In one embodiment, a conferencing device detects a potential echo effect between two or more of a plurality of participant devices in an online conference the two or more participant devices being co-located. The conferencing device presents an echo warning to a user interface of a particular one of the co-located participant devices, in response to detecting the potential echo effect. The conferencing device groups the co-located participant devices into a group. The conferencing device provides audio data from a selected one of the co-located participant devices in the group for presentation by the plurality of participant devices as part of the online conference.