The One Systems SF-4 is a high-quality, high-order analog high-pass filter system. The SF-4 consists of four user-selectable 4th-order Butterworth high-pass filters. The SF-4 is a line level device designed for use in professional sound reinforcement systems immediately prior to the main power amplifier. All sound reinforcement speaker systems need high-pass filtering in order to deliver maximum performance. The basic function of a high-pass filter is to limit low frequency signals that are below the loudspeaker's tuning frequency. Filtering these low frequency signals substantially improves loudspeaker reliability, increases power handling and reduces system distortion. In addition to improving loudspeaker performance, high-pass filters also increase the power amplifier's headroom by reducing the power required to reproduce subsonic input signals. The SF-4's high-pass filter frequencies are 35 Hz, 45 Hz, 60 Hz and 80 Hz. Although these frequencies were selected to deliver optimum performance with One Systems models, other speakers brands and models can also benefit from the use of the SF-4. To ensure maximum system flexibility, the SF-4 delivers +6 dB output so that it can be used to drive long output cable lines while still delivering low noise. The SF-4 also features a universal power supply that allow it to be switched between 120 and 240-volt operation, 50 - 60 Hz. Use of the SF-4 will ensure the highest possible system reliability as well as maximum headroom. The cost-effective SF-4 is easy to set up and use.