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.
A speaker is someone who delivers a speech or a device that makes sounds louder. The speaker gave a great speech but you couldn't hear it because the speaker was turned off. Speaker has a few different meanings, from the person who addresses a group, to the piece of equipment that amplifies sound to someone who is fluent in a particular language. For example, a native Spanish speaker can usually tell if someone learned the language in high school because textbooks don't always include the slang and idioms of everyday speech.