Патент USA US2127110код для вставки
Aug. 16, y 1938. 2,127,110 c. |_. FARRAND ACOUSTIC DEVICE Filed Aug. 3, 1956 2 SheeJts-Sheet 1 5 1 l. /\\\\\ „w w oL E . „ . ,of,M \\\\\\\\\\\\\\\ 5 u u. Aug. 16, 1938.4 2,127,110 c. l.. FARRAND.' ` ACOUSTIC DEVICE Filed Aug. 3, 1956 ZISheets-Sheet 2 E 3,7' 55 29 'al 52 / - ‘ INVENTOR. CLA/z2 L. “F.'AQQA/va BY4 ATTORNEY. Patented Aug. 16, 1938 2,127,110: UNITED STATES PATENT CFFICE 2,127,110 ACOUSTIC DEVICE Clair L. Farrand, Beverly Hills, Calif., assigner to United Research Corporation, Burbank, Calif., a corporation of Delaware Application August 3, 1936, Serial No. 94,072 10 Claims. This invention relates to loud speakers. It is well known in the art to allocate a part of the acoustic range of a sound reproducing apparatus toy one type of loud speaker and another 5 part or parts to another type (or other types) of loud speaker. _ . This invention relates to the type of loud (Cl. 181-31) is provided around the core 3, and receives a Supply of direct current so as to produce a con stant magnetic flux between the two separated pole pieces 4 and 6. As will be noted in Fig. 2, the adjacent outer 511 and inner edges of the pole pieces, 4 and 6, ref spectively, are undercut as at I0, leaving only a speaker useful in a so-called two-way system, wherein the acoustic range is handled by only l0 two types of loud speakers, the type of loud speaker of the present invention being particu- short length of parallel, closely adjacent,`pole faces at I|. The space thus provided between the parallel faces II of the pole pieces 4v and 6, l‘òïï l larly adapted to reproduce acoustic frequencies from about three hundred cycles to the upper limit, i. e., eight thousand cycles or higher. l5 The objects of the present invention comprise an `efficient reproduction of sound waves over a wide frequency range, with large power, and annular diaphragm I3. The diaphragm I3 is supported below its inner and outer edges by means of inner and outer concentric supporting rings I4 and |41, respectively. Upper concentric 1%? clamping rings l5 and I6 Clamp the edges 0f tho’ diaphragm upon the supporting rings I4 and I41 while attaining a substantially uniform distribu_ tion of the soundwaves, particularly of the higher 20 frequencies which have a tendency to remain in a narrow beam. The novel features of one embodiment of rthe invention will be described in the accompanying speciñcation, and particularized in the appended 25 claims in connection with the .accompanying by means of bolts I'I. A frusto-conical member I8, with a co-exten sive conical member I9, secured together and to 20 the upper surface of the inner clamping ring I5 by means o-f bolts 20 and the central bolt 5, and a casing member 2|, all concentric with the dia phragm I3, form an annular sound passage 22 leading to the central portion of the annular 25 drawings, wherein; Fig. 1 is a sectional elevational View of a loud speaker embodying the present invention. Fig. 2 is an enlarged fragmentary sectional 30 View of the annular diaphragm and the accompanying sound chamber forming parts. Fig. 3 is a front view looking toward the mouth portions of the nested horn assembly. Fig. 4 isl a plan sectional y View through the 35 throat block and is taken along the line 4-4 of Fig, 1_ Fig. 5 is 'a sectional plan view through the lower set of diaphragm clamping rings and is taken along the line 5_5 of Fig. 1. 40 Fig. 6 is a. bottom plan View of a portion of the annular diaphragm showing the connection of accommodates the voice or driving coil I2- of an diaphragm I3. The annular sound passage 22, at the tip of the conical member I9, communicates with a tubular passage 23 formed in an adapter 24. This pas Sage 23 iS CO-EXÈGDSNB With a Similar passage 25 30 formed in a throat block 26. Adapter 24 is fitted in a Counter-bored portion on the topi of the casing member 2|, and has an' annular shoulder portion 241, which is engaged by a locking nut 21 threadably secured to the cas- 35 ing member 2|. 'I‘he throat block 26 is thread-r ably scoured at 261 to thoupper portion of adapter 24. The upper portion of the throat block 26 is formed in a funnelfshape having divergíïlg flanges 28, S0 aS t0 I‘eCeíVo the thI‘OaÈ 40 DOI'ÈÍOHS Of a plurality `0f 110m SSCÈÍOHS 29`t0 44, the Voice coil thereto. Referring now to Figs. 1 and 5, the driving unit I of the loud speaker comprises a U shaped mag45 netic frame 2, having a central core 3 of magnetic material secured thereto. A circular plate 4, comprising an inner pole piece, is provided on the upper surface of the core 3, and this assembly, including the frame 2, core 3, and pole 50 piece 4, is secured together by means of a bolt 5. inclusive. A suitable cement 54 is provided to secure the throat portions of the various horns together between the flanges 28 of the throat block 26. These various‘horns‘are all identical 45 in Shape and SiZey having their IODgïtudinal aXeS` diverging from each other away from their throat portions. This arrangement of nested horn sec tions eliminates the well known directional or beam effect of the higher'frequencies by means 50 An annular plate 6, comprising an outer pole piece, is secured to the magnetic frame 2 by means of bolts '|, with its inner edge concentric with and closely adjacent to the outer edge of the 55 inner pole piece 4. An electro-magnetic coil 9 of the approximate spherical surface formed by the combined mouth opening 45 thereof. That is, in the case of a spherical source of sound, suchl as a diaphragm in the shape of a sphere, the sur face of which vibrates radially in accordance 55 2 2,127,110 with the frequency and amplitude at every point thereon, sound would be radiated through the entire frequency range, including the higher fre quencies, in all directions. In case, however, the source from which the sound is radiated consti tutes only a segmental portion of a sphere, this uniform sound radiation would still prevail through the solid angle subtending the segmental surfaces and the center of curvature thereof. 