US3718763A

US3718763A - Audiometer apparatus

Info

Publication number: US3718763A
Application number: US00100054A
Authority: US
Inventors: V Cannon; G Stowe
Original assignee: Beltone Electronics Corp
Current assignee: Beltone Electronics Corp
Priority date: 1970-12-21
Filing date: 1970-12-21
Publication date: 1973-02-27
Anticipated expiration: 1990-02-27

Abstract

Disclosed is audiometer apparatus including a tone generator portion, attenuator network, accoustical transducer and twodimensional plotting mechanism for automatically recording the subject''s response to signals received at the transducer. The tone generator includes a plurality of continuous running oscillators whose discrete frequency signals are coupled through pulser circuitry to the attenuator by way of magnetic reed switches actuated by the movement of the plotter. Hearing loss information is plotted with a pair of different color ink pens disposed within a carriage on the plotting mechanism. Switching mechanisms control the movement of the plotter and the carriage in their respective directions, selectively move the pens into and out of contact with recording material, and switch the signals received by the transducer from one earpiece to the other. Random validity mechanism is incorporated with apparatus for periodically or manually inserting an additional intensity change to the generated tones. Pulser circuitry, utilizing a photoresistor, is adapted for periodic interruption of the generated signal, the rise and decay characteristics of the generated signal being controlled by the circuitry.

Description

United States Patent 1 Cannon et al. [4 1 Feb. 27, 1973 [54] AUDIOMETER APPARATUS [57] ABSTRACT 7 Inventors; Vernon w Cannon, Austin, Tex; Disclosed is audiometer apparatus including a tone Gordon Stowe, Northbmok L generator portion, attenuator network, accoustical transducer and two-dimensional plotting mechanism Assign: nelfone Elecmmics Corporation for automatically recording the subjects response to cmcago signals received at the transducer. The tone generator [22] Fil d; D 21, 1970 includes a plurality of continuous running oscillators whose discrete fre uency si nals are con led throu h [2]] Appl l00054 pulser circuitry to the atteniator by way of magnet ic reed switches actuated by the movement of the [52] US. Cl. ..179/1 N plotter. Hearing loss information is plotted with a pair [51] Int. Cl. ..H04r 29/00 of different color ink pens disposed within a carriage [58] Field of Search ..179/l N, 1 MN, 1 AA on the plotting mechanism. Switching mechanisms control the movement of the plotter and the carriage References Cited in their respective directions, selectively move the pens into and out of contact with recording material,

UNITED STATES PATENTS and switch the signals received by the transducer from 2,563,384 8/1951 Von Bekesy ..179/1 N one earpiece to the other. Random validity 2,985,7l8 5/1961 Hunsicker e N mechanism is incorporated with apparatus for periodi- 2,744,l58 5/1956 Grandjot ..l79/l N Cally or manuany inserting an i i l i t i Primary ExaminerRalph D. Blakeslee Assistant Examiner-Jon Bradford Leaheey AttorneySheldon W. Wilcoff 20w 20Ic I 2OI o I AUTO STANT change to the generated tones. Pulser circuitry, utilizing a photoresistor, is adapted for periodic interruption of the generated signal, the rise and decay characteristics of the generated signal being controlled by the circuitry.

15 Claims, 11 Drawing Figures 209 ZIO PATENTEDFEBZYISB 3,718,763

SHEET 10F 7 INVENTORS VERNON W. CANNON GORDON N. STOWE FIG. 4

PATENTED FEB27I373 SHEET 2 BF 7 mm 9N 24mm moss nmN mN INVENTORS VERNON w. CANNON GORDON N. STOWE ATTORNEY NI 009 I NI OOON NI ooom Y NI ooov EON ON EON PATENTEDFEBZYIQH $718,763

sum

3 or 7 INVENTORS VERNON w. CANNON GORDON N. STOWE ATTORNEY PATENTED 3,718,763

SHEET t Of 7 F' IG 6 m w o m N TT 8 l 0B x w o o y no 0 o (\1 9 Q 9 co (0 0 w (\l co co N 2s CO m N 2 w "no rn w s -m w o m o w 59 co 9. g o i O *2 r w Q INVENTORS VERNON W. CANNON GORDON N. STOWE ATTORNEY This invention relates generally to audiometers, more particularly to improvements in automatic audiometers, and even more particularly to improvements in the tone generation, tone intensity, frequency selection, and plotter portions of audiometers.

Audiometers have been used for many years as a basic tool for the testing of hearing and, as such, have been employed by industry, schools, the military, and others, to provide initial screening of individual hearing sensitivity, as well as by the medical profession to detect the presence of hearing defects and diseases in humans.

Basically these audiometers comprise a tone generator portion for furnishing audio signals of discrete frequencies to a set of earphones worn by the subject being tested, an intensity varying or attenuator portion for varying the intensity level of the generated tone, and some type of means for recording the hearing sensitivity of the individual being tested in response to the varying frequency and intensity tones being presented thereto.

The increased use of and reliance upon the audiometer have also demanded that equipment be developed which, among other things, is substantially automatic or self-recording to reduce dependency upon operatortechnician accuracy; provide a permanent and accurate record of the hearing status of both ears of the subject being tested; and afford minimum maintenance and ease of servicing. In addition, it has been found that it is important that some means be incorporated into the audiometer which can detect the malinger or one who is intentionally attempting to alter thetrue test results. To meet these objectives, many forms and designs of audiometers have been developed in the past, all of which have many disadvantages associated therewith.

It is therefore a primary object of the invention to provide a new and improved audiometer whose operation and construction overcomes previous deficiencies and offers advantages heretofore unobtainable.

Itis a further object of the invention to provide im- Another object of the invention is the provision of a random validity test which is programmed into the operational sequences of the audiometer to insure the accuracy and reliability of the test results.

In accordance with these and other objects, the

present invention is directed to audiometer apparatusv which not only embodies an overall improved and unique construction and operation, but incorporates subsystems which are novel and unique in themselves, and offers particular adaptability to audiometer apparatus of the type described.

Accordingly, the apparatus includes a tone generator portion which, in its preferred embodiment, comprises a bank of continuously running oscillators for respectively producing a plurality of output signals of different frequencies, the output signals therefrom being selectively switched by a unique switching system through an attenuator network to an output audio portion coupled to a set of earphones. Improved twodimensional plotting apparatus is provided for recording information, and in particular information representative of the variable intensity and frequency proved audiometer apparatus which is automatic or self recording, provides a permanent, continuous, and accurate record of the hearing sensitivity of the subject being tested, and offers increased reliability in the test results obtained therefrom.

