US2212389A - Sound control apparatus - Google Patents

Description

Au8.20, 1940 c. M. CHORPENING 2,212,389

SOUND CONTROL APPARATUS Filed Sept. 29. 1938 CREED M.CH0RPEN1NG I 20 eral amplitude of the lower frequencies.

.Patented Aug. 20, 1940 PATENT OFFICE 2,212,389 SOUND CONTROL APPARATUS Creed M. Chorpening, Youngstown, Ohio, assignor to Astatic Microphone Laboratory, Inc., Youngstown, Ohio, a corporation of Ohio Application September 29, 1938, Serial No. 232,357

4 Claims.

'Ihis invention relates to a sound reproducing system, and more particularly to a method and apparatus for controlling sound reproduced from a record. The invention is especially applicable 5 to a system in which a condenser type generator, as a piezo-electric crystal, is utilized as the pick-up element and has as its principal object the provision of a pick-up circuit which will simultaneously compensate for low frequency I0 deficiency in the amplitude of the recording and provide `frequency' discriminating characteristics whereby the sound reproduced will be of high fidelity and controlled tone. "For reasons well understood in the art it is common practice to record the lower frequencies (below approximately 250 cycles per second) at constant wave amplitude and the higher frequencies at constant needle velocity which results in substantial curtailment of the volume or gen- Inasmuch as a translating device of the kind mentioned,'if sufiicient load resistance is provided,

has an output proportional to the Wave amplitude or'`amplitude of'vibration regardless of yfrequency,'its normal output is constant for the lower frequencies and declines steadily asv the higher frequencies" 'are reached.' `rNow by providing means discriminating against the lower frequencies the output of `the'pick-up may be rendered substantially constant throughout the audio frequency range thus providing a response of high fidelity.

In the reproduction of sound and particularly in reproduction of sound from records a certain amount of objectional noise resulting from extraneous pick-up of signals composed principally of the higher frequencies is reproduced and unless some means against such frequencies the final reproduction may be unsatisfactory. Also it is desirable to utilize such means to compensatefor variations in the characteristics of the pick-up device, for

desired low or high frequency preponderance in the sound being picked up, forl imperfections in the frequency response of the loudspeaker, and

for other purposes well understood in the art.

Accordingly, a further object of the invention is the provision of a pickup circuit requiring but simply constructed and inexpensive electrical accessories by means of which the tonal qualities of the sound being reproduced may be satisfactorily controlled simply by actuating a three position switch of conventional design and connected into the signal circuit between the pickup and the amplier.

is provided to discriminatel The invention will be ydescribed by way of ex ample with reference to a reproducing system, shown schematically in the drawing in which the pickup device hereinbefore mentionedis a translator of the piezo-electric crystal type,y the 5 invention being particularly adaptable to such use. Other objects and advantages of the `invention should become apparent asthe description proceeds.

In the drawing: c 1o'v Figure l is a schematic diagram of a system embodying'my invention for reproducing'sound from phonograph records; and

Figure 2 is a graph illustrating the character y istics of operation of the tone controlofmy in- 15 vention.

Referring now to Figure 1, the piezo-electric translator, generally indicated at I0, is physically actuated by the stylus II and is vconnected p through circuit I2-I6 and conductor 25.,to a 20 suitable amplifier 28 which in turn feeds loud-l speaker 32 through conductors 30. The circuit referred to consists ofvconductor I2, a fixed resistance I3, conductor I4, a variable resistance I5. constituting the volume control, ,and con- -25 ductor I6. A condenser I9 has one of its ter-` minals connected with an arm 20 of athreepoint switch I1, the center terminal 22 of which is open. The other two terminals of the switch 2| and 23 are connected, respectively, with con- 30 ductors I2 and 25 leading from the translator device l0.

