When you stick a driver in a box and plot the SPL vs. frequency of that system (ie. the frequncy response), the graph will be "all over the place". By programming equation coefficients into a DSP, the desired response is produced. For frequencies where the graph is too high, the DSP will compensate by requesting less power from the amp. For frequencies where the graph is too low, the DSP will compensate by requesting more power from the amp. While this sounds great in theory, in practice it can introduce problems like phase delays and harmonic distortion.
Now when you take a sub like the 600 which was designed for a flat frequency response and stick it in a room and graph the frequency response, the graph will likely not be flat because the DSP has no knowledge of the room. Enter the equalizer. If you know where your peaks and valleys are, you can knock them down or bring them up by adjusting the equalizer. This again sounds good in theory but in practice you don't have discrete control over each and every frequency using an equalizer.
