Modern Xiaomi Mi 9 smartphones feature a sophisticated sound recording system that includes several sensitive elements hidden in the case. Understanding exactly where the microphone is located is critical not only for self-repair, but also for correctly diagnosing problems with recording voice or transmitting sound during calls. Owners often confuse the speakers and microphone holes, leading to mistaken conclusions about the device’s failure.
In this article, we will take a closer look at the 2019 flagship audio system architecture, explain the purpose of each hole at the ends of the case, and provide a step-by-step algorithm to check the performance of each recording channel, learn how to distinguish regular volume reduction from real hardware failure, and get instructions on how to safely clean the sound holes without risking damage to moisture membranes.
Audio system architecture and number of microphones
Xiaomi engineers have introduced an advanced noise reduction system into the Mi 9, which is impossible without using multiple microphones. Unlike budget models, where a single main sensor is often installed, it uses a bundle of three microphones that work synchronously, which allows the smartphone to effectively filter the background noise of the wind and street hum, focusing on the speaker's voice.
The main microphone, which is responsible for transmitting your voice during a speakerphone conversation and when recording video, is located on the lower end. The second element, often called the upper or additional, is on the upper edge and participates in the noise reduction system, and also works as the main one in normal conversation (by bringing the phone to the ear). The third microphone is hidden inside the case or combined with the camera module for recording stereo sound, although the user physically sees only two main holes.
⚠️ Warning: Attempt to clean the holes with sharp metal objects (needles, pins) can lead to piercing of the protective mesh and getting moisture inside the body, which will cause oxidation of the contacts.
Multiple recording channels also allow audio zoom to be used in video recording. When you zoom in on a camera, the software amplifies the signal from a particular microphone directed at the subject, creating a presence effect. Understanding this logic helps you quickly identify which channel is out of order if the sound is only lost in certain use cases.
Technical characteristics of the Mi 9 microphones
Physical location of microphones on the body
To determine exactly where the microphone is on Xiaomi Mi 9, you need to carefully examine the ends of the device. On the lower edge, next to the Type-C connector and speaker, you will see several holes. The symmetrical arrangement is often confusing: the hole closer to the center (usually one or two small ones) is the main input for sound. The remaining holes can be technological or serve to output the mono speaker sound.
There's a small hole on the upper end, next to the IR port and the secondary microphone, and that's what's activated when you bring the phone to your face during a call, and if the person you're talking to is not hearing well in this mode, but they're hearing well when you're on speakerphone (the bottom microphone is used), the problem is localized to the upper channel.
For clarity, consider the distribution of functions of holes in the table below:
| Location. | Function | Mode of work | Signs of malfunction |
|---|---|---|---|
| Lower end (centre) | Main microphone | Speaking, voice recorder, video | The interviewee can't hear on speakerphone. |
| Upper end | Secondary microphone | Ear Talk, Noise Canceling | Badly heard in normal call mode |
| Rear panel (camera) | Additional channel (optional) | Stereo recording video | No surround sound in the video |
It is important to note that in some revisions of the Xiaomi Mi 9 board, the location of the sensitive elements may differ slightly, but the logic of the work remains the same: the lower part of the case is more likely to be contaminated with dust and pile from pockets, so it is the bottom microphone that requires regular prevention.
Diagnostics of performance without third-party software
Before you take your device to the service center or disassemble it, you need to run a software diagnostic. In the MIUI shell (and in pure Android), there is a built-in engineering menu that allows you to test each module separately. To run the test, open the Phone app and enter the code ##6484#. If the code does not work, go to the settings menu through the "About Phone" item and repeatedly click on the kernel version until the CIT menu opens.
In the test menu, find the audio section, usually called Receiver (for the top speaker/microphone) or Speaker (for the bottom one). However, to check the microphones, select Mic or Main Mic. The system will ask you to say a phrase, and the screen will display the level of the incoming signal in the form of a graph or numerical values. If the graph responds to voice, then the microphone is physically healthy.
It's also worth checking the permission settings. Often users accidentally deny the Dictophone app or messengers access to the microphone. Go to Settings → Apps → All apps, find the right program and make sure that the Microphone slider is activated. Lack of this permission is a common cause of "quiet" sound, which is mistaken for a breakdown.
☑️ Checklist of primary diagnostics
Software Causes of Silent Sound and Their Elimination
Sometimes the problem isn't hardware, but software conflicts or equalizer settings. In the Xiaomi Mi 9, the sound is handled by Dolby Atmos, which may not process the input properly. Try turning off any audio enhancements in the Sound and Vibration settings. Resetting the audio settings to factory values often solves the problem of distortion or low volume.
Another reason could be the process that handles audio services getting stuck, and in this case, cleaning the cache of system applications helps. Go to the storage settings, find the applications that are associated with sound (e.g., Sound, Audio System), and clear their cache. Don't be afraid to delete the cache of system services, which won't cause you to lose personal data, but will restart the audio drivers.
⚠️ Note: If the problem persists after resetting and flashing, the probability of hardware failure is more than 90.
Also worth paying attention to protective cases. Some tight silicone or leather cases can cover the microphone holes, especially if they do not have accurate cutouts for the Mi 9 model. Remove the case and test voice recording again. If the sound appears, the problem is solved by simply replacing the accessory.
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Use headphones with a built-in microphone for calls, a temporary solution that allows you to communicate comfortably even if the main microphones of the phone are damaged.
Mechanical cleaning and maintenance of holes
The most common cause of poor sound quality is the banal clogging of the microphone mesh. Pile, dust and skin fat form a dense plug that muffles the sound. Do not use high-pressure compressed air to clean, as this can damage the microphone membrane. The best method is to use a soft toothbrush or a special sticky tape.
Carefully walk with a dry brush along the holes, sweeping the dirt out. If you see a greasy plaque, you can slightly (literally a millimeter) touch a cotton swab dipped in isopropyl alcohol, but try not to pour liquid into the body. Alcohol quickly evaporates and degreases the surface, restoring the permeability of the sound.
After cleaning, be sure to let the device dry for 10-15 minutes, even if dry cleaning was used to remove static electricity. Check the sound again. Regular prophylaxis once every 3-4 months will avoid critical contamination and prolong the life of your Xiaomi audio system.
Hardware repair and replacement of the module
If software methods and cleaning didn't work, hardware repairs would be needed. In the Xiaomi Mi 9, the bottom microphone is often soldered on the charging port plume or is part of a separate module. The top microphone can be displayed on a separate plume coming from the main board. Replacing these components requires soldering skills and the presence of a microscope, since the contacts are very small.
Often, a microphone plume connector departs from the motherboard from long-term use or after a fall, in which case it is enough to carefully disassemble the smartphone, disconnect the battery and reconnect the plumes, making sure that they are intact. Visual inspection of the board for oxides (green or white plaque) is also mandatory, especially if the phone has come into contact with moisture.
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Replacing a microphone in a service center is usually inexpensive, but requires professional equipment to seal the case after opening.
It is worth considering that after changing the microphone, it may be necessary to calibrate the volume levels through the engineering menu to ensure that the new sensor works correctly and does not create a background. Self-replacement without experience can damage other components, such as the plumes of the display or battery.