The most important task for an assistive listening device is to amplify speech and reduce noise. General amplification of sound, for example by using suspended microphones, is not enough. The microphone must be as close as possible to the person speaking. You can test this for yourself here. Select suspended microphone or student microphone and then sound environment. A person with a 60 dB hearing impairment needs a signal-to-noise ratio which reaches the green zone in the graph to obtain good speech perception.