The Mission 753 is a favourite speaker of mine.  It was supplied in two versions. The standard, and then later on a revised edition described as the Freedom model

At the beginning of the series the tweeter supplied with the Mission 753 was a metal dome tweeter.  This gave a very crisp top end to the speakers voice.  However also detectable was a slight tizz in the top end that masks some of the detail.  Worse than that, in time the top end tizz or sharpness begins to get a little wearing on the listener.

Mission received criticism for the overly sharp top end, and when they wished to revitalise sales in the speaker they replaced the metal dome tweeter with a  softer sounding silk dome tweeter,much to the delight of the critics.This freedom model was considered an improvement.