US 2593031 A
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April 15, 1952 G. N. @WATT LOUD-SPEAKER 2 SHEETS--SHEET l Filed May l, 1948 INVENTOR.
April l5, 1952 G. N. HowATT 2,593,031
v LOUD-SPEAKER Filed May 1, 1948 2 SHEETS- SHEET 2 Patented Apr. l5, 1952 LOUD-SPEAKER Glenn N. Howatt, Metuchen, N. J., assigner to Gulton Mfg. Corp., Metuchen, N. J., a corporation of New Jersey Application May 1, 1948, Serial No. 24,663
My invention relates to loud speakers and particularly to the reproduction of high delity, higher frequencies in a loud speaker.
Loud speakers have been developed to the point Where a uniform response over a moderate frequency vvband may be obtained in a single diaphragm speaker of the type commonly used in broadcast receivers. The. best of such speakers have been capable of operation up to about 9000 cycles, vand since the audio frequency spectrum of the usual broadcast band has been Wellwithin the range of such speakers, and frequency has not exceeded 5000 cycles, the utility of single cone speakers' has been good. In high fidelity broadcastingjsystems, however, such as in frequency modulation or as would be obtained from high fidelity,phonographrecords, the frequency range is greatly extended and to reproduce the higher frequencies of the resulting audio frequency spectrum, the loud speaker should have a response up to 15,000 cycles. There have been many suggestions to' increase the over-al1 range of loud speakers such as by the use of more than one speaker mounted coa-Xially, coplanar and both coaxially and coplanar. The use of two speakers, one to cover the higher frequency band and the other to cover the lower frequency band requires a special cross over network and besides the system so constructed has other drawbacks regardless of how the speakers are mounted.
The object of my invention is the provision of an improved loud speaker systemwhich overcomes the disadvantages of arrangements heretofore suggested.
Another object is the provision of aloud speaker in which two cones are employed but in which across overnetwork is not required. p I
lStill another object isI to add to a conventional loud speaker having a uniform response over a moderate frequency an additional element ing a uniform response over a range from about 0000 cycles to about 15,000 cycles. The high frequency loud speaker, preferably mounted coaxial and coplanar with the low frequency loud speaksclaims. (C1. 179-116) er, comprises a relatively small cone driven by a piezoelectric ceramic, preferably a polygranular `which is so matched to the impedance of the tion.
piezoelectric ceramic that no cross over network or other means is required for successful opera- The low frequency loud speaker is connected to a secondary of the output transformer Yto balance the voltage with the impedance oi the voice coil in a mann-cr conventional in the art. The piezoelectric ceramic vibrates in response to so much of the alternating output po-- tential as lies Within its frequency range of vibration, and the characteristics of the piezoelcnn tric ceramic are, as previously explained, preferf' ramic.
ably controlled to provide for vibration within the range of about 9000`cycles to 1.5;000 cycles. The piezoelectric ceramic is mechanically connected to the high frequency cone to reproduce in the cone the vibrations imparted to the cen In a preferred arrangement, two strips of ceramic are employed being soldered together with a center lead connected to ground. The ceramics will have been charged with opposite polarities so that they complement each other, and the center connection is grounded so that when the minus side of the B power circuit is grounded in the usual manner, there will always be a positive charging potential on the ceramics and even though characteristics may develop, such'as raising the temperature of the ceramic above the Curie point, which would normally tend to obliterate or reduce the initial charge, the charge is maintained throughout the life of the instrument.
In the drawings, I show details of certain ein bodiments of the invention wherein:
Fig. 1 is an elevational view of a loud speaker constructed in accordance with my invention;
Fig. 2 is a sectional view taken on the line `2---2 ofFig. 1, and also including a portion of a radio circuit associated with the speaker;
` Fig. 3 is an enlarged sectional view showing only a portion of Fig. 2 and illustrating struc tural features;
Fig. 4 is a fragmentary sectionalvicw taken on the line il--il of Fig. 3;
Fig. 5 is a perspective viewshowing the two ceramics considerably enlarged over those which would have to be employed to drive the small cone; Y
Fig. 6 is a greatly enlarged longitudinal sectional view showing the electrodes applied to the faces of the ceramic strips;
Fig. 7 is a transverse sectional view on the same scale as Fig. 6 but showing the three leads in position;
Fig. 8 is a partially schematic view of the piezoelectric ceramics and shows the manner in which they are connected into the output circuit of a radio amplifying unit;
Fig. 9 is a partly schematic view of the high frequency loud speaker including cone and piezoelectric ceramics with somewhat more of the circuit than is shown in Fig. 8;
Fig. 10 is an enlarged sectional view similar to Fig. 3 but showing a modified arrangement; and
Fig. l1 is a fragmentary sectional view taken on the line I I-I I of Fig. 10, looking in the direction of the arrows.
