Equivalent Input Noise Measures
Background
The Equivalent Input Noise (EIN) of a hearing aid is the level of environmental input noise that is required to produce an output voltage that is identical to the voltage of the device's internal noise. If a hearing aid has an EIN that is too high, the noise may be audible to listeners with mild thresholds.
Methodology for Equivalent Input Noise (EIN) Measures
The following methodology details the data collection procedures for quantification of EIN. These methods apply to all test devices whenever possible. If deviation from these methods is required for data collection, it will be explicitly noted.
Often EIN measures will be completed in the early morning or late evenings to minimize ambient noise levels. This step is taken for the quantification of EIN in all products. Testing is completed in an 8'9" x 8'9" x 6'9" anechoic chamber with the hearing aids placed inside an enclosure. Each hearing aid is sealed to a 2cc coupler using soft putty. EIN levels are then recorded using an instrument such as TEF20 real-time spectrum analyzer and reported in 3rd octave band levels. The measurements involve recording the noise output of the hearing aid without stimulus, and then deriving EIN values by subtracting the gain from the measured noise. Attempts are made to set each of the evaluated hearing aids to a linear configuration, while ensuring that the gain settings for each device fall within the mid-range of each hearing aid’s targeted fitting range.