Earmoulds and Frequency Response Modifications Flashcards
Infra Red
Much higher frequency that FM
Carried modulated by the audiowave
Travels in straight lines
Not commonly use in hearing aids, basically only useful in TV transmission, because you sit straight on front of it
Sound Field Amplification
Improvement in SNR is limited to about 10dB
Essential Functions of Earmoulds
Sound bore couples the sound to the ear canal
Venting - extent to which canal is open to air
Retains aid in the ear
Shore value
The high the shore value the more viscous the material is
Shore 40 is harder/less flexible than a shore 20mould
Which mould type for which hearing loss?
Hard acrylic = average of 2&4kHz is up to 75dB
Soft acrylic = av. of 2&4kHz up to 85dB
Polyflex = av. of 2&4kHz up to 110dB
Audisil = av. of 2&4kHz up to 110dB
MDX = av. of 2&4kHz off the chart
Five ways to produce a tightly fitting mould
take an impression with jaw open
take a two or thress stage impression
request build up
use a viscous impression material
pat down the impression before it hardens
Different vent types
Pressure Vents
- for pressure equalisation no effect on gain frequency response. Very tiny, 0.06-0.8mm in diameter
Trench Vents
- when the ear canal is too narrow for a parallel vent
IROS
- Ipsilateral rooting of signals; biggest possible vent still maintaining the canal shape
Y-Vent
- should be avoided unless ears are too small. May even choose to make the vent small and risk occlusion rather than doing this
When will occlusion stop being a concern?
When low frequency 250/500Hz are worse than 40dBHL
For these people it is better to use under 2mm of venting
Why would you use a constriction?
For a profound high frequency loss/audiogram where you can’t turn the high frequencies down enough without compromising the mid frequency sounds they need
