Wilson Audio Specialties Alexandria XLF loudspeaker Aspherical Group Delay
Sidebar 2: Aspherical Group Delay
Wilson claims that its Aspherical Group Delay technology is as effective harmonically and texturally as it is spatially, helping to precisely reintegrate, at the listening position, the frequencies that have been separated by the crossover and sent to the various drivers.
To do this, each of the three drivers in the Alexandria XLF's MTM array can be independently adjusted fore and aft, as well as rotated on its polar axis. Of equal importance, once the appropriate position has been found, each module can be rigidly locked in place with tether bolts of various lengths, secured with wing nuts. Each module is moved along a pair of rails, each with a center notched track. There's one set of rails atop the woofer box, and one set each atop the lower-midrange and tweeter cabinets. There's also an assortment of spikes of different lengths. It's a major feat of mechanical engineering and precision manufacturing that needs to be seen to be appreciated.
All you have to do is measure the distance of each drive-unit from the listening position, and the height of your ears when you're sitting down, and Wilson's charts tell you into which numbered notch each spiked module should sit, and which length of tether bolt should be used to set the module's elevation. But no, you don't do any of thisyour Wilson dealer will.
The goals are to time-align the drivers so that the combination of their outputs produces the equivalent of a single point source, and, by adjusting the modules' polar axes, to precisely focus the sound propagation on the actual listening positionnot at a theoretical point a set distance from the speakers dictated by a design that might not suit the realities of the room. It's sort of like the difference between cameras with fixed and adjustable lenses.Michael Fremer