as far as my eyez work the difference was to be done b/w kenwood 3010 and pioneer 309.
apart from that, there is nothing such as 309d2, 309 is available 309d4 and 390s4 models, also that d4 or s4 has nothing to do with more or less power output sound wise, its just that u configure them in ways like d4 can be connected in series to become 8ohms resistance and in paraller would cast 2ohm load, while s4 if connected alone will cast load or 400rms@4 ohms.
the output of all the 309 series is 1400 watts max.
kenwood 3010 is 1000watts and requires 200rms so the comparision isnt good as both the subs in order to be compared need to be of same category
