Found it ?

Posted by wunhuanglo [ 68.222.11.132 ] on June 21, 2005 at 12:41:19:

In Reply to: Re: Compressiondrivers in general posted by wunhuanglo on June 21, 2005 at 12:25:20:

Definitely an 18 Sound patent for a phase plug - can't say if it's the right one.