It is a still further object of the invention to provide a new and unique means for the selective switching of the different frequency audio signals to the earphones worn by the test subject.

It is an even still further object of the invention to provide a new and improved non-mechanical signal interrupter or pulser, which interrupter can be advantageously employed in an audiometer to reduce the eardrum fatigue normally associated with a continuous tone as well as to eliminate key clicks normally associated with the switching from one frequency to the other.

Another object of the invention is to provide improvements in two dimensional plotting apparatus, which improvements may be advantageously incorporated into the plotting mechanism of an audiometer for automatically recording the hearing status of the subject being tested.

signals received by the earphones. The plotting apparatus includes carriage means supporting a pair of writing implements for recording the hearing sensitivity of the subject being tested, the movement of the plotting apparatus, carriage means, and the writing implements being uniquely controlled by mechanisms and circuitry subsequently described. Means are also provided for the selective coupling of the generated signals to either one or the other earpiece of the set of earphones.

Signal interrupting apparatus of unique construction is advantageously incorporated between the tone generator portion and the intensity varying or attenuator portion for selective interruption of the signals being received at the output audio portion. Additionally, a random validity mechanism is incorporated with the audiometer apparatus for periodically or manually inserting an additional intensity change of the generated tones, this insertion, in the preferred embodiment, being periodically effected by magnetically operated switching means which couples additional resistance with the attenuator network of the apparatus.

Additional features of the invention, as well as further objects and advantages thereof, will become apparent with reference to the following detailed description taken in conjunction with the drawings, in which:

FIG. 1 illustrates a perspective view of the external housing of the audiometer of the present invention;

FIG. 2 is an overall block diagram schematic of the preferred embodiment of the invention;

FIG. 3 is a partial sectional view of the audiometer taken along the section line 3-3 of FIG. 1, illustrating the improved plotting mechanism of the invention;

FIG. 4 is a partial sectional view of the plotting mechanism taken along section line 44 .of FIG. 3, illustrating additional details of the plotting mechanism;

FIG. 5 is a plan view of a portion of the plotting mechanism illustrating the pen carriage;

FIG. 6 is an exploded perspective view of the pen carriage assembly of the plotting mechanism;

FIG. 6a is an enlarged plan view of the pen carriage;

FIG. 7 is a view, partially in section, showing the, motor drive for the overall plotting mechanism, taken along the line 7-7 of FIG. 3.

FIG. 8 is a schematic of the improved tone or signal interrupter of the present invention;

FIG. 9 is a view, partially schematic, of the improved switching mechanism of the audiometer of the present invention; and

FIG. 10 is an illustration of a typical record of the hearing response of one ear produced by operation of the audiometer of the present invention.

Referring now to the drawings, wherein like reference characters designate like or corresponding parts throughout the several views, there is shown in FIG. 1 an audiometer 20 for use in testing hearing and an earphone assembly 22 with

ear pieces

25a and 25b electrically connected to the audiometer 20 through cable 24. The audiometer 20 has a cover 26, a carrying handle 27 and a control panel 28. The unit 20, due to its size and construction, is lightweight and portable.

During the course of the test, the earphone assembly 22 is placed over the ears of the test subject, tones of varying frequency and intensity being alternately and automatically presented to the right and left ears through

ear pieces

25a and 25b, as subsequently described. A two-dimensional plotter 30 for permanently recording the subjects response to these tones is disposed over a sheet record material 32 mounted thereunder, holes 31 provided therein to enable the record material 32 to be properly indexed with the plotter 30.

Referring now to FIG. 2, the audiometer 20 includes a tone generator portion 200 comprising a bank of oscillators 201a through 201f for respectively producing discrete frequency signals or tones as, for example, 500 Hz, 1,000 Hz, 2,000 I-Iz, 3,000 Hz, 4,000 Hz, and 6,000 Hz. While each of these oscillators may be of a conventional design, as a significant feature herein, each oscillator is a continuous running unit having a substantially constant output amplitude.

A unique switching network 202 couples the output signals from a selected one of the oscillators to the input of a tone interrupter or signal pulser 205 and thereafter to the audio output portion of the system. More specifically; the network 202 includes a plurality of magnetic reed switches 203a through 203]. Individual coils 204a through 204f are respectively associated with each reed, the coils 204 being connected between a common positive voltage supply and respective contact terminals 190-196. When a selected coil 204 is excited, it is effective to close its associated reed switch 203 in a manner well known in the art, the soclosed reed thus coupling the output signal from its associated oscillator 201 to the input of pulser 205.

Selective excitation of the coils 204a through 204f is accomplished by the connection of the terminals 190-196, respectively, to a common negative voltage bus bar 186 by way of a sliding contact assembly 170 carried by the plotter 30. As a consequence, the individual frequency signals or tones are sequentially applied to the input of the pulser 205 as the plotter 30 proceeds along its path of travel in the horizontal or X direction. For example, in the system illustrated in FIG. 2, as the plotter proceeds from left to right, sequentially coupling the terminals 190-196 to the bus bar 186, an initial 1,000 I-Iz practice tone is selectively switched from the output of oscillator 2011; to the pulser input, followed sequentially by 500 Hz, 1,000 Hz, 2,000 Hz, 3,000 I-Iz, 4,000 Hz, and 6,000 Hz tones. It is thus observed that the output signals from each of the continuously running units may be switched to the audio output portion of the network by use of a non-mechanical indirect switching technique whereby the switch portions 203a-203f themselves are protected against fusion, environmental corrosion, and other deleterious efiects which could adversely affect the switching operation.

- The selected output signals or tones from the network 200 are thus applied to a tone interrupter or pulser 205. When the network 205 is in the CON- STANT position or mode, the tone signals inputed thereto pass through and are uninterrupted or substantially unafi'ected. When the pulser 205 is in the AUTO position, however, the network 205 is effective to periodically {interrupt the tone. As subsequently described, temporary disconnection of the output signals from the tone generator portion 200 may also be effected utilizing the network 205 during the switching from one frequency to another, thereby eliminating the key clicks normally associated with this switching. Control of the rise and decay of the frequency signals or tones during the pulsing and disconnect operation is also maintained by circuitry 205, as subsequently described in greater detail.