Referring now to Figs. 1 9, inclusive, of the drawings, I show a conventional bale I2 to which the outer rim of a cone I3 is suitably secured in any Way conventional in the art. The cone has a voice coil I4 which extends into the annular gap of an electromagnet I which may be a permanent magnet of the alnico type or anl electromagnet in which charging windings are inductively associated with the center pole piece in a manner conventional in the art. The arrangement of core, voice coil and associated electrical parts, in other words, is entirely conventional and may be employed without change.
Suitably secured to the baille I2 are a pair of brackets il supporting at their inner end an annular mounting ring I8. This mounting ring has a pair of insulating supporting pads I9, which may comprise bakelite or the like, and secured to the pads is a driving unit, indicated generally by the reference character 20, and comprising two piezoelectric ceramics 2l and 22 secured together to form a single assembly as will be described. A driving rod 2S is secured to the ceramic strip 2l and has its outer end connected to the apex of a small cone 24. All of the parts, including the pads I9, driving rod and cone, may be secured together by means of any suitable adhesive.
A terminal block 2t is mounted in a recess at the rear of the ring i8 by merely sliding it into formed channels comprising a part of the mountingring. The terminal block has three terminals 2l, 28 and 29 which are employed to connect the relatively fragile driving unit into the circuit and facilitate making connections thereto.
Looking now rst to Figs. 5-7, inclusive, Where the larger scale employed facilitates the showing, the ceramic strips 2l and 22 have external electrodes SI and 32 and a common center electrode 33 which functions to bind them together to form a single unit. Leads 34 and 35 are connected to the electrodes 3i and e2, respectively, and a lead 3l lies between the units and is common to them because of its connection to the center bonding conducting layer. The lead 34 is connected to the terminal 2, the lead 3'! to the terminal 2S and the lead 32 to the terminal 29.
In Figs. 2, 8 and 9, I show enough of the audio output portion or a conventional reproducer to indicate the manner in which my high frequency addition may be associated therewith. The circuit shows a pair of audio amplifying tubes 38 and 39 having the usual push-pull relation and having their output connected to a primary winding 4I of an output transformer. A secondary winding 42 is connected to terminals 43 and 4d extending in a suitable conventional manner for connection to opposite ends of the voice coil I4 (see Fig. 3). Since the voice coil is of relatively low impedance, the secondary windingT 42 is conventionally engineered to have a much smaller number of turns and is otherwise designed to produce the desired response in the speaker. The full primary voltage, however, is impressed upon Vthe piezoelectric ceramics by means of leads 41 and 48 which are connected in the manner particularly shown in Fig. 9 to the terminals 2l and 29, respectively, and thereby to the oppositely positioned electrodes 3l and S2. This arrangement is also schematically shown in Fig. 8. The impedance of the piezoelectric ceramics is, of course, very high and their characteristic is such that when employed in the manner disclosed only the higher electrical frequencies are effective to set them into vibration and, therefore, only the higher sound frequencies are reproduced. Moreover, the relatively very small mass of the ceramics would prevent their vibrating in the lower' audio frequency ranges. Details of the design of specific crystals will be explained below.
The center terminal 2l is grounded at 49 as shown particularly in Fig. 9 and I indicate at 5l the conventional grounding of the negative side of the B power supply. The plus B supply is connected at 52 (see Figs. 8 and 9) to the center of the primary 4I of the output transformer so that the full B voltage is always positively impressed on the piezoelectric ceramics in such a manner as to charge them with opposite polarities with the result that their action is in aid rather than opposing. The leads 4l, 48 and 49 are brought to the terminals v2l, 28 and 29 in any convenient manner, suitably as indicated in Figs. l and 2, by running a three-wire cable along one of the supporting brackets I'l Where it will be concealed by the usual grill cloth.
