Why does the upper/lower speaker have no sound or low sound after using the Xiaomi 15 for a while?

Please check the following settings to ensure the audio balance slider is in the middle position, then restart the phone and check if the issue is resolved.
The setting path is as follows:
1. Go to [Settings];

2. Scroll down and tap [Additional settings]; 
3. Select [Accessibility], and tap [Hearing];
4. Adjust [Audio balance].
After adjusting the audio balance, restart the phone to refresh the settings and check if the issue is resolved. If the issue persists, please check if there are any obstructions near the speaker area or any other audio settings that could be interfering with normal sound output.