The pulsed or constant tone, whichever the case may be, is thereafter coupled from the output of the interrupter 205 through a conventional amplifier 206 to an attenuator network 207 for varying the intensity of the tone being applied thereto. The attenuator is of conventional design known in the art and may be a ladderresistor arrangement, as illustrated. A sliding contact 208 mechanically coupled to the carriage 54 of the plotter 30 varies the location of the application of the output signal from amplifier 206 to this attenuator network in response to the Y-axis movement of the carriage 54, thus varying the intensity or attenuation of the I tone at the output of the network 207. The attenuated frequency signal is thereafter coupled through

relays

209 and 210 to either the right or

left earpiece

25a or 25b, respectively, as subsequently more fully described.

The plotting of the hearing sensitivity is effected by the X-Y plotter 30 in combination with a sheet of record material 32 which is suitably positioned under the plotter 30. The plotter 30 is moved in the forward direction in the X plane by low-speed motor 42 mechanically coupled thereto, and is moved in the rearward direction in the X plane by high speed motor 43, each motor being selectively engaged as required. The plotter 30 carries a pen carriage member 54 which is reversibly movable in the vertical or Y plane by a motor 86. The carriage 54 carries two marking

pens

79 and 81, each of which can be selectively engaged with the record material 32. These pens are desirably of different colors or other distinguishing characteristics (such as different point widths) so that a record of the response of both ears of a test subject can be recorded and distinguished on a single sheet of record material,

32. This can be accomplished by having the pen "/9 in engagement with the record material 32 during the testing of the right ear, for example, while the pen 8] is in engagement with the record material during the testing of the left ear.

During the testing operation, the plotter 30 is initially disposed in the left-most position with one of the pens,

for example pen 79, in contact with the record material 32 and the signal being presented to one of the ear pieces, for example 250. The plotter 30 is then moved to the right at a continuous rate by X motor 42 during which time switch mechanism 170 selectively presents various frequencies of audio sound to the earphone a.-During this period, the carriage 54 (and the sliding contact assembly 208) is alternately traveling in opposite directions in the vertical or Y plane, this vertical movement being controlled by reversible motor 86. As a consequence, a trace of hearing sensitivity is made on the record 32 in response to the frequency and intensity changes of the tone being presented to the subject.

When the plotter reaches the right-most position, the motor 42 is disengaged, the motor 43 engaged, the pen 79 is lifted from the paper, and the plotter 30 is moved to the left-most position. When the plotter 30 reaches this left-most position, the pen 81 is placed in engagement with the paper, the motor 43 is disengaged, and the motor 42 is again engaged to drive the plotter 30 in the forward X direction. The various frequencies and intensities are again presented this time to the other ear through earphone 25b until the plotter 30 reaches the right-most position whereupon the motor 42 is again disengaged, and motor 43 is engaged to return the carriage to the left-most position, the test thereby being completed.

The

motors

42 and 43, which are normally running when power is applied thereto, have electrically actuated means for the respective engagement and disengagement of clutches (59, 61) of these motors (and the consequent relative movement of the plotter 30 in the X plane), the engagement and disengagement of the respective motor clutches (thus the engagement and disengagement of the motors) are controlled by relay 215 electrically connected thereto; the relay 215 when actuated, causes the plotter 30 to be driven in either the forward or reverse direction. Actuation of this relay 215 is, in turn, effected by a number of inputs thereto. Specifically, forward travel of the plotter 30 is initially effected by depression of start switch 218 which, through cooperation of logic amplifier 218a, actuates relay 219, the relay 219 then actuating relay 215 to engage motor 42 and disengage motor 43. When plotter 30 reaches the right-most position (the testing of one ear having thus been completed, as subsequently described), it engages limit switch 217 which then actuates relay 215 to disengage forward motor 42 and engage return motor 43, the plotter 30 thus being returned to its starting position. When plotter 30 reaches this left-most position, limit switch 216 is engaged to actuate relay 215 to disengage motor 43 and engage motor 42 to again move plotter 30 in the forward direction (during which time the testing of the other ear is effected) until limit switch 217 is again reached and plotter 30 returned as before. End cycle lockout switch 223 which is connected through relay 210 to the power source (not shown) for

motors

42 and 43, is effective to assure that the

motors

42 and 43 remain energized during the test cycle of both ears, and de-energizes the

motors

42 and 43 when the plotter 30 reaches the left-most position after the second ear has been tested.

External stop-switch 220, when depressed, actuates relay 215 through cooperation with logic amplifier 221 to disengage motor 42 and engage motor 43 to return plotter 30 to the left-most position and engage switch 223. Limit switch 222 assures that initiation of movement of plotter 30 in the forward direction occurs only after plotter 30 has first reached the left-most position. As another particular feature herein, a number of audiometers 20 may be coupled together for simultaneous testing of many subjects. Initiation of the testing cycles for all of these apparatus may then be effected by a signal received from external start means 218b, rather than from depression of switch 218.

During the motion of the plotter 30 in the forward X direction, the Y position of the carriage 54 on the plotter (consequently the intensity of the sound presented to the particular earphone as well as the position of the marking pen along record 32) is controlled by the reversible Y motor 86 which, in turn, is controlled by relay 212 which, when actuated, is effective to alternately change the direction of rotation of the motor 86. A switch 211 is depressed or released by the test subject in response to the apparent presence or absence of sound detected by his ear, thereby actuating the relay 212 to alternately move the carriage 54 back and forth, thus making a record of the hearing sensitivity during the movement of the plotter 30 in the forward X direction. Another input from relay 215 actuates the relay 212 to return the carriage 54 to the 0 db position in response to the rearward or return movement of the plotter 30.

Disengagement of motor 86 is effected by way of inputs coupled from a minimum, say 0 db, limit switch 213 and a maximum, say db, limit switch 214 so that if the carriage 54 reaches the 0 or 100 db level,

switch

213 or 214, respectively, is effective to terminate the direction of travel of the motor 86 and carriage 54.

Relay 210 is effective, when actuated, to switch the transmitted audio signals or tones of varying frequency and intensity to either the

earpiece

25a or 25b. Initial actuation of this relay 210 is in response to a pulse applied from logic amplifier 214 in response to depression of start switch 218 (or signal from 21812). The relay 210 is also actuated to switch the audio signal from one earpiece to the other when plotter 30 reaches the forwardmost position to engage limit switch 227.

Relay 209 is effective to energize either pen marker solenoids 1 14 or 1 16 to selectively engage

pen

79 or 81 with record material 32, as well as to provide additional attenuation to the transmitted tone, in accordance with a specific feature herein. Accordingly, one input to relay 209 is provided from the output of relay 210 so that whenever the tones are switches to

earpieces

25a or 25b, the

respective pen solenoid

114 or 116 is actuated. A limit switch 226 is also engagable by the plotter 30 when it is disposed at its forward-most position to deactuate both

solenoids

114 and 116 to lift both

pens

79 and 81 and prevent their contact with record material 32 during return of the plotter 30 to its leftmost position.

