Type of the tweeter. Common designs are cone, dome, semi-dome, balanced dome, and whizzer.
Cone tweeters are efficient and the most economical.
Dome tweeters, the type found in most home speakers, sound smoother and more accurate.
A semi-dome driver is one with a dome placed inside a cone.
"Balanced dome" drivers are semi-domes with equal reproduction area given the cone and dome portions of the driver.
A "whizzer" tweeter is a separate tweeter cone driven by the woofer's voice coil.