The term "crystal mike" refers to a type of microphone that uses a crystal to convert sound waves into an electrical signal. Some common synonyms for this type of microphone include crystal microphone, piezoelectric microphone, and ceramic microphone. These types of microphones were popular in the mid-20th century and were often used for amplifying guitars and other instruments. While they have largely fallen out of use in professional settings, they can still be found in antique and vintage audio equipment. Today, most microphones use dynamic or condenser technology, which offer higher quality and more precise sound reproduction.