As a particular feature of the invention, an additional loss network is provided within relay network 209, the loss network, when inserted, providing additional attenuation (decreased intensity) of the audio signal being presented to the test subject. In this respect, magnetic reed switch 229, when closed, inserts this network as, for example, by incorporating additional resistance fected by a magnet 251 which is periodically rotated in communication with the magnetically actuated reed switch 229 by motor 250. In this manner, when the motor 250 is started, a random insertion of additional attenuation to the tone is provided at a time unknown to the subject being tested. Insertion of the extra attenuating network may also be manually effected by depression of switch 228.

Referring now to FIG. 3, a detail of the plotter 30 is shown with the cover removed. The plotter 30 is constructed from a support member 34, which is mounted to move along elongated tracks 36. These tracks 36 (FIGS. 3 and are attached to the audiometer, and are positioned with their lengths parallel to the X direction of the plotter travel shown by the arrow in FIG. 1. A plurality of rollers 38 are mounted to rotate about shafts 40 and are positioned in cut-out portions 39 in the vertical members 44. These rollers 38 contact the upper surface of the elongated track 36 to roll therealong. By mounting the support 34 in this manner, it is free to move along the tracks 36 in an X direction while being supported by rollers 38.

A suitable motor assembly 40a (comprising motors 42 and 43) can be provided to move the support 34 along the track 36 in the X direction. This assembly is shown in detail in FIG. 7 as having a support 41 attached to a horizontal member 46 with the forward X motor 42 and the high speed return X motor 43 mounted thereon. These two X motors have extending lower flanges 45 which are pivotably mounted on the support 41 by pins 47 so that the motors can rotate as shown by arrows 49. Each of the X motors is provided with an upper flange 51 between which a tension coil spring 53 is attached to resiliently urge the motors to rotate in a direction toward each other. The motors eachhave a gear member 55 which engages an elongated rack 57 which is in turn mounted on the frame of the audiometer and extends along its length in the X direction. It can be seen that by mounting the

motors

42 and 43 in the above described manner, that the spring 53 resiliently holds each motor in engagement with the rack 57. The

motors

42 and 43 are provided with the electrically actuated

clutches

59 and 61, respectively, which can be actuated as previously described to selectively drive the plotter 30 in the desired direction by either

motor

42 or 43.

' The carriage member 54 is mounted for reciprocating movement in the Y direction along the guide members 48 as shown by the arrows in FIGS. 2, 3, and 5. The carriage is provided with a plurality of rollers 63 which contact and support the carriage on the upper surface of the guide members 48.

By examining FIG. 6, the details of the construction of the carriage member 54 can be seen as consisting of two identical plate-like side members 56 arranged in a spaced parallel relationship and having V shaped grooves 58 on the inside faces. These inside faces of the I plate members 56 are also provided with two parallel spaced grooves or cut-out portions 60. These two side members 56 are held together at their ends by

end pieces

62 and 64 to form a rigid rectangular-shaped carriage.

Two

slide members

66 and 68 are each provided with two extending flanges 70 on their outer faces. These two flanges 70 are of a size and relative spacing so that they mate with and slide in the grooves 60. The two

slide members

66 and 68 are also each provided with two vertically extending openings or

slots

72 and 74 which are centered in the

vertical grooves

75 and 76, respectively. A first and second

U-shaped pen holder

78 and 80 respectively, are provided to support the marking

pens

79 and 81 in mounting openings 83. The

pens

79 and 81 have different color ink and are desirably of the capillary feed type known in the art. The pen holder 78 has two pins 82 which are inserted through the openings 72 in the

slide members

66 and 68 and then into the V-shaped grooves 58. Cor respondingly, the pen holder 80 is provided with its two pins 84 which are inserted through the respective openings 74 in the

slide members

66 and 68 and thereafter into the V-shaped grooves 58. The relative dimensions of the

pins

82 and 84 and the grooves 58 are such that the

pen holders

78 and 80 are free to move in the vertical direction when the

pins

82 and 84 are engaged in and movable with respect to the groove 58. The

pen holders

78 and 80 during the vertical movement are adapted to slide in

grooves

75 and 76, respectively.

Y motor 86 (shown in FIGS. 3, 4 and 6) is attached to and carried by the plotter 30. This Y motor is a reversible AC type and has a drive wheel attached to an output shaft 102. The drive shaft 102 passes completely through the wheel 100 and into an attenuator housing 104 in which the attenuator portion 207 is disposed, the housing 104 being suitably mounted on the plotter 30. As can be seen in FIG. 6, a positioning cord 106 has one end attached to end piece 62 at 108 with the other end attached to other end piece 64 at 110. The cord 106 engages a plurality of positioning pulleys 1 12 and is wrappedaround the drive wheel 1,00. Means are provided (not shown) for preventing slippage of the cord 106 on the drive wheel 100, so that as the drive wheel 100 is rotated in the clockwise direction, tension is placed on the positioning cord 106 on the right hand side, and the carriage member 54 is pulled along the guide rods 48 in the direction of arrow 113. It can also be seen that when the drive wheel 100 is rotated in a counterclockwise direction, the positioning cord 106 is tensioned on the left hand side, and the carriage member 54 is moved along the guide rods 48 in the direction of arrow 115. ltcan thus be seen that the position of the carriage 54 can be selected by operation of the motor 86.

Turning now to the pen switching mechanism, two

solenoids

114 and 116 are provided with

translatable shafts

118 and 120 extending respectively therefrom. Actuation of the two

solenoids

114 and 116 will result in the retraction of the shafts118'and 120, respectively. The

shafts

118 and 120 are pivotally attached to right and

left leg members

122 and 124 at pivot points I 126. These two

leg members

122 and 124 are pivotally attached at 128 to a support 130. The support 130 is fixed to the horizontal member 46 and at right angles thereto (FIG. 4). The two

leg members

122 and 124 are connected by a spanning member 132 so that when one of the leg members is moved, the movement is transmitted through the spanning member 132 to the other leg member. A right spanning pulley 134 and a left spanning pulley 136 are rotatably mounted on the spanning member 132 and are spaced apart as shown in FIG. 6. It can thus be seen that the leg members can be moved in either direction about their pivots 128 by the actuation of the

solenoids

114 and 116 so that actuation of solenoid 114 rotates the right leg 122 and left leg 124 in a counterclockwise direction about its pivot points 128, thus moving the spanning member 132 from left to right. By actuation of the solenoid 116, the whole assembly is moved in the opposite direction.

