A piezoelectric tweeter is a type of audio speaker built to generate high-frequency sounds. This variety of speaker uses a special piezoelectric crystal that is connected to a movable diaphragm. Piezo tweeters, as they are sometimes called, are usually used to create sounds between the 2,000 hertz (Hz) and 20,000 Hz frequencies. This audio is near the top range limit of sound that can be detected by the human ear.
The word “tweeter” is an informal expression that nonetheless has become a standard term among audio enthusiasts. This name comes from the high frequency “tweet” noise that birds make. In contrast, a “woofer” takes its name from the low frequency bark or “woof” of a dog. Both tweeters and woofers are often used to enhance the sound quality of audio at the extreme high and low audible ranges.
In a piezoelectric tweeter, the physical vibrations which generate sound waves are created using a piezoelectric material such as quartz. These types of crystals are naturally occurring, and change size when they are connected to an electrical charge. This phenomenon was known as early as the 18th century; however, scientists did not create practical piezoelectric devices until the 1900s.
Although they were not known by this name, piezoelectric tweeters were first used not for music but rather for sonar. The high frequency capabilities of piezoelectric speakers were put to use during World War One to bounce sound waves underwater. Each echo was timed to determine the distance to an underwater object. Modern piezo tweeters use the same fundamentals of these early sonar transducers.
When a sound signal is passed through a piezoelectric crystal, the structure oscillates in sync with the audio source. A diaphragm made of paper or another flexible material is attached to the crystal of a piezoelectric tweeter. This structure amplifies the crystal vibrations and creates vibrations in the surrounding air. These resulting sound waves are interpreted by the ear as high frequency noises. The faster the crystal and the diaphragm oscillate, the higher the pitch of the sound.
A piezoelectric tweeter is not found in every audio setup,. Some basic sound systems simply rely one a medium sized speaker to create vibrations on a general range of frequencies. In high fidelity audio installations where accurate sound and music reproduction is important, however, tweeters help enhance the sound by generating the top range of audible sound.