US2957054A - Transducer - Google Patents

Description

Oct. 18, 1960 s. E. LEVY EI'AL TRANSDUCER 4 Sheets-Sheet 1 Filed June 12. 1958 INVENTOR SIDNEY E. LEVY BERNARD C. SHARP W K v v n w z ATTORNEY Oct. 18, 1960 s E. LEVY EIAL 2,957,054

TRANSDUCER Filed June 12, 1958 4 Sheets-Sheet 2 ATTORNEY Oct, 18, 1960 s. E. LEVY ET'AL 2,957,054

TRANSDUCER Filed June 12, 1958 4 Sheets-Sheet 3 url! 1: I, I

INVENTOR SIDNEY E. LEVY BERNARD C. SHARP dm/fww" ATTORNEY Oct. 18, 1960 s. E. LEVY ETAL 2,957,054

TRANSDUCER 4 Sheets-Sheet 4 Filed June 12, 1958 III I III/III? IZ- i 634/ 65 III fi I, ,1 III! 57 INVENTOR 2/ SIDNEY E. LEVY BERNARD C. SHARP ATTORNEY Patented Oct. 18, 1960 time TRANSDUCER Filed June 12, 1958, Ser. No. 741,601

17 Claims. (Cl. 179115.5)

This invention relates more particularly to loudspeakers utilizing a reflex horn but is applicable to microphones also.

It is an object of this invention to provide a reflex horn speaker having high efficiency and a rugged construction.

A further and most important object is to provide a reflex horn speaker having a minimum number of separate parts for accurate control of the basic acoustical proportions.

A still further object is to provide a loudspeaker wherein acoustic ducts are fabricated with enhanced accuracy by the use of only two complementary die-formed members.

It is Well-known in the art that, to obtain high eificiency, the acoustic impedance of the air in front of the diaphragm must be matched with the mechanical impedance of the diaphragm. An impedance matching coupler consists basically of an extremely narrow air chamber next to the diaphragm in which the latter moves,

and an arrangement of air escape ducts leading from this chamber to the throat of the horn. These ducts may form part of the horn by having a taper corresponding thereto. There is a theoretical limit upon the maximum distance from any point on the diaphragm to the nearest duct opening, which is that it must not exceed one-' quarter wave length of the highest sound wave which it is desired to reproduce efiiciently. where a fairly small diaphragm is adequate for the acoustic power desired, the ducts may have the form of annular segments.

It is another object of the invention to provide a combination acoustic coupler and reflex horn member adapted to be economically die cast or molded with no intrinsic limitations on the upper frequency range. I

Other objects and features of the invention will appear when the following description is consideredin connection with the annexed drawings, in which:

Fig. 1 is a perspective view of the loudspeaker with parts broken away;

Fig. 2 is a front elevational view of the same;

Fig. 3 is a vertical sectional view of the loudspeaker taken on the line 33 of Fig. 2; p

Fig. 4 is a sectional view taken on the line 4+4 of Fig. 3;

Fig. 5 is a sectional view taken on theline 5-5 of Fig. 3.

Fig. 6 is a sectional view taken on the line 66 of Fig. 3;

Fig. 7 is a sectional view taken on the line 7-7 of Fig. 2;

Fig. 8 is an enlarged vertical sectional view of the magnetic system and diaphragm;

Fig. 9 is a front elevational view of the central portion of the outer horn member;

Fig. 10 is a sectional view taken on the line 1010 of Fig. 9;

In cases such as this;

Fig. 11 is a front elevational view of the plastic re-' Fig. 12 is a sectional view taken on the line 12--12 of Fig. 11; and,

Fig. 13 is a plan View of a chart illustrating the acoustic performance of several loudspeakers.

Referring now to Fig. 1 of the drawings, it willbe seen that the speaker comprises four main parts, exclusive of bolts, screws, terminals, and the like. These parts consist of a driver =unit generally indicated by the reference numeral 21, a diaphragm assembly generally indicated by the reference numeral 29, a mechanical acoustic body consisting of the parts identified by the reference numerals 20, 19, 18, and 60, and a reflector generally indicated by the reference numeral 56 an inner part of which extends into a central conical recess in said body and an outer part of which lies between portions of .said body to form sound ducts or traverses.

Referring to Figs. 1, 3, and 8, the driver unit 21 comprises the annular magnet 22, the magnetic core 23, the annular pole piece 24, the annular non-magnetic spacer 25 which. disposes the annular pole piece 24 in such manner that a desired annular air gap 26 is formed between it and the inner core 23.

