Does this make me a heretic? Will I be ex-communicated? I switched from HDT Mk II drivers to the DFR-8 with the alternate tuning, and in my temporary room was thin on all but well recorded deep bass. Maybe the drivers are still breaking in from their mod, but I wanted to try something...and for me it really worked:
http://www.quarter-wave.com/Project05/BSC_Circuit.pdf I love the live quality of these speakers are and this circuit doesn't change that. Yes, efficiency is compromised, but pinpoint imaging and accurate tone are not. This circuit (for me) made the HDT - known to be being revealing of bad recordings - friendly to bad recordings without losing the magic of good ones. I'm still not using all 8 watts before it's too loud--plenty of headroom.
I believe that most of my issues are due to my limited and temporary room setup where the speakers are in front of a stair (and the bass goes upstairs). The DFR-8 mod improved my well worn 206's, but with the circuit in line there are no audible bright spots or humps.
To build the circuit, I used air-core transducers from my ancient AR-5's, mills resistors and a Sonicap on the zobel.
I'm still playing with the value of the resistor in series to fine tune to my liking, but hey - anybody else doing this?