Charlie
We searched for the possibility to use less power in our amps because of the environmental issue. We then developed a small 12 Watt per channel amp. Thereafter we looked at the needed loudspeaker.
From 1982 until 1999 I was the publisher of a Dutch audio magazine and we once developed a FR loudspeaker named: "PMR", the Poor Man's Reference. We used that loudspeaker as a reference indeed because it enabled us to easily distinguish differences (and faults) in the existing high end amplifiers we tested. That PMR became quite famous and still is in use in various recording studios.
So we needed something new (and relatively cheap) to combine with our D-122 amplifier. We now have two versions, one with a metal cone in the center. That cone enhances the highest ocatave (21 kHz -3 dB) but also introduces some distortion. So we made a second model which is in that picture and now without that cone. That loudspeaker unit performs quite well up to 18 kHz (-3 dB) and IMHO is a pleasure to listen to.
All other loudspeaker models are also constructed in a round tube which enhances the width of the stereo image and leaves out the "hot spot".
Filtering is always done with a series filter, we developed our own software program for that.
Christian at Xerocommaudio his some of our bigger models for demonstrations.

John
response at http://www.hawkaudio.be/lspic/fr1-respons.JPG