The diaphragm assembly is shown in detail in Fig- 8 and has a generally curved acoustic driving portion 30 symmetrical about a central axis 3 1-31, an annular, generally flat rim 32, an annular step 33 at the edge of the curved portion, a cylindrical voice coil form 34 affixed'to the step, and a voice coil 35 wound on the form. The rim 32 is cemented between the various spacer washers 27, 28.

-The driver 21 is assembled into an inner compartment 49 of the mechanical acoustic body with the spacer.

Washer 28 pressed against the diaphragm assembly contacting shelf or seat 38 to make a tight acoustic seal. The arcuate portion 30 ofthe diaphragm is positioned in closely spaced relationship to the rear surface 39 of the partition 40, which is an integral part of the mechan-- ical coustic body 20, 19, etc., such partition 40 bridging the rear end of the throat 43. The air chamber 41 formed between the arcuate portion 30 of the diaphragm anclthe rear surface 39 of this partition constitutes an acoustic coupler, when used in combination with the sound ducts 42 leading through the throat 43. These ducts 42 begin as-arcuate segmented apertures in the parj tition 40, see Fig. 5. It should be noted that these apertures are so arranged as to provide no more than a predetermined spacing 44 between any point in the acoustic coupler and the edge of the nearest aperture.

These ducts 42 are formed continuously along the length of the throat 43 beyond the partition 40, by the elongated spaces formed between longitudinal ridges 45 on the body. The taper of these ducts is arranged to be similar to that of the outer part of the horn, so that they constitute a part of the horn.

The driver 21 is resiliently pressed against the shelf- 38 by the strap 46, which is retained at the ends by screws 47, which are in turn screwed into holes in bosses 48. The rear of the driver compartment 49 is covered by a cover 50, which has apertured tongues 51 on the outside for the reception of screws to fasten it to the housing, the cover also having terminals 52, and a boss 53 in the middle having a threaded cavity therein'for the reception of a screw to fasten the terminal plate 54 in place on the cover 50. The plate 54 is a small round- The tongues 51 on the cover 50 and" corresponding bosses 55 on the outside of the housing '69 plastic member.

act as stiffening members. I

Referring again to Fig. 1, the reflector 56'is illustra as a generally cup-shaped member having a coaxial cor portion 57 extending internally and rearwardly from the closed end 69 thereof, this core portion 57 being adapted to fit within the conical recess of the mechanical acoustic member. The space between the outer surface of the core portion 57 and the inner surface of the forwardly extending portion 20 of the mechanical acoustic body forms the throat 43. The external surface of this core portion 57 forms part of the boundary of the ducts. In the embodiment shown in the drawings, the ridges 45 (see Figs. 6 and 9) separating the ducts 42 are integral with the internal wall of the forwardly extending portion 20 of the mechanical acoustic body, although alternatively they may be integral with the outer wall of the reflector core portion 57, as shown in detail in Fig. 7. The inner edge of the skirt 58 of the reflector fits in the annular groove 59 formed between the outer surface of the rearwardly extending cylindrical portion of the mechanical acoustic body, such portion forming the driver unit compartment 49 and the outer skirt 60, forming therebetween two traverses of the horn. The said inner edge abuts radial ridges 59a (see Figs. 3 and 7).

The annular area between the housing skirt 60 and the reflector 57 is tapered to form part of the horn. The outer end of the horn has an annular flange for mounting purposes. The skirt 60 is joined to the portion 19 by part 18 extending substantially at right angles thereto, so that the skirt 60 and the skirt 58 form the outer traverse 16, and a second or intermediate traverse 17, which may be termed a sound duct, is formed between the skirt 58 of the reflector and the rearwardly extending portion 19. Thus, it will be seen that three distinct communicating ducts or traverses are formed within the relatively short axial dimension of the speaker.

Referring now particularly to Figs. 1, 3, 9, and 12 of the drawings, further details of the traverses and mechanical acoustic body can be seen, such as the part 61 of partition 40 bridging across the throat 43, the screw socket 62 in the central partition 40, the key portions 63 for preventing rotation of the reflector 56, and the various bosses. The key portions or abutments 63 are disposed along a diametrical portion of the throat 43. Conjugate recesses 63a are similarly disposed in the reflector core 52, as shown in Fig. 12.

At the outer end of reflector 56 is a shallow recess 65 adapted to receive an identifying escutcheon 66, which can be cemented in place.

It may be seen that the mechanical acoustic member shown in Fig. 1 constitutes a mechanical acoustic body having many functions, such as acoustic coupling chamber 41, horn throat 16, driver compartment 49, and one surface of each of a plurality of reflex horn traverses or ducts 17 and 43. The reflector 56 constitutes a coordinating member which completes the configuration of the composite duct and contains the opposite surfaces of the reflex horn traverses or ducts 16, 17, and 43.

