UMTS/HSPA Module Series
WCDMA UGxx Audio Design Note
WCDMA_UGxx_Audio_Design_Note Confidential / Released 20 / 56
The best installation way of microphone socket is to encase microphone by silicone cover except for front
cavity, and design a cylindrical hole whose center is the exit hole inside the chassis, make the microphone
with silicone cover just fit the cylindrical hole, so as to only let voice enter into microphone from the exit
hole, and not from leak of chassis interior. Certain air space room should be reserved in the front cavity of
microphone as it is necessary for good microphone performance.
Figure 13 shows recommended design for speaker socket.
Figure 13: Speaker Socket Design
A good way to suppress the internal echo path is to seal the rear cavity of receiver, which is usually
expensive. The rear cavity of receiver and speaker is important for good voice quality. A sealed rear cavity
with sufficien
t space could produce a good voice output. An 8Ω speaker is often big and difficult to give an
independently sealed rear cavity for it. However, sealing microphone socket in chassis is always useful.
Furthermore, the whole chassis must be sealed as far as possible. If there is any unavoidable leak hole,
keep it far away from microphone. If the leak hole is close to microphone, the voice coming from the hole
could be picked up by MIC, and then leads to echo at the far end. If the leak hole is close to speaker, the
output voice quality could be aggravated at certain extent.
4.5. Component of SPK
A SPK and receiver with higher sensitivity, flatter frequency response, less THD and impedance of 32Ω
(receiver), 16Ω (receiver) or 8Ω (speaker) is recommended. These technical data are often shown in data
sheet of SPK and receiver. For SPK, its frequency response and THD performance can be tested by
speaker test system. SPK frequency and THD response are shown in Figure 14 and Figure 15.
NOTE
Quectel
Confidential
