US2727949A - Loudspeaker - Google Patents

Description

Dec. 20, 1955 J, a LOKKESMOE 2,727,949

' LOUDSPEAKER Filed Sept. 22, 1951 IZ g. .Z

12 fig 2 INVENTOR.

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H 5 ATTORNEYS United States Patent-O LOUDSPEAKER Julius B. Lokkesmoe, Berkeley, Calif. Application September 22, 1951, Serial No. 247,779 4 Claims. (Cl. 179-1155) My invention relates to improvements in loudspeakers, and particularly to loudspeakers of the electro-dynamic type.

An object of my invention is to provide a novel and improved electro-dynamic loudspeaker having high fidelity response at both the low and high frequency ends of the audio frequency range.

Another object is to provide novel and improved means for improving the low frequency response of an electrodynamic loudspeaker.

This and other objects of my invention together with various advantages thereof are set forth in the following description of the embodiment of my invention illustrated in the accompanying figure wherein:

Fig. 1 is a partially sectional view of my improved loudspeaker; and

Fig. 2 is a wiring diagram of a circuit employed in connection therewith.

in Fig. 1 there is illustrated an electro-dynamic loudspeaker embodying my invention. This loudspeaker comprises a conventional type resiliently mounted coneshaped diaphragm 12 having a cylindrical voice coil 14 mounted coaxially at the apex thereof, and a permanent magnet structure 16 involving a stem or pin 18 projecting a short distance into the voice coil 14, and tapered pole tips 20 opposite the free end of the pin, externally of the voice coil. The free end of the pin 18 and the pole tips 20 define a gap in which the voice coil is free to move in response to currents flowing through the voice coil.

In order to render such a loudspeaker efiicient in transforming electrical energy into acoustical energy, the voice coil 14 is normally of light weight compared to the weight of the diaphragm 12. Such loudspeakers, however, are normally inherently deficient in the regions covering both the low and high frequency ends of the audio frequency range and particularly at frequencies in the range below about 100 to 125 cycles per second. In that low frequency range, such loudspeakers generally attenuate the low frequency sounds to such an extent that the deficiency requires remedy of some sort in order to attain high fidelity.

According to my invention high fidelity of such a loudspeaker is attained by mounting an auxiliary coil upon the pin 18 in magnetically coupled relationship to the voice coil and connecting this coil in a tuned circuit that is electrically connected in parallel to the voice coil. With this arrangement I find I am able by adjusting the frequency characteristic of the circuit, to not only improve the low frequency response, but also the high frequency response of the speaker at the same time.

As illustrated in Fig. 2 a condenser 22 connected in series with the auxiliary coil 21, forms a series tuned circuit 24 that is connected in parallel with the voice coil 14 across the secondary winding 26 of an output transformer 28. The resonant frequency of the tuned circuit 24 depends in part upon the inductance of the coil 21 and the inductances of the voice coil 14 and the effective inductance of the secondary winding 26 looking into the transformer 28 from the output side thereof. The value of the condenser 22 is so chosen relative to the values of the three inductances mentioned that it tunes the circuit 24 to a low audio frequency of about 25 to 30 cycles, thus causing the currents flowing at low frequencies in the tuned circuit 24 to be emphasized compared with currents flowing at other frequencies. Inasmuch as the voice coil 14 is inductively coupled to the auxiliary coil 21, increased currents flow at such low frequencies in the voice coil as well as in the auxiliary coil, the flux produced by such low frequency currents being confined to the magnet structure.

It appears, however, that at the high frequency end of the audio frequency range, the flux is no longer confined entirely to the magnet structure. An increasing amount of the coupling between the auxiliary coil and the voice coil becomes air coupling, thus cutting down the iron losses and thereby permitting the higher frequency currents to be of greater magnitude and freer from distortion. In this manner, the higher frequency response is enhanced. The auxiliary coil is preferably of higher inductance than the voice coil, thereby reducing the magnitude of the capacitance required of the condenser 22 in order to tune the circuit to the desired low frequency.

The mutual inductance of the coupling may be either positive or negative, depending upon whether the two coils 14 and 21 are wound in the same direction or in the reverse direction on the pin 18, when considered with reference to their connections to the secondary winding 26. While either of these arrangements is effective, I prefer to wind both coils in the same and preferably clockwise direction on the pole pin, looking in the direction of the cone.

From the foregoing description of my invention, it is apparent that I have provided a novel and improved electro-dynamic loudspeaker arrangement in which higher fidelity is achieved by improving the frequency response characteristics at both ends of the audio frequency range. While my invention has been described with reference to a particular structural arrangement of an auxiliary coil upon the pin of a magnet of an electro-dynamic speaker, it is to be understood that various modifications of my invention may be made without departing from the principles of my invention. It is therefore intended to cover all such modifications thereof that fall within the scope of the appended claims.

I claim:

1. In combination with a loudspeaker employing a diaphragm driven by a movable voice coil that is mounted in the gap of a magnet, said diaphragm and coil having a response characteristic that falls off at low sound frequencies, a tuned circuit involving a stationary coil fixedly mounted on said magnet, said circuit being tuned to a low frequency of the order of 25 cycles per second whereby due to the magnetic coupling between said coils at such low frequency resulting from the fixed mounting of said stationary coil on said magnet, the low audiofrequency currents through said voice coil will be emphasized.

2. In combination with a loudspeaker employing a diaphragm driven by a movable coil that is mounted in the gap of a magnet, a condenser and an inductance connected in series across said movable coil, said inductance being formed by a stationary coil fixedly mounted on said magnet and inductively coupled at low audiofrequencies to said voice coil by said magnet whereby low audio-frequency currents will be emphasized.

3. A sound reproducing system comprising a magnet formed with a ga a movable coil mounted in said gap and arranged to drive a diaphragm, a stationary coil fixedly mounted on said magnet, the inductance of said low irequency' in the audio. range whereby due to the magnetic coupling at such, low audio-frequency between said; coils. resulting from the fixed mounting of said stationary coil on said magnet, the low audio-frequency currents through said, voice coil will be emphasized.v

4. A sound reproducing system comprising a magnet formed with a'gap, a movable coil mounted in said gap and. arranged to drive a diaphragm, a stationary coil fixedly mounted on ,said magnet, the self inductance. of said stationary coil being large in comparison with the self inductance of said movable coil, and a circuit tuned to a low frequency in the audio range. and formed in part by said stationary coil being connected in series across said movable coil whereby due to the magnetic on said magnet, the low audio-frequency currents through said voice coil will be emphasized.

References Cited in the file of this patent UNITED STATES PATENTS 1,830,402 Miessner Nov. 3, 1931 1,868,607 Kolster July 26, 1932 1,878,232 Chromy Sept, 20, 1932 2,004,735 Thomas June 11, 1935 2,007,746 Ringel July 9, 1935 2,007,748 Olson July 9, 1935 2,007,749 Anderson July 9, 1935 2,269,284 Olson Jan. 6, 1942 2,286,123 Steers June 9, 1942

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