Патент USA US2411004код для вставки
.Nw12,1946- ‘ _ A. A... SAW. 2,411,004 SOUND AMPLIFYING APPARATUS I Filled Sept. 1, 1945 2 Sheets-Sheet 1 4 M ' 7.\L A INVENTOR. I ' ' ?ri/zur I Jazz/a! FL4. _. - ' - BY ‘j‘ INov. ~12,. 1946. A. J.‘ SANIIAL 2,411,004 SOUND AMPLIFYING APPARATUS Filed Sept. 1, 1945 2 Sheets-Sheet 2' .724 ZZZ-2' INVEN TOR. BY ?riitur .I Sauz'al W Patented Nov. 12, 1946 2,411,004 UNITED STATES PATENT OFFICE 2,411,004 SOUND AMPLIFYING APPARATUS Arthur J. Sanial, Flushing, N. Y. Application September 1, 1943, Serial No. 500,785 13 Claims. 1 (01. 179——1) 2 . This invention relates to sound amplifying apparatus, more particularly to electronically trating the sound focusing operation of the unit; powered sound amplifying apparatus embodying both microphone and loudspeaker units. Fig. 5 is a schematic view of the electrical cir cuit of the embodiment of Fig. 1. In accordance with the illustrative embodiment of the invention, the electronic megaphone unit and, Objectsand. advantages of the invention will be set forth in part hereinafter and in part will be obvious herefrom, or may be learned by practice with the invention, the same being re alized and attained by means of the instrumentali ties and combinations pointed out in the ap 10 pended claims. The invention consists in the novel parts, con~ is made up of a microphone and a loudspeaker, each of special type, positioned in de?nite, and preferably ?xed, spatial relationship and inter connected by an ampli?er. The microphone has both sides of its dia phragm, or other sound wave sensitive element, open to the atmosphere, at least to the extent that sound waves will have access to both back and front. Thus, sounds directed at it from a structions, arrangements, combinations and im» provements herein shown and described. The accompanying drawings, referred to herein distance will travel’ substantially along paths and constituting a part hereof, illustrate one of almost the same length from the source to the embodiment ‘of the invention, and together with front and back of the diaphragm, so that they the description, serve to explain the principles will have a comparatively small vibrating effect. of the invention. On the other hand, however, sounds directed at .20 An object of this invention is to provide an the front of the diaphragm from a source close electronic megaphone unit with which sounds thereto will not be subject to this cancelling effect delivered to the input will issue from the output due to the large difference in path length of the in greatly ampli?ed volume. sound from the sound source to front and back Another object of this invention is to provide 25 of the diaphragm, respectively. nev»7 and improved electronic sound-amplifying The loudspeaker is of such construction that apparatus which is compact and portable so that the sounds emanating therefrom will be con it can readily be carried by an individual and with which the ampli?ed sounds can be readily verged and directed thereby toward a region on the central axis in front of the horn. Project directed where desired. 30 ing the sound to a region in space a distance Another object of this invention is to provide in front of the horn actually creates what may be a combination microphone and loudspeaker unit thought of as a virtual source of the radiated of which the microphone and loudspeaker are in sound. This gives the effect of a longer horn than close physical relationship and which when held the physical length of that actually used. The close to a person’s mouth, but not touching, will source of sound is thus removed farther from the amplify the voice to a very great volume without microphone so that the acoustic feedback tend acoustic feedback. ency is reduced. Even though the sound ulti Another object of this invention is to provide mately diverges beyond the focal region, the a combination microphone and loudspeaker unit degree of divergence is much less from this device which will be free of undesirable energy transfer than from a conventional horn exit. Hence, either by electrical, acoustical or mechanical even such sound as does diffuse backwards from means between the loudspeaker and‘ the micro beyond the focal region is largely attenuated in phone, when they are interconnected by means the distance it must travel back to the micro of an ampli?er. Of the drawings: Fig. 1 is a view in side elevation of an electro— acoustic megaphone unit and its ampli?er con stituting a typical and illustrative embodiment of this invention; Fig. 2 is a sectional view in elevation of the megaphone unit of Fig. 1; Fig. 3 is a view in end elevation of the mega~ phone location and is of substantially no conse 45 quence at the microphone because of the cancel lation effect arising from both sides of the micro phone diaphragm being open to the atmosphere. A spatial relationship of the microphone and loudspeaker is established such that the micro phone is centered on, and is normal to the cen tral acoustic axis of such sound waves as may radiate backward from the loudspeaker mouth. This is not necessarily the geometric central axis, so that the microphone is located by trial in this megaphone unit of Fig. 1 schematically illus~ 55 null position when ?rst mounted, or the mount phone unit of Fig. 2, as viewed from the left; Fig. 4 is a somewhat diagrammatic view of the 2,411,004 3 4 ing is provided with means to permit it to be adjusted to the