10 This condition is approximated by the nested horn assembly 29 to 44, inclusive, by angularly disposing the longitudinal axes thereof so as to form at their combined mouth opening a spheri cal segment from which the sound is radiated 15 into the atmosphere. It will thus be seen that the individual sound waves propagated in the various horns will have exactly the same charac teristics and will be so timed that they will unite at the combined mouth opening to form a spheri 20 cal wave front. The combined throat opening 46 of the various horns 29 to 44, inclusive, is also in the shape of a spherical segment. Preferably, the height of the segmental surface thus formed, as indicated by the dimension “A”. between the single throat opening of the center horn 43 and the chordal line passing through the throat por tions of the outer horns 29 and 35 (Fig. l) is of the order of one-quarter wave-length of the high est frequency sound to be reproduced so as to 3.01 prevent distortion and/ or cancellation of a nearly `planar wave front on entering the combined throat opening 46 and emerging from the com bined mouth opening 45. It will be seen, there fore, that since all of the horns are of the same 3.5'. length, intersection “B” of the longitudinal axes of the horns also forms the center of curvature for both the combined throat openings 46 and the combined mouth openings 45. As will be seen in Fig. 3, the combined throat portion as indicated by the dotted line 461 is rectangular in shape and opens into the sound passage 25 of the throat block 26, which is of the same rectangular shape and size in cross-section at its upper end (Fig. 4). The passage 25 and 45.. the co-extensive passage 23 in the adapter 24 gradually change in cross-sectional shape until they assume a substantially circular cross-sec ticular auditorium or theatre in which the loud speaker is to be placed. The length and rate of taper of the various horns is determined by the lowest frequency sound to be reproduced and are preferably such that the smallest dimension of the combined mouth opening of the various horns is on the order of one-half of the wavelength of the lowest frequency to be radiated. Referring to Fig. 2 it will be noted that the annular diaphragm I3, which in the present case 10 is constructed of Duralumin on the order of .002 inch in thickness, comprises, in radial cross-sec tion, an annular trough 46, with relatively smaller annular corrugations 41 and 48 on either side thereof. These corrugations 41 and 48 in 15 crease the flexibility at the edge to allow the an nular trough portion 46 to be reciprocated as a rigid section by the voice coil I2. The sound chamber or sound box 49, as defined by the upper surface of the diaphragm I3 and the lower sur 20 faces Aof the ring I6 and member I8, closely fol lows the contour of the cross-sectional shape of diaphragm I3. That is,-the under surfaces ofthe ring I6 and member I8, directly above the active portion of diaphragm I3, are similar in shape to 25 the cross-sectional form of the annular trough 46 and corrugations 41 and 48. However, the curva ture of the bottom surfaces of the ring I6 and member I8, directly opposite the trough portion 46, and which extend thereinto, is slightly less 30 than that of this trough portion. The distance from the annular throat opening 55 of the annular passage 22 to the inner and outer edges of the diaphragm sound chamber 49, or in other words, to the supported edges of the 3,5 diaphragm I3, is of the order of one quarter wavelength of the highest frequency sound in tended to be reproduced. In the present case, the dimension is about 0.4 inch. Thus, there will be no undue cancellation of a sound wave of 8000 cycles generated in the chamber 49 due to the difference between the time required for a wave originating at the extreme inner or outer edge of the diaphragm I3 to enter the sound opening 55 and the time required for a corresponding wave generated at the central portion of the trough 46 of diaphragm I3 to enter the same sound opening 55. If, for example, this distance be tween the supported edges of diaphragm I3 and tion adjacent the tip of the plug I6. Preferably, the annular passage 22, tubular _passages 23 and 25, and the passages forming the various individual horns 29 to 44, inclusive, the opening 55 were as great as one-half the have an exponential rate of taper or exponential rate of cross-sectional increase along the lengths thereof, increasing from the throat to the mouth tended to be reproduced, a wave originating at the furthermost point in the chamber 49 would be 180° out of phase with a wave originating at 55. portions thereof, this rate being the same throughout. The size of these various passages a point directly opposite the opening 55 and therefore the two waves would cancel each other. Referring to Figs. 2 and 6, the Voice coil I2 is secured to the central portion of the annular is determined by the upper and lower frequency limits. For example, the size of the throat open ing of the annular passage 22, adjacent the dia: 60 phragm I3, is determined by the amount of air velocity change between the diaphragm chamber and the annular passage 22. The limiting factor in making the throat