Before microphones, singers and speakers had to practice carrying their voices across large, crowded rooms, auditoriums, and theaters. Only performers with booming voices could make it, although that did not stop plenty of others from ruining their vocal chords trying. When microphones hit the market in the late 19th century, performers and speakers were suddenly free to lend their voices more expression, dynamic, and emotion, as the innovation could pick up quieter, subtler sounds and amplify them across large spaces. Modern microphones are still used for performances and public speaking, but the technology also lends itself well to things like sound and video recording and digital communication. They range in size from large devices, such as the wireless microphones that public speakers often use to micro-sized parts placed in cell phones. Some mics are designed to hook into an existing sound system, while others plug directly into a computer's USB port. You can find microphones of all shapes, sizes, and types on eBay. Choose from well-known brands such as Shure and Behringer and browse through a wide variety of excellent deals on new and used equipment.