All the satellite speakers contain twin 2" drivers. The theory behind this is dual drivers will give you a richer, fuller sound. The problem with this theory is when you have two drivers so close to each other the high frequency sounds can cancel each other out creating holes in the sound field or you hear areas where the sound is over-saturated, fat and nasty. The two problems together can create a very uneven sound field. You've either got too much distorted sound or none at all. This phenomenon is called lobing by audio geeks. To get around this Logitech employs what they term, "Frequency Directed Dual Driver technology" or FDD2, which is a very fancy term for adding a low pass filter to one of the drivers. The filter eliminates the problem frequencies from one of the drivers giving you a warmer mid-tone without the choppy treble response.



Link: PC Apex