of passage 22 as small as possible is the frictional resistance of the air with 65 the walls of passage 22 when moving at the in creased velocity and `the harmonic distortion which results when the instantaneous pressures depart too far from atmospheric pressure. The 4,0 wavelength of the highest frequency sound in tro-ugh 46, directly below the annular sound pas sage 22. This construction allows »the driving force, i. e., the coil I2, to be directly in the center of the plunger portion, i. e.. the trough 46 of dia phragm I3, and also directly in line with the exit of sound through the passage 22. .As will be noted in Figs. 2 and 6, the drivingl or Voice coil I2 is secured to the central portion of diaphragm I3 by means of a cylindrical support 56 of card board or the like material around which coil I2 number of horns is determined by the solid angle through which the sound, particularly of the higher frequencies, is to be distributed. In the present case (Fig. 3), the horns are arranged in is wound. One edge of theV support 56 is serrated with alternate serrations 51 and 58, etc., extend 70 ñve Vertical rows with three horns in each row. the under surface of the annular trough portion 45. Vents 59 (Figs. 2 and 5) in the form of a plu 7.5 This particular arrangement of horns, however, may be varied to suit the conditions of the par ing on the same side, horizontally, to form a base which may be cemented or otherwise secured to 3 2,127,110 rality of holes arranged in a concentric path about the diaphragm I3 are provided in the inner l pole piece 4 to communicate the inner back the inlets of the outside horns, to the inlets of the center horns, and the distance from the edges of the annular diaphragm to the sound exit open chamber 6‘0, formed between the back surface of diaphragm I3, pole piece 4 and ring I4, with the outer atmosphere. A second series of vents in the form of radial slots 6I, provided in the dia ing of said sound box portion being of the order ' phragm supporting ring M1, communicate the 5. An acoustic device in accordance with claim 4 in which the back of said diaphragm is con nected with the open air through a plurality of 10 outer back chamber 62, formed by the back sur face of diaphragm I3, outer pole piece 6 and ring M1, with the outer atmosphere. These two series of one-quarter wavelength of the highest fre quency to be produced, and means for driving said diaphragm. vents. of vents thus >assist the very narrow spaces be tween the voice coil I2 and the adjacent inner 6. An acoustic device in accordance with claim 4 in which said last mentioned means comprises and outer edges II of the pole pieces 6 and 4', respectively, in relieving the damping eiî'ect on the diaphragm due to the practically enclosed back chambers 60 and 62. I claim: 1. An acoustic device comprising an .annular a voice coil attached to the center of the convex side of said diaphragm, said attachment compris ing a serrated medium uniformly distributed on said diaphragm about the line of attachment to said coil. ' . 7. A sound reproducer comprising an annular diaphragm having a central annular curved 20 diaphragm having a single annular trough thereY 20 trough body portion, a casing forming a sound in, a housing forming a sound box for said dia phragm, said sound box having a sound exit box for said diaphragm, and means for mounting opening therein at the center of and within the said diaphragm, said body portion being sup ported by said mounting means by flexible in trough portion of said diaphragm, and means at tegral inner and outer circumferential corrugated 25 tached to the convex side of said trough for actu 25 portions concentric with said diaphragm. ating said diaphragm. 8. A sound reproducer in accordance with claim 2. An acoustic device in accordance with claim 1 in which said last mentioned means comprises "7 wherein the corrugations of said corrugated portions are small in comparison with said curved a driving coil connected to said diaphragm di 30 rectly opposite said sound ein't opening in said i housing. 3. An acoustic device in accordance with claim 1 in which said housing forming said sound box has a convex portion thereof extending into» said 35 sound box and into the concave trough portion of said diaphragm and conforming to the outline of said trough. l 4. An acoustic device comprising a sound pro ducing unit having an annular diaphragm, iiex 40 ible corrugations at the edges thereof, a casing forming a sound box for supporting the edges of said diaphragm, said sound box having a sound exit opening therein, a common throat portion for said sound box, a plurality of horns connected to said throat portion, the inlets of said horns 45 being arranged .along an arc concentric with the arc along which the outlets of said horns are arranged, the distance from the chord connecting trough body portion. 30 9. A sound reproducer in accordance with claim 7 in which said sound box casing has a convex portion thereof extending into and conforming to the curvature of the annular curved trough body portion of said diaphragm and also con 35 forming to the curvature of said corrugated por tions. 10. An acoustic device comprising an annular diaphragm having a central annular curved trough portion with corrugated flexible inner and 40 outer portions, a casing forming a sound box surrounding said diaphragm, said casing having a convex portion thereof extending into and con forming to the trough body portion of said dia phragm, and a driving coil mounted along the 45 central portion and on the convex side of the trough body portion of said diaphragm. CLAIR L. FARRAND.