I've done serious seat-time with the ML Motion 60 XTi in two different shops with, obviously, different listening rooms & acoustics. Both listening rooms, however, were somewhat similar in dimensions. Here's my take and please remember this is all, of course, IMHO:
First shop used a 60 watt NAD integrated amp whose model number I can't remember. Room dimensions were something like 17' X 20' with 7' ceiling. Kinda like a conventional living room with carpeting, bookcases, sheetrock construction, etc. I think the NAD might have been a Class D design. The ML sounded very nice but I don't think that NAD had enough power for them and I don't think it was the right match for 6 ohm nominal load speakers like that, even though those ML are relatively sensitive. The money chair or sweet spot in that room was about 9' away from the ML. The ML were about 6' apart and the wall behind the sweet spot was about 3 or 4 feet away. This would make for around 2 or 3 feet behind the ML front baffles and wall behind them. IMO, speakers with AMT tweeters need more room behind the sweet spot or listening position. A friend and I both got significant listening fatigue after about 30 minutes or so of concert level volume and a little less.
Second shop used a Simaudio Moon NEO 340IX. This is one outrageously and hellaciously nice amp! The ML in this shop only had, we were told, about 40 hours play time on them. Probably not enough but they still sounded really, really nice. In fact, my friend and I thought they sounded a hair better than a pair of GoldenEar Ttriton 2+ we A/B'd them with. However, to be fair, we were told those GE only had about 20 hours play time on them. Probably not nearly enough. The listening room was a little larger than the first one but chock full of other speakers & components behind the speakers we listened to. It, too, was like a conventional living room. The money seat was about 9' from the speakers but had about 12 to 14 feet to a wall behind the sweet spot. The ML and GE were separated by about 6'. The wall behind their front baffles was about 6' away but, again, just chock full of other speakers and components. Not the greatest set-up but I believe these ML definitely benefitted from the space behind the sweet spot. No listening fatigue at all after about an hour & a half to two hours at concert level volumes. I was impressed by both speakers but definitely gave the nod to the ML.
My advice: if your listening room doesn't have at least 6' (preferably more) of empty space behind the sweet spot, you might like something else, like Revel Performa3 F206. That's what I bought after auditioning somewhere around 18 different pairs of speakers and they sound even better in my living room set-up than they did in the shop I bought them from. I also liked the PSB Imagine T2 and the Monitor Audio Silver 500 but the Revel were just jaw-droppers!
Because of my experience with AMT tweeters (not my first, BTW-I demoed the old ESS AMT back in the day) I've always wondered if Beryllium tweeters might need similar room placement (i.e. lots of empty space behind the sweet spot). Anybody have any experience with this?
