TriMic™-System: A highly effective directional microphone system with three individual microphones

With the world first TriMic™ System, Siemens offers a outstanding directional microphone with excellent directional abilities available in a Mini-BTE housing. This technology is is available for ACURIS P, TRIANO 3 and TRIANO 3P. The TriMic™ directional microphone with three individual microphones theoretically has a 2 dB higher directivity than a TwinMic™.

To date, no other manufacturer has been successful in designing a Mini BTE hearing instrument housing capable of accommodating three individual microphones. For this reason, the TriMic™-System of TRIANO 3 received a great deal of attention from hearing instrument users. To achieve such excellent directivity, this high-performance microphone was designed to provide a precise and accurate balance between the three microphones. This superior directivity promises a 10 - 30% improvement in speech intelligibility, particularly in situations involving large groups of people, such as in restaurants or cafeterias - in other words, environments where consistently loud noise is prevalent. An automatic directional microphone can also be programmed with the TriMic™-System. Thanks to the optimal directivity at high frequencies, however, it is not necessary to provide adaptive directivity over the entire frequency range. Only in the lower frequency range do the directional characteristics behave adaptively as with the TwinMic™-System, adjusting to the direction of loud sources of noise and fading out background noise.

A physical measure for quantifying the benefit of directional microphones is the Directivity index (DI). The Directivity index is defined as difference between microphone sensitivity to sounds arriving from the front compared to sounds arriving from all other directions for a specific frequency. An omnidirectional microphone in the free field has a DI of 0 dB, because the sensisity is the same for all directions. If an omnidirectional BTE is mounted on a KEMAR, even negative values are achieved (see figure below). This means that sounds from the back may be perceived as louder than sounds arriving from the front! In contrast, the human pinna "amplifies" sounds between 2 and 4 kHz by about 2 dB. Directional microphones like the TwinMic™ have a theoretical maximum of 6 dB in the freefield. With the Siemens TriMic™ even 9 dB are possible. However, on the KEMAR typically smaller DI values are measured due to head shadow effects. The chart below shows that on KEMAR a TriMic™ achieves DI values up to 7 dB as opposed to 4 dB for a TwinMic™. A TriMic™ possesses optimal directivity particularly at frequencies above 1000 Hz (i.e. a high DI). At lower frequencies, the TriMic™ performs similar to the TwinMic™.