null position when in use. The microphone and loudspeaker may be sepa rately supported having regard to the require ment of the null position of the microphone. at its outer end substantially in the plane of the outer periphery of the bell 4. The annular passageway which the plug forms with the members 3 and 4 comprises front and Preferably, however, suitable means are provided convenience are sometimes hereinafter referred for incorporating them in a single unit which may also incorporate the ampli?er if so desired. to as the annular passageways 3! and 32 re Suitable provision for reducing mechanical vi rear sections 32 and 3! respectively, which for spectively. , The annular passageway 3! .may follow any ‘oration impressed by one upon the other or upon 10 desired rate of ‘acoustic expansion. The pas sageway 3| serves to conduct the sound waves either or all from external sources is preferably ‘issuing from the horn 2 angularly outwardly made in the form of cushioning devices of resil therefrom in a con?ned path to the junction at lent material located at the most advantageous P with the‘annular passageway 32. Thus, in the points of support. Similarly the various electri- ~ initial portion of their travel through the outer cal circuits that are above ground potential are horn, the sound waves are carried radially out grounded and dissimilarly polarized, to prevent wardly from'as well as along the central axis regeneration and electrical feedback. A—,A of the assembly. It will be understood that the foregoing gen The annular passageway 32 diverges from its eral description and the following detailed'de junction at P with the passageway 3! to the scription as well are exemplary and explanatory outer periphery of the bell '4 so as to provide but are not restrictive of the invention. an expanding passageway from which the sound Referring now more particularly to the ac waves issue in the form of annular rings travel companying drawings, there is provided as is ling in the forward direction. This annular pas best shown in Fig. 2 a conventional loudspeaker sageway is of uniform width at any plane normal driver unit 5 of any suitable type, to which is connected an intermediate or inner baffle mem ber or horn 2, of any suitable type which may be straight, folded or re-entrant, the latter termi nated by a second or outer horn of novel type comprising ba?le members 3, 1i and 5, for the so purpose of providing a focusing effect for the radiated sound. It is not intended to con?ne the rate of ex to the central axis A—A, the rate of expansion being uniform, exponential or at such other rate as may be most suitable to the purpose. It will be understood in this regard that the ‘rate of expansion of the air column so chosen may have different values in different portions of the horn as a whole, this being governed by theacoustical design requirements of the particular type of frequency characteristic. pansion through the inner horn 2 to ‘any speci?c The minimum diameter of baffle member 3 formula. On the contrary, the rate may be in where it joins baffle member 45 is substantially accordance with any conventional design for equal to the maximum diameter or" member 4 mula familiar to one skilled in the art. However, where it is exposed to the atmosphere, that is, a speci?c con?guration of the second or outer the open end. in this manner the diameter of horn should preferably be adhered to from the the annular ring section of the air column in the point where it joins the inner horn. For pur plane of the greatest diameter of plug 5 can be poses of illustration in Fig. 1 the inner horn 2 is made as large as the maximum limiting diameter shown as of the straight horn, tubular extension of the structure as awhole will permit. In addi type, which expands uniformly at a chosen rate tion, the actual width of the annular ring section along the center axis A--A. The outer or terminal horn is attached to " that results is as small as can be obtained at this maximum diameter for a given expansion rate of the end of the inner horn 2 in the following the air column. Each element of the thin annu manner. The external portion of the terminal lar ring of sound at the opening, P, can be then horn comprises a ba?le member 3, preferably considered as a small source of sound originating frusto-conical, the small end of which is sealed , at the small end of the expanding air column to the terminal periphery of inner horn 2. At formed by the outer section of plug 5, and the the large end of member 3, a second ba?le mem bell 4. ber ‘01' bell it, preferably frusto-conical in con As the acoustic axis, indicated by the dash-dot tour, is secured and sealed in the same manner. lines in Figs. 2 and 4, of any section of the an The internal portion of the terminal horn com nular horn formed by these members is directed prises a plug baffle member 5 forming an annu- ’ toward the central axis A-—~A. of the assembly as lar expansion passageway with the ba?ie mem a whole and substantially to the same region R, bers 3 and d serving to direct and focus the Fig. 4, because of symmetry, the greater portion sound issuing from the terminal horn at a focal of the sound emanating from the horn is thus point R, Fig. 4, in front of and on, or substan 60 focused in a manner similar to that occurring tially on, the central axis A—A of the assembly. with light in an optical lens system. ' The plug 5 may be solid, but as