A tweeter is a louspeaker designed to produce high frequencies, typically from around 2,000 hertz to 20,000 hertz (20,000 Hz is generally considered to be the upper limit of the human ear). Some tweeters can manage effectively flat response up to an octave or more higher (30 to 45 kHz). The name is derived from the high pitched sounds made by some birds, especially in contrast to the low woofs made by many dogs after which low frequency drivers are named (woofers).