Having explored the practical limits of full range single driver loudspeakers these last 6 years, we realized that the area of bass response needed improving and that the only way to achieve realistic bass levels was to bring in augmentation with additional “bass modules”. However we were very sure we did not want to disturb the full-range part of the speakers, and therefore still run that unit as a full range unit, with no filters. The bass modules come in only below 100hz, and are driven independently, with its own bass amplifier, also custom-made by us.