The scientific advantages of the unitary construction are that every thousandth of an inch is calculated by fundamental principles, the dies are fabricated to an accuracy of five thousandths, and the resultant structure is reproduced with complete exactitude without danger of variation due to human errors which normally occur in such processes as spinning or hand-forming. This is borne out by the illustrative frequency characteristics, The acoustic performance which may be secured from this loudspeaker is illustrated by the chart of Fig. 13, in which the line 67 is the unretouched characteristic measured on the speaker as described herein and the line 68 is the curve taken on a previous model having many separate parts defining the acoustic passages. It thus may be seen that in actual practice the present device has better performance below 1000 c.p.s., presumably due to lack of leakage between successive portions of the acoustic chamber and horn traverses. It also has greatly enhanced response from 5000 to 12,000 c.p.s., due to greater precision in laying out and duplieating the successive portions of the sound channels.

The region between 1000 and 5000 c.p.s. averages substantially similar; in the case of the previous model the rise from 1200 to 2200 c.p.s. is no substitute for the losses at adjacent portions of the spectrum. In general, the embodiment described herein has superior low frequency performance to the speaker described in the Levy Patent No. 2,545,961, for example, since the effective horn length is greater, there being three reflex traverses as compared to two in the prior patent.

The invention has been described as embodied in a loudspeaker, though it is to be understood that the same construction is usable as a sound pickup device.

In the drawings the mechanical acoustic body is shown as being formed of metal and the reflector as being made of plastic material. It is to be understood, however, that either of these parts may be formed of either metal or plastic material.

The drawings and description are to be taken generally as illustrative rather than restrictive of the broad invention. Various changes may be made in manufacture, such as different locations of the casting parting surfaces, and the like,

In the claims the term transducer is used to indicate a sound translating device usable either as loudspeaker or microphone.

I claim:

1. In a transducer of the type described, a diaphragm with a generally curved acoustic driving portion symmetrical about a central axis, a generally flat annular rim and a voice coil concentric therewith; a driver unit having an air gap concentric with said axis; a mechanical-acoustic body having a central axis coincident with said firstnamed axis, said body including a wall perpendicular to the axis having a rearwardly facing surface generally conformant to the driving portion of the diaphragm, apertures therein, said wall having an annular portion concentric with said axis adapted to support said rim and thereby dispose the acoustic driving portion at a narrow spacing from said rearwardly facing surface whereby to define an acoustic coupling chamber, said body having an annular portion concentric with said axis extending forwardly from said wall, and having an annular portion concentric with the central axis extending rearwardly from said wall and surrounding said driver unit, and also having a flange portion extending outwardly from the rear end of the rearwardly extending annular portion, and additionally having an annular flared portion extending forwardly from the outer edge of said flange and surrounding the aforementioned portions in spaced relationship; a generally cup-shaped reflector member, having a core portion coaxial with said axis, extending internally from the closed end thereof, said core portion of said reflector fitting within and spaced from the inner surface of said forwardly extending tubular portion of the mechanicalacoustic body, whereby to form one annular duct of a reflexed horn, the inner surface of said reflector cooperating with the outer surface of said forwardly extending tubular portion and with the outer surface of said annular rearwardly extending portion of the mechanical-acoustic body whereby to form a second tapered annular duct of said reflexed horn.

2. In a transducer of the type described, the combination of a mechanical acoustic body, a driver unit, a diaphragm assembly, and a reflector, said body comprising a rearwardly-facing diaphragm seat, inner annular portions extending forwardly and rearwardly from said seat, said driver unit being enclosed within said rearwardlyextending annular portion and said diaphragm assembly being juxtaposed to said seat, said body having an .outer annular forwardly-extending tubular portion, and'said reflector having an outer annular skirt and a core extending inwardly from the middle thereof, said bore being seated within and spaced from said forwardly-extending annular portion of said body to form an annular duct arrangement, said rearwardly-extending annular portion of said body being spaced from an inner surface of-said' annular reflector skirt to form an intermediate duct and an outer surface of said annular reflector skirt being spaced from the inner surface of the annular flared outer portion of said body to form an outer annular flared duct.

3. A transducer as set forth in claim 2, wherein said body is an integral, metallic member and said reflector is an integral member formed of plastic material.

4. A transducer as set forth in claim 2, wherein said array of annular ducts comprises a plurality of annular equi-spaced ducts.

5. A transducer as set forth in claim 2, wherein each of the ducts in such array of annular ducts progressively increases in width from the area adjacent said diaphragm assembly.

6. A transducer as described in claim 2, characterized by a plurality of ribs formed on that surface of the inner portion of the mechanical-acoustic body which faces the reflector skirt for disposing the reflector in concentric spaced relationship with said inner portion.

