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1 Dec. 17, 19. H. F. LS LUD-SPEAKER Filed March 31, Sheet-Sheet l SSSS ayssaaaaaaa. S, ) S. L 2 t YaYa YaYa YaYa YaYa SSSSSSSSSS1 '.. ZZZZZZZz Y. Spentor

2 Dec. 17, 19. H. F. LS LUD-SPEAKER Filed March 31, Sheet-Sheet 2 A-4 S 27.6 AAAAAAAAAAAAAAAA 1 M / /2 YaYa YaYaYYaYa YaYa YaYYYYYSSY SSSYSSYSSSSSSY 2 YYYYYYYYY SXSA 4ZZZ Z.Z Aaz 3 A77-z/A Zez a AzyA/oz -1 Gittorney Smpetitor

3 Patented Dec. 17, UITED STATES 17 Claim. Thi invention relate to loud-speaker, and more particularly to loud-peaker of the con pound type. It ha long been recognized that the efficient tranformation of electrical variation into cor reponding acoutical vibration ver a wide fre quency range i, in general, retricted by prac tical limitation. Experience ha hown that mot efficient reproduction over a wide fre quency range may be obtained by an arrange ment wherein a cone or other uitable diaphragm i employed to drive both a hort horn for repro duction of high frequencie and a long horn for reproduction of low frequencie, and Variou ar rangement of thi ort have been propoed here tofore. It i alo Well known that high frequency Wave are highly directional and are eaily ab Sorbed and affected by reflection. With com pound horn type loud-peaker of the prior art, little attention ha been given to minimizing at tenuation of the higher frequencie in inexpen ive horn loud-peaker, and a a reult, the efficiency of ditribution of high frequency Sound where uch loud-peaker have been ued ha Suffered. The primary object of my preent invention i to provide an improved compound horn loud Speaker of the type referred to above which i particularly uitable for reproduction over a Wide range. More particularly, it i an object of my preent invention to provide an improved loud-peaker a aforeaid which will reproduce the high fre quencie in a manner not to caue them to Suffer Seriou attenuation or reflection. Another object of my preent invention i to provide improved acoutic filter for dicriminat ing between the range of frequencie upplied by the repective high and low frequency Sytem of the loud-peaker. A further object of my preent invention i to provide an improved loud-peaker of the type Set forth which i very imple in contruction, yet highly efficient in ue, and which i relatively inexpenive of manufacture. In accordance with my preent invention, I provide a cabinet having upper and lower open ing in one of it wall and divide the cabinet into two chamber or compartment. A mall, Straight axi horn adapted to particularly tran mit high frequencie i placed in the upper com partment and fit into the upper opening, while a long, folded, low frequency horn i dipoed partly in the upper and partly in the lower com PATET FFICE LUD-SPEAKER Harry F. lon, Audubon,.J., aignor to Radio Corporation of America, a corporation of Dela Ware Application March 31, 1937, Serial o. 134,100 (CI. 8-31) partment and terminate at the lower opening, a ingle driver feeding both horn. The Small horn i arranged at ubtantially the level of the litener' ear, whereby very little lo of high frequencie i obtained a a reult of aborption and reflection. If deired, the Small horn may be omitted and the cone or diaphragm of the ingle driver arranged to feed directly into the atmophere a a direct radiator. In either cae, the low frequency horn i preferably provided with an acoutic filter which efficiently pae only the low frequencie, and the high frequency horn, in the firt modification referred to above, may be provided with an acoutic filter which efficiently permit tranmiion of only the high frequencie. The novel feature that I conider character itic of my invention are Set forth With par ticularity in the appended claim. The inven tion itelf, however, both a to it rganization and method of operation, together with addi tional object and advantage thereof, will bet be undertood from the following decription of Several embodiment thereof, When read in connection with the accompanying drawing in Which Figure 1 i a front elevation of one form of my invention, Figure 2 i a ectional view taken on the line II-II of Fig. 1, Figure 3 i a ectional view taken on the line III-III of Fig. 1, Figure 4 i a circuit diagram of the electric equivalent of the acoutic arrangement of thi modification of my invention, Figure i a front elevation of another form of my invention, Figure 6 i a ectional view taken on the line WI-VI of Fig., Figure it i a Sectional view taken on the line WII-VII of Fig., Figure 8 i a diagrammatic illutration of a horn embodying a low pa filter and acoutic capacitance according to my preent invention, and Figure 9 i a diagrammatic illutration of a modified form of combined low pa filter and acoutic capacitance according to my invention. Referring more particularly to the drawing, Wherein imilar reference character deignate correponding part, there i hown, in Fig. 1, 2 and 3, a cabinet, the front wall of which i provided with a relatively mall opening 3 at the top and a relatively large opening at the bot tom, and the cabinet being divided into upper 2 3 0

