Cortex has made Loudhailer functionality available on the M1 in firmware version 1.7. To access this feature, the M1 is wired to the loud hailer using the audio cable, which also is used for the external speaker.
Connecting these devices is discussed in this link.
If you do not have an existing loudspeaker, the Cortex is designed to be used with any loudspeaker which accommodates 30W at 4 ohms. The Icom SP 37 has been tested with the M1, which meets these specifications. Shakespeare, Standard Horizon, Icom have hailers which match.