One thing to remember about dipole planars is that the rear wave reaches the front wall (behind the speakers), is reflected off that wall at the same angle but in the opposite direction, eventually reaching the listeners ears delayed in time in relation to the same sound coming from the front of the speaker. The front and rear waves may reach the listener’s ears in perfect phase, 180 degrees opposite each other, or anywhere in between. That creates the possibility (probability, actually) of comb filtering. And that’s just with the planar section of the ET LFT-8b (and all other hybrid designs).
The x/o in the LFT-8b is symmetrical 1st order, so the bottom of the Linear Field Transducer’s (hence it’s model nomenclature) passband and the top of the sealed dynamic woofer’s have a broad area of overlap, centered at 180Hz. You want the output of the two drivers to sum rather than cancel, which brings into play the relationship between the front and rear waves of the LFT drivers, as discussed above.
One cool benefit of using the GR Research/Rythmik OB/Dipole Sub in place of the stock ET woofer is that the Rythmik plate amp (included in the Sub kit) has a phase/delay control that provides continuously-variable phase rotation/delay, from 0 to 16ms/180 degrees rotation. This allows one to position the LFT-8b and the OB/Dipole Sub side-by-side for maximum coherence and imaging, while simultaneously allowing optimum phase alignment regardless of speaker/sub distance from the front wall. Another benefit is with both speaker and sub being dipole, their relative outputs remain constant regardless of their distance from the listening position (the output of dipole and direct radiators fall off at different rates as listening/measuring distance changes).
The x/o in the LFT-8b is symmetrical 1st order, so the bottom of the Linear Field Transducer’s (hence it’s model nomenclature) passband and the top of the sealed dynamic woofer’s have a broad area of overlap, centered at 180Hz. You want the output of the two drivers to sum rather than cancel, which brings into play the relationship between the front and rear waves of the LFT drivers, as discussed above.
One cool benefit of using the GR Research/Rythmik OB/Dipole Sub in place of the stock ET woofer is that the Rythmik plate amp (included in the Sub kit) has a phase/delay control that provides continuously-variable phase rotation/delay, from 0 to 16ms/180 degrees rotation. This allows one to position the LFT-8b and the OB/Dipole Sub side-by-side for maximum coherence and imaging, while simultaneously allowing optimum phase alignment regardless of speaker/sub distance from the front wall. Another benefit is with both speaker and sub being dipole, their relative outputs remain constant regardless of their distance from the listening position (the output of dipole and direct radiators fall off at different rates as listening/measuring distance changes).