The subwoofer is a speaker specialized in the reproduction of low tones. When playing music, deep tones are less heard than perceived in the form of a noticeable bass. Subwoofers can be divided into active and passive variants. The technical difference is that passive subwoofers do not have an integrated amplifier. The speaker has to provide the energy for the subwoofer itself. Since most Bluetooth boxes are speakers for mobile use, it is not possible to install an active subwoofer. This requires a separate power supply for the integrated amplifier.