US1675031A - Loud-speaker system - Google Patents

Description

June 26, 1928.

1,675,031 F. A. KOLSTER LOUD SPEAKER SYSTEM Filed Sept. 1'7, 1925 FIE J (NI/EN Toe fiede/v'ck 14. ho/sfer:

Patented June 26, 1928.

UNITED STATES GRAPH COMPANY, FOB-KIA.

I 1,675,031 PATENT oFF cE.

FREDERICK A. KOLSTEB, or PALO ALTO, CALIFORNIA, assrenon To FEDERALTELEM or SAN EEAncIsoo, CALIFORNIA, A CORPORATION or can:-

- LOUD-SPEAKER SYSTEM.

Application filed September 17 1925. Serial No. 56.800. W

broadcast receivers for converting the de-,

tected and amplified radio energ into sound.

It is an object of this invention therefore to devise a' translating system-which will translate electrical energy modulated at voice frequencies into sound waves with substantially no distortion; that is, a system in which a translator will. give substantially the same response for any frequency within the entire range of Voice frequencies.

It is a further object of this invention to devise such a system in which the voice frequency range is divided up into a plurality of frequency bands by means of a plurality of electrical units. It is proposed to allow each unit to translate its frequency band into mechanical vibrations.

Itis a further object of this invention to provide .a single aperiodic reproducer for' It is a further object of this invention to devise a system which converts the electrical energy into mechanical vibrations by means of a plurality of electricalunits and to im-' pose these vibrations longitudinally upon a plurality of rods and to connect these rods to a common aperiodic diaphragm.

Further objects of the invention will appear from the following description where I have disclosed the"preferred embodiments of my invention. N

Referring to the drawings:

Figure 1 showsa loud speaker system applied to the output of a vacuum-tube amplifier and constructed according to the principle of m invention.

Fig. 2 s ows sound response curves for the systemdisclosed' in Fig. 1.

Fig. 3 is an application of the system' shown in Fig. 1.

Fig. 4. is another modification of the systom shown in Fig, 1.

\Vhen electrical energy is modulated by means of the human voice or byfmusic-the result is to produce a plurality 'of superposed electrical vibrations which range in frequency all the way from 50 to 10,000 cycles per second. In the past loud speak- "crs have usually" been constructed with' a single magnetic unit whiclrliad its pole pieces placed in proximity-tea; steel diaphragm. WVith such loudspeakers there are two different inherent sources distortion. One is the natural resonance of'the winding of the magnetic unitwhich is resonant at some point within the'voice frequency range. The other is due to the natural mechanical resonance of the diapliragm. If a sound response curve for such a loud speaker j is plotted between sound response and fre quenry for a given energy input','it will be found that the curve will have several,

humps or peaks which correspond to these resonant points. The curye'sLalsofall off rapidly for the lower-frequencies and for the higher frequencies. .Therefore, such a loudspeaker will convert thelelectrical vibrations into sound at greater'efiiciency for certain frequencies than for .fothers, thus producing distortion. i 1 I q i It has been found by experimentation that if a loud speaker will give uniform response or faithful reproduction for frequencies ranging from 50110 5000 cycles per second no appreciable distortion will be apparent. The system of this invention has therefore been designed to give a flat top characteristic response curve for frequencies ranging from 50 to 5000 cycles per second. However. it should be underitood that the same principles may be applied 'to produce a fiat top response curve for frequencies ranging. up to as high as 10,000 cycles per second.

In that embodiment of the invention shown in Fig. 1 of the drawings the system is shown as applied to the out-put of :1 cascade vacuum tube amplifier. This amplifier .is preferably of the standard impedance 13, electron emission element 14 and plate 15. The input circuit 16 of the vacuum 10 is suitably coupled to some source of electrical energy'modulated at voice frequency and is connected to the grid 13 and electron emission element 14 in the usual manner. In the output circuit 17 of the'tube 10 there is an impedance. 18 having its upper terminal electrically connected with the grid 13 of the vacuum tube 11 in series with the condenser 19. The usual grid leak 20 is connected between the grid 13 of the vacuum tube 11 and the electron emission element 14 of this tube. The electron emission elements 14 of the vacuum tubes 10 and 11 are. energized from a common A battery 21, and the output circuits 17 and 12 of the two vacuum tubes are energized from a common B battery 22.

In the output circuit 12 of the vacuum tube 11 there is provided a plurality of electrical units, each of which converts a portion of the output energy into mechanical vibrations. These electrical units are so designed that they: 821th convert electrical energy into mechanical vibrations most. efficiently at a certain point along the voice frequency range, and these points are distributed along the voice frequency range from 50 to 5000 cycles. Three of these electrical units 125, 225 and 325 have been shown and they each preferably comprise a transformer or other coupling arrangement 26 having a primary winding 27 and a sec ondary winding 28. The secondary 28 is connected to the magnet windings 29 of a telephone unit which telephone unit also in the case of theunit 125 includes a diaphragm 130. 'A capacitance 30 is connected in shunt with the windings '29. The inductance value of the windings.

