Method to measure real-ear-to-coupler difference
View Patent ↗A method ( 10 ) of obtaining acoustical measurements of an individual ear that are compensated for errors caused by ear canal resonances.
1. A method of compensating for sound pressure measurement errors caused by ear canal resonance occurring in an occluded ear canal, comprising:
a. measuring the sound pressure of a sound source in an ear simulator;
b. measuring the sound pressure of the sound source in the ear canal;
c. carrying out both sound pressure measurements over a frequency range of the sound source;
d. calculating over the measured frequency range a real-ear-to-coupler difference (RECD) measurement using the sound pressure measurements;
e. identifying a frequency notch in the calculated RECD measurement associated with ear canal resonance; and
f. calculating a corrected RECD measurement including calculating a correction to the RECD measurement using the identified frequency notch to compensate for errors caused by ear canal resonance and combining the RECD measurement calculation and the correction calculation to obtain the corrected RECD measurement.
2. The method of claim 1 , wherein calculating a corrected RECD measurement comprises measuring the frequency of the ear canal resonance and its specific frequencies at −3 dB from the level at the ear canal resonance.
3. The method of claim 1 , wherein the measuring the sound pressure of the sound source in the ear canal comprises measuring the sound pressure of the sound source in the ear canal near a reference plane of the ear.
4. The method of claim 1 , wherein the sound pressure is registered by a sound pressure level (SPL) probe positioned near the sound source.
5. The method of claim 3 , wherein the sound pressure measurements are stored by a processor with a tangible data storage medium that may be operatively connected to the SPL probe.
6. The method of claim 3 , wherein the SPL probe comprises a probe microphone.
7. The method of claim 3 , wherein the SPL probe comprises a specially-adapted microphone of a hearing aid facing the ear canal.
8. The method of claim 1 , wherein the ear simulator comprises a 2 cc coupler.
9. The method of claim 1 , wherein the ear simulator comprises a specially-adapted coupler with an internal volume less than 2 cc.
10. The method of claim 1 , wherein the sound source comprises an insert earphone or a hearing aid.
11. The method of claim 2 , wherein calculating a corrected RECD measurement comprises calculating the correction as a frequency response of a complex transfer function over a selected frequency range.
12. The method of claim 11 , wherein parameters of the complex transfer function comprise the identified frequency notch and the quality factor of the frequency notch.
13. The method of claim 1 , wherein the step of calculating a corrected RECD measurement comprises calculating the correction using the following:
Corr
=
20
*
log
s
*
K
(
s
*
K
)
2
+
s
*
K
Q
+
1
+
1
,
where s:=i2πf, a complex operator; i:=√{square root over (−1)}; f is the current frequency in Hz; Q is the quality factor of the notch; K is a frequency scaling factor equal to π/(20*F); and F is the frequency of the notch in Hz.
14. The method of claim 13 , wherein the current frequency f comprises a value in the range of 100 Hz-10 kHz.