US2537911A - Audiometer - Google Patents

Description

Jan. 9, 1951 s, REGER 2,537,911

AUDIOMETER Filed Sept. 18, 1946 INVENTOR SCOTT N. REGER ATTORNEYS Patented Jan. 9, 1951 AUDIOMETER Scott N. Roger, Iowa City, Iowa, assignor to Patent Management, Incorporated, Minneapolis, Minn., a corporation of Minnesota Application September 18, 1946, Serial No. 697,822

17 Claims.

My invention relates to audiometers and has for an object to provide an audiometer by means of which a number of patients may be simultaneously examined.

Another object of the invention resides in providing an audiometer having a number of outlets from which the same sounds may emanate, and in modifying the sounds without changing their frequency so that the patient may differentiate the different sounds and designate the same without knowing the frequency or intensity of said sounds.

A still further object of the invention resides in providing an audiometer having a generator adapted to produce a continuous audible sound and in further providing a control device adapted to initiate said sound and to terminate said sound after a predetermined period.

An object of the invention resides in providing an audiometer in which the continuity of the sound may be varied in accordance with different predetermined sound patterns to produce one or more sound pulses of varying duration, number or arrangement.

A feature of the invention resides in provid ing a plurality of control devices for controlling the effectiveness of said generator, each adapted to produce a different sound pattern, and in providing selector means for selectively rendering any one of said control devices effective.

An object of the invention resides in utilizing in said generator, at thermionic oscillator and in providing means for making and breaking one of the circuits associated therewith in accordance with predetermined sound patterns.

Other objects of the invention reside in the novel combination and arrangement of parts and in the details of construction hereinafter illustrated and/or described.

In the drawing, the figure is a wiring diagram of an audiometer illustrating an embodiment of my invention.

In the operation of my invention, a generator is employed which is adapted to produce continuous audible sounds of different frequencies and intensities. These sounds are interrupted in a manner to give individual sounds of definite duration and separated by dwell periods of predetermined length. These individual sounds have been referred to in the specification and claims as sound pulses to distinguish from the resultant sound which has merely been designated as a sound and which may consist of one or more pulses.

The invention consists of an oscillator it which produces an alternating or pulsating electric current. This current passes through an amplifier II and through an attenuator I 2 from which the same is directed into a number of sound producing devices [3. The sound producing devices 13 convert the alternating current into audible sounds which may be discerned by the patients being examined. The oscillator l9 and the sound producing devices It constitute a generator for the sounds utilized in the invention. The current produced by the generator is controlled by a number of control devices l5, l6, I1 and 18 which interrupt or vary the current in different ways so as to enable the patient to distinguish the difierent sounds produced by means other than by the frequency or intensity of the sound. Each control device interrupts the sound in a different predetermined manner which I have referred to as a sound pattern, the said sound patterns depending upon the form and construction of the particular control device. In addition, a signaling device M informs the patient when the device is in operation. A power supply unit l9 furnishes suitable current for operating the invention. These parts of the invention will now be described in detail.

