The frequency range across which an audio system can reproduce sound. In most cases, bandwidth is given as plus or minus some level of decibels (usually 3 dB). In such a case, the bandwidth figure states that the system can reproduce a range of sounds at a useful level (plus or minus 3 dB) over that stated frequency. For example, the bandwidth of bookshelf speaker system may be given as 72 Hz to 22 kHz plus or minus 3 dB meaning that the system can reproduce a useful sound level all the way down to 72 Hz and up to 22 kHz. In such a system, there would be a lack of low frequency information making the use of a subwoofer desirable.