US2890760A - Transducers - Google Patents

Description

L. J. BOBB TRANSDUCERS June 16, 1959 2 Sheets-Sheet 1 Filed Aug 16, 1956 NEE IN V EN TOR. a am A 5055 muwr L. J. BOBB TRANSDUCERS June 16, 1959 2 Sheets-Sheet 2 Filed Aug. 16, 1956 INVENTOR. [10/0 4/ 19055 United States Patent() TRANSDUCERS Lloyd J. Bobb, Glenside, Pa., assignor to Philco Corporation, Philadelphia, Pa., a corporation of Pennsylvania Application August 16, 1956, Serial No. 604,377

2 Claims. (Cl. 181-31) This disclosure has to do with the art of reproducing sound, such as music and speech. It relates particularly to loud-speakers such as those of broadcast receivers, phonographs, and the like, for carrying reproduced speech or music, by direct acoustical transmission, to a number of persons, constituting an audience. More specifically, the invention is concerned with a diaphragm of novel, characteristic form, in or for a dynamic speaker.

Heretofore dynamic speakers generally had diaphragms of conical shape with circular base, although sporadically, speakers of modified forms were used or proposed. The modified shapes included cones of oval base, pyramids, etc., which were considered for a variety of reasons, including for instance the idea that the working area or vibrating portion of a cone could be increased by integral reinforcement features. However, matters such as the provision of a large area for direct radiation are only some of the many and complex elements of eflicient speaker performance; and the overall performance was not greatly improved by the prior constructions modifying the circular cone, or was sometimes even impaired thereby.

It is known that in the lower octaves of acoustical work the conical speaker of circular base is generally adequate and that the problem in the higher octaves is complicated by narrowness of directive pattern, rather than insufliciency of radiating area. For this reason much consideration was given to designs wherein conventional dynamic speakers with circular cones Were combined with special horn structures or bafile structures, having long and narrow mouth sections; and when broad diffusion over a large horizontal area was desired the narrow and elon gated mouth section was vertically arranged. The narrowness of such a section caused improved average dilfusion of high frequency sound, transversely of the slot, while the elongation of the slot was relied on to insure adequate average emission of medium and low frequency sound. However, the acoustical power output of a speaker, provided by a given number of watts or fractional watts of electrical power input, was greatly reduced, mainly in the low and medium frequencies, by the acoustical resistance of the air confined between the wide, vibrating diaphragm and the narrowly apertured bafile or horn. In addition the ever-present dangers of sound distortion were increased as the baffles or horns, the material thereof and the air enclosed thereby introduced new disturbing possibilities of specific resonance, damping and the like; the speaker diaphragm no longer radiated the sound directly to the audience.

It is now usual to combine two or more speakers of different type, for instance so-called woofers and tweeters, whenever it is desired to reproduce sound with low distortion for any audience. However, the provision and matching of such speakers is not only expensive and space-consuming but is also conducive to further acoustical difficulties. For instance the cost and space requirements are approximately doubled whentwo speakersare 2,890,760 Patented June 16, 1959 used, one as a so-called woofer and one as a so-called tweeter; and in addition it becomes necessary to arrange for a so-called cutting off and matching of frequency response characteristics of the two speakers, incident to which irregularities of response curves of the two speak ers may be intensified in that portion of the complete frequency range where the one curve tapers off and the other rises.

It has occurred to me, and accordingly forms an object of my present invention, to construct a single-source, direct-radiating, high-fidelity sound generator; that is, a speaker which not only provides adequate emission of all sound, including that of low frequency and broad diffusion of all sound, including that of high frequency, but also avoids such troubles as those caused either by in-' direct radiation through a partially enclosed air space or by the cost, space and matching problems of speaker sys-' tems with more than one kind of speaker. The new type of speaker basically involves the use of a single motordriven loud-speaker diaphragm having a novel and characteristic, elongated and narrow form which resembles the form of a small boat. According to this idea, then, there may be used an outline approximating those which were usedas the forms of a mouth section in some of the previous constructions; but according to my new idea I the long and narrow outline in question defines the form taper off toward narrower ends 14. Thus the diaphragm.

of anentire direct-radiating speaker, and no structure confining a narrow air space need be used in front of the speaker.

