How do Directional Microphones Work in Hearing Aids?

Hearing aid microphones are given certain amplification characteristics based on design requirements, types of components, and the listening effects required. The method by which microphones amplification characteristics are described is 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.

The most commonly used polar patterns that are built into hearing aid microphones are: omnidirectional (omni), cardioid, and figure eight, which is a combination of the first two.

	Omni-directional Pattern An omni-directional microphone picks up sound equally from all directions, and is a basic feature on our Digi-Ear D1 and Melody A1 hearing aids.
	Cardoid Pattern A modified directional microphone in a hearing aid might have a cardoid pattern. This type of  microphone feature picks up sound from the source it is pointed at, but also offers a graduated rejection of sounds from the side, and very little input from the rear. When shown as a graph, the pickup response looks very much like a heart shape, hence the term ‘cardioid’. These microphones are also referred to as ‘pressure-gradient’ or modified multi-directional microphones. Our Digi-Ear D2 and our Melody A2 hearing aids have these types of microphones in them.
	Figure 0f Eight Pattern Another common polar pattern is figure-of-eight, which picks up an equal response from the front and the rear of the microphone but offers excellent sound rejection from both sides or ‘off-axis’. To make a directional polar pattern, the omni and figure-of-eight patterns are combined. Consequently, by varying this combination, you can create different variations on the cardioid pattern, such as hypercardioid. The hypercardioid pattern offers a good overall rejection and a flatter frequency response, while having a low sensitivity to sounds coming from the rear of the microphone.  Microphones in our Digi-Ear DS and Melody A3 hearing aids have hypercardoid microphones