US 2004/0176702 A1 · Method and apparatus for the measurement of the acoustic impedance

Abstract

A probe has an acoustic stimulator, such as a loudspeaker, and a microphone. The probe is located in an area to be measured. Acoustic signals are sent by the stimulator and received by the microphone. The signals received by the microphone are transformed into electrical signals and transferred to an analysis unit. Using a defined stimulation followed by a two-port chain transfer matrix connected to an impedance as a model, the voltage ratio between the stimulation and the impedance is described as a dimensionless transfer function in the form of a complex function of the stimulation frequency. A series of acoustic calibration signals are generated by a number of known acoustic impedances covering different calibration scopes by means of the defined stimulation. The calibration signals are recorded and the electric values are merged with the respective voltage values of the stimulation for evaluation of the results of the respective transfer functions. The transfer functions of the calibration signals are merged together into an over-determined linear system of equations. The system of equations is solved and two coefficients are calculated. The impedance to be calculated is determined by evaluating the transfer function under the defined stimulation by use of the coefficients determined by the calibration.

Claims25

Dependent claims

Method for the determination of the acoustic impedance, comprising the steps of

arranging a probe with a mean for the acoustic stimulation and a microphone at the area to be measured;
sending out acoustic signals over said mean and receiving again over the microphone;
transforming the received signals by the microphone into electrical signals and transferring them to an analysis unit, in which the amount of the impedance will be determined;
using a defined stimulation followed by a chain transfer matrix in form of a twoport until the impedance Z as a calculation base,
whereby the voltage ratio between stimulation and impedance is described as a dimensionless transfer function in form of a complex function of the stimulation fequency;
generating a series of acoustic calibration signals by a number of known acoustic impedances covering different calibration scopes by means of the defined stimulation;
recording the calibration signals received by the microphone and merging the electric values together with the respective voltage values of the stimulation for the evaluation of the results of the respective transfer functions;
merging together the transfer functions of the calibration signals into a over determined linear system of equations and solving the system of equations and calculating the two coefficients;
and finally
determining the impedance to be calculated by evalutating the transfer function under defined stimulation by use of the coefficients determined by the calibration.

7 more elements

Method for the determination of the acoustic impedance of cavities, such as the ear in connection with hearing aids, comprising the steps of

arranging a probe with a microphone and a speaker at the area to be measured;
sending out acoustic signals over the speaker into the cavity and receiving again over the microphone;
transforming the received signals by the microphone into electrical signals and transferring them to an analysis unit;
using a defined stimulation followed by a chain transfer matrix in form of a twoport until the impedance Z as a calculation base,
whereby the voltage ratio between stimulation and impedance is described as a dimensionless transfer function in form of a complex function of the stimulation fequency;
generating a series of acoustic calibration signals by a number of known acoustic impedances covering different calibration scopes by means of the defined stimulation;
recording the calibration signals received by the microphone and merging the electric values together with the respective voltage values of the stimulation for the evaluation of the results of the respective transfer functions;
merging together the transfer functions of the calibration signals into a over determined linear system of equations and solving the system of equations and calculating and storing the two coefficients;
and finally
determining the impedance to be calculated by evalutating the transfer function by use of the coefficients determined by the calibration.

7 more elements

Dependencies are inferred from the claim text.

Method and apparatus for the measurement of the acoustic impedance

Life of this patent

Method and apparatus for the measurement of the acoustic impedance

Life of this patent

Abstract

Claims25