Its a ScanSpeak ring radioator.
I think some of the process can be seen here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=8241&perpage=15&pagenumber=1
I think some of the process can be seen here:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=8241&perpage=15&pagenumber=1