Some speakers such as Sonos or Ultimate Ears allow you to pair multiple. to both of the Bluetooth speakers that you wish to stream music to on your Mac.
It should work for all MacOS and any recent Mac (I am using a Mid-2014 Macbook. Both should say connected on the Bluetooth setting page.
"How do I connect my Bluetooth speakers together?" OTONE 3D+ It's a question which everyone wonders.
This video is about Audio Midi.