Thinking in audio implies thinking through the recording and transmission of sound signals. Sound, a more broad term, remains open to any source of sound. Think soundwalk for something that might be accomplished without technology.
Audio requires a source, whether received through transmission (i.e. radio) or recording and playback (i.e. speakers).
Transmission possibilities include a signal tuned in from a low power radio fm station on site.
Or a signal received through a 2-way radio—shortwave, walky talkies, or perhaps a live phone call.
In recording & playback, what kind of object is the speaker? Headphones? Boombox? Over-ear or earbuds? Handheld speaker? Walkman? Speakers installed in the route? The phone?
Also in recording & playback, the question of storage: is the audio received through download? Is it in an app (whether bespoke or hosted). Does the listener call in to a voicemailbox or a phone tree? Is a tape and walkman received in the mail, to be sent on by post to the next member of the audience after the walker has done their walk?