29 and of the capacitances of the condensers 30 are so selected that the electrical units will be resonant at some frequency within the voice range and the arrangement is such that the resonant points are spaced throughout the voice frequency range or at least from 50 to 5000 cycles per second. To prevent the resonance peaks from being too sharply defined a large amount of damping is introduced by making the windings 29 of comparatively high resistance. To prevent the introduction of distortion due to the mechanical resonance of the diaphragms, it is preferable to constructthe diaphragm for the telephone units which translate the higher frequencies relatively. smaller in diameter than the diaphragms which are employed to translate. the lower frequencies. It is also preferable to provide a common sound amplifying horn which is constructed in such a manner that the low; frequency sound waves will be radiated out of the sound horn with equal efficiency to thesoundwaves of higher frequency. Thus the diaphragm 230 for the unit 225 is made. relatively larger in diameter than the diaphragm 130 and accordingly the diaphragm 330 for the electrical unit 25 is made relatively largerin diameter than the diaphragm 230. Also, the throat 231 of the sound amplifying horn 32 is made relatively larger than the throat 131 of the electrical unit 125 and also the throat331 of the electrical unit 325 is made relatively larger than the throat 231.

Fig. 2 ofthe drawing shows response curves for the electrical unit disclosed in Fig. 1. These response curves are plotted between sound response and frequency in cycles per second. Curves 1, 2 and 3 show the response of the individual units 125, 225 and 325 at different voice frequencies for constant input of energy. It will be noted that the resonant peak of curve 3 is arranged to be substantially at 50 cycles while the peak of curve 2 is positioned at 500 cycles and the peak of curve 1 is at 5000 cycles. The resultant response curve for the individual units taken together is represented by means of curve 4 which will be substantially a straight fiat line between the frequencies of 50 to 5000 cycles. This means that for a given input of energy into the system the response will be substantially the same between the frequencies of 50 to 5000 cycles per second. The electrical units in reality serve to divide up the voice frequency range into a plurality of frequency bands which are spaced along the voice frequency range and to translate these frequency bands into sound waves.

Instead of having these electrical units operate separatemechanical reproducers it is preferable to have them operate a single aperiodic reproducer. Thus, as shown in the modification in Figs. 3 and 4 the electrical units 125, 225 and 325 actuate a single aperiodic diaphragm. This reproducer is preferably in the form of a conical aperiodic diaphragm 33 suitably supported at its edges as by a rigid rim 34. The magnetic unit 129 of the electrical units 125, 225 and 325 in this case are provided with armatures 35, 36 and 37 which connect with rods 38, 39

and 40. These rods connect to the apex 41 of the conical diaphragm 33 and actuate this diaphragm by their joint action. In the operation of this system the magnetic units 29 set the armatures 35, 36 and 37 into mechanical vibration and these armatures vibrate the rods 38, 39 and 40 longitudinally to actuate jointly the conical diaphragm 33. Since this diaphragm is aperiodic'no distortion will be introduced due to mechanical resonance.

The system shown in Fig. 4 is somewhat similar to that shown in Fig. 3 but differs in the manner in which the electrical units 125, 225 and .325 are coupled to the, output 12 of the vacuum. tube 11. In this case, the magnetic units 29 are individually connected in series with the condensers 142, 242 and 342, and are connected in parallel by the conductors 43 and 44. The conductors 43 and 44 are suitably coupled to the output circuit 12'as by means of an impedance 45. The operation of this arrangement is substantially the same as the system shown in Fig. 3. The values of the series inductances and capacitances are so selected that the electrical units 1, 2 and 3 will attain a value of minimum impedance at spaced points along the frequency range, as for example, at 50 cycles, 500 cycles and 5000 cycles. As in the case of the other system, the comb ned effect of the electrical unit upon the diaphragm 33 will be to obtain a fiat top characteristic response curve for the entire system.

I claim:

1. In a system of the source of electrical energy modulated at voice frequencies, means for separating said voice frequencies into a plurality of frequency bands spaced along the voice frequency' range, and translator'means including a single aperiodic diaphragm for converting said energy into sound waves.

2. In a system of the class described, a source of energy modulated at voice frequencies, a plurality of magnetic units electrically associated with said source, means tor distributing the energy to said units in accordance with the frequency of the same, and a single aperiodic reproducer mechanically vibrated by energy from said units 3. In a system of the class described, a source of. electrical energy modulated at voice frequencies. and means for translating said energy into sound vibrations comprising a plurality of tunedmagnetic units having their resonant peaks distributed along the voice frequency range, and a single aperiodic sound reproducer actuated in'accordance with the energy in said units.

4. in a system of the class described, a

class described, a

source of electrical energy modulated at voice frequencies, a plurality of separate magnetic telephone units electrically connected with said source, a capacitance associated with each unit whereby said units voice frequencies, means for converting said energy into separate groups of mechanical vibrations applied to separate mechanical members, a conical aperiodic'diaphragm, and means for connectingsaid mechanical members to the center of said diaphragm.

7. In a system of the class described, a

source of electrical energy modulated at voice frequencies, means fortranslating said energy into mechanical vibrations including a plurality of magnetic units having separate armatures, means associated with said units whereby the energy in each unit Will rise to maximum for a certain frequency, the maximum points of the diilerent units being distributed along the voice frequency range, a

plurality of rods separately vibrated by said units, and an aperiodic diaphragm, said rods jointly acting to vibrate said diaphragm from each of said armatures.

In testimony whereof, I have hereunto set my hand.

rannnarcrr a. KOLSTER.

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