Most headphones use moving coil units and in a way headphone design is easier than for loudspeakers because the power requirements are substantially less. A single headphone unit can produce adequate sound levels and a wide frequency range at the same time. A headphone's advantage is its cost and comfort. Headphones are much cheaper than speakers of corresponding quality and are portable. PA and Outdoor Speakers PA and outdoor speakers are used in buildings for announcements and for outdoor music.
Similar technology is used in car alarms.
These types of speakers require more power since they are driven hard and with a lot of volume since they need to be heard over long distances. They must also be able to withstand different weather conditions and must be waterproof. Being exposed to bad weather and heavy power destroy outdoor speakers over an extended period of time.