here preferably It is recognized that due to thev relatively wide embodied, is of hollow construction and tapers frequency spectrum embraced in‘ acoustic sounds from a locus of maximum diameter and circular that the focusing point B will not be exactly'the contour intermediate its ends, in either direction 65 same for all frequencies. However, the converg to its endsso as to form front and back tapered ing effect is present over the entire band of im surface portions having a common axis of sym portant speech frequencies as contrasted to the metry, The plug is nested in the space formed more diverging pattern present with conventional by the ba?ie members 3 and 6., being supported types of loudspeaker horns. ‘therefrom in annularly spaced relation thereto, 70 It is apparent thatyif the amount of sound as‘by means of studs 30, coaxially with the center radiating backwards from the region in front of axis A-A of the assembly. > The plug is suitably the loudspeaker is reduced to a low value, less dimensioned'in length so as to‘terminate at its energy will be available to cause acoustic feed‘ inner end substantially in the plane of the ter back between the radiated sound and the micro minal periphery of the horn 2 and to terminate 77 5 phone. The design of the outer radiating horn 2,411,004 5 6 cordance with a requirement described herein greater proportion of the sound emanating from after. the horn 2 toward a region on the central axis It will be apparent to one familiar with the art in front of the horn at a distance that can be de that a microphone so mounted is most efficient termined within limits by the designer. As the m for close talking purposes, as sounds directed at natural tendency of radiating sound from a it from a distance will travel substantially along is therefore such as to converge and direct the source large portion is to diverge, of it to athe small ability region to results converge in a greater transfer ef?ciency. There is thus less ' Mills of almost the same length from the source to front and back of the diaphragm, so that they will have a comparatively small vibrating effect. sound radiated in diverse directions i. e. toward When talking close to the front of the diaphragm the rear, hence the great reduction in the tend ‘i -is cancelling effect is insigni?cant due to the large difference in path length of the sound from the talker’s mouth to the front and back of the ency for the device to cause acoustic feedback into the microphone. ’ Even though the sound ultimately diverges be diaphragm, respectively. yond the focal region, the degree of divergence is ‘ This effect of cancellation of sounds other than those originating close to the front of the dia much less from this device than from a conven tional horn exit. Projecting the sound to a re phragms is utilized in this combination. With gion in space a distance in front of the horn actu~ the microphone located on the acoustic axis of ally creates what may be thought of as a virtual the sound which radiates backward from the source of the radiated sound, which gives the - loudspeaker opening, as described above, the path effect of a longer horn than the physical length lengths from any point in a sound wave in space of that actually used. The source of sound is originating from the loudspeaker, to opposite thus removed farther from the microphone which as one skilled in the art knows, reduces the acous~ tic feedback tendency. Hence, even such sound as does diffuse backwards from beyond the focal region is largely attenuated in the distance it must travel back to the microphone location. A tubular housing 5 is secured to the horn structure as by means of screws 33 engaging the loa?le member 3, to serve as an enclosure to pro» tect the inner working parts, but is proportioned points on either side of the diaphragm is substan tially the same. This effect is assisted by the shape and size of the tubular housing 6 and the space between the microphone l’ and housing 6, which tend to bend the direction of travel of the , ’ stray sound from directly backwards parallel to the axis, to a, direction more nearly parallel to the plane of the microphone diaphragm. Thus, the sound pressure of a sound wave strikes opposite sides of a point on the diaphragm to guide any backward radiated sound as dc~ substantially simultaneously, so that the net force exerted on the microphone diaphragm by A microphone unit I’ is provided which is of a 35 sound radiating back from the loudspeaker is type so designed that both sides or” its diaphragm practically zero, provided the constants of the de or other sound wave sensitive element, are open to vice are correctly designed and constructed, The the atmosphere to the extent that sound Waves tendency for acoustic feedback between the loud have access to both back and front. Covering 40 speaker and the microphone is therefore reduced screens 8 of such design that will pass the sound to an insigni?cant value, permitting very large waves but prevent foreign matter, spray, etc, ratios of ampli?cation to be used between the from reaching the diaphragm may be added. microphone and the loudspeaker, without produc The microphone is held in. a position separated ing audible oscillation or howling. from the rear of housing 5, as by adjustable legs 45 Thus it will be seen that because the con?gura— or similar means 9, suf?ciently far so that sound ti-on of the horn, the