US2533667A - System for testing hearing - Google Patents

Description

Dec. 12, 1950 Filed Nov. 2'7, 1946 B. M. HARRISON SYSTEM FOR TESTING HEARING 2 Sheets-Sheet 1 5 FIG. I

mmvroa. BERTRAM M. HARRISON HIS ATTORNEY Dec. 12, 1950 B. M. HARRISON SYSTEM FOR TESTING HEARING Fild Nov. 27, 1946 2 Sheets-Sheet 2 FIG. 3

INVENTOR. BERTRAM M. HARRISON BY WWW HIS ATTORNEY Patented Dec. 12, 1950 UNITED STATES PATENT OFFICE 2 Claims.

The present inventionrelates to a device for testing and analyzing the hearing response of individuals, particularly for the purpose of determining the utility, nature, and character of hearing aids which may be required by the individual. The present method of analysis applies to individuals who may use hearing aids of the bone or air conduction type.

It has been observed that an individual who is hard of hearing will often hear certain tones much more readily than other tones and efforts have been made to determine the so-called hearing characteristics or hearing curve of the individual over the normal range of audible frequencies. A determination of these factors greatly aids in the design of the type of apparatus to be used, particularly in showing what frequencies should be amplified greater in in tensity than others. The determination of such an individual characteristic or frequency curve is not a simple matter and in the methods and systems which have been used, unavoidable errors or mistakes occur for a number of reasons, depending either upon the individuals observation or response to questions asked by the doctor or examiner. oftentimes a patient may state that he can hear a sound well when he hears it poorly or not at all. This may be done unwittingly or willfully, but in either event it hampers the observer in providing the proper type of hearing aid. The same situation also applies to comparison of sounds on an intensity basis. Asking the observer to express an opinion or to make a choice is not always reliable in providing true results.

In the present invention, the method and system employed in such that the patient must make his selection and observation in such a manner that there will be little chance for deception, either knowingly or unknowingly, by him. In each case the patient makes his own observation without the aid or assistance of the observer, and then the observer, by simple comparison with electrical apparatus, determines how far off the patient has been. This method of study is particularly useful in determinin the frequency characteristic curve of the patient, i. e., the curve which gives an indication of the patients ear sensitivity at different frequencies.

In the present invention, the patient is required to tune an oscillator producing a pure acoustic vibration to the frequency of a given oscillator, both oscillators preferably being of substantially the same tone intensity. The patient will be able under normal conditions to obtain a close tuning, I have determined, where his hearing is relatively good. Where, however, he has diiiiculty in hearing, i. e., hearing sounds of a certain pitch or frequency, his ability to adjust the tone to a given tone materially decreases. The measure by which he is off frequency is a good and fair indication of his relative insensitivity for the particular frequency. In order to make the run of tests complete, it may be necessary to make observations with the patient first at a given tone volume of the test note, and then at lower tone volumes, depending upon the ability of the patient to hear. If the patients ears are very bad, observations must necessarily be made with a higher constant volume, whereas if the patient has hearing below normal but not exceeding poor, a lower volume signal or tone may be used.

The present invention will be more fully described in connection with the apparatus illustrated in the drawings which form a part of the invention and by means of which the method of the present invention may be carried out.

In the drawings,

Fig. 1 shows schematically a circuit used in the present invention;

Fig. 2 shows a more complete system embodying the same principles of the invention as set forth in Fig. 1; and

Fig. 3 shows a still further modification of the system in accordance with the present invention by which the method thereof may be carried out.

In Fig. 1, the individual under test may be seated before the oscillator l with one or a pair of head phones 2 on his cars. If desired, each ear may be tested separately by using only a single phone or by using a pair of phones or bone conduction transducerswith a switch which may cut in the right or left ear, whichever is desired. The patient under test has readily available the control knob 3 for adjusting the frequency of the oscillator I. A second oscillator 4 is provided which is under the control of the observer by means of the knob 5. The output of both oscillators l and 4 may be connected in parallel by means of the line 6 across which the head phones 2 are connected through a volume control I and a volume meter 1 reading in decibels or the like, for regulating the volume of the oscillator heard in the head phones. The oscillators l and 4 produce a substantially pure or sinusoidal note so that no difficulty is encountered with multiple frequencies which often go to make up the character of musical instruments. A keying switch 8 is provided for use either by the patient or ob server. This key may comprise a single pole double throw switch so that in its upper position, as viewed in Fig. 1, the sounds of oscillator I will be impressed across the head phones, while when the key is in its lower position the sounds of oscillator 4 will be impressed across the head phones.

In the making of observations or tests on the patient, the calibrated oscillator 4 may be set at a definitely chosen frequency and the volume control I may also be adjusted to a desired volume control position. The patient is then asked to adjust the oscillator I to the same frequency as the oscillator 4. He does this by turning the knob on the oscillator I and then throwing the key 8 up and then down to compare the note heard from the oscillator I with the note heard from the oscillator 4. The key 8 is so arranged that sounds of only one of the oscillators may be heard ata time. When the patient has made his setting, the observer will deduct the frequencies indicated. on the two calibrated oscillators Iand 4 to get the difference or error frequency. He may also, if desired, listen to the 1..

beat note by throwing the switch 9, in which case both oscillators will be heard together.

