Hearing Aid Components Flashcards
What is a hearing aid?
A hearing aid is an electronic device enabling a hearing impaired person to make maximum use of their residual hearing
What are the components of a hearing aid
- microphone
-receiver - amplifier
- volume control
- battery
What does a microphone do?
It transducers acoustic and mechanical energy into electrical signals and sends this into the hearing aid
What does the amplifier do?
Takes the electrical signals from the microphone that has been converted to digital signals through A/D converter and manipulates them. This sound is now a digital signal and is either amplifier or limited for comfort ability.
Volume control
Sits separate from the amplifier and gives the patient the ability to control the volume.
What does the receiver do?
Acts as a transducer, turns electrical energy back into acoustical windows energy to be received by the ear.
What does the batteries do?
They are chemical stored energy converter into electrical energy when connected that power the hearing aids.
How to calculate battery life?
Battery life(time) = capacity(c)/ current(I)
Time is measured in hours
Capacity is measured in MAHrs
Current is measured in MA
What are directional microphones
They have two or one microphone, sound enters through both and there is a time delay applied to the rear microphone signal - these two signals are subtracted to produce directivity. Modern directional microphones allow you to change the direction of the hearing as required.
What are omnidirectional hearing aids?
They only have one microphone which responds equally to the sounds from all directions - the microphone is equally sensitive to all incoming sound. No sounds are reduced in relation to others.
What is a polar pattern?
It is the plot of the devices sensitivity as a function of the angle around the device in 360 degrees. Plotted results show the effective range of a hearing aid when placed into the ear.
What are trimmers?
Used before digital aids were a thing - would need to use a screwdriver to manually adjust the frequency. This was for analogue aids. There is bass cut (reduces occlusion)and top cut trimmers( reduces feedback)
Explain tubing
Tubing length and diameter can affect the frequency response of the hearing aid, narrowing the tube results in loss of high frequencies and vice Versa.
Explain acoustic horns?
These can be used if venting is impossible due to feedback or size of ear. They vary the internal diameter of the sound bore along the length and Modifies high frequency response. Useful to reduce lower freq response and at the same time improve high frequency clarity. Lower frequencies will dissipates which gives the ear the effect that higher frequencies are clearer.
Explain ear hook dampers?
As sound travels through tubing resonance occurs - this creates peaks in frequency response resulting in acoustic feedback. These peaks can be smoothed out using plastic or metal dampers in the ear hook - used to smooth out frequency response curve as they reduce random spikes.
