AE Speakers
1. Controlled gap flux improves linearity, reduces distortion
2. Thermal conductivity reduces, power compression
3. Core geometry is the same throughout the excursion range, wider bandwidth
4. Copper ring (Faraday) greatly lowers inductance, flatter phase response
Purple: ceramic magnets Green- top plate 3/4" thick Blue: pole piece with copper sleeve (Brown)
TD15H+ 
PR15 passive radiator
Woofers are available in 10", 12", 15" and 18" sizes Ultra Heavy Duty passive radiators in 12" 15" and 18" sizes Peak to Peak excursion up to 2 1/3 inches
Made in the USA
An audio paper that explains how a Copper Shorted turn (Faraday) works in a loudspeaker. http://www.diy-audio.narod.ru/litr/FaradayRingsVoiceCoilImpedance.pdf
Answers to Frequently asked Questions about passive radiators. http://www.aespeakers.com/PRFAQ.php 
CGN audio labs Page 13