It has actually be found that acoustical results improved over those of prior single speakers can thus be achieved; there can be used fewer parts and cheaper constructions than are required by the more complex highfidelity systems, with two or more than two types of speakers; and the performance of the new single speaker can often be at least as good as, or better than, that of the systems with two types of speakers, while being muchcheaper and simpler and more compact. In addition, the design of cabinets and the like, associated with loudspeakers, has been improved by certain applications of these devices.

The improvements of cabinet design and the like as well as the novel acoustical features of the new speaker, will now be explained in conjunction-with the drawing appended hereto, wherein Figures 1 and 2 are front and side views,'respectively, of a preferred embodiment of the new diaphragm, and Figure 3 is an enlarged section through the same, the section being taken along line 3-3 in Figure 2.

Figure 4 is a perspective exploded view of a loud-.: speaker comprising the new diaphragm, and

Figures 5 and 6 are diagrammatic sketches showing respectively a television cabinet and the rear parcel shelf of an automobile, both having typical embodiments of the body 10, having the approximate shape of a miniature boat. Usually the diaphragm has, as shown,a marginal, outwardly extending, corrugated, desirably integral collar 11.

A central portion of the diaphragm may have a small,

desirably circular neck 12, desirably extending toward the.

convex side; and this neck may be covered by an elongated dust shield 13. The diameter of the neck is somewhat smaller than the width of the adjacent parts of the diaphragm; and said width of the diaphragm is approximately uniform over a substantial, inner part of its length, but this width as well as the height of'the diaphragm may may also be compared with a two-armed, outwardly tapering trough or channel with a central header or collector.

The width of the new diaphragm is a feature of paramount importance particularly in connection with the diffusion of high frequency sound radiation. While this width may differ to a limited extent, depending upon the specific use for which a particular embodiment of the new diaphragm may be intended, the new diaphragm is always considerably narrower than any of the diaphragms which previously were used or built in forms adapted to be used for comparable purposes. Allowable variations of the width of the new diaphragm are not dictated by considerations of acoustical power, which was the controlling factor for the dimensioning of prior forms of diaphragms but by consideration such as: use of the diaphragm for the reproduction of speech or of music, and mounting of the speaker in front of a wide wall or in the corner of a room. The mentioned forms of mounting call for diffusion of the various sounds in patterns of different angularities; and the different types of sound to be reproduced involve somewhat different problems of diffusion, since the highest important frequencies, including the most important overtones, range up to about 4,000 or 5,000 cycles per second in the case of spoken sound, whereas they range considerably higher in most cases of musical reproduction. Correspondingly the width of the new diaphragm should be limited in manners which will readily be understood by persons skilled in the art in the light of the disclosure given herein. For in stance if the speaker serves to reproduce human speech only, it can often be made about two or three inches wide; if a wide range of musical sounds shall be reproduced with low distortion, it is preferable to make the speaker only about one inch wide and in some cases to mount it in a corner.

While diffusion of sound is thus benefited by narrowness of the diaphragm, it is generally undesirable to reduce the width of the diaphragm beyond certain lowermost limits, such as about three-quarters of an inch, or for practical purposes, about one inch; these values being smaller than one-half the wavelengths of the highest fundamental musical sounds and being equal to one-half the wavelengths of the most important harmonics. This relationship between width of the diaphragm and halfwavelength of the highest significant sounds emitted has been found to be controlling. Any further reduction of the width of the diaphragm would gain no further, practical advantage with respect to diffusion of sounds re quired for undistorted reproduction, whereas it would lead to new difliculties, such as specific resonance and impaired amplitude, the latter mainly in the bass register; and these phenomena can be, generally speaking, as critical and as damaging as an unsatisfactory directional pattern.

