Lecture 5: Electroacoustic Measures Flashcards
What is the purpose of EA Measurements?
- Measurement in controlled environment
- Real time
- Compare with specifications
- Performance over time
- Verify after programming
- Suitability for the individual
- Hearing aid failture
What equipment is used for EA measurements?
- Solid dense walls
- Absorbment materials inside
- 2 speakers
- Test microphone (coupler microphone)
- Reference microphone
What is a coupler?
- A metal assembly that couples the output of the hearing aid to the microphone of the electroacoustic system (takes the place of the ear)
- Different types of couplers for different kinds of hearing aids
- Coupler is used for in the box testing
What are the measurement signals (2)?
Pure tone sweep
Broadband signal
What are the equipment standards?
- Anechoic chamber, sound source and microphone must be periodically calibrated to ensure accuracy
- Must maintain standard operating conditions
- Appropriate coupler must be used
List and describe the different EA measurements.
- See info. from lecture *
What are the advantages of EA measures?
- Real-life settings
- Processing of stimulus that resembles natural speech
- Visibility of compression effects
What are the limitations of functional gain measures?
- Subjective measure
- Cannot create small changes <10 dB
- Time consuming
- More gross frequency response increments
- Cannot measure effects of varying input level on output
- Cannot measure saturated sound pressure level in the ear
What are the advantages of REM?
- Objective measure
- Measures changes as small as 1 dB
- We can always measure things like: compression features, max output, venting effects, occlusion, and directional microphone performance
- Much faster
What is REUR or REUG?
Real Ear Unaided Response or Real Ear Unaided Gain
- Describes the acoustic transformation from the SF to the TM
- May be altered by ME pathology or surgery
- REUG refers to SF outside the ear (ear canal SPL - input SPL)
What is REAR?
Real Ear Aided Response
- The response of the hearing aid measured at or near the TM
- Evaluate smoothness of response in the ear
What is REIG?
Real Ear Insertion Gain
REAR - REUR = REIG
or
REAG - REUG = REIG
- indirect measure
- used to compare with the prescriptive target
What is REOR?
Real Ear Occluded Response
- SPL at or near the TM with HA in place but turned off
- Useful for checking vent resonance
- A peak in the REOR can cause a dig in the REAG
- Patient complains of loudness or sound quality of their own voice (occlusion effect)
- Can measure effectiveness of venting changes/shell changes with this measure
What is RESR?
Real Ear Saturation Response
- HA output with loud input (estimation of max output)
- Used to verify that HA output does not exceed LDLs
- Not defined by ANSI standard
- Measured values of RESR depend on the bandwidth of the signal
What is RECD?
Real Ear-to-Coupler Difference
- Difference between sound measured in coupler & sound measured in ear canal
- Affected by ME pathology
- Not defined in ANSI standard
Define bandwidth.
Range of frequencies presented by a signal at a given time
Define spectrum.
Relative amplitudes and phases of frequencies presented by a signal
Define crest factor.
Refers to dB ratio of signal peak amplitude vs. RMS or long-term effective amplitude of the signal
Define temporal properties.
Way in which the signal varies over time.
Describe the calibration process for the REM.
Room acoustics: the distance between the patient and the loudspeaker to any reflective surface (wall, desk, REM system) should be at least 2x the distance between the patient and the loudspeaker
Probe mic calibration: place end of the probe over the reference mic for a broadband signal
- See details in lab report & Verifit instruction book*
Describe the placement of the probe tube in the ear canal.
6 mm rule
- Otoscopic method
- Acoustic Method
- Use a continuous 6000 Hz and you move the probe in the ear canal while you’re looking at the SPL - Average length method
- 6 mm placement is about 18 mm from the ear canal opening - Earmold Method
- Hold up the probe next to the earmold
Describe the process for positioning the loudspeaker and the patient.
- Use 1 to 2 feet between the loudspeaker and the patient
- Azimuth angle = horizontal angle
Describe the best test signal for REM and EA.
- Pure tones or pure-tone sweeps recommended
Describe the speech mapping test.
- Uses a speech signal and not broadband or narrow band noise
- Allows patient to listen to varying levels of speech with the devices
- Same targets as your standard REMs
Describe the process for troubleshooting measurements for REM.
- Probe factors
- Hearing aid factors
- Test environment factors
