An unusual problem

I hate to be the one to point this out but wouldn’t $50 of simple springs be a little bit more cost effective? Hel-loo!

Perhaps a Townshend isolation platform for your subs would be a way to go.
I own a lot of their products and can attest to their efficacy in isolating vibrations. They also work great on isolating components- resulting in a much cleaner sound.
Bob

I actually just got rid of an awesome REL simply because it provided a 15% gain in sound quality for me and a 75% gain in irritation for my room mate.

 

So there you have it- REL: the sub so good even when its bad its because its so good.

There's next to zero chance this will work but just in case the wall is super thick concrete or whatever and the glass really is where all the sound is coming through.... 

Bass is making the window pane vibrate like the skin of a drum. You can stop that with a bead of silicone all along the wall/glass corner. But that will mostly stop the glass rattling against the wall. Which will be an improvement for sure. 

But then the window pane will still be vibrating, only now the wall will be like a pivot point. The easiest cheapest most unobtrusive thing you can do is glue a 2x2 into that corner all the way floor to ceiling. 

Try the silicone first, that will at least stop the rattle and give you a clue if anything else is even possible.

I actually just got rid of an awesome REL simply because it provided a 15% gain in sound quality for me and a 75% gain in irritation for my room mate.  
I’d look into finding enjoyment in a set-up that doesn’t bother your neighbors.  Sell the sub and put that $ into upgrading the transparency, resolution  and musicality of your set-up!

Magnepans might be something to consider as I’ve heard that they don’t transmit bass through walls quite like conventional box speakers.  Magnepans are more directional so they may not sound quite as good when walking around your loft but that directionality may help you out as well since it sounds like you have glass along the entire 1 side of your listening area.

Good Luck!

bass waves are so long that they penetrate easily. best suggestion I read was just go to headphones at night....harmony with your neighbor is important.

I have a Subdude in my bedroom.  I live in a house, but my neighbor's house is not too far away.  I think it helps a little, I never went outside with my SPL meter to see if it made a difference or not.  Eventually I just quit using the sub in there.  They never complained, but I was trying to be proactive.

There's this thing called consideration that you can get for free.  If you live in a box right next to someone in another box, don't play your music loud after 10 PM.  Headphones are a good suggestion.  That's what I do late at night.

Buy an Auralex Sub Dude isolation platform.  I've had one for years ...not only does it improve the sound but it eliminates many rattles associated with having a sub.  My mom had been complaining that my dad's sub was boomy and keeping her up....  he's 76 so sometimes movies are a little louder than they should be.  He says "does anybody ever say turn it down at the theater?"   Touche, I guess.  Anyway  I went over there one Saturday when he wasn't home and slipped a sub dude under the sub and ran the Anthem room correction software again and it's never sounded better.  Boominess is gone and you don't feel it in other rooms now unless it's loud.  One of the greatest accessories ever.

but realistically you’re just going to have to turn everything down in the late hours.

Not just late hours but all the time except when theyre not in. 

Unfortunately your problem isn’t that unusual, it’s just one of the pitfalls of sharing a common wall with your neighbor. You can try some mitigation, but realistically you’re just going to have to turn everything down in the late hours.

Dynamat products are used to dampen the inside of car doors to quiet the inside of your car, improving the sound of car audio.  This may work well to dampen the glass vibrations.  

There are also quilted blankets, woven with batting available, much like the packing blankets Penske trucks issues.  These can be found with metal grommets so one can suspend them on the wall with small nails.  They can weigh 9lbs. each.

It may help if the sub was right next to your seat. In phase and lower volume. Or headphones. 

Acoustic panel to absorb the bass at the windows or some means of damping the glass? 

Turn your subwoofer off after 10pm. Headphones is another suggestion. This is one of the drawbacks of apartment living. On the flip side,I’m sure they’ll create noise that will disturb you as well. It just one of the many compromises in life.

    I suppose you could also try a “subdude “ subwoofer platform. I’m just not sure how well this would work in your situation. Lower frequencies just seem to travel everywhere.