Albert: I don't know the specifics of your speakers, but if their resonance point is noticeably above 12 Hz, and i suspect it is, introducing gain below that point will actually increase distortion, reduce transient response and lower the max spl ( dynamic range ) of the system.
In such a case, one might be better off limiting the bandwidth of the woofer section and lowering the gain at a higher frequency. This in turn reduces power draw from the amps, lowers the operating temperature of the woofers due to a reduction in power dissipation and increases the performance capacity of the system above the actively equalized cut-off frequency.
This is a common trick used by intelligent designers of vented speakers that are bandwidth limited i.e. using active equalization and a high-pass filter to both increase extension while lowering distortion. Bobby Palkovic of Merlin uses such an approach in his "BAM" module. Electro-Voice also used this approach in their "Interface" series of speakers back in the 1970's, which were the first vented designs based on Thiele-Small parameters.
As a side note, this type of circuitry is more effective with sealed designs as sealed designs have a shallower roll-off below resonance. In effect, they can get away with less active boost below resonance, therefore reducing power draw and thermal dissipation. On top of that, sealed designs maintain consistent damping characteristic below resonance, whereas vented designs lose any damping characteristics that the cabinet itself may have contributed. The lack of damping increases excursion and distortion as the driver is now "unloaded". This is where the high-pass filter comes in, limiting the lower frequencies and letting in the higher frequencies that won't cause as much excursion and distortion. Sean
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