housing, and the micro waves can freely pass between it and the housing. phone and its mounting, and the spatial relation Further, the microphone is so positioned that it ship between these parts, a much greater increase is centered on, and is normal to, the central in volume of ampli?ed speech than has hereto acoustic axis of such sound waves as may radiate 50 fore been possible with similar devices, can be backward from the loudspeaker mouth. This is obtained without acoustic feedback. not necessarily the geometric central axis A-A A handle i3 is attached to the assembly under although it may coincide substantially therewith, the center of gravity for ease in holding the unit so that the microphone is located by trial in this A push button switch l4 such as used on portable null position when ?rst mounted, or the mounting 55 electric tools, etc., is mounted in the handle to is provided with means to permit it to be adjusted permit the electric circuits to be turned on and to the null position when in use, by adjustable off easily when using the electronic megaphone, mounting means, 9 and it, or other methods. so that current is only drained by the ampli The front opening to the microphone dia ?ers from its batteries or power supply, when it phragm is substantially equal to, or less than, the 60 is desired to talk. size of the average mouth when talking, to pro Separately shielded conductors are run through vide_as high acoustic impedance as possible the handles and switch from the microphone 7 without sacri?cing efficiency. Any chamber and the loudspeaker driver unit 1, respectively. scribed hereinafter. formed by an aperture or mounting means on They cannot be connected haphazardly however. front and back of the diaphragm is constructed 65 It is necessary to electrically phase the two cir so that its cavity resonance is at a frequency cuits so that the input and output conductors that other than those uniformly transmitted in the are above ground potential are dissimilarly polar speech frequency band of the system. ized, to prevent regeneration and electrical feed Some means of protecting the microphone from ack. mechanical vibration, in accordance with are 70 The microphone is connected through the cable quirement well known by those skilled in the art, i5 to the ampli?er input. Means are provided, is provided in its mounting, such as pads of resil such as the rubber insulation 62, to have the ient material I l and I2, (rubber, etc.). This ma— structure of the microphone electrically separate terial may be used to electrically insulate the mi from that of the horn housing, and the micro crophone housing from the horn structure in ac phone is connected to the electric shield of the . 2,41 1,004 7 8 cable l5 to isolate the microphone from the horn to be free to the atmosphere not only on the front electrically. The loudspeaker I, is connected through cable l5 to the ampli?er output, the shield of this cable being connected to the horn structure as shown of the diaphragm but also on the back. - It is thereby understood that although the pro portions of the horn, the radiating mouth, and other parts of the loudspeaker will be maintained in Fig. 2. The shields of cables I 5 and I6 are as described hereinbefore, the absolute values of properly connected into the ampli?er circuit as the dimensions are only limited by the maximum is shown diagrammatically in Fig. 5. The switch size within which it is desired to keep the device. l4 may interrupt either circuit I5 or IE or pref However, it is well known to the art that all acous erably the circuits to the power supply of the am 10 tic radiating devices tend to produce more diver pli?er unit I9 through a separate cable such as gent sounds at lower frequencies, particularly be low the frequency at which the diameter of the The combination comprising the complete sys radiating aperture is less than approximately 1/2 wave length of the sound. It is a common prac tem, Fig. 1, shows how the input and output con tice to attenuate proportionately frequencies be ductors referred to above are connected through low this value in acoustic loudspeaker systems, a receptacle IS in a conventional manner, to a a practice which is intended to be followed in the suitable electronic tube ampli?er l9, such as, a invention described herein. portable type operated by batteries. Fig. 5 shows In like manner following conventional prac the electrical schematic connections between the microphone ‘and the ampli?er input, and the 20 tice known to the art, mechanical vibrations and mechanical energy transferred from external loudspeaker and the ampli?er output. sources and from the body of the loudspeaker por It will be apparent, therefore, that this de vice is to be used with an ampli?er, such as a portable type, which can be carried by a strap over the shoulder or rest on a convenient support 25 within the limits of the extension cables i5, i6 and I1, so that the electronic megaphone unit may be held by the handle to the user’s mouth. tions are reduced to an insigni?cant amount by cushioning the microphone in its support. Other combinations of the electronic mega phone and its ampli?er may be used, such as in corporating the two in one unit or detaching the microphone from its supports on the loudspeaker in the event that it may be desirable to mount the As soon as ready to talk the operator closes the switch in the handle thereby energizing the