My New Magnepan 1.7i's sound dull and lifeless on the top end...why?

One difference between open baffle dipoles (such as planars) and dynamic drivers in enclosures (whether sealed or ported) is that dipoles "move" air from one side of the planar to the other---leaving the air pressure inside the room unaffected, while box speakers change the air pressure inside the room (and inside the enclosure, which is why the suspensions of drivers intended for use in enclosures differs from that intended for open baffle use).

@kingbarbuda, did you mean to say "percussiveness" rather than "persuasiveness"? If so, I find the bass panels of the big Maggies to have a very percussive sound, which is why they reproduce piano and drums so well. But that’s more a mid-bass rather than deep-bass (40Hz and down) phenomenon. Magnepan has been working on a dipole woofer system for a few years now, which uses multiple dynamic drivers in a sealed enclosure. It will be available as an add-on for current Magnepan models, and as the woofer system for a new model: the 30.7 For Condos.

Eminent Technology already offers such a woofer system, and then there is the state-of-the-art OB/Dipole Sub from Rythmik Audio/GR Research.

I sold off my 1.7i’s not long after I had them solely because their height and overall presence in my room made me feel as though I was on Easter Island…

I replaced the 1.7i’s with a pair of .7’s, which I found to be much more responsive, perhaps even “brighter”, for lack of a better description. I had a Pass Labs X150.5 during this period, as well as a couple of tube preamps - all was good. 
Fast forward to the present and I’m now absolutely digging a pair of original MMG’s whilst I await the arrival of the new LRS+.  Pass with Maggies and Thiels is usually a solid matchup. 
 

My current setup is a good deal less involved with equipment. I’m enjoying a Belles 250i hybrid Mosfet integrated amplifier with the MMG’s, a coupla Schiit dacs, a cd transport, a cheap-seats pro-Ject turntable, and an Aurender 2TB music server. Back to basics more or less and everything is fine. Oh, and no sub. 

@bdp24 Yes. I meant “pecussiveness”. Autocorrect messing me up again.

My experience with Magnepans are my former 1.7i and the AXPONA tests of the LRS and the LRS+. I added a pair of REL T/9i subs to my Maggies and it made a world of difference. Not hard to dial in. But I think the addition of the subs and what kind of subs could be room dependent. I have thought about getting a pair of LRS+ just for kicks. I haven’t pulled the trigger on that yet though. Going to AXPONA at the end of the week. Maybe something will happen there. 

I just received a call from the hifi shop that my Maggie LRS+ speakers have arrived. I would say “finally” but it was only a three month wait, which is a rather big departure for me since I’ve always bought everything I own from stock. I’m not a very patient guy…

Immediately upon receiving the call I put my pair of original MMG’s up for sale on another site, at a price I hope someone long interested in a pair of Maggie’s but hesitant about taking a more substantial financial plunge will decide to buy. I mean $275 for a pair of speakers as good as these is a pretty good deal.  It’s worth a toe in the water at that price. 
 

 The audio press went fairly gaga over the original MMG model when it was first released, and if the equally gaga opinions currently being tossed out there for the LRS+ are even half accurate I’ll be a happy camper. The two brands of speakers that have consumed most of my interest and money over the years are Magnepan and Thiel. There’s more than just “something about them” that keeps me wanting one or the other. 
 

I pick up the speakers this coming Saturday. Woohoo!

I’ve high passed my 1.7is at 100hz with dual tekton 2x10 subs, rca inputs.

played around a bit with sub xover, volume and phase settings for room/placement.

Happy camper here..