Acoustic Concepts, Class 2

  1. An electrical current traveling through a wire generates a magnetic field. (In other words, it creates an electromagnet.)

  2. Reversing the polarity of an electrical current reverses the polarity of an electromagnet. 

  3. The changing polarity of an alternating current in an electromagnet can be used to move a permanent magnet back and forth to create a linear motor. 

  4. The frequency of the alternating current determines the rate of movement of the linear motor. 

  5. At lower rates (less than 20 cycles per second) the back-and-forth movement is visible. At higher rates (greater than 60 cycles per second) the back-and-forth movement cannot be seen, but is experienced as sound. 

  6. An electrodynamic speaker is a specialized version of a linear motor. 

  7. The speaker cone amplifies the sound, making it louder.