Large Area Assistive Listening Systems: Review and Recommendations

3.1 Selecting the Appropriate Microphone

The selection of appropriate microphone types is crucial when they are to be the primary source of input into an ALS. In order to ensure adequate signal strength and maximum speech intelligibility, microphone specifications should meet or exceed the specifications of the rest of the system components. Poor quality microphones will limit the effectiveness of an ALS. To minimize background noise, it is desirable to utilize noise-suppressing directional microphones (such as those with a cardioid or hypercardioid pattern).

The most desirable situation is where all talkers have available a microphone in close proximity to their lips. If a situation, such as theatrical performances that require multiple microphones, then it's desirable to either utilize an automatic mixer (one that switches on only the microphone being spoken into) or for the microphone gain and activation to be controlled by a sound technician. In this latter instance, the sound technician can also control the relative level of the various sound signals in order to favor speech or lyrics and de-emphasize other competing stimuli such as background music. Currently, the provision of a separate wireless microphone for each performer is evidently practiced in only major theaters and then unpredictably. (Theaters do not publicize the details of their sound reproduction system, other than to indicate that one is available as required by the ADA).