The moving iron speaker was the first type of speaker that was invented. Unlike the newer dynamic (moving coil) design, a moving-iron speaker uses a stationary coil to vibrate a magnetized piece of metal (called the iron, reed, or armature). The metal is either attached to the diaphragm or is the diaphragm itself. This design was the original loudspeaker design, dating back to the early telephone. Moving iron drivers are inefficient and can only produce a small band of sound. They require large magnets and coils to increase force.