Break-in - about 10 minutes.
Well yes that was to get your attention, and my honest answer is I do not know for sure, except that brain break-in is by far the biggest factor. In October I did an update to the code, getting ready for final production. This update had a SQ change, and it was not small.
I did the change on a unit that had at least 10,000 hours on it, so it was well and truly broken in. But the SQ change from the code took several months for the feeling that SQ was improving to stop, so brain break-in (getting used to the sound and I suspect the brain learning new ways to process the SQ) is very real - at least to me.
I actually have a brand new unit coming next week, so I can test for how much is down to hardware changes.
Rob