The Yaesu SP-9000 is designed to match the FT-9000 series. The SP-9000 features two 4 inch (100 mm) speakers, affording independent audio paths for the Main and Sub VFO output; the left speaker puts out Main VFO audio, while the right speaker yields Sub VFO audio, and a front panel switch also allows you to combine the audio signals from both receivers for mixed distribution from the two combined speakers. This produces an effective aperture of 8 inch (200mm), for outstanding tonal quality. The dual audio filters provide three steps of high-cut (2400/1000/700 Hz) and two steps of low-cut filtering (500/300 Hz), and each audio path (Main/Sub) may be filtered independently, allowing you to experiment with optimum settings in a diversity dual reception filtering mode. And you also get individual mute switches, useful for dual receive operation.