4 and lower compartment 7 and 9, repectively, by a partition. Mounted in the upper compart ment i a uitable electro-acoutical driver 3, uch a an electro-dynamic loud-peaker which include a cone or diaphragm and Which i preferably adapted to reproduce acoutic ignal ver a Wide range. A hort, traight-axi horn 7, which preferably i of the exponentially ex panding type, i alo located in the compartinent and loads ne Side (for example, the front) f the diaphragm, and, by terminating at the Small opening 3, erve to etablih communica tion between front ide of the diaphragm, and the pening 3 a well a the atmophere. Alo mounted in the upper compartment 7 are the two divided ection 9a, and 9b of a long, folded horn 9 which load the rear. Side of the dia phragm. The ection 9a, and 9b are di poed ymmetrically with repect to the dia phragm and each communicate, through opening 2 in the partition, with the ingle Section, 9c. of the horn 9 located in the lower compartment 9. The horn 9, preferably alo of the exponentially expanding type, terminate at the large opening and thu erve to etab lih Communication between the rear ide of the diaphragm and the opening. a well a the atmophere. The horn i employed to tranmit high audi ble frequencie with great efficiency and the horn 9 to tranmit low frequencie Within the audi ble range with great efficiency. For thi pur poe, I provide one or more opening 23 in the horn. 7 in proximity to it throat and place about the throat end of the horn 7 a partition or caing which provide a cloed chamber 2 in parallel relation to the horn, the chamber 2 having communication with the horn 7 nly through the opening or opening. 23, a the cae may be. The pening 23 and the chamber 2 form a Serie reonant circuit and they are o deigned a to reonate at the lower cut-off fre quency of the horn 7. Thu, only ubtantially thoe vibration above the reonant, or predeter mined cut-off, frequency of the reonant circuit Will be tranmitted by the horn it, and in order to minimize the lo of the tranmitted high fre quencie, the Cabinet and the partition are So arranged that the horn f i ubtantially at the level of the litener' ear. In thi way, the loss of the high frequencie by aborption and reflection i very greatly reduced. A tated previouly, the horn ection 9a, and 96 are dipoed Symmetrically with repect to the driver 3, one on each ide thereof. By eparating thee two ection which, in effect, contitute but a ingle horn portion with each ection of half the cros ectional area of the combined horn portion in the compartment 7, a chamber 2 i formed immediately behind the diaphragm. The chamber 27 ha a cro Sec tional area which i appreciably greater than the total throat area of the combined ection 19a, and 9b and provide an acoutic capacitance which i comparable to the impedance of the horn 9 at the high frequency cut-off frequency of the horn 9, and thi i preferably in the vi cinity of the low frequency cut-off frequency of the horn 7. To further inure againt tran miion of high frequencie by the horn 9, it may be provided With one or more axially paced baffle 29 (Fig. 8) each provided with an opening 3 therein of an area. Smaller, of coure, than the cro ectional area of the horn 9 at the point where the baffle 29 are located and each opening 3 preferably of progreively larger diameter a the cro ectional area of the horn 9 increae. The effect of the baffle 29 i to cut down radia tion of high frequency vibration by reflection thereof back toward the chamber 27 and by at tenuation due to the contriction at the open ing 3. In the modification of my invention il lutrated in Fig. 1 to 3, the baffle 29 are con Stituted by thoe portion of the partition Which border n the opening 2 and the open ing 2 correpond to the opening 3 of Fig. 8, being of an area appreciably maller than the CrSS Sectional area.s. of the horn Section 9d. and 9b at the point where the opening 2 are provided. The combined effect of the chamber 27 and the opening 2 i to keep the repone of the horn 9 down below it intended, or pre determined, high-frequency cut-off frequency. Thu, the horn 9 will tranmit only the lower frequencie and the horn 7 only the higher fre quencie, and each with great efficiency. The equivalent electrical circuit of the modi fication of my invention jut decribed i hown in Fig. 4. If m1 repreent the combined ma of the diaphragm, it voice coil upport and the Voice coil, m2 the ma of air in the opening 23, C1 the capacitance of the upenion of the cne, C2 the acoutic capacitance of the cham ber 21, C3 the acoutic capacitance of the cham ber 2, Z1 the impedance of the horn 7 and Z the impedance of the horn 9, the electrical analogue Will be arranged a hown. It will be noted that the inductance m2 and the capaci tance C3. form a Serie reonant circuit in hunt With the impedance Z1 and that the capacitance C2 i hunted acro the impedance Z2. Thi arrangement i eential to provide efficient cut off for the two