There are a number of directional microphone systems and these may be engaged manually (program button or remote control) or automatically based on signal processing decisions designed for given listening environments (for example speech in noise or speech in quiet).
Directionality is best illustrated by polar plots [Fig1] which show how a sound input can be more focused (0 = a person facing forward).
Microphones amplification characteristics are best described by “polar patterns”. Polar patterns assume that there is a 360° area around a microphone i.e. around the wearer in which a microphone’s amplification characteristics can be manipulated. This amplification manipulation allows patterns of noise enhancement and patterns of noise suppression defined within the polar circle and are typically described as Cardioid configurations (heart-shaped).
Fixed directional uses one of the polar patterns; automatic fixed directional can access the same cardioid patterns as fixed but usually engage automatically in the presence of background noise. Automatic adaptive systems can switch the directional microphones on or off and also change polar patterns according to the relationship between the listener and a noise source.
Automatic Adaptive directionality is usually a feature in the ‘high end’ product range and allows either a manual or automatic selection of available polar plots, thus maximising potential signal to noise ratios.