am 30 loudspeaker on a separate support such as a tri pod, with the user holding the microphone in his pli?er circuits so that speech directed into the hand. In this event the user only has to observe microphone diaphragm opposite the talker’s the restriction of holding the microphone on the mouth generates electrical currents in the micro null acoustic axis at the rear of the loudspeaker phone. The electric energy from the microphone is fed 35 as described above in order that the device may be operated at optimum e?iciency. In like man through the cable IE to the ampli?er input and is ner a conventional power operated ampli?er in increased many-fold in power by the ampli?er. place of a battery operated ampli?er may be used, The ampli?ed output is fed through the cable l6 if power from an electric generator is convenient. to the loudspeaker driver unit I. The force ex The invention in its broader aspects is not erted by these amplifiedv currents actuates the 40 limited to the speci?c mechanisms shown and diaphragm,'setting up sound waves of a great described but departures may be made therefrom ly ampli?ed pattern of those directed into the microphone. In this way the power of a human voice is ampli?ed tremendously and is then di rected by the electronic megaphone to the desired location by simply aiming the device at this region. The operation is therefore, similar to that when using an ordinary megaphone except for one great dilference: whereas with an ordinary mega phone the talker may, and usually does, bring the small end up to and touching the area around his mouth without mu?ling the speech so as to render it unintelligible, with the electronic meg aphone, the megaphone must not actually touch within the scope of the accompanying claims without departing from the principles of the in vention and without sacri?cing its chief advan tages. What is claimed is: 1. An electronic megaphone comprising in com bination a loudspeaker; and, a microphone located out of the direct soundpath of the loudspeaker, the microphone having openings for the entry of sound waves on opposite sides of its diaphragm so that sound waves emanating from a source relatively remote therefrom will strike opposite sides of said diaphragm substantially simulta neously and eifect substantially no energizing of said diaphragm whereas sound waves emanating the speaker’s mouth which is open to the atmos phere, no matter how small this space may be, and from a source closely adjacent to one side of said indeed it is desirable for the greatest e?iciency diaphragm will strike opposite sides of said dia to keep the distance betwen the two as small as 60 phragm successively and energize said diaphragm. possible. Inasmuch as the inlet of the microphone 2. An electronic megaphone comprising in com must be at all times open to the atmosphere, by bination a microphone and a loudspeaker, with virtue of this spacing, in all known devices or sys the microphone positioned behind the exit of the tems using a microphone and ampli?er and loud loudspeaker horn, said horn comprising an inner speaker, so as to maintain intelligible speech re horn of conventional exponential or conical de production, all such devices are inherently sub sign, terminated by an additional outer horn com ject to acoustic feedback due to the sounds from prising outside ba?‘le members and an inner plug the speaker entering the front of the micro ba?ie member together forming a sealed annular phone. This invention therefore greatly overcomes this inherent tendency to acoustic feedback by sounds entering the front of the microphone both by converging the projected sound from the loud I speaker toward the region to which communica tion is desired and by permitting the microphone passage extending forwardly from the inner horn to the exit of said outer horn for sound to follow from the inner horn through said passage to the exit of the outer horn. 3. An electronic megaphone comprising in com bination a, loudspeaker; and, a microphone sup ported therefrom, said microphone having both £411,664 9 10 sides of its sound sensitive unit open to the at mosphere and said loudspeaker having its mouth facing in the opposite direction to the far side of annular sound passage from said inner horn to the loudspeaker mouth, said sound passage com mencing at said inner horn being directed out both sides to the atmosphere, said diaphragm unit being substantially centered on and substantially er in front of its mouth; and a microphone car wards from the central axis of symmetry so as said unit. 4. Electronic sound amplifying apparatus com 2.21 to form at the junction of said intermediate and terminal ba?ie members an annular ring of sound prising in combination a loudspeaker having a of large diameter substantially equal to the diam driver unit and baf?e members forming a sound eter of said terminal baffle member and said pas passage from said driver unit to the exit of the sage commencing at said junction having a cross loudspeaker for focusing the sound waves gener ated by said unit at a locus in front of said exit -. section in the plane of the axis of symmetry which has a geometric axis from said junction to the substantially on the geometric axis of the loud loudspeaker mouth which slants toward a point speaker; and, a microphone back of the loud on the central geometric axis of the loudspeak speaker mouth having a diaphragm unit open at normal to the central acoustic axis of said loud speaker so as to be in an acoustic null position with respect to sound waves which radiate back ward from the mouth of said loudspeaker. 