A first pin actuation cord 138 has one end attached to

side members

66 and 68 by means of a rod 140 and passes through an opening 142 in the end piece 62 and from there around pulleys 144 and 145. The cord 138 then passes around an idler pulley 146, around the left hand spanning pulley 136, by another idler pulley 147, down the length of the support 46, and around

pulleys

148 and 149, and is thereafter attached to the end piece 64 at 150.

A second pin actuation cord 152 is attached to the

side members

66 and 68 by a rod 153. The cord 152 then passes through an opening 154 in the end piece 64, around pulleys 155 and 156, then around idler pulley 158 and right hand spanning pulley 134, thereafter around another idler pulley 160 and

pulleys

161 and 162, and is thereafter attached to the end piece 62 at 163.

Right and left

hand spring members

165 and 166, respectively, are attached between the support member 130 and the right and left

hand leg members

122 and 124, respectively. These springs maintain the

leg members

122 and 124 in a central position when neither of the

solenoids

114 and 116 are actuated.

Operation of the pen switching portion of the plotter 30 is as follows. If it is desired to move marking pen 79 into contact with the record material 32, solenoid 114 is actuated to move the spanning member 132 to the right, thus tensioning pin actuation cord 152 and moving

slide members

66 and 68 in the direction of arrow 1 13. This relative movement causes the

pins

82 and 84 to also move in the direction of arrow 113 along grooves 58 in side members 56 with the pins 82 thus moving down toward the apex 117 of the grooves 58, the pins 84 moving toward upper right hand portion 119 of the grooves 58. This movement lowers pen holder 78 downward until the pen 79 contacts the record material 32 while the pin 81 and holder 80 are correspondingly moved away from the record material 32.

Conversely, to move marking pin 81 into contact with the record material, solenoid 116 is actuated, thus tensioning pin actuation cord 138 and moving

slide members

66 and 68 in the direction of arrow 115, pen holder 78 moving toward upper left hand portion 121, and pen holder 80 moving downward toward apex l 17, pen 81 thereby being moved into contact with the record material 32 in the same manner as described with respect to pin 79 above.

It should also be noted that the pen switching mechanism is so designed that when it is desired to switch from a first pen to a second pen, the second pen will be moved to begin its marking at the same spot that the first pen discontinued its marking. This is accomplished by means of the above-described unique structure of the pen switching mechanism and by examining FIG. 6a, the advantages of this structure can be more fully appreciated.

Initially, it is important to appreciate that pens 79 and 81 are centrally positioned in the

pen holders

78 and 80, respectively. These pen holders 78 and and the slide,

members

66 and 68 are constructed so distance (A) measured between one end of the slide members and the pen 81 and distance (B) measured between the other end of the slide members and pen 79 remain constant during the pen switching operation. By selecting dimension (C) measured between the inside surfaces of the

end pieces

62 and 64 to equal distance (A) plus distance (B), each pen is moved to begin marking at the same spot enabling the pens to be switched during the test without affecting the accuracy of the record. It can also be seen that the pens are mounted in such a manner that they are held against the record material solely by the gravitational force of the weight of each pen and its respective holder.

Referring now to FIG. 8, there is illustrated the unique pulser or interrupter circuitry 205. Ac cordingly, the selected signal or tone from switching network 202 is applied at input terminals A and A to a resistor bridging network 300 comprising fixed resistors R R and R and variable resistor means 301. In accordance with a specific feature of the invention, the variable impedance element 301 is a photoresistor having two sections 301a and 301b, the resistance of which is controlled by the incidence of light received from a lamp 303 adjacent thereto. The photoresistor 301 and lamp 303 are normally packaged together in a light tight enclosure so that stray light does not affect the operation of the unit. Maximum impedance of the photoresistor 301 (and therefore maximum attenuation of the incoming signal) occurs when the lightoutput from the lamp 303 is at its minimum, and conversely minimum attenuation of the incoming signal is achieved when the light output is at its maximum. Thus, interruption of the incoming signal from 202 may be controlled by regulating the current input to lamp 303.

This regulation is effected by a conventional freerunning multivibrator or flip-flop network 305 comprising matched cross-coupled transistors Q and Q emitter bias and feedback resistors R, and R and collector load resistors R and R Frequency of oscillation of the multivibrator is determined by resistorcapacitor pairs (R and C and (R and C all as presently known in the art. Desirably, the conduction times of transistors Q and Q, are equal, thus providing substantially equal pulsing of the incoming signal from 202. Zener regulation of the collector voltage and filtering is accomplished in conventional manner by zener diode Z bypass capacitor C and resistor R The lamp 303 is connected in the collector leg of one of the transistors, for example Q and is excited in response to actuation of, and current flow through,

transistor Q An external switch control 310 coupled to the base of transistor 0,, determines the state of conduction of transistor 0:, as follows. When switch 310 is switched to the AUTO position, (thus opening the con nection to the base of transistor Q the multivibrator will oscillate at its operating frequency, the alternating conduction and nonconduction of the transistor 0;;

thereby causing the lamp 303 to glow or darken, thereby producing a pulsed output signal at terminals 8-3. When the switch 310 is.moved to the CON- STANT position, the positive voltage applied through the external resistor 309 is applied to the base of the transistor 0;, thereby being locked into the conduction mode, and the incoming signal from 202 passes through the network 205 with a minimum of attenuation. Conversely, when the switch 310 is moved to the OFF position, a negative voltage from bus bar 186 maintains the transistor 0;, in nonconduction (0., being in conduction), the output from lamp 303 at a minimum and the consequent high value of resistance presented by resistor 301 providing maximum attenuation of the incoming signal.

The rise and decay characteristics of the interrupted tone signal from means 202 are controlled in the following manner. The attack (or rise) time is controlled by the current supplied to the lamp 303, the lower the current, the longer the rise time.

As a significant feature of the circuitry, however, the decay time, as well as the maximum attenuation of the incoming signal, is controlled by the portion of the circuitry now described. Transistor Q along with base bias resistors R and R collector and emitter resistors R and R respectively, provide a single stage Class A, common emitter amplifier with emitter degeneration due to R Field effect transistor Q, has its source and drain terminals coupled to the collector and base of transistor Q capacitor C providing DC blocking between drain of Q and base of Q The base of transistor 0 is connected through DC blocking capacitor C intermediate the two sections of photoresistor 301.

