Test Box

Question 1

What is a test box?

Answer 1

It is a computerised equipment contained in a sound proof box. The sound proof box is lined with dense foam and contains a calibrated speaker. Aid is placed in box and connected to a 2cc coupler or occluded ear stimulator

Question 2

What do test box’s do?

Answer 2

It stimulates aids performance and gives a standard reference that is used to compare aids on a like for like basis.

Question 3

What is FOG?

Answer 3

Full on Gain. Test box produces a full frequency sweep at 60dBSPL. Test box then measures the output from the aid. Aid is on and VC turned up and trimmers off.

Fog figure - gain applied at 1.6khz
Peak gain - max gain at any frequency
High frequency average- average of 1k. 1.6k and 2.5khz. Add then and divide by 3

Question 4

What is OSPL90?

Answer 4

Output sound pressure level. Test box measures maximum power output (MPO) the aid is capable of producing. Aid is on, VC is on full and trimmers off. Test box does full frequency sweep at 90dBSPL and finds figure at 1.6kHz

Question 5

What is distortion?

Answer 5

Distortion is caused by components in aids adding something to the original signal. This should be kept to a minimum but can be caused by microphone, speaker and also happens naturally due to our natural resonance.

Question 6

What is intermodulation distortion?

Answer 6

The input consists of Atleast 2 frequency’s.
Distortion is sums and differences of the two og frequencies. For example at 1k and 250hz intermodulation distortion will happen at 1250khz and 750hz

Question 7

What is harmonic distortion?

Answer 7

Measurement of extra frequencies being produced. Harmonic frequencies will be whole number multiples of original input signal

Question 8

Equivalent input noise level

Answer 8

This is the noise made by the circuit of the hearing aid. Internal noise levels should be below 30dB. More severe losses can cope with higher levels of noise as patient will not hear it.

Question 9

Frequency distortion

Answer 9

Caused by sharp peaks in frequency response, often due to receiver resonance

Question 10

Transient distortion

Answer 10

Ringing sound due to rapid changes in signal. Amplifier cannot deal with the rate of change in signal. Sharp/quick rise and fall times