Acapella Ion Tweeters: Diff btwn TW1 and TW1S

Looking for expert technical advice here... is there a difference between the TW1 and the TW1S? If so, can you elaborate?
Thanks Glory. I emailed Brian and he suggested that I contact Acapella. I did and got an answer several hours later saying that the older "ATR" labelled TW1 model was the same as the "Acapella Audio Arts" labelled TW1S.