When transistor Q, is driven to saturation (turned on"), maximum shunt negativefeedback is provided for Q the input impedance Z, of transistor 0, thereby being maintained at a minimum. This low input impedance Z, shunts resistor R increasing the overall resistance of network 300, and increasing the attenuation of the incoming tone signal.

Triggering of the FET Q is effected by the coupling of the gate electrode thereof to the collector leg of the transistor 0., through the decay timing network of resistors R and R and capacitor C At the start time of maximum signal attenuation (Q conducting) capacitor C is controlled rate charged through resistor R and transistor 0,. Conversely during the time of minimum signal attenuation (Q conducting), capacitor C discharges through resistors R R and R In this manner, a controlled decay time is maintained.

As previously described with reference to FIG. 2, the switching mechanism 170 is mechanically coupled to plotter 30 so that as the plotter moves in the X direction, discrete frequency tones are sequentially presented to the test subjects ear. As observed in FIGS. 3-5, and particularly FIG. 3, the switch mechanism 170 comprises a plurality of

switch arms

172, 174, 176, 178 and 180 attached to the vertical member 44 and resiliently held against switch plate 182.

This switching mechanism 170, as well as the switch plate 182, which is attached to the body of the audiometer, is shown in greater detail in FIG. 9. Accordingly, the switch plate 182 has a rectangular shaped face or substrate 184 formed of electrically nonconductive material upon which the contact terminals or pads are disposed. A plurality of mounting slots 185 through which suitable fasteners (not shown) can be inserted are provided for attachment of the plate 182 to the audiometer.

Disposed along the line 180a are a plurality of

conductive terminals

198a, 198b, and 198a which are electrically connected by means (not shown) to a positive voltage supply. Disposed along lines 178a and 176a are conductive terminals 190-196 electrically connected by means (not shown) to coils 204a-204f, as illustrated in FIG. 2. Disposed along line 172a is bus line contact 186 coupled to negative voltage source (-v).

In addition to the switching

arms

172, 174, 176, 178 and 180, mechanism includes a relay 197 carried thereon which operatively connects the switching arm 172 (and consequently bus bar 186) to either switching arm 17s (and consequently

pads

191, 193 or 195 or switching am 176 (and consequently

pads

190, 192, 194 or 196).

The terminal pads 190-196 are so spaced with respect to one another that adjacent frequency pads (500 Hz and 1,000 Hz, 1,000 Hz and 2,000 Hz, etc.) slightly overlap one another, as illustrated. The edges of the

contact pads

198a, 198b, 1980 are then disposed to be in alignment with the areas of the overlapping portions. Thus, for example as the switch mechanism 170 moves to the right in conjunction with the plotter movement, the relay 197 is actuated from B to the A position when the switch arm reaches the left-most edge of the contact 198b, for example, the frequency of the tone to the test subject thus changing from 1,000 Hz to 2,000 I-Iz. Switching of the relay 197 back to the B position then occurs when the switch arm 180 passes beyond the right end of contact pad 198b, the frequency then becoming 3,000 Hz. The overlapping of frequency pads and 191, 192 and 193, etc. thus avoids discontinuities in these tones. While the switching

arms

172, 174, 176, 178, and 180 are illustrated as being mutually aligned, use of relay 197 avoids the necessity of direct alignment between

arms

176 and 178, and enables the overlapping of the adjacent frequency pads (190 and 191, 192 and 193, etc.).

As an additional feature, discrete contact pads 188 are provided along a line 174a and have a portion of their areas in mutual alignment with the overlapping areas of

adjacent frequency pads

191 and 192, for example. Each of the pads 188 is electrically connected by means (not shown) to the base of transistor Q, of pulser 205 illustrated in FIG. 8. Electrical connection of these pads by switch arm 174 to negative bus line 186 thus corresponds to to the OFF position of the switch 310 illustrated in FIG. 8. In this manner, the

tone may be temporarily interrupted during the transition from one frequency to the next to eliminate the clicks" normally associated with this transition.

To conduct a test with the audiometer, earphone set 22 is placed over the ears of the test subject and the plotter 30 is moved to the left-most position. The audiometer is then turned on and a 1,000 cycle per second practice audio signal is presented to only the right earpiece, for example, of the earphone set 22. During this initial period, the

X motors

42 and 43 remain disengaged so that the plotter remains in the leftmost position, but the Y motor 86 is in the on condition, its direction of rotation being controlled by the hand switch 211, the test subject thus becoming accustomed to the operation of the equipment.

Once a sufficient period of time has passed for the test subject to become accustomed to the operation of the audiometer, the X motor 42 is engaged and the plotter is moved slowly to the right with pen 79 engaging the record material 32. As the plotter moves from left to right, the switching mechanism 170 selectively presents the initial 1,000 cycle test signal to the ear of the test subject and thereafter the 500, 1,000, 2,000, 3,000, 4,000 and 6,000 cycles per second audio signals. The record material 32 is aligned under the plotter such that the transition between the presentation of audio signals of different frequencies correspond to

vertical lines

230, 231, 232, 233 and 234 on the record material 32, as shown in FIG. 10.

As previously described, the vertical position of the carriage 54 is controlled by the hand switch 211 which also, in turn, controls the intensity of the sound presented to the ear of the test subject. During the course of the test, the test subject regulates the switch 211 to control the intensity of the sound presented to his ear at his threshold of hearing. Since the carriage 54 carries the marking pen 79, a record 235 of the vertical position of the carriage 54 is made on the record material 32, an example of which is shown in FIG. 10.

When the carriage 30 has completely moved across the record material to the end of the last test frequency, pen 79 is lifted from the record material 32 and the audio signal is removed from the right earpiece. Also, when the plotter 30 reaches the right-most position, the motor 42 is disengaged and motor 43 is engaged to return the carriage to the left-most position whereupon the pen 81 is moved into contact with the record material 32 and the audio signal is presented to the left earphone whereupon the plotter 30 moves to the right while the switch mechanism 170 causes the above mentioned frequencies to again be selectively presented to the left earphone. When the plotter 30 again reaches the right-most position, the motor 42 is disengaged and motor 43 is engaged to return the carriage to the leftmost position, whereupon the test is complete. By use of different color ink in

pens

79 and 81, both the right and left ear hearing sensitivity may be recorded on the same chart. FIG. illustrates a typical record of a test of one ear by the audiometer. Within each frequency increment a large number of peaks and valleys are formed representing the points at which the apparent sound disappeared and reoccurred. The average of these recorded points thus represents the threshold of hearing for the test subject at the given frequencies.