The oscillator H3 consists of a thermionic tube 2| having a grid 22, a plate 23, a cathode 24 and a heater 25 for said cathode. The tube 2i is coupled with a portion of an inductance 25 and any of a number of condensers 21, 23, 29, 30, El, 32, 33 and 34. which are connected in series to form a resonant circuit. This construction provides an oscillator which produces an alternating or pulsating current whose frequency depends upon the relation between the inductance and condenser connect d in the circuit. For connecting a certain portion of the inductance 26 and any one of the various condensers in the circuit, two multiple contact switches 35 and 5!! are employed. The switch 35 has a number of fixed contacts, 36, 31, 38, 39, 49, M, M and and a movable switch arm 10. The switch 69 has a number of fixed contacts, 44, 45, 46, M, 43, 4d, 5d and 5| and a movable switch arm 80. Both of the switch arms to and are mounted on the same shaft, which is diagrammatically indicated at [El in the drawing, and travel in unison so that certain of the sections of the inductance 26 are always connected to certain of the condensers 2! to 34 inclusive. The inductance 26 is provided with three taps 52, 53 and 54. A conductor 55 is connected to the tap E52 and also to both of the contacts 36 and 31. Another conductor 55 is connected to the tap 53 and to both of the contacts 38 and 89. While another conductor is connected to the tap E5 5 and to all of the contacts 5Q, ii, ii and it. One side of each or" the condensers H to 3 5 inclusive is connected to a conductor 53 which is grounded. The other sides of these condensers are connected by means of conductors @2, E3, 6%, 3'6 and 68 to the respective contacts to El inclusive. The inductance 26 is connected by means of a conductor iiii with a resistor H which, in turn, is connected by means of a conductor 72 with the grid 22 of tube 2!. The cathode 2d of this tube is connected by means of a conductor E3 with a resistor it which, in turn, is connected by means of a conductor 55 with both of the switch arms To and 86. It will thus be seen that one of the condensers 2? to 3 inclusive and a portion of the inductance 2%; are connected in series in the grid circuit of the tube 25.

For the purpose of providing current for operating the invention, the power supply it is employed. This power supply includes a transformer it having a primary '1? adapted to be connected to a suitable source of aiternating current. This transformer also has a secondary it! which is provided with a center tap "iii and which is connected to ground by means of a conductor 8!. The ends of this secondary are connected by means of conductors and 33 to the plates 8 and 85 of a rectifier tube 86. The filament 8? of this tube is connected by means of a conductor 58 to a secondary winding 89 on the transformer 16. This winding is connected to a condenser 53! by means of a conductor $2. Condenser BI is grounded through a conductor lit. Another conductcr st connects the other side or the filament 8'? to conductor 92. The output of the tube 55 is directed through a filter system 53 3 and from which direct current is furnished to the audiometer by means of a conductor $5. The filter system 94 includes two resistances 95 and iii and in addition to the condenser 9E, two other condensers 58 and cc. Both the condensers es and iii are grounded through conductors 55E and E132. The resistance 92% is connected to the conductor 92 and by means of conductor IE3, to the resistance iii. This resistance is, in turn, connected to the conductor .15. Condense 93 is connected by means of a conductor lil i with the conductor Eta while condenser 9* is directly connected to the conductor 95.

The plate 23 of tube 25 is connected to a filter system E95 which consists of three condensers E86, it? and E538 and two resistors its and Iii. The plate 23 is connected by means of a con ductor M2 to the resistor Hi9 which is connected by means or" a conductor its to the resistor iii. A. conductor lid connects the conductor H2 with condenser hi6 and another conductor H5 connects the conductor HQ with condenser idi. In a similar manner, a conductor H 5 connects the resistor Ell with the condenser i538. All three condensers Hit, it? and 9 E33 are grounded through conductors Ell, H5 and lid. Plate voltage is procured for the tube 2! from the conductor 95. A branch conductor E25 is connected to the con ductor $5 and to a resistance 23. This resistance is connected by means of a conductor E31) to conductor I it.

Due to the fact that certain frequencies are more audible to the human ear than other frequencies, it becomes necessary to equalize the output of the oscillator it in accordance with the frequencies of the currents produced thereby. For this purpose, a series of equalizing resistors E22, E25, E2 E, E25, E26, E21, E28 and 129 are employed. Also, an additional multiple contact switch ESE is used. This switch has a number of contacts 632 to E39 inclusive which are connected to the various resistors 22 to i292 by means of conductors M2 to M9 inclusive. Switch E3! also includes a switch arm ME which is adapted to make contact with any of said contacts. The three switches Gil and it! are all ganged and the switch arms it, 88 and i 'll of the same are all connected to the common shaft E5 i, previously referred to. By the selection of suitable values for the resistors i222 to E23 inclusive, the output from the oscillator is can be so regulated that the sounds produced by the sound producing devices E3 are comparable. All of the resistors E22 to :29 inclusive are connected to a common conductor 52 which will be subsequently referred to. The switch arm Mi is connected by means of a conductor E53 with the conductor l5 which is associated with switch 35 and E8.

