Well, if I am following this correctly I would have to guess that the pipe resonance of the bare driver has been addressed by removing phase plug and re-working or removing the throat of the TAD 4001. Also, from the web site, it seems the motivation is that the designer feels that this achieves better driver integration with regard to point source driver integration issues than if he were to use a horn. I don't have an opinion as to better or worse, but find it interesting and hope I get a chance to hear their speaker some day.In the meantime, this forum rocks and I hope to build a pi kit at some point soon. My current hifi set up is becoming boring and I would like to hear the dynamics that all you horn fans are always talking about...
Regards,
Greg Jensen