There are two ways to get sound output for Reolink NVRs:
1. Attach the NVR to a monitor/TV via the HDMI port. The resolution of the monitor/TV should be 1920*1080 or 1080*720. The NVR will not have a sound output if the monitor/TV has other resolution used.
2. Plug a loudspeaker box into the "audio out" jack at the back of the NVR to get the sound output for the cameras attached to the NVR.