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Hearing aid audio test
1、Overview
Hearing aid is essentially a small loudspeaker, which can amplify the sound that was originally inaudible due to hearing loss and transmit it to the earphone, so that the sound can be sent to the auditory center of the brain, allowing the hearing-impaired to hear the sound more clearly.
According to the conduction mode classification, it can be divided into air conduction and bone conduction hearing aids.
According to the classification of wearing style, it can be divided into box type, behind-the-ear, in-ear, glasses type and hairpin type hearing aids.
So for the above different types of hearing aids, we have a complete system from software test algorithms to hardware test equipment, which can quickly and accurately present the test data in a visual way.
2、Hearing aid application testing
2.1、Hearing aid test configuration
AB 09 shielding box features:
Audio RF Dual Isolation
Rich access and output terminals
Support manual, program-controlled design
CM 313 Hearing aid strong coupling + A 803 preamp features:
Complies with IEC 60318-5 requirements for 2cm³ acoustic coupler
Cost-effective acoustic coupler compatible with 1" and 1/2" microphones
PM 6143 DAQ features:
4 inputs, 4 outputs
Power amplifier, signal conditioner, acquisition three-in-one
MegaSign private drive, more stable test
AudioExpert audio analysis software features:
Complete Audio Analysis Algorithm Library
Supports automatic sequence editing
Support LabVIEW call
Support for remote control
M 663+A 802 free-field microphone characteristics:
Prepolarized free-field measurement microphone for measuring the undistorted real sound pressure before the microphone is placed in the sound field
SB 05 far-field measurement speaker:
Low frequency boost
For audio tests with high low frequency requirements
AM 581 artificial mouth features:
Accurately simulate the sound source of the sound field near the human mouth, suitable for frequency response, distortion and other acoustic parameter testing of telephone microphones and microphones (microphones)
Higher low frequency transducer efficiency (especially 100-200Hz)
Extremely high sensitivity across the entire frequency band
U 982 Bluetooth adapter features:
Support Bluetooth protocol of SCB \ AAC \ LHDC. (MegaSig also provides other models of Bluetooth adapters that support Bluetooth protocols such as aptX \ LC3 \ BLE)
Supports audio services such as A2DP, HFP (Narrowband, Wideband)
2.2、Hearing aid test item
a)Calibration of test chambers
Significance of sound field calibration: During calibration, first test the response of the anechoic box, and then correct it by computer to obtain a "flat" sound field. See the table for the test data before and after calibration.
By comparing the test data before and after calibration, it can be seen that the performance parameters of hearing aids are very different, so it is very important to calibrate the anechoic box before the test.
b) Saturated sound pressure level OSPL90
OSPL90:
Frequency Response-OSPL90: Output SPL at 90dB Input SPL
Max @ xxxHz: The maximum value in the frequency response curve of OSPL90
HFA Avg: high-frequency average high-frequency average, the average gain or sound pressure level at 1000Hz, 1600Hz and 2500Hz expressed in decibels (dB)
c) Full-scale acoustic gain FOG50
FOG50:
Frequency Response - FOG50: Output SPL for 50dB input SPL input sound pressure level is 50dB output sound pressure level
Gain Frequency Response - FOG50: FOG50 Curve - 50dBSPL Curve (FOG: FULL on gain)
Max @ xxxHz: the maximum value in the frequency response curve of OSPL50 Gain
HFA Avg: High-frequency average value, the average gain value of the high-frequency average full-on gain at 1000Hz, 1600Hz, and 2500Hz at 3 frequency points
d) Reference test gain
OSPL60:
RTS: The reference measurement position of the gain controller, the position of the gain controller where the difference between the high-frequency average gain produced by the hearing aid and HFA-OSPL90 minus 77dB is controlled within ±1.5dB under the condition of inputting a sound pressure level of 60dB. (the actual test does not do control)
RTG (reference test gain) Target: the calculated (target value) reference test gain
RTG (reference test gain) Measured: The measured (actual value) reference test gain
e) Equivalent input noise level
OSPL50:
EQ Input Noise: L1=Measure high frequency average value (HFA) output L1 under the state of 50dB input sound pressure level
L2=turn off the sound source (OFF), measure the sound pressure level L2 in the ear simulator caused by the inherent noise
Equivalent input noise level (EQ Input Noise) = L2- (L1-50)
f)Frequency response range
OSPL60:
Response Limit: Response Limit=Obtain the high-frequency average (HFA) output level from the basic response curve (i.e. the average value of the sound pressure level at the three frequency points of 1000Hz, 1600Hz, and 2500Hz), and subtract the 20dB difference from the HFA output level
F1 F2: Take the Response Limit as the value, draw a horizontal line on the frequency response curve to intersect at ƒ1 and ƒ2, and the frequency response range is from the lower frequency limit ƒ1 to the upper frequency frequency ƒ2
(Note: If it is uncertain because ƒ1 and ƒ2 are below 200Hz or over 8000Hz, ƒ1~ƒ2 can be regarded as < 200Hz and >8000Hz respectively.)
g)THD
OSPL70:
500Hz 70dB/800Hz 70dB: sound source output 70dBSPL, measure the distortion at 500Hz, 800Hz (harmonic distortion tolerance: should not be greater than the nominal value plus 3%)
1600Hz 65dB: Sound source output 65dBSPL, measure the distortion at 1600Hz (harmonic distortion tolerance: should not be greater than the nominal value plus 3%)
2.3、Hearing aid test link
Take a behind-the-ear hearing aid with a Bluetooth chip as an example:
Hearing aid performance test:
After adjusting the gear and volume of the hearing aid, place it on the custom fixture, and then AudioExpert audio analysis software controls the PM 6143 signal acquisition card to make the SB 05 far-field measurement speaker produce sound. After the hearing aid microphone collects the sound signal, it passes through the earphone Processing, the sound from the hearing aid speaker is collected by the CM 312+A 802 hearing aid coupler kit, and then the collected signal is sent back to AudioExpert for analysis through PM 6143.
Hearing aid routine acoustic testing:
Hearing aid speaker test: AudioExpert audio analysis software controls the U 982 Bluetooth adapter to control the sound of the hearing aid speaker, which is collected by the CM 312+A 802 hearing aid coupler kit, and then the collected signal is sent back to AudioExpert through PM 6143 for analysis.