horn. - The modification of my invention hown in FigS., 6 and 7 i practically identical with that previouly decribed inofar a the low frequency horn 9 i concerned. However, in thi modifi cation, the high frequency horn 7 i omitted and the diaphragm f i mounted immediately behind the Small opening 3 to have direct com munication therewith and with the atmophere, Whereby it act a a direct radiator. Such a contruction i preferable to... that previouly de Scribed in certain cae, a in radio. receiver loud-speaker, monitoring loud-peaker, with centralized radio Sytem, and the like, ince a direct radiator i uually ufficiently efficient in the mid- and high-frequency range. Alo, ince the intenity level of reproduction in mall room i coniderably le than the intenity level of the original ound, ome accentuation of low frequency repone may be required. Coupling the horn 9 to one ide of the diaphragm ( provide a good Sytem of low-frequency eff ciency and, ince the diaphragm i a direct radiator in the arrangement hown in Fig. to 7 and cover Wide angle of ditribution, it i poible to ue a mall and light vibrating y tem for the efficient reproduction and ditribu tion of the mid- and high-frequency range from the open ide of the cone. While I have hown and decribed but two modification of my invention, I am fully aware that many other modification thereof and change therein may be made within the pirit of my invention. For example, in place of a Single driver, two eparate driver may be 'em ployed, a may alo a driver having a ingle field Supply for two eparate cone; and voice coil of the type dicloed and claimed, for example, in 7 0 6

5 6 7 3 the copending application of Frank Maa, Se phragm contituting an acoutic capacitance ad rial o. 113,47, aigned to the Radio Corpra jacent aid diaphragm. tion of America. It will alo be obviou that the 8. The invention et forth in claim 2 charac horn 7 and 9 may be of any deired hape in terized in that aid horn i o contructed and cro ection intead of Square a hown, and arranged within aid cabinet that it cooperate that thee horn may be made to expand in any With aid cabinet to provide a chamber behind deired way. Alo, if deired, the baffle 29 may aid other ide of the diaphragm contituting an be placed in the chamber 27 intead of in the acoutic capacitance immediately behind aid horn 9, a hown in Fig. 9. Many other diaphragm. change will, no doubt, readily ugget them 9. The invention et forth in claim 2 charac Selve to thoe killed in the art. I, therefore, de terized in that aid horn i provided with one Sire that my invention hall not be limited except or more perforated baffle therein contituting an inofar a i made neceary by the prior art and acoutic filter adapted to pa only Vibration by the Spirit of the appended claim. below a ubtantially predetermined frequency, I claim a my invention: and characterized further in that aid horn i 1. Signal tranlating apparatu compriing, in provided with a chamber behind aid diaphragm combination, a hollow cabinet, a partition therein contituting an acoutic capacitance, the capac dividing aid cabinet into a pair of compart itance of aid chamber being comparable to the ment, aid cabinet including a wall provided impedance of aid horn at Subtantially aid with a pair of opening one of which etablihe predetermined frequency. communication between the atmophere and ne 10. Signal tranlating apparatu compriing, of aid compartment and the other of which in combination, a hollow cabinet, a partition etablihe communication between the atmo therein dividing aid cabinet into upper and phere and the other of aid compartment, an lower compartment, an electro-acoutical driver electro-acoutical driver in one of aid compart in aid upper compartment, aid driver including ment, aid driver having a diaphragm. ne ide a diaphragm, a relatively hort, traight-axi of Which i in communication with the opening horn in aid upper compartment coupling one aociated with one of aid compartment, and ide of aid diaphragm with the atmophere, a horn coupled to the other ide of aid dia and a relatively long, folded horn coupling the phragm, aid horn extending through aid par other ide of aid diaphragm. With the atmo tition and having it terminal at the other of phere, aid lat named horn extending through aid openings. aid partition and having a portion located in 2. Signal tranlating apparatu compriing, in aid upper compartment and a portion located combination, a hollow cabinet, a partition there in aid lower compartment and communicating in dividing aid cabinet into upper and lower with the atmophere from aid lower compart compartment, aid cabinet including a Wall pro ment. vided with a relatively mall opening which 11. The invention et forth in claim 10 charac etablihe communication between the atmo terized in that the portion of aid long horn phere and aid upper compartment and With a which i located in aid upper compartment i relatively large opening which etablihe com divided into two ection ymmetrically dipoed munication between