The amplifier ii is merely shown diagrammatically and a single stage has been illustrated. It can, however, be readily comprehended that any type of amplifier may be employed and as many stages as found necessary utilized. The amplifier 5E includes a thermionic tube 5% hava grid a plate 553, a cathode I51. and a heater 55 for the same. The conductor i 52 previously referred to, is connected directly to the grid 455 of the tube E54. A resistor Hi l is connected by means of a conductor E5 to the conductor 152. Said resistor is further connected by means of a conductor E56 to ground. The cathode l5? of this tube is connected by means of conductors Kit and it! to a condenser 62 and a resistor M3. This condenser and resistor are in turn connected by means of conductors Eti' and its to the conductor E66 and thus grounded. The plate E58 of the tube !54 is connected by means of a conductor N59 with one side of the rimary Eli of an output transformer H2. The other side of this primary is connected by means or" a conductor lit with the conductors E2! and 95. Thus, plate voltage is furnished through the primary of this transformer to the plate I58 of the tube [5 1. The secondary PM of the transformer F2 is connected to conductors I and El which impresses the amplified voltage upon the attenuator E2.

The attenuator it comprises five resistors ill, H5, H9, EB! and 82 which are connected in series by means of conductors E83, i8 5, E35 and 566. The resistor iii is further connected by means of a conductor It! with the conductor H6. Resistor i322 is connected by means of a conductor Etc with the primary we of a transformer iSl. In addition'to the five resistors ill, E18, ElQ, it! and i822, three other resistors I92, i923 and I93 are employed. These resistors are all connected at one end to the conductor Hi5 from the secondary lid of transformer H2. The other ends of these resistors are connected to the conductors i8 5, Hi5 and 33 pr viously referred to. The attenuator E2 also includes a selector switch 2% which comprises a number of contacts E95, ifi'i, i538, W9, 29E and 2632. These contacts are connected by means of conductors 2&3, 2%, 235, 2%, till and 2533 to the various conductors E83, ltd, E85, Hi6 and 588 respectively. Said switch includes a switch arm 2% which is adapted to make contact with any of the said contacts. This switch arm is connected by means of a conductor 2| l with the primary Hit; of transformer [9L The sound producing devices I3 may be of any suitable character or construction. For the purpose of illustration, ear phones have been shown, there being as many of the said ear phones as there are patients to be examined. Each of the ear phones I3 is connected by means of conductors 2I2 and 2I3 to two other conductors 2I4 and 2I5. These latter conductors are, in turn, connected to the secondary 2I6 of the transformer I9I.

The control devices I5, I6, I! and I 8 include switches 2H, 2I3, 2!!) and 22!. These switches each have a fixed contact 222 and a movable contact 223. The contact 223 has a lug 224 adapted to engage one of a correspondin number of cams 225, 226, 22'! and 228. All of these cams are mounted on a single shaft 229 which is connected to a system of reduction gearing which is diagrammatically indicated at 23!. This gearing is operated by an electric motor 232. Motor 232 has connected to it, conductors 233 and 234 which, in turn, are connected to a suitable source of electric energy such as the line used for energizing transformer I6. A manually operated switch 235 is disposed in the conductor 233 and serves to actuate or shut off the motor 232. The cam 225 has a single hump 236 on the same which is adapted to engage the lug 224 of switch arm 223 and to open the switch 2!! once for every revolution of the shaft 223. The cam 226 has two humps 23! and 238 which are successively adapted to engage the lu 224 of switch arm 223 of switch 2I8 and open said switch, twice in succession. In a similar manner, cam 22! has three humps 34!, 342 and 343 which similarly open the switch 2 I 9 three times during each revolution of shaft 229. Cam 223 has four humps 344, 345, 346 and 34! which operate in the same manner and which serve to open the switch 22! four times during each revolution of the shaft 229. All of the contacts 222 are connected by means of conductors 348 to ground. The movable contacts 323 of the switches 2I'!, 2I8, 2I9 and 22! are connected by means of conductors 35!, 352, 353 and 354 to the contacts 355, 356. 35? and 358 of a selector switch 359. This switch also includes a movable arm 36! which is connected by means of a conductor 362 to the conductor H6 previously referred to.

