cabinets to dampen sound waves in the cavities.

29. The audio transducer system of claim 20 wherein the transducer positioning means includes a plurality of column-like members sufficiently thin so as to provide a spacious opening between the first and second audio transducers to permit sound waves to travel radially outwardly therefrom.

30. The audio transducer system of claim 20 wherein the first and second audio transducers each comprise a cone-style transducer.

31. An audio transducer system comprising: a substantially cylindrical first cabinet; a first audio transducer having a first cone style diaphragm supported in an acoustic suspension manner by the first cabinet; a substantially cylindrical second cabinet; a second audio transducer having a second cone style diaphragm supported in an acoustic suspension manner by the second cabinet; transducer positioning means for fixedly positioning the first and second transducers with respect to one another such that the first and second cabinets are substantially axially aligned with one another, and such that the first and second diaphragms are positioned in proximate, spaced apart face-to-face relationship with respect to one another; the first and second diaphragms having substantially the same size, shape, mass, and maximum excursion limits; the first and second diaphragms being spaced apart a distance about equal to the sum of the maximum excursion limits of the first and second diaphragms such that, in normal operation, the first and second diaphragms rarely, if ever, contact one another; and electrical coupling means for coupling the first and second transducers together such that they are in phase electrically with one another.

32. The audio transducer system of claim 31 wherein the electrical coupling means includes a common electrical circuit containing the first and second transducers together in electrical parallel.

33. The audio transducer system of claim 32 further including signal source means for generating alternating current impulses in proportion to audio signals and supplying the current impulses to the first and second audio transducers through the electrical coupling means.

34. The audio transducer system of claim 31 wherein the transducer positioning means includes a plurality of column-like members sufficiently thin so as to provide a spacious opening between the first and second audio transducers to permit sound waves to travel radially outwardly therefrom.

35. An audio transducer system comprising: a first cone style audio transducer having a first diaphragm; a first cabinet which supports the first audio transducer in an acoustic suspension manner; a second cone style audio transducer having a second diaphragm; a second cabinet which supports the second audio transducer in an acoustic suspension manner; electrical coupling means for coupling the first and second audio transducers in electrically in phase relationship, whereby the first and second diaphragms are stimulated in synchronous fashion to move toward and away from one another in mirror fashion; and transducer positioning means for rigidly positioning the first and second transducers with respect to one another such that the first and second diaphragms are disposed in substantially axially aligned, spaced apart face-to-face relationship with respect to one another with an air space therebetween, the first and second diaphragms being spaced sufficiently close such that movement of the diaphragms toward and away from each other causes rarefaction and compression of the air space and yet not so close as to contact one another.