the atmophere and aid with repect to aid diaphragm, Said ection lower compartment, an electro-acoutical driver each terminating into the portion located in aid in aid upper compartment, aid driver including lower compartment. a diaphragm one ide of which i in communi 12. The invention et forth in claim 10 charac cation with aid Small opening, and a horn cou terized in that aid mall horn i provided with pled to the other ide of aid diaphragm, aid at leat one opening in the Wall thereof adjacent horn extending through aid partition and hav it throat and characterized further by the addi ing it terminal at aid large opening. tion of mean providing a chamber in parallel 3. The invention et forth in claim 2 charac relation to aid Small horn, Said chamber con terized in that the firt named ide of aid dia municating with aid Small horn through aid opening. phragm ha direct communication. With the at mophere through aid mall opening. 13. The invention et forth in claim 10 charac 4. The invention et forth in claim 2 charac terized in that Said Small horn i provided with at leat one opening in the wall thereof adja terized by the addition of a econd horn which i coupled to aid firt named diaphragm Side cent it throat, and characterized further by the addition of mean providing a chamber having and which terminate at aid mall opening. communication. With aid horn through aid. The invention et forth in claim 2 charac opening, aid chamber contituting an acoutic terized in that aid horn i of the folded type capacitance and the ma of air in aid opening and i relatively long, aid horn being particu contituting an acoutic inductance in erie. With larly adapted to tranmit low frequency vibra aid capacitance, and Said chamber being o tion, and characterized further by the addition arranged. With repect to aid horn that aid of a relatively hort, traight-axi horn particu erie connected capacitance and inductance larly adapted to tranmit high frequency vibra form a reonant circuit in hunt with the in tion, aid econd horn being coupled to aid pedance of aid horn, aid reonant circuit being firt named ide of aid diaphragm and termi uch a to reonate at the low frequency cut-off nating at Said Small opening. frequency of Said Small horn. 6. The invention et forth in claim 2 charac 14. Signal tranlating apparatu compriing, in terized in that aid horn i provided With one combination, a cabinet including a ide wall, a or more perforated baffle therein contituting partition in aid cabinet dividing it into upper an acoutic filter adapted to pa only Vibration and lower compartment, aid lower compart below a Subtantially predetermined frequency. ment having an opening in aid wall whereby 7. The invention et forth in claim 2 charac communication i etablihed between the atmo terized in that aid horn i provided With a phere and aid lower compartment, an electro chamber behind Said other ide of aid dia acoutical driver in aid upper compartment, and

6 a horn coupled to aid driver and terminating at aid opening, one portion of aid horn being located in aid upper compartment and another portion thereof being located in Said lower com partment, aid partition contituting a Wall com mon to all of Said horn portion, and aid par tition having at leat one opening therein for etablihing communication between aid horn portion. 1. The invention et forth in claim 14 charac terized in that aid horn increae uniformly in cro-ection along it length and characterized further in that the opening in aid partition i of maller area than the cro-ectional area of the horn at the ame point, the area of aid opening being o related to the CrSS-Sectional area of the horn at aid point a to contitute an acoutic filter adapted to pass only vibration below ubtantially a predetermined frequency. 16. The invention et forth in claim i4 charac terized by the addition of mean in aid upper compartment providing a chamber interpoed between aid driver and the throat of aid horn, the cro-ectional area of aid chamber being appreciably greater than the cro-ectional area, of aid throat whereby aid chamber contitute an acoutic capacitance, and characterized fur ther by the addition of an acoutic filter in aid horn adapted to pa only vibration below ub tantially a predetermined frequency, aid acou tic capacitance being comparable to aid horn impedance at ubtantially aid predetermined frequency., 17. Signal tranlating apparatu compriing, in combination, an electro-acoutical driver, a horn loading one ide of aid driver, aid horn having a mall opening therein in proximity to aid driver, and mean providing a chamber about the throat end of aid horn having Cm munication with aid horn through aid open ing, aid chamber contituting an acoutic ca pacitance and the ma of air in aid opening contituting an acoutic inductance, aid cham ber and aid opening being o related to aid horn a to form a Serie reonant circuit in Shunt with the impedance of aid horn, and aid reo nant circuit being uch a to reonate at a pre determined frequency. HARRY F. LS. 0 2