Ask A Scientist© Engineering Archive

Index Key:   ENG018
Author:      harden
Subject:     Magnets in speakers
Text:        Why is there a permanent magnet in a speaker?

Response #:  1 of 1
Author:      dipper
Text:        There are actually two magnets in a common audio speaker.  There 
is one permanent magnet attached to the framework of the speaker, and one 
electromagnet attached to the cone of the speaker (usually mylar now instead 
of paper).  The wires that go to the coil of  wire on the pack of the cone 
supply the current to an air core coil, which produces an electric field that 
either repels or attracts to the permanent magnet, depending on the 
instantaneous polarity.  The higher the frequency of the electric current 
being sent by the amplifier, the faster the field is set-up, broken down, and 
re-set-up in the other direction, so the faster the cone moves back and forth.  
Because all the cone does is move air, if it is moved back and forth fast, you 
hear a high tone from the vibration.  Low frequency current, low frequency 
tone.  Large amount of current, big movements of the coil and cone, producing 
loud tones, and small amounts of current will produce small movements of the 
cone.  Now the only trouble is a thing called impedance, but that is for 
another discussion.