5. An electronic megaphone comprising in com- ~ bination a loudspeaker capable of focusing sound Waves at a locus ahead of its mouth; and a micro phone in back of the loudspeaker at a ?xed dis tance therefrom, said microphone being normal to the central acoustic axis of the loudspeaker and adjustable relative thereto whereby said micro ried by said loudspeaker in a position out of the direct soundpath of the loudspeaker. 11. An electronic megaphone comprising in combination a microphone ‘and a loudspeaker of which the horn focuses a substantial portion of the radiated sound to a region on the central geometric axis of the loudspeaker in front of its mouth, housing means for the rear of said loud speaker of such shape that sounds from the loud speaker which diffuse to the rear are refracted to wards the central axis of the loudspeaker, a micro phone unit spaced from the rear of said housing means so that the refracted sound may pass be phone may be centered on said axis. tween the microphone and housing, the front 6. An electronic megaphone comprising in com and rear of the microphone diaphragm being open bination a loudspeaker capable of focusing sound Waves at a locus ahead of its mouth, said micro 30 to sound waves in the atmosphere and said dia phone having both sides of its sound sensitive unit open to the atmosphere; a housing for the rear phragm being so positioned that the diffuse sound from the loudspeaker acts upon opposite sides of any point on the diaphragm at substantially the of said loudspeaker; and, a microphone supported same time and with the same pressure. by said housing out of the direct soundpath of 12. Electronic sound amplifying apparatus said loudspeaker. 35 comprising in combination a sound focusing loud 7. An electronic megaphone comprising in com speaker unit, a microphone unit carried by said bination a loudspeaker, said loudspeaker com loudspeaker, an electronic ampli?er, electric con prising baffle members forming an annular sound ductors interconnecting the microphone, loud passage terminating at the mouth of the loud speaker, the acoustic axis of said passage at the 40 speaker and ampli?er, a handle unit for the loud speaker-microphone assembly by which the oper exit converging toward the central geometric axis ator can direct the focused ampli?ed sound to a of the loudspeaker; and, a microphone supported chosen region, and a switch in said assembly for from said loudspeaker. energizing the electronic circuits, said micro‘ 8. An electronic megaphone comprising in com phone having a diaphragm unit open at front and bination a loudspeaker, said loudspeaker com prising baffle members forming a sound passage of annular shape having a central axis of sym metry, said passage increasing in maximum diam eter for a distance and thereafter increasing in width to the loudspeaker mouth so as to provide a terminal portion converging toward a point on said axis; and, a microphone located out of the direct soundpath of the loudspeaker. 9. An electronic megaphone comprising in com— rear to sound waves in the atmosphere, and said ampli?er unit having high ampli?cation such that if the back or front of the microphone dia phragm were closed to the atmosphere, acoustic feedback would occur between the loudspeaker and microphone. 13. An electronic megaphone comprising in combination a microphone and a loudspeaker, the loudspeaker comprising an inner horn terminated bination a loudspeaker capable of focusing sound , waves at a locus ahead of its mouth; a housing for by an outer horn with a two section sound outer horn comprising a terminal ba?ie member of larger diameter than the exit diameter of said inner horn, an intermediate ba?ie member con necting said inner horn with said ?rst baffle mem to provide an annular entry to said second sec tion equal to the exit of said ?rst section, the cross section of said second section from its en passage of substantially annular shape, the ?rst section of said passage forming the sound into said loudspeaker; a microphone having its sound thin annular rings during its passage there sensitive unit exposed at opposite sides to the through from the exit of said inner horn, said atmosphere; and, means for adjustably support ing said microphone from said housing in a posi 60 ?rst section soundpath being directed angularly outwards from the central axis of symmetry to tion out of the direct soundpath of said loud the junction with said second section so as to form speaker and with its sound sensitive element sub an annular ring of sound of large diameter sub stantially centered on and normal to the central stantially equal at said junction to the diameter acoustic axis of the loudspeaker. 10. An electronic megaphone comprising in P of the second section of said passage, said second section being formed by an outer ba?le member combination a loudspeaker, said loudspeaker com and an inner plug baffle member positioned so as prising a driver unit, inner and outer horns, said ber; and a plug ba?le member positioned in the chamber formed by said ?rst mentioned, ba?lc members and forming with said baffle members an try to its exit having a geometric axis which slants toward a point on the central geometric axis of the loudspeaker. ARTHUR J. SANIAL.