Acoustic admittance testing apparatus

Claim 2

Apparatus for testing a patient''s ear, said apparatus comprising: a first electro-acoustic transducer adapted to be acoustically coupled to the patient''s ear canal; means for energizing said first transducer to produce an oscillatory air flow in an ear canal to which said transducer is coupled and for providing a signal which is correlated with said flow; means, including a second electro-acoustic transducer adapted to be coupled to the ear canal, for generating a response signal which is correlated with the acoustic pressure in the ear canal; means for controllably varying the static air pressure in the canal; and means interconnected with both transducers for measuring, with respect to one of said signals, both the relative amplitude of the in-phase component of the other signal and the relative amplitude of the phase quadrature component of said other signal at different levels of static air pressure in the ear canal, whereby changes in said relative amplitudes caused by stiffening of a patient''s eardrum by the varying static pressure are indicative of characteristics of the unstiffened eardrum.

Claim 3

Apparatus as set forth in claim 1 wherein said measuring means comprises at least one analog signal multiplier.

Claim 4

Apparatus as set forth in claim 2 wherein said means for varying static pressure comprises a plenum chamber and means for providing a flow of air relative to said chamber thereby to generate therein a pressure which varies as a function Of time.

Claim 5

Apparatus as set forth in claim 1 including means for phase shifting said pressure signal 90* and performing a cross-correlation and time averaging of said flow signal with both said shifted and unshifted pressure signals.

Claim 6

Apparatus as set forth in claim 4 wherein said means for performing a cross-correlation and time averaging comprises an analog signal multiplier and a low pass filter.

Claim 7

Apparatus as set forth in claim 1 including AVC means controlled by said pressure signal for varying the energization of said first transducer to maintain the amplitude of said pressure signal substantially at a preselected level.

Claim 8

Apparatus as set forth in claim 1 including an adjustable phase shifter in the path of one of said signals to compensate for phase shifts which are not a function of the acoustic admittance of the patient''s ear.

Claim 9

Apparatus as set forth in claim 1 wherein said measuring means includes means for differentially amplifying relatively rapid changes in at least one of said components.

Claim 10

Apparatus for testing a patient''s eardrum, said apparatus comprising: a first electro-acoustic transducer adapted to be acoustically coupled to the patient''s ear canal; means for energizing said first transducer to produce an oscillatory air flow of adjustable amplitude in an ear canal to which said transducer is coupled and for providing a signal which is correlated with said flow; means, including a second electro-acoustic transducer adapted to be coupled to the ear canal, for generating a signal which is correlated with the acoustic pressure in the ear canal; means operating in response to the amplitude of said pressure signal for adjusting the amplitude of said oscillatory air flow to maintain said pressure signal at a substantially constant level; means for controllably varying the static air pressure in the canal; means for phase shifting said pressure signal by substantially 90*; and means for cross-correlating said flow signal with both the phase shifted and unshifted pressure signals thereby to generate respective admittance component signals, whereby stiffening of the patient''s eardrum by varying static pressure permits the measurement of the characteristics of the ear canal alone and the determination of the effect of the unstiffened eardrum.

Claim 11

Apparatus for testing a patient''s eardrum, said apparatus comprising: a first electro-acoustic transducer adapted to be acoustically coupled to the patient''s ear canal; means for energizing said first transducer to produce an oscillatory air flow of adjustable amplitude in an ear canal to which said transducer is coupled and for providing a signal which is correlated with said flow; means, including a second electro-acoustic transducer adapted to be coupled to the ear canal, for generating a signal which is correlated with the acoustic pressure in the ear canal; means operating in response to the amplitude of said pressure signal for adjusting the amplitude of said oscillatory air flow to maintain said pressure signal at a substantially constant level; means for controllably varying the static air pressure in the canal; means for phase shifting said pressure signal by substantially 90*; and means for cross-correlating said flow signal with both the phase shifted and unshifted pressure signals thereby to generate respective admittance component signals, whereby stiffening of the patient''s eardrum by varying static pressure permits the measurement of the characteristics of the ear canal alone and the determination of the effect of the unstiffened eardrum.

Claim 12

Apparatus as set forth in claim 9 wherein said cross-correlating means comprises a respective analog signal multiplier and low pass filter for each said shifted and unshifted pressure signals whereby the respective admittance component signals are available simultaneously.

Claim 13

Apparatus as set forth in claim 9 including means for indicating the values of said admittance component signals.

Claim 14

Apparatus as set forth in claim 9 including means for recording the values of said admittance component signals.

Claim 15

Apparatus for testing admittance at the plane of a patient''s eardrum, said apparatus comprising: a first electro-acoustic transducer adapted to be acoustically coupled to the patient''s ear canal; means for energizing said first transducer to produce an oscillatory air flow of adjustable amplitude in an ear canal to which said transducer is coupled and for providing a signal which is correlated with said flow: means, including a second electro-acoustic transducer adapted to be acoustically coupled to the ear canal, for generating a signal which is correlated with the acoustic pressure in said ear canal; amplitude control means operating in response to the amplitude of said pressure signal for adjusting the amplitude of said oscillatory air flow to maintain said pressure signal at a substantially constant level; means for varying the static air pressure in said canal as a function of time; means, including an analog signal multiplier and a low pass filter for cross-correlating said flow signal with said pressure signal thereby to generate a conductance signal; means for phase shifting said pressure signal by substantially 90*; means, including an analog signal multiplier and a low pass filter for cross-correlating said flow signal with the phase shifted pressure signal thereby to generate a susceptance signal; and means for recording said susceptance and conductance signals as a function of static pressure.

