Dynaudio Core SUB Active Quad 9-Inch Reference SubwooferCore Sub is the ideal low frequency extension for all speakers in the Core studio monitor range. And when we say 'low', we mean it: it digs down with a flat response to 15Hz with a 6dB roll off at 13. 5Hz. There's no meaningful low frequency that it won't reproduce utterly faithfully. Combine its handcrafted cabinet made at Dynaudio's factory in Denmark with four of our latest low frequency drive units and 1000W of Pascal class D amplification, and