In conjunction with the sound generator used in the audiometer, the visible signaling device I4 is employed which includes a lamp 363. This lamp is controlled by means of a switch 364 similar to switch 2!!. The switch 2!! is normally open and has a fixed contact 365 and a movable contact 366. The lattercontact has a hump 35'! which is adapted to be engaged by a raised portion 358 of a cam 369. The raised portion 368 is coextensive with the circumferential extent of all the humps 344, 345, 346 and 34! of cam 228. By means of this construction, the light 363 is turned on during such portion of the cycle of operation of the shaft 229 in which the various sound pulses are given.

The operation of the invention is as follows: When the switch 235 is closed, a circuit is established through the motor 232 which drives the shaft 229. When the hump 36! of switch arm 363 of switch 364 engages the raised portion 363 of cam 363, the light 363 becomes illuminated. At the same time, a circuit is established through one of the switches 2I'I, 2I3, 2!!) or 22! depending I upon the position of the switch arm 36! of switch 353. If the said switch arm engages contact 355, the circuit is established through switch 2!!. This circuit includes conductor 362 which is connected with the plate of tube 2|. This circuit, when closed, reduces the potential to the plate 23 of said tube and renders the oscillator I6 inoperative. As soon as hump 224 of switch arm 223 engages the raised portion 236 of cam 225, the said switch is opened and the oscil lator II] allowed to function for the period determined by the circumferential extent of the raised portion 236 of said cam. This produces one pulse by the oscillator I!) which, in turn, is converted into one sound pulse in each of the ear phones I3. The output of tube 2! is taken from the cathode 24 of said tube and passes through the equalizing resistors I22 to I29 inclusive and to the grid I55 of tube I 54. The output of the tube I54 is delivered to the attenuator I 2 which delivers the energy to the ear phones I3 by means of which the same is converted into sounds.

The device is so constructed, that the oscillator I6 can be caused to operate at any of l a certain number of frequencies which are determined by the values of the condensers 2'Ito 34 inclusive and the portions of the inductance 56 connected in series therewith. The switch I3!, being connected to the shaft I5! which also operates switches 35 and 66, causes the oscillator to deliver comparable alternating currents of predetermined frequency depending upon the setting of the said shaft and switches.

The attenuator I2 operates to vary the intensity of the alternating current from the output transformer I12 and delivers the same to the transformer I3!. The ear phones I3 are fed from the secondary 2I6 of this transformer.