Claim 16

Apparatus for testing admittance at the plane of a patient''s eardrum, said apparatus comprising: a first electro-acoustic transducer adapted to be acoustically coupled to the patient''s ear canal; means for energizing said first transducer to produce an oscillatory air flow of adjustable amplitude in an ear canal to which said transducer is coupled and for providing a signal which is correlated with said flow: means, including a second electro-acoustic transducer adapted to be acoustically coupled to the ear canal, for generating a signal which is correlated with the acoustic pressure in said ear canal; amplitude control means operating in response to the amplitude of said pressure signal for adjusting the amplitude of said oscillatory air flow to maintain said pressure signal at a substantially constant level; means for varying the static air pressure in said canal as a function of time; means, including an analog signal multiplier and a low pass filter for cross-correlating said flow signal with said pressure signal thereby to generate a conductance signal; means for phase shifting said pressure signal by substantially 90*; means, including an analog signal multiplier and a low pass filter for cross-correlating said flow signal with the phase shifted pressure signal thereby to generate a susceptance signal; and means for recording said susceptance and conductance signals as a function of static pressure.

Claim 17

Apparatus as set forth in claim 13 including means for differentially amplifying relatively rapid changes in said susceptance signal and said conductance signal.

Claim 18

Apparatus for testing admittance of a patient''s eardrum, said apparatus comprising: a first electro-acoustic transducer adapted to be acoustically coupled to the patiet''s ear canal; means for energizing said first transducer to produce an osciallatory air flow in an ear canal to which said transducer is coupled and for providing a signal which is correlated with said flow; means, including a second electro-acoustic transducer adapted to be acoustically coupled to the ear canal, for generating a signal which is correlated with the acoustic pressure in the ear canal; means for phase shifting said pressure signal by substantially 90*; means for mixing a first signal which is a preselectable proportion of the amplitude of said pressure signal, a second signal which is a preselectable proportion of said shifted pressure signal, and said flow signal thereby to obtain a sum signal; means for controllably varying the static air pressure in said canal; and means for separately indicating the amplitude of the in-phase and quadrature components of said sum signal with respect to said pressure thereby to permit said components to be nulled whereby the proportions of said pressure signal and phase shifted pressure signal required to be mixed to obtain a null are representative of the conductance and susceptance respectively of the patient''s eardrum and canal and whereby stiffening of the patient''s eardrum by varying static pressure permits the measurement of the characteristics of the ear canal alone and the determination of the admittance at the plane of the unstiffened eardrum.

Claim 19

Apparatus for testing admittance of a patient''s eardrum, said apparatus comprising: a first electro-acoustic transducer adapted to be acoustically coupled to the patiet''s ear canal; means for energizing said first transducer to produce an osciallatory air flow in an ear canal to which said transducer is coupled and for providing a signal which is correlated with said flow; means, including a second electro-acoustic transducer adapted to be acoustically coupled to the ear canal, for generating a signal which is correlated with the acoustic pressure in the ear canal; means for phase shifting said pressure signal by substantially 90*; means for mixing a first signal which is a preselectable proportion of the amplitude of said pressure signal, a second signal which is a preselectable proportion of said shifted pressure signal, and said flow signal thereby to obtain a sum signal; means for controllably varying the static air pressure in said canal; and means for separately indicating the amplitude of the in-phase and quadrature components of said sum signal with respect to said pressure thereby to permit said components to be nulled whereby the proportions of said pressure signal and phase shifted pressure signal required to be mixed to obtain a null are representative of the conductance and susceptance respectively of the patient''s eardrum and canal and whereby stiffening of the patient''s eardrum by varying static pressure permits the measurement of the characteristics of the ear canal alone and the determination of the admittance at the plane of the unstiffened eardrum.

Claim 20

Apparatus as set forth in claim 15 including respective adjustable potentiometers for preselecting the proportions of said shifted and unshifted pressure signals.

Claim 21

Apparatus as set forth in claim 15 wherein said mixing means includes a resistive mixing network having a series resistance coupling each of the mixed signals to a summing junction.

Claim 22

Apparatus as set forth in claim 15 wherein said means for separately indicating includes means for cross-correlating said sum signal with either the phase shifted or unshifted pressure signal.

Claim 23

Apparatus as set forth in claim 18 including AVC means for bringing either the phase shifted or unshifted pressure signal to a substantial predetermined amplitude prior to cross-correlation.

Claim 24

Apparatus as set forth in claim 18 wherein said cross-correlating means incldes an analog signal multiplier and a low pass filter.

Claim 25

Apparatus as set forth in claim 20 including a null meter for indicating the value of the cross-correlation product signal.