The user must place the microphone in a soft rubber mount to eliminate audio coupling in the plastic enclosure. No part of the microphone must touch anything other than the rubber, and there must be no air gaps in the gasket to minimize vibration coupling. The gasket must not compress too much as it can pinch off the microphone hole.
The following figure illustrates the MEMS microphones; however, the analog microphone must be mounted in the same manner.Figure 6-1. MEMS Microphone
Ensure the microphone opening is larger than the microphone aperture and that the microphone is aligned with the microphone hole. If this hole is too small, the microphone is going to pick up more sound from behind when compared to the front (in general, this causes a poor signal-to-echo ratio, which can impact the performance of the AEC).
The microphone tube lengths must be kept to a minimum (in general, 0.5 mm) and a maximum of 4 mm to ensure lower frequencies are not attenuated. The user can use the rear-mounted microphone, but must be aware about the addition of the extra tube length by the PCB. The following figure illustrates the microphone design.Figure 6-2. Microphone Design
The following figure illustrates the common errors when mounting the microphones.Figure 6-3. Common Errors when Mounting Microphones
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