If you can't hear others on Zoom: click the arrow next to the speaker icon and select the correct output device. Check that Zoom's volume isn't muted in the Windows Volume Mixer (Settings > Sound > Volume mixer). Make sure you joined the meeting with "Join Audio" — if you see an audio icon in the bottom left, you haven't connected audio yet. Test your speaker in Zoom: Settings > Audio > click Test Speaker and you should hear a ringtone. If you hear the test tone but not meeting audio, the meeting may have technical issues on the other end. If you can't hear anything at all, check your OS volume isn't muted, try different headphones or speakers, and make sure no Bluetooth device is secretly capturing the audio output. Update Zoom to the latest version.
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