Equivalent Input Noise - Interacoustics Affinity 2.0 Additional Information

2.0
Affinity Additional Information
3.7.7

Equivalent Input Noise

Every amplifier and microphone will generate noise to some extent. The internal noise of a hearing device is
expressed as the Equivalent Input Noise. More specifically this term covers the amount of noise that would
need to be added to the input of a noiseless hearing aid with the same frequency response if the noise
coming out is to be the same as the tested hearing aid.
According to Dillon (2001) there are three reasons as to why it makes sense to express the noise relative to
the input:
•
Most noise in good quality hearing aid comes from the microphone and most of the remaining noise
comes from the input amplifier.
•
The noise of the output will vary with the position of the volume control in hearing aids with volume
control. This is not the case with the input related noise
•
If the noise was expressed relative to the output hearing aids with little gain would always have less
noise that hearing aid with high gain.
The Equivalent Input Noise is performed by measuring the noise of the hearing aid output followed by
subtracting the gain.
Below is an example:
Note: Equivalent Input Noise can be displayed as a curve or figure depending on your preference.
Output noise – Gain = Equivalent Input Noise
Select test
The Equivalent input noise
is shown in dB SPL as a
function of frequency
Page 284
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