When the operator is about to test a num ber of patients, the procedure is as follows: Each of the patients to be examined is given one of t e ear phones I3 and instructed to watch the light 363. He is told when the light goes on, to listen and count the number of sound pulses he hears. He is then required to note on a suitable record, the number of sound pulses he heard and if he heard no sounds whatsoever, to so note. The operator first sets the shaft I5! to the proper position to cause the oscillator I5, when energized, to generate the desired frequency on which the test is to be made. He usually starts at one end or the other of the audible frequency range. The contact arms I0, and I4! of the three switches 35, 66 and I3! are brought to the proper contacts to give the desired frequency. Attenuator I is then set by moving the switch arm 2!!! to the desired contact givin the greatest intensity of the sound. The operator then selects by means of switch 353, the particular pattern of the sound to be given. In the particular device shown, the sound may be interrupted so as to produce one, two, three or four successive pulses. If the switch arm 36! is positioned as indicated in the drawing, the circuit through the switch 2!? is closed and the device gives a single pulse. Switch 235 is then closed and the motor 232 actuated. When the cam 369 comes around the proper position, switch contact 366 is caused to ride on the raised portion 363 of cam 369 which closes switch 364. This causes the light 333 to become illuminated and the patients all listen for the sound. As the shaft 229 continues to rotate, the raised portion 236 of cam 225 opens switch 2i! and breaks the circuit through the conductor 362 which is connected to the plate circuit of the tube 2!. When the said switch is open, full plate voltage is applied to the plate 33 and the oscillator op- 7. crates. The output from the oscillator feeds through the equalizing resistors i122 to M9 inclusive and to the amplifier Ii. The output of the amplifier ii is delivered to the attenuator i2 which delivers the energy to the ear phones 13 by means of which the same is converted into audible sounds. While the light 363 is lit, the single hump 236 of cam 225 causes a single pulse to be heard in the ear phones. The operator then changes the position of the selector switch 359, maintains the frequency of the generator the same and changes the intensity of the sound. If the maximum intensity was produced on the first test, the successive tests Will be for lesser intensities. When the operator has gone through the various intensities for one frequency, he changes and does the same for another frequency. The number of pulses heard each time is dependent upon the will of the operator and the listener never knows how many pulses he is about to hear. It therefore becomes impossible for the patient to falsify and claim he heard sounds which he was unable to hear since he has to mark down the number of pulses heard and he would be unable to guess at the right number of pulses. While the operator usually gives the tests with the different frequencies and intensities in succession, it can be readily comprehended that these may be mix-ed up and the patients still further put on guard.

In the form of the invention illustrated, the sounds have been broken up into a number of successive pulses of equal duration, and with equal dwells between the same. It may, how ever, be readily comprehended that other sound patterns may be employed. For example, the sound pattern may consist of pulses of different duration. It is also possible to vary the pattern by varying the dwell between the pulses. Likewise, any combination of sound patterns may be employed.

My invention is highly advantageous in that it is possible to test numerous patients at the same time. With my invention, it becomes practically impossible for the patient to falsify due to the fact that he has to note the number or character of the pulses heard. An audiorneter constructed in accordance with my invention, can be constructed at a cost not greatly exceeding that of the ordinary audiorneter. The audiometer may also be used in the conventional manner. My invention is simple in construction and practical in operation.

Changes in the specific form of my invention, as herein described, may be made within the scope of what is claimed without departing from the spirit of my invention.

Having described my invention, what I claim as new and desire to protect by Letters Patent 1. In an audiorneter for simultaneously testing a number of persons, an oscillator for producing a continuous alternating current, sound producing means actuated thereby, means including an attenuator for varying the intensity of said sound, a cyclically operable control device including means to interrupt the. continuity of the alternating current flow according to a predetermined sound pattern during each cycle and visual means for indicating the beginning of the cycle during which the control device is functioning and operating concurrently with said control device.

2. In an audiorneter, an oscillator for producing a continuous alternating current, sound producing means actuated thereby, means including an attenuator: for varying the intensity of said sound, a plurality of cyclically operated control devices each including means to successively interrupt the continuity of said current according to a different predetermined sound pattern during each cycle and means for selectively rendering any of said control devices eiiective.

3. In an audiorneter, a generator for producing a continuous alternating current, sound producing means actuated thereby, means including and electric circuit, an attenuator for varying the intensity of said sound and a cyclically operated control device for successively interrupting the alternating current flow in said circuit in accordance with a predetermined sound pattern during each cycle.

4. In an audiorneter, an oscillator for producing a continuous varying current, sound producing means actuated thereby, means including an electric control circuit for controlling the production of the sound, and a plurality of branch circuits connected thereto, a switch in each of said branch circuits for rendering said control circuit operative to control the production of the sound, a plurality of cyclically operated cams each operating one of said switches to control the sound in accordance with a predetermined sound pattern, selector means for connecting any of said branch circuits with said control circuit, a signal for indicating the beginning of the cycle durin which said branch circuit switches are operated and means for simultaneously operating all of said cams and said signal.

