From 1992 until his election to the U.S. Senate in 2004, Barack Obama served as a professor in the Law School. He was a Lecturer from 1992 to 1996. He was a Senior Lecturer from 1996 to 2004, during which time he taught three courses per year.
Traditional speakers produce sound by using an electromagnet to move a flexible cone back and forth. They use drivers to help translate electrical signals into physical vibrations so that you can hear recorded sounds. A tweeter is the type of speaker driver that produces the highest range frequency. The other two main drivers are woofers and midrange. Basically, a driver moves a flexible cone, or diaphragm, back and forth very quickly to produce sound waves.
Williams used two different types of speakers in the back box: a midrange on the left side and a tweeter on the right side. In most games the left side speaker is a 5-1/4 inch midrange, and the right side speaker is a 3 inch tweeter. Some of the early WPC games with the Bally-style back box (Gilligan's Island, Harley Davidson, and Party Zone) used a 6 inch midrange on the left side and a 4 inch piezo tweeter on the right side.