6.2.1 Speaker Mechanical Design
The speaker must be soft-mounted to eliminate audio coupling into the plastics. There must be soft rubber around the ring of the speaker where it is mounted against the front of the device. There must not be any hard mounting on the back of the speaker. The speaker bracket must only press against rubber or foam at the rear of the speaker.
Ensure there are sufficient sound holes placed in front of the speaker to allow a clear path for the sound pressure to the user. Insufficient sound holes can cause more of the sound pressure to be transmitted into the plastic enclosure and cause a reduction in the perceived volume and increase the acoustic coupling.
The acoustic coupling inside the plastics must be minimized using baffling or a box around the speaker itself. A box around the speaker can be very effective at reducing the return echo inside the product, but care must be taken not to impact the bass response of the speaker.
If the plastics do not have screw-down points, it can result in vibrations at specific audio frequencies. These vibrations result in high non-linear echo returning to the echo canceller and can greatly impact system performance. If there are any vibrations, it is very important to eliminate them as much as physically possible within the constraints of the phone design. It can be as easy as soft-mounting certain sections or adding an additional screw or two to hold the plastic case together more solidly.