5. In an audiorneter, an adjustable oscillator, means including a sound producing device energized by said oscillator, means including an attenuator for varying the intensity of the sound produced by said sound producing device, means including a plurality of control devices for controlling the initiation and termination of the sound produced by said sound producing device said control devices each operating in accordance with a different sound pattern, selector means for selecting the frequency at which said oscil ator op crates, selector means for varying the intensity of the sound produced by said sound producing device and selector means for selecting the particular control device to control said oscillator.

6. In an audiorneter, an oscillator for producing a continuous alternating current, sound producing means actuated thereby, means including an attenuator for varying the intensity of said sound and means including a cyclically operated control device adapted to convert said continuous sound into a number of separate sound pulses during each cycle.

7. In an audiorneter, generating means for producing alternating current and including a plurality of thermionic tubes, sound producing means actuated thereby, means including a control circuit connected to one of said tubes for controlling the conductivity of said tube, a plurality of branch circuits connected thereto, a switch in each of said branch circuits for causing said control circuit to function, a plurality of cyclically operated cams each of different form, each operating one of said switches, each of said cams causing said sound producing means to produce a series of sound pulses of a difiering predetermined sound pattern and selector means for connecting any of said branch circuits to said control circuit.

8. In an audioineter, generating means for producing alternating current and including a plurality of thermionic tubes, sound producing 'mean's actuated thereby, means including a control circuit connected to one of said tubes for controlling the conductivity of said tube, a plurality of branch circuits connected thereto, a switch in each of said branch circuits for causing said control circuit to function, a plurality of cyclically operated cams each of different form, each operating one of said switches, each of said cams causing said sound producing means to produce a series of sound pulses of a differing predetermined sound pattern, selector means for connecting any of said branch circuits to said control circuit, a signal for indicating the beginning of the cycle during which said branch circuit switches are operated and means for simultaneously operating all of said cams and said signal.

9. In an audiometer, generating means for producing alternating current and including a plurality of thermionic tubes, sound producing means actuated thereby, means including a control circuit connected to one of said tubes for controlling the conductivity of said tube, a plurality of branch circuits connected thereto, a switch in each of said branch circuits for causing said control circuit to function, a plurality of cyclically operated cams each of differentform,each operating one of said switches, each of said cams causing said sound producing means to produce a series of sound pulses of a differing predetermined sound pattern, selector means for connecting any of said branch circuits to said control circuit, a signal for indicating the beginning of the cycle during which said branch circuit switches are operated, a cam for operating said signal and means for simultaneously operating all of said cams.

10. In an audiometer, generating means for producing alternating current and including a plurality of thermionic tubes, sound producing means actuated thereby, means including a control circuit connected to one of said tubes for controlling the conductivity of said tube, a plurality of branch circuits connected thereto, a switch in each of said branch circuits for causing said control circuit to function, cam means for operating said switches to produce with each branch circuit a number of sound pulses difiering according to predetermined sound patterns and means for selectively connecting any of said branch circuits to said control circuit.

11. In an audiometer for simultaneously testing a number of persons, an electrical generator including an adjustable oscillator, means whereby energization of said oscillator produces alternating currents of various frequencies, means including a plurality of sound producing devices having substantially indentical sound producing characteristics, one for each person in the group, means whereby said sound producing devices are simultaneously actuated by said oscillator, means including an attenuator for simultaneously regulating in each of said sound producing devices the intensities of the sounds, a time controlled mechanism, oscillator energizing means, a control circuit connected thereto and including switch means operated by said time controlled mechanism for intermittently actuating said oscillator energizing means to energize said oscillator to cause said sound producing devices to produce a certain sound pattern, asecond control circuit connected to said oscillator energizing means and including switch means operated by said time controlled mechanism for intermittently actuating said oscillator energizing means to energize said oscillator to cause said sound producing devices to produce a second sound pattern, and visual indicating means actuated by said time controlled mechanism for indicating the listening period and operative during actuation of either of said control circuits.

