A doubling or halving of frequency with the bottom octave usually given as 20 to 40 Hz. From 40 Hz the second octave would be 40 to 80 Hz, then 80 to 160, 160 to 320, 320 to 640, 640 to 1280, 1280 to 2560, 2560 to 5120, 5120 to 10240, and 10240 to 20480. ach octave lower on the spectrum requires speakers to move four times as much air. Thus from the second octave to the first octave (from 40-80 Hz to 20-40 Hz) a speaker would need to move four times more air. It is for this reason (along with the increasing size of the sound waves at lower frequencies) that speaker drivers must get larger and travel farther as they move down the frequency spectrum. Additionally, speaker drivers reproducing low bass need more power with the bass driver in a full range system often using half or more of the available power to the system – another reason separate powered subwoofers are beneficial (they use their own large amplifiers taking a significant amount of strain off the primary amplifier and speakers).