The operator may desire to test the patient at a high volume, in which case the potentiometer or volume control I is adjusted to permit a comparatively loud sound to be heard on the head phone .2. The volume control .meter 1 may, of course, be calibrated in acoustic or electrical units and should be associated witheach observation curve made on the individual under test. It

For instance, if a curve is taken with the volume control in a given position, this curve should be marked for the particular volume setting at which it was taken. It has been found that with a louder volume, a patient may be more able to adjust frequencies than with a lower volume, and, in fact, the most useful results are usually obtained when the volume is low enough so that the patient has some difiiculty over the entire frequency range but yet not so low but that observations can be made over the whole range.

In the form shown in Fig. 2 the same elements as used in Fig. 1 are included, with the addition, however, of a mixer stage III, a double pole double throw selector switch I I and a frequency indicator I2 to which the output of the mixer is connected. This modification is chiefly for the use of the operator. The patient, as before, will use the head phones with the switch I I thrown in the downward position. When he has made asetting, the operator will throw the switch II upward, connecting the output of oscillators I and t to the mixer, where the beat frequency will be created, which frequency will be indicated on the frequency indicator I2. In this way, a ready indication of the frequency difference between the oscillators i and 4 may be obtained.

In the circuit shown in Fig. 3, three oscillators A, B, and C may be used, the oscillator B being chiefly used as a constant frequency source while the oscillator A is controlled by the patient and C,-by the observer. The output of each oscillator, which may be of any usual well known type, is fed to the corresponding amplifier A, B or C.

In this circuit, there is further provided a gang switch I3 operable by a single mechanism, which gang switch controls seven .independent single sections I, 2, 3, 4, 5', 6', and 8. The gang switch is under the control of the observer. Besidesthe elements previously described, there .is

also included in the system a mixer stage I4, the purpose of which is to mix the output of the amplifiers A and B, or B and C, or A and C. The output of the mixer stage may be connected to a low pass filter I5, which acts as the intermediate element in the circuit, which ends with the audio amplifier I1 provided with a volume control I8.

The gang switch in its upper position In as indicated in Fig. '3 connects the oscillators A and C in parallel to the grid I9 of the mixer stage, while the oscillator B is connected to the grid of the mixer state. Oscillators A andC however in this setting, as in Figs. 1 and 2, are not used simultaneously by the patient, but are alternately selected by means of the key 2|. When the key is in its upper position, oscillator A is selected, and when the key is in its lower position, oscillator C is selected. In the arrangement of Fig. 1, the note which the patient and the operator both hear is the beat frequency between the oscillators .A and B or the oscillators B and C, depending upon the position of the switch -2-I. Since oscillator B is set at a constant frequency and oscillator C is set by the observer, oscillator A must be set by the patient to match the frequency beat between the oscillators B and C. The head phones 22 are used by the patient. The volume to the phones is of course controlled by the volume control I8, which is preferably calibrated, so that for any desired run over the frequency range the volume may be maintained at a definite intensity. The low pass filter I5 may be used to purify the oscillator note, if that is necessary. I

The patient will make an observation with the gang switch set in the position indicated in Fig. 3. If the gang switch position is changed so that its switch arms are in position 20, the oscillator A and its amplifier will be connected to the grid I9 while that of oscillator C will be connected to the grid 20. In this position, the oscillator B by virtue of section 9 will be out of circuit. The position of the sections 5 and 6 of the gang switch .in the second position short circuits the key 2!, thus preventing either oscillator A or B from being disconnected from the mixer circuit. This enables the two oscillators A and B, by establishing a zero beat note, to be set at the identical frequency of oscillation. The amount of readjustment necessary to accomplish this is a measure of the error made by the patient.

A further position of the gang switch throws the oscillators A and C on pairs of plates of a cathode ray tube such that a visual observation of frequency identity may be obtained. In this case, the switch '8 cuts out the constant condenser 38 and throws into circuit the condenser 3I which has a range of from 0 to double the value of the constant condenser so that tuning of the oscillator C in both directions may be accomplished with respect to the oscillator A. In this way, whatever change in frequency may take place between oscillators A and C, the two oscillators may be tuned again to the same frequency. Condenser 3I carries a calibrated dial 32 so that reading of its setting at zero beat indicates the number of cycles error made by the patient.

Afrequency sensitive voltmeter 3d maybe con nected in circuit across the phones 22 to measure the intensity level of the signal heard in the phone. This intensity level may be maintained constant for a frequency run and varied for successive runs.

I claim: 1. A system for testing an individual for de fective hearing comprising a pair of oscillators for independently producing notes of desired frequency, means under control of the individual under test for varying the frequency of one oscillator in accordance with the sound he hears to match that of the other, means under control of the tester for changing the frequency of the other oscillator to the desired pitch which the individual is to match, listening phones connected to both oscillators, a switching means for selectively operating one or the other oscillator, and a switching means for operating both oscillators simultaneously.

2. A system for testing an individual for defective hearing comprising a pair of oscillators for independently producing notes of desired frequency, means under control of the individual under test for varying the frequency of one oscillator in accordance with the sound he hears to match that of the other, means under control of the tester for changing the frequency of the other oscillator to the desired pitch which the individual islto match, listening phones connected to both oscillators, a switching means for selectively operating one or the other oscillator, and a switching means for operating both oscillators simultaneously, said latter being under control of the tester.

BERTRAM M. HARRISON.

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

UNITED STATES PATENTS Number Name Date 1,528,774 Kranz Mar. 10, 1925 2,217,394 Wengel Oct. 8, 1940 2,235,733 Witting Mar. 18, 1941 2,416,353 Shipman et a1 Feb. 25, 1947

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