The distance a speaker driver travels to reproduce an audio frequency. Tweeters have extremely minute excursions since they are reproducing thousands of tiny sound waves each second (at 20,000 Hz a tweeter is producing 20,000 cycles or 20,000 extremely small sound waves). Larger drivers intended to move more air for reproducing lower frequencies have progressively longer excursions. Some subwoofers travel a maximum of up to two inches. enerally, longer excursions are more difficult to achieve and tend to create more distortion since the speaker driver must move such a long distance. Subwoofer drivers with very long extensions tend to have high levels of distortion unless they have very large magnet structures accompanied by large amplifiers able to tightly control the driver and its long travel or excursion. However, the long excursions allow subwoofers to move large amounts of air and play to the lowest levels of the audible spectrum and beyond (some subwoofers are able to reproduce 10 to 15 Hz tones which cannot be heard by humans but which we feel as the massive sound waves hit us).