684 features a new combination of a pair of Kevlar® cones for delivering its bass and midrange. The lower cone is dedicated to bass, which relieves the upper bass/midrange unit of the duty to handle heavy bass and leads to clearer, crisper midrange than you might find in smaller speakers. The Nautilus tube-loaded, aluminium dome tweeter, featuring a new surround material to improve spaciousness and imaging, adds needle-sharp top end all the way to 50kHz and beyond.