In order to insure acoustical amplitude or power, the new diaphragm has not only a positive although limited width, as just explained, but also substantial elongation. Thus it is a principal function of the elongation of the diaphragm to insure adequate air coupling-a feature which is known to be important mainly in the lower and medium ranges of spoken and musical sounds. However, important limitations are again encountered: the elongation of the diaphragm must not be driven to the point where the unit resembles a string or the like, having a preferred frequency of its own and disturbing the frequency response of the unit. Practically, I found it most advantageous to provide the diaphragms of this invention with a length of about five to seven times the aforesaid width, preferably using a length to Width ratio or aspect ratio of about 7:1 for the narrowest diaphragms of about one inch width, and aspect ratios ranging between 5:1 and 7:1 for the wider diaphragms, of about two to three inches in width. Thus a radiating area of about seven square inches is provided in the case of a diaphragm of one inch width, and either proportionately or almost 4 proportionately more in the case of the relatively wider diaphragms. Of course a plurality of the new diaphragms can be used together, with proper precautions of generally known kind; and such a combination can be and is considered as basically a single source of sound, it being unnecessary to combine different variants of the new diaphragm, such as woofers and tweeters. The combining, if any, of several units of the new speaker will usually be limited to the building up of greater acoustical power.

The height of the diaphragm, measured between the collar 11 and neck 12, is desirably made as small as or even smaller than the aforementioned width, in order to maintain the high frequency diffusion and to avoid breaking down of the frequency response curve. Such breaking down is otherwise caused by an excessive degree of longitudinal reinforcement of the diaphragm, a reinforcement efiect being inherent in the boatshaped or troughshaped design and particularly in the use of longitudinal wall sections as part of this design.

The volume and other characteristics of sound emitted by the new diaphragm are as satisfactory as those of a circular conical diaphragm of equal area, whereas the direcive patterns are widened and the frequency response obtained in the outer portion of the sound radiation area is improved. The improvements are substantial and they can be attributed entirely to the combined features of a diaphragm width absolutely limited to the range from about one to about three inches and a diaphragm length limited to the range of about five to about seven times this width. The improvements are independent of the diaphragm material, the electrical power source and other similar factors: these can be the same as in ordinary dynamic speaker cones.

The criticality of the combined features of aspect ratio and width is unique to the new form of diaphragm. For instance there is no such criticality of dimensions in any of the circular cone-shaped speaker diaphragms known to the art; on the contrary, any attempt to reduce their width or diameter to anything like one or three inches or a half or full wavelength of a typical high sound would make those known diaphragms entirely too small and feeble to radiate low and medium sounds so as to reach a plurality of listeners and thus to serve as loud-speakers at all. There is not even any close similarity between the performance of the present loud-speaker and that of the known, circular cone speaker with a narrow horn or narrowly slotted bafile in front, when using identical forms and sizes for the slot in the baffle of said speaker and for the new speaker, and identical operating conditions in all other respects; there is, on the contrary, a perplexing multiplicity of differences in details of the respective performances, mainly with respect to frequence response, and of course, as mentioned, with respect to acoustical output.

It will be seen, in summary, that the invention may be defined ias comprising or including a vibratory diaphragm of long, narrow design which may be generally oval and which should have no more than about three, inches and desirably only about one inch width, having similar or smaller depth and having a length of several times the said width; the vibratory diaphragm having a continuously curved boat-like cross-sectional shape (see Figure 3), thereby avoiding the use of straight-lined and cornered portions. The use of such portions, as mentioned, would cause acoustic disadvantages because of excessive reinforcement of the vibratory diaphragm, as was the case in said prior speakers constructed with pyramid-shaped diaphragm elements.

