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.
Okay, to start, there is a huge difference between preteen and tween. Preteen: Someone between the ages of 9 and 13. Tween: A little girl, who thinks that she's an teenager because she's wearing a training bra, and she continues to act like a child.