Sound Absorbing Drapes

My wife made drapes for the music room years ago, they’re on the back wall covering a sliding glass door. They work fantastically but it’s a h-u-g-e undertaking. For one thing, for the drapes to be effective, you need a whole lot of fabric because it’s all those little hanging folds that help the drape be effective sound-wise. I don’t recall exactly, but I’m pretty sure the fabric is more than twice the length of the door opening. You’ll also need heavy fabric (you seem to know that) and a liner, and that makes sewing tricky because it’s so heavy. Then, you need to choose your buckram wisely. It can make or break the appearance of the drapes.

A few years ago, we decided to replace our living room and dining room drapes. This time we had them done professionally. It was very expensive to get them done properly and frankly, the ones my wife made looked better.

I think drapes are relatively cost effective treatment than the purposely installed panels. It passes WAF easily if done right. 

@hikerneil  Can you tell us if your Martin Logan speakers are electrostatic or typical box-type that the company got into more recently?  I ask because I personally wouldn't treat the front wall behind the speakers the same way with such different types of speakers.  With my SoundLab electrostatics, they sounded best (to me) when pulled about 5feet from the front wall and it was left untreated with just a wooden front wall to reflect the rear firing sounds.  But with my front firing box speakers (Acoustic Zen) the front wall is well treated.

Have you measured your T30 decay time as a large thick curtain will reduce your mids/highs decay times and could lead to a "dead' sounding room that is not musically engaging; it could dilute the benefits of the other treatments you have done elsewhere.

I've used sound absorbing drapes for a decade to attenuate the music coming from  my audio room.

They do well with high frequencies. But anything below about 300Hz or so is only slightly attenuated, if at all. 

When listen I to music coming from my audio room from  outside the room, I hear what sounds like a subwoofer. This effect gets more and more bassier as I move away from the drapes.

Fiberglas traps made properly, such as the ones from Real Traps will do a far better job with frequencies down to 100Hz, below that, corner traps definitely help but still don't fully tame room resonances. 

M conclusion is that sound absorbing drapes make great room dividers.

I would experiment with blankets or sheets before committing to the drapes. While dynamic speaker nearly always benefit from heavy damening, planar speakers are different. I used planar for over thirty years and often only a small patch of dampening was required on an unadorned wall. so I would experiment with different thicknesses of sheets, blankets... etc. To determine the level that it best...