7. A transducer as described in claim 2, characterized by means for aflixing the reflector to the mechanicalacoustic body by a single coaxially disposed screw, and interlocking abutments and recesses on said forwardlyextending inner portion and on the reflector core for preventing rotation of one member relative to the other which would otherwise tend to loosen the screw.

8. A transducer as described in claim 2, characterized by said rearwardly and forwardly-extending portions being cylindrical in cross-section, the diameter of said rearwardly-extending portion being greater than that of said forwardly-extending portion.

9. In a transducer of the type described, a one-piece integral mechanical-acoustic body having an interior rearwardly-directed diaphragm seat, an interior annular portion extending forwardly from said seat, said portion having a central recess, an interior annular portion extending rearwardly from said seat, and an exterior annular skirt spaced from said annular forwardly and rearwardly-extending portions.

10. A transducer as described in claim 9, wherein said exterior skirt is provided with a radially extending mounting flange at the outer extremity thereof.

11. A transducer as described in claim 10, wherein said diaphragm seat has a bridging partition associated therewith and disposed in front thereof.

12. In a transducer of the type described, a one-piece integral mechanical-acoustic body having an interior rearwardly-directed diaphragm seat, an interior annular portion extending forwardly from said seat, said portion having a central recess, an interior annular portion extending rearwardly from said seat, and an exterior annular portion spaced from said forwardly and rearwardlyextending annular portions; said diaphragm seat having a bridging partition associated therewith and disposed in front thereof, said bridging partition being provided with a central forwardly-extending portion having a screw socket therein.

13. In a transducer of the type described, a reflector adapted to be received within the folds of sections of a folded horn, said reflector comprising an outer annular skirt and a central core extending from the inside surface of the middle thereof, said core being substantially cylindrical in cross-section and having a cavity in the rearwardly directed end thereof, and said skirt consisting of two interconnected portions, one of which is smaller in diameter than the other.

14. In a transducer of the type described, a mechanical acoustic body having a central axis, said body comprising a tubular concentric portion constituting at least part of a horn throat, a second tubular concentric portion having a generally larger diameter than the throat, extending rearwardly from the throat and adapted to surround a driver unit, a flange portion extending outwardly from the rear end of the rearwardly-extending cylindrical portion, and a concentric annular flared portion extending forwardly from the outer edge of said flange and surrounding the aforementioned tubular portions in spaced relationship thereto.

15. In a transducer of the type described, a mechanical acoustic body having a central axis comprising a tubular concentric portion constituting at least part of a horn throat, a second tubular concentric portion having a generally larger diameter than the throat, extending rearwardly from the throat and adapted to surround a driver unit, a flange extending outwardly and forwardly from the rear end of the rearwardly extending cylindrical portion, a concentric exterior annular portion extending forwardly from the outer edge of said flange and surrounding the aforementioned portions, a generally cup-shaped reflector member, having a core portion coaxial with said first-named axis, said core portion extending internally from a closed end thereof, said core portion of said reflector fitting within and spaced from the inner surface of said throat portion of the mechanical acoustic body, whereby to complete the formation of an interior horn throat, the inner surface of said reflector cooperating with the outer surfaces of both the forwardly extending and the rearwardly extending tubular portions whereby to form a traverse of a horn acoustically contiguous with the said throat portion, and the outer surface of the reflector cooperating with the inner surface of the skirt to form another traverse of said horn acoustically contiguous with the previously mentioned traverse.

16. In a transducer of the type described, having a diaphragm with a generally curved acoustic driving portion symmetrical about a central axis, a generally flat annular rim and a voice coil concentric therewith, a magnetic system having a concentric air gap for surrounding the voice coil, a substantially cylindrical housing having a throat for conducting sound, the throat having a partition thereacross, the rear side having a central symmetrical portion curved to fit with closely spaced relationship to the acoustic driving portion of the diaphragm and defining therewith a narrow acoustic chamber, a plurality of apertures in said partition, an equal number of ridges depending from the inner surface of the throat defining thereby a plurality of slots, and a substantially cylindrical member disposed concentrically within the ridges to form a plurality of channels, the apertures communicating with the channels for conducting sound from the narrow acoustic chamber through the throat.

17. A transducer as described in claim 16, characterized by the ridges being tapered to form channels expanding in cross-section from the acoustic chamber outwards according to a predetermined relationship.

References Cited in the file of this patent UNITED STATES PATENTS 2,692,913 Kaminori Oct. 26, 1954 2,858,377 Levy Oct. 28, 1958 FOREIGN PATENTS 742,889 Great Britain Jan. 4, 1956

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