I The audiometer also has provisions for a random or manual validity test, as previously described, which may be applied during the course of the hearing test either automatically by the audiometer itself or by the test operator. In this portion of the test, the tone was attenuated an additional 10 db, for example, the pens being switched on the carriage 54 so that the different colored record portion 236 indicated that the validity test was in progress. By noting where the pens have changed, (by color change, for example) the operator can determine when the validity test was in progress,

and at what frequency this occurred, and by noting the subjects response to this change in intensity, to verify the authenticity of the test. The validity mechanism itself is arranged to randomly present the 10 db signal during the test so that neither the operator nor the test subject will know when the validity test will occur. The validity mechanism also enables the operator to manually insert the 10 db attenuation, for example, to the audio signal when he senses that the test subject is attempting to alter the results of the test.

Variations to the disclosed embodiments may be made consistent with the teachings of the present invention. For example, rather than using different colored ink in the marking pens 79 and 80, other means may be utilized to differentiate therebetween, for example the line widths may be different.

Additionally, the validity test has been described by reference to the insertion of additional attenuation to the audio signal presented to the test subject. Alternatively, it may be desirable to increase, rather than decrease, the intensity of the audio signal during the validity test. Furthermore, it may be desirable, particularly when testing individuals with high frequency hearing loss, to begin the testing of each ear with the intensity level of the tone at a minimum.

Various other alterations or modifications of the disclosed embodiments, as well as other embodiments, may become apparent to one skilled in the art without departing from the spirit and scope of the invention as defined by the appended claims.

What is claimed is:

1. In an audiometer of the type including tone generating means for producing a plurality of discrete frequency signals, attenuator means for varying the intensity of said frequency signals, an audio output portion for receiving said varying intensity frequency signals, and plotting means for recording information representative of signals received by said audio output portion, the improvement comprising:

a. a plurality of continuous running oscillators providing said tone generator means, said oscillators producing output signals having respectively separate and distinct frequencies,

b. switching means coupling said tone generator means to said audio output portion, said switching means comprising a plurality of first means respectively directly connected to said oscillators, select ones of said plurality of first means, when actuated, coupling the output signals from the respectively connected oscillator to the attenuator means; said switching means also comprising a plurality of second means, select ones of said second means, when excited, actuating the said select ones of said first means, and

c. means carried by said plotting means for actuating the select ones of said second means.

2. The improvement as described in claim 1 wherein said plurality of first means are normally open magnetic reed switches, said plurality of second means are coils in proximity with said plurality of first means, and the means carried by said plotter is effective to selectively cause current to flow through said coils.

3. The improvement as described in claim 2 including an insulating substrate having formed thereon a plurality of electrically isolated contact terminals respectively electrically connected to one end of said plurality of coils and an elongated contact terminal electrically connected to a voltage source of one polarity; a second voltage source of relatively opposite polarity electri-' cally connected to the other end of said plurality of coils; and switching means carried by said plotter for selectively coupling said electrically isolated contact terminals with said elongated contact terminal.

4. Audiometer apparatus, comprising:

a. a tone generator portion for producing signals of discrete and differing frequencies,

b. intensity varying means for altering the intensity of said signals,

c. acoustical transducer means including an earphone having right and left ear engaging portions for reproducing said varying intensity signals,

. two-dimensional plotting means for recording information on record material associated therewith representative of said varying intensity signals reproduced by said acoustical transducer as a function of the different frequencies thereof, said plotting means carrying first switching means for selectively coupling select frequency signals from said tone generator to said acoustical transducer means as said plotting means moves in one dimension with respect to said record material,

e. carriage means carried by said plotting means movable in the other dimension with respect to said record material, said carriage means coupled to said intensity varying means so that as said carriage means moves in said other dimension, the intensity of the signal reproduced by said acoustical transducer means is varied, said carriage means also supporting a pair of writing implements for marking said record material, the characteristics of the mark produced by one of said writing implements when in contact with said record material differing from the characteristics of the mark produced by the other of said writing implements,

f. means for first selectively presenting the varying intensity signals to one of the said ear engaging portions and moving only one of said writing implements into contact with said record material during said first selective presentation, and thereafter secondly selectively presenting the varying intensity signals to the other of said ear engaging portions and moving only the other of said writing implements into contact with said record material during the said second selective presentation,

. means for selectively controlling the direction of travel of said plotting means in said one dimension, and

. means for selectively controlling the direction of travel of said carriage means in said other dimension.

5. The apparatus as described in claim 4 wherein the said differing characteristics of the marks produced by said writing implements is color.

6. The apparatus as described in claim 4, wherein said tone generator portion comprises a plurality of continuously running oscillators, and furthermore including a bank of magnetically actuated switches respectively coupled to the outputs of said continuously running oscillators, the switching means carried by said plotting means selectively actuating said magnetically actuated switches.

7. The apparatus as described in claim 6 including an insulating substrate member having a plurality of first conductive terminals disposed thereupon respectively coupled to said magnetically actuated switches, said plurality of first conductive terminals arranged in a pair of vertically disposed rows with the conductive terminals of one row coupled with the said magnetically actuated switches coupled to the outputs of the oscillators producing signals having frequencies adjacent the frequencies of the signals produced by the oscillators coupled to the magnetically actuated switches coupled to the conductive terminals of the other row, portions of said conductive terminals of one row being vertically aligned with portions of said conductive terminals of the other row, a second plurality of conductive terminals disposed upon said insulating substrate arranged in a row vertically disposed from said first and second row, portions of said second plurality of conductive terminals being vertically aligned with the vertically aligned portions of the conductive terminals of said first and second row, third conductive terminal disposed upon said insulating substrate vertically disposed from the said first and second plurality of conductive terminals, the said first switching means carried by said plotting means selectively electrically connecting the first, second, and third conductive terminals, thereby to control the selective coupling of the frequency signals from the said oscillators to said acoustical transducer means.

8. The audiometer apparatus as described in claim 4 including means for randomly varying the intensity of said signals and moving one of said writing implements out of contact with, and the other writing implement in contact with, the said record material during the time of said random variation.

9. The audiometer apparatus as described in claim 8 wherein said first mentioned intensity varying means is an attenuator, and said random varying means is a loss network comprising resistance means which is periodically coupled with said attenuator to provide additiona attenuation of said signals.

10. The audiometer apparatus as described in claim 4 including signal interrupting means coupled between said tone generator portion and said acoustical transducer for controlled interruption of the signals provided to said transducer.

