the 4b's have 8" woofers vs the IIb's 10". both are 3-way designs. the reference six is a 4-way with a 10" woofer.
comparing frequency response:
rs4b: 40hz - 32khz
rsIIIb: 34hz - 32khz
reference six: 35hz - 40khz
power handling:
rs4b: 40 - 150 watts
rsIIIb: 50 - 200 watts
reference six: 35 - 225 watts
IIIb and 4b are rated at a vague 4 - 8 ohms, the reference six at 6 ohms.
personally, i find the reference six superior. the technology was better. the emit-r has better frequency response and dispersion. the IMG (injection molded graphite) cones are superior in both performance and longevity to the poly drivers of the rs (and not prone to the disintegration problems of poly drivers). also the addition of a mid-bass driver adds more flavor to the sound.
the rs do have nicer looking cabinets though.
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