12. In an audiometer for simultaneously testing a number of persons, an electrical generator including an adjustable oscillator, means whereby energization of said oscillator produces alternating currents of various frequencies, means including a plurality of sound producing devices having substantially identical sound producing characteristics, one for each person in the group, means whereby said sound producing devices are simultaneously actuated by said oscillator, means including an attenuator for simultaneously regulating in each of said sound producing devices the intensities of the sounds, a time controlled mechanism, visual indicating means actuated thereby for indicating the listening period and operable for a definite time period, oscillator energizing means, a normally inactive control circuit connected thereto and including switch means operated by said time controlled mechanism, said circuit upon actuation intermittently actuating said oscillator energizing means to energize said oscillator to cause said sound producing device to produce a certain sound pattern, a second normally inactive control circuit connected to said oscillator energizing means and including switch means operated by said time controlled mechanism, said second circuit upon actuation intermittently aotuating said oscillator energizing means to energize said oscillator to cause said sound producing device to produce a second sound pattern, the switch means of both of said control circuits being operated during said period, and means for selectively actuating either of said control circuits.

13. In an audiometer for simultaneously testing a number of persons, an electrical generator including an adjustable oscillator, means whereby energization of said oscillator produces alternating currents of various frequencies, means including a plurality of sound producing devices having substantially identical sound producing characteristics, one for each person in the group, means whereby said sound producing devices are simultaneously actuated by said oscillator, means including an attenuator for simultaneously regulating in each of said sound producing devices the intensities of the sounds, a time controlled mechanism, including a rotating shaft, visual indicating means actuated by said shaft for indicating the listening period. and operable for a definite period, oscillator energizing means, a normally inactive control circuit connected to said oscillator energizing means and including switch means, means on said shaft for successively operating said switch means to cause said circuit upon actuation to intermittently energize said oscillator and cause said sound producing device to produce a number of sound pulses, a second normally inactive control circuit connected to said oscillator energizing means and including switch means operated by said shaft, means on said shaft for successively operating said second named switch means to cause said circuit upon actuation to intermittently actuate said oscillator energizing means to energize said oscillator and cause said sound producing device to produce a difierent number ll of sound pulses, the switch means of both of said control circuits being operated during said period, and means for selectively actuating either of said control circuits.

1%. In an audiometer, an oscillator for producing a continuous varying current, sound producing means actuated thereby, mean including an electric control circuit for controlling the production of the sound, and a plurality of branch circuits connected thereto, a switchin each of said branch circuits for rendering said control circuit operative to control the production of the sound, a plurality of cyclically operated camseach of different form for operating one of said switches to control the sound in acin each of said branch circuits for rendering said controlcircuit operative to control the production of the sound, a plurality of cyclically operated cams each operating one of said switches to control the sound in accordance with a predetermined sound pattern, selector means for connecting any ofsaid branch circuits With-said control circuit and means for simultaneously operating all of said cams.

16. In an audiorneter, an oscillator for producing a continuou varying current, sound producing means actuated thereby, means including an electric control circuit for controlling the production of the sound, and a plurality. of branch circuits connected thereto, a switch in each of said branch circuits for rendering said control circuit operative to control the production of the sound, a plurality of cyclically operated cams each operating one of said switches to control the sound in accordance with a predetermined sound pattern, selector means for connecting any of said branch circuits-with said control circuit, a signal for indicating the beginning of a cycle during which said branch circuit switches are operated, a cam for operating said signal and means for simultaneously operating all of said cams.

17. In an audiometer, an oscillator for producing a continuous alternating current, sound producing means actuated thereby, and producing a continuous sound, means including an attenuator for varying the intensity of said sound, means including a plurality of cyclically operated control devices each converting said continuous sound into a different predetermined number of separate sound pulses during each cycle.

SCOTT N. REGER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date Re.21,735 I-Iuth et a1. Mar. 4, 1941 2,052,167 Coyne Aug. 25, 1936 2 072,705 Bloomheart Mar. 2, 1937 2,257,262 Koren Sept. 30, 1941 ,257,263 Koren Sept. 30, 1941 2,394,569 Strommen Feb. 12, 1946

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