11. The apparatus as described in claim 10 wherein said interrupting means comprises input and output terminals; variable impedance means coupled between said input and output terminals, said variable impedance means including a variable impedance photoresistor having two sections thereof; a source of light directed to said photoresistor; first means coupled to said light source for controlling the intensity of light impinging on said photoresistor, thereby to control the impedance presented to and the interruption of said signals at said input terminal; second means for controlling the attenuation and the decay time of the said signals at said input terminal, said means being coupled between said first means and an intermediate point between said two sections of said photoresistor, said second means including a first transistor having its base coupled to said intermediate point and its emitter shunting a portion of said variable impedance means; a field effect transistor having its source and drain terminals respectively coupled to the collector and base of said first transistor, the gate electrode of said field effect transistor being connected through a resistorcapacitor timing network to said first means.

12. The apparatus as described in claim 7, including signal interrupting means coupled between said tone generator portion and said acoustical transducer for controlled interruption of the signals provided to said transducer, and furthermore including a fourth plurality of conductive terminals disposed upon said insulatin g substrate in a row vertically disposed from said first, second, and third plurality of conductive terminals, each of said fourth plurality being aligned with the aligned portions of the conductive terminals of said first and second row, said fourth plurality being electrically coupled to said signal interrupting means, said first switching means including means for coupling select ones of said fourth plurality to said third conductive terminal, thereby to interrupt signals from said tone generator during the switching of one frequency signal to another frequency signal to said transducer.

13. An audiometer comprising the combination of tone generating means for producing a plurality of discrete frequency signals, attenuator means connected to said tone generating means for varying the intensity of said discrete frequency signals, audio output means connected to said attenuator means for receiving the varying intensity frequency signals, plotting means for recording information representative of the signals received from said audio output means, and means for randomly varying the intensity of said frequency signals, said last-named means including additional resistance means caused to be periodically coupled to the attenuator means at intervals of time unknown to the audiometer operator or to the subject being tested.

14. An audiometer as described in claim 13 wherein said means for randomly varying the intensity of said discrete frequency signals comprises magnetically operated switch means effective when closed for coupling said additional resistance means to said attenuator means, and magnetic means periodically operated for effecting the periodic closing of said switch means.

15. An audiometer as described in claim 14 wherein said additional resistance means is a loss network which, when coupled to said attenuator means, increases the attenuation of said discrete frequency signals.

Claims

1. In an audiometer of the type including tone generating means for producing a plurality of discrete frequency signals, attenuator means for varying the intensity of said frequency signals, an audio output portion for receiving said varying intensity frequency signals, and plotting means for recording information representative of signals received by said audio output portion, the improvement comprising: a. a plurality of continuous running oscillators providing said tone generator means, said oscillators producing output signals having respectively separate and distinct frequencies, b. switching means coupling said tone generator means to said audio output portion, said switching means comprising a plurality of first means respectively directly connected to said oscillators, select ones of said plurality of first means, when actuated, coupling the output signals from the respectively connected oscillator to the attenuator means; said switching means also comprising a plurality of second means, select ones of said second means, when excited, actuating the said select ones of said first means, and c. means carried by said plotting means for actuating the select ones of said second means.

3. The improvement as described in claim 2 including an insulating substrate having formed thereon a plurality of electrically isolated contact terminals respectively electrically connected to one end of said plurality of coils and an elongated contact terminal electrically connected to a voltage source of one polarity; a second voltage source of relatively opposite polarity electrically connected to the other end of said plurality of coils; and switching means carried by said plotter for selectively coupling said electrically isolated contact terminals with said elongated contact terminal.

4. Audiometer apparatus, comprising: a. a tone generator portion for producing signals of discrete and differing frequencies, b. intensity varying means for altering the intensity of said signals, c. acoustical transducer means including an earphone having right and left ear engaging portions for reproducing said varying intensity signals, d. two-dimensional plotting means for recording information on record material associated therewith representative of said varying intensity signals reproduced by said acoustical transducer as a function of the different frequencies thereof, said plotting means carrying first switching means for selectively coupling select frequency signals from said tone generator to said acoustical transducer means as said plotting means moves in one dimension with respect to said record material, e. carriage means carried by said plotting means movable in the other dimension with respect to said record material, said carriage means coupled to said intensity varying means so that as said carriage means moves in said other dimension, the intensity of the signal reproduced by said acoustical transducer means is varied, said carriage means also supporting a pair of writing implements for marking said record material, the characteristics of the mark produced by one of said writing implements when in contact with said record material differing from the characteristics of the mark produced by the other of said writing implements, f. means for first selectively presenting the varying intensity signals to one of the said ear engaging portions and moving only one of said writing implements into contact with said record material during said first selective presentation, and thereafter secondly selEctively presenting the varying intensity signals to the other of said ear engaging portions and moving only the other of said writing implements into contact with said record material during the said second selective presentation, g. means for selectively controlling the direction of travel of said plotting means in said one dimension, and h. means for selectively controlling the direction of travel of said carriage means in said other dimension.

9. The audiometer apparatus as described in claim 8 wherein said first mentioned intensity varying means is an attenuator, and said random varying means is a loss network comprising resistance means which is periodically coupled with said attenuator to provide additional attenuation of said signals.

11. The apparatus as described in claim 10 wherein said interrupting means comprises input and output terminals; variable impedance means coupled between said input and output terminals, said variable impedance means including a variable impedance photoresistor having two sections thereof; a source of light directed to said photoresistor; first means coupled to said light source for controlling the intensity of light impinging on said photoresistor, thereby to control the impedance presented to and the interruption of said signals at said input terminal; second means for controlling the attenuation and the decay time of the said signals at Said input terminal, said means being coupled between said first means and an intermediate point between said two sections of said photoresistor, said second means including a first transistor having its base coupled to said intermediate point and its emitter shunting a portion of said variable impedance means; a field effect transistor having its source and drain terminals respectively coupled to the collector and base of said first transistor, the gate electrode of said field effect transistor being connected through a resistor-capacitor timing network to said first means.

12. The apparatus as described in claim 7, including signal interrupting means coupled between said tone generator portion and said acoustical transducer for controlled interruption of the signals provided to said transducer, and furthermore including a fourth plurality of conductive terminals disposed upon said insulating substrate in a row vertically disposed from said first, second, and third plurality of conductive terminals, each of said fourth plurality being aligned with the aligned portions of the conductive terminals of said first and second row, said fourth plurality being electrically coupled to said signal interrupting means, said first switching means including means for coupling select ones of said fourth plurality to said third conductive terminal, thereby to interrupt signals from said tone generator during the switching of one frequency signal to another frequency signal to said transducer.