@dysfun @ShadowJonathan electrically it's essentially trivial. the challenge is primarily mechanical and material, i.e. designing something with the right shape to act like a speaker box, while remaining a good fit for people's ears, and being durable and manufacturable.
most earbuds are injection moulded plastic too so you need to be at 100k+ unit scale to make it cost effective. not sure if there's a lower volume process that's suitable; not really my area.