The mounting of the new diaphragm, as shown in Figure 4, can be very simple. The peripheral part of the collar 11 may be fastened, for instance by cementing, to the corresponding part of a flange structure 15 forming part of a bridge 16, whereas the neck 12 may be flexibly secured to the center part of the bridge by a small collar 17. Centrally of this small collar, a suitable acoustical motor 18 is installed, for instance a dynamic voice coil unit, the details of which need not be explained herein since they may be conventional. The coil or equivalent part of this unit is directly or indirectly secured, in known manner, to the diaphragm neck 12. The flange may provide for mounting screws 19 or the like, for attaching the entire periphery of the loudspeaker to a panel or the like, not shown, with a resilient gasket 20 interposed between the flange structure and the panel and an acoustically transparent cover 21, such as a sheet of fabric and/or system of fret work, secured to the mouth of the speaker.

As further shown in Figure 5, the mounting panel 22 of a single loud-speaker according to this invention may constitute one of the vertical sides of the front panel of a television receiver; in other words, it may practically fill the narrow, vertical area provided in such a receiver, between the screen 23 and one side edge of the cabinet. The speaker motor can be powered by the single speaker output (not shown) of a relatively simple TV set, as usual. This construction is facilitated by the fact that the aforementioned longitudinal dimensions of a speaker according to this invention, ranging approximately between seven inches and twenty-one inches, happen to agree admirably with such vertical dimensions of direct-viewing TV receiver screens as have been found most favorable, in the development of such screens. At the same time the extreme narrowness of the new speaker, often involving only about one or two and generally not more than three inches, has the effect that no costly, lateral enlargement of the cabinet and woodwork is required. No more than one speaker is usually required, even where the standards for acoustical quality are quite high; thus the aforesaid problems, such as those of the matching of plural speakers, of different kind, are avoided by the new speaker design.

The characteristic form of the new speaker provides acoustical as well as structural advantages in a number of other instances, where sound reproducers are built into cabinets or other units which must fit limited dimensions of other equipment and which, nevertheless, must serve the acoustical needs of relatively large spaces. As one further example, Figure 6 shows a sectional view of the rear parcel shelf 24 in an automobile 25, with a speaker 16 according to the present invention installed on the underside of this shelf, the elongated diaphragm extending transversely of the car. The speaker motor is normally connected with the automotive radio set, not shown. The quality of the reception of music which may be enjoyed by the different occupants of the car,

in motion as well as at rest, is greatly improved by this design. In the present case, much of the sound emitted by the speaker reaches the listeners by reflection from the top of the car; but Whether the sound be received with or without reflex, the important point is that the entire range of frequencies is uniformly distributed to the entire space between the speaker and a number of listeners.

While only a single embodiment of the diaphragm and speaker and two types of mounting thereof have been described, it should be understood that the details of the description and illustration are not to be construed as limitative of the invention, except insofar as set forth in the following claims.

I claim:

1. In apparatus for reproducing speech and musical sound and for efliciently diffusing the reproduced sound throughout a wide listening area, a diaphragm unit comprising: a vibratory diaphragm, having the general shape of a long, narrow boat, the width thereof being no greater than about three inches, the length thereof being of the order of at least approximately five times said width, and the shape thereof being substantially smoothly curved in cross section; a diaphragm neck, formed in central position on said diaphragm, for connection to an acoustic motor; and a diaphragm collar, formed in peripheral position on said diaphragm, for connection to a structure supporting the diaphragm at one location in said wide listening area.

2. Apparatus for generating and widely diffusing audible sound, comprising: a vibratory diaphragm, having the general shape of a long, narrow boat, substantially no Wider than one-half of the shortest wavelength of said sound, the length of the vibratory diaphragm being of the order of at least approximately five times the width thereof, and the shape of the vibratory diaphragm being substantially smoothly curved in cross section; a diaphragm neck and acoustic motor structure, connected to a central portion of said vibratory diaphragm; and a. collar, formed in peripheral position on said vibratory diaphragm, for connection of the diaphragm to a support structure.

References Cited in the file of this patent UNITED STATES PATENTS 1,819,627 Staunton Aug. 18, 1931 1,930,328 Tichenor et al. Oct. 10, 1933 2,350,889 Harman June 6, 1944 2,470,620 Jackson May 17, 1949

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