Those skilled in the art will understand that the invention may take various forms and may be carried out in many specic ways. In accordance with one example, the piezoelectric ceramic comprises a substantially pure barium titanate and two fiat pieces corresponding to the members 2l and 22 were prepared .020 thick by SA long by 1A" wide. These pieces were first painted with a, silver fritted paint and baked in an oven for a period of 20 minutes and then removed and allowed to cool. This provided a surface for application of electrodes. One surface of each piece was then tinned with solder and the two tinned surfaces placed together to form a common interface. The `resulting composite piece measured .045" in thickness, .050 of the total thickness being represented by the soldered layer. The three leads made of brass .010" thick by .050" wide were then soldered to the composite element and these comprise the three leads S4, 3S and 31. One lead was soldered to the interface by heating the composite piece sufliciently to softenthe solder and then lifting the top piece sufiiciently to enable one to place the flexible brass lead between the two pieces. The other two leads were readily soldered to the previously applied fritted paint portions which also act as electrodes. The resulting composite body with the three leads attached was then cemented to the Bakelite pads IS. Following this same specic example, the diaphragm comprised a spun aluminum alloy body 1.1" in diameter by .002
thick and with the cone dening a 130 degree angle. The driving rod was .050 in diameter and .3" in length. When the total high frey quency unit was assembled it was placed in an oven and baked for two hours at 100 degrees C. in order to thoroughly dry the cemented sections. After baking, the unit was allowed to cool and then mounted and electrical connections made in the manner shown in the drawings. The barium titanate polygranular ceramic strips were then charged by connecting the lead 31 to the positive pole of a charging source and the leads 34 and 36 to the negative pole thereof. The total speaker combination, including the low frequency and high frequency units assembled as shown in Figs. 2 and 3, were then placed in a sound chamber and an extremely high fidelity microphone was placed 1%/ directly in front thereof. A signal of 10 volts was applied to the speaker and the acoustic output plotted. The over-all response of the speaker showed a substantially flat curve with a variation of not appreciably more'than plus or minus 5 decibels from 50 to 15,000 cycles. The large speaker alone had a flat accoustical response up to about 9000 cycles and the high frequency speaker complemented the low frequency speaker to produce a resultant flat response up to approximately 15,000 cycles. Functional testing showed that high i'ldelity records could be played having a range of frequencies from the very lowest, of the order of 50 cycles, up to about 15,000 cycles and there was no detectable cancelling out, blasting, or other acoustical aberration throughout the entire series of tests.
In the form of the invention shown in Figs. and 11, the mounting ring I I8 is mounted directly into the base of the low frequency cone H3. In all other respects, the high frequency unit was substantially the same as shown in the main embodiment. In this form of the invention, the same circuits can be employed, the only difference being that the high frequency speaker moves as a unit with the low frequency cone and in a very real sense the speakers are coaxial and coplanar. This form of support is made possible by the extremely light Weight of the cone itself and its driving mechanism. I shall not describe the details of this form of the invention but the corresponding parts have the same numerals as in the main embodiment with, however, the prefix "l to indicate modification.
What I claim as new and desire to protect byl Letters Patent of the United States is:
1. In a loud speaker, a piezoelectric element including two fiat titanate ceramic members secured together face to face and having a common electrode therebetween and each having an outer uncommon electrode, means for supporting the element at its extremities, a speaker cone supported at its extremities, a driving rod secured to the element intermediate its ends and having driving relation with the apex of the speaker cone, signal leads secured to the uncommon electrodes for direct coupling to an amplier, and a signal lead secured to the common electrode for connection to ground to maintain the uncommon electrodes positive with respect to the common electrode,
2. The combination in a reproducing system of a relatively large diameter low frequency cone speaker having a voice coil, a relatively small diameter high frequency cone speaker having a piezoelectric element including two flat titanater ceramic members secured together face to face and having a common electrode therebetween and each having an outer uncommon electrode, means for supporting the element at its extremities, a speaker cone supported at its extremities and a driving rod secured to the element intermediate its ends and having driving relation with the apex of the speaker cone, a transformer having a secondary and a center tapped primary, the ends of the transformer primary being connected to the output of an amplifier and the center tap thereof to a source of plus potential, electrical connections between the voice coil and the transformer secondary, signal leads connecting the uncommon electrodes to the ends of the transformer primary, and a signal lead connecting the common electrode to ground to maintain the uncommon electrodes positive with respect to the common electrode.
3. The combination in a reproducing system of a relatively large diameter low frequency cone speaker havinga voice coil in series with the secondary of an output transformer, and a relatively small diameter high frequency cone speaker having driving means actuated by the primary voltage of the output transformer, said driving means comprising two titanate ceramic bodies secured together to form a common electrode and each having an outer uncommon electrode, signal leads connected to said uncommon electrodes for attachment to the primary of the said output transformer, a lead from said common electrode connected to ground, and a driving rod secured to said ceramic -bodies intermediate their extremities and to said small diameter speaker for driving the same at high frequencies, whereby the reproducing system comprising the two cones may be made to have a generally flat acoustical response between about 50 and about 15,000 cycles.
GLENN N. HOWA'I'I.
REFERENCES CITED The following references are of record in the le of this patent:
UNITED STATES PATENTS Number Name Date 2,051,200 Christensen Aug. 18, 1936 2,053,364 Engholm Sept. 8, 1936 2,383,832 Williams Aug. 28, 1945 2,402,515 Wainer June 18, 1946 2,453,521 Marquis Nov. 9, 1948 2,477,596 Gravley Aug. 2, 1949 2,484,950 Jaife Oct. 18, 1949 2,486,560 Gray Nov. 1, 1949 2,487,962 Arndt Nov. 15, 1949 OTHER REFERENCES Physical Review, vol. 71, pages 890-895, June 15, 1947.