I would love to tell you that Etymotic finally creates a new flagship IEM 19 years after the ER4 series was released - No, unfortunately not. As far as I can tell, this new Etymotic, called the ER4PT, comes with two more things that are not included in the original ER4P: an airline adapter and a certificate of channels matching test. Now I suppose the airline adapter could be what is adding the T (as in 'Travel') to the new name, or maybe it is the sudden important emphasis on 'Testing'? Well, for what I know Etymotic has been doing channels matching on the ER4 series for a long time now, so adding a certificate really doesn't make it better than it is. All in all, I am really just seeing a marketing decision rather than a real change in the ER4 series. Don't get me wrong though, I still love the ER4 series - with T or not.