With the switch arm 20 in the neutral position shown in the drawing, condenser I 9 is ineffectual and the impedance of the pickup circuit is solely 35 that of the fixed resistance I3 and the variable resistance I5 in series in the circuit. This condition results in a volume-frequency relation graphically shown by curve C22 in Figure 2. With switch arm 20 moved to contact terminal 40 2l, theA capacitance of I9 is placed in series with the pickup circuit and in parallel with resistance I3 resulting in relative attenuation of the lower frequency signals and emphasizing the higher frequency responses. The result of the series 45 coupling of the condenser I9 is depicted graphically by the volume-frequency curve C2I of Figure 2.

'I'he third terminal 23 of switch I1 being connected with the conductor 23 places condenser 50 I9 in shunt relation with translator I0 when switch arm 20 is moved to contact this terminal and in this condition of the circuit the higher frequency responses are more severely discriminated against resulting in a volume-frequency 55 relation indicated by curve C23 of Figure 2. It has been found that the above described three circuit conditions provide an adequate control of the sound reproduction under all methods and conditions of detection and that for all ordinary purposes a finer degree of control is unnecessary, It should be observed that the control is accomplished simply by the manipulation of a conventional three point switch which is readily installed and operated and which is not likely to fail in service.

In practice, I have found that a resistance ofy approximately 1 megohm is suitable for resistance I3 and that 1/2 megohm resistance is suitable for resistance l5. The capacity of condenser I9 may, of course, be varied depending onA the characteristic of the translator but in general it may be in the nature of .0005 microfarad when coupled with a commercial double piezo-electric crystal actuated by a stylus as shown.

It can thus be seen that I-have provided a tone control for use as described which accomplishes the objectives initially set out. By the use of a simple arrangement the signal response from the translator is caused to selectively flow either through a circuit having only series resistance in which the various frequencies maintain their normal relative strength, through a circuit having series coupled capacitance in which the lower fre- SiQlquencies are attenuated, or through a circuit having shunted capacitance in which the higher frequencies are attenuated. The arrangement is further simplified by utilizing the same means, specifically the condenser I9, to providethe ca- 3Q; pacitance in both instances.

4Q? ing, the broken line represents the Volume Yor amplitude of the recording and shows the decrease in the lower frequency range. The line C22 represents the response attained when sufficient resistance is placed in the output circuit 45j to render the output proportional to the amplitude of` vibration of the pickup stylus. The respense is -iiat at lower frequencies and curves downwardly in the4 higher ranges. By coupling the condenser i9 across resistance I3 the higherl frequency signals are relatively strengthened, giving a response curve illustrated by line C2| and resulting in high fidelity production.

The above specifically described embodiment ci' my invention should be considered as illustrative only as obviously many variations in the arrangement of the frequency discrimination method specifically disclosed herein may be made without departing from the spirit or scope of my invention. l

What I claim is:

l. In a sound reproducing system, a source of audio frequency signals comprising a piezo-electric translating element,a circuit connecting said element with a sound reproducing assembly, frequency discriminating means comprising two impedance elements connected with said circuit, the ilrst impedance element being a resistance fixed in rseries relation with said circuit, the second irnpedance element being a condenser, means to conne-ct said condenser in series relation with said circuit and shunting said resistance, means to connect said vcondenser in parallel with said resistance and translator, and means to disconnect said condenser from said circuit.

- 2. A system according to claim 1 in which said lastthree mentioned means comprise a unitary three position switch.

3. In a. sound reproducing system, a source of audio frequency signals, a circuit connecting said source with a sound reproducing assembly, vfrequency discriminating means comprising tWo impedance elements connected with said circuit, the rst impedance element being a resistance fixed in series relation with said circuit, the second impedancey element being a condenser, means to connect said condenser in series relation with said circuit andv shunting said resistance, means to connect said condenser in parallel with said resistance and translator, and means togdisconnect said condenser from said circuit.

4. A system according to claim 3 in which said last three mentioned means comprise a unitary three position switch.

f A CREED M. CHORPENING.

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