[Housteau]

When having the opportunity to build in DIY bass trapping into a rooms floor to ceiling corners I was wondering how important building in an air gap and having a membrane of some sort would be?  Would it be important at all if the room and trap itself was large enough?  In other words would that air gap space be best utilized using more rigid fiberglass instead?  When I enlarged my listening room a few years years ago I went with the complete corner fill method without any kind of membrane, which was my wisdom at the time.  It has worked well for me.  The traps are large and triangular measuring about 3 feet across running floor to ceiling.  The room measures very well.  I do use some manual DSP to lower some peaks, but there are no dips to worry about.

Although the corner fill method has done well for me, could I have done better by creating a different trap design and possibly eliminate some of the DSP I am now using?  Would an air gap have added efficiency?  Would having some sort of membrane, soft, or rigid add to it as well?  For example, would spanning a corner with say 1/8" hardboard and having that space behind full of either OC 703, or 705 be a better design?  The nice thing about corner traps is that that can be quite large and still not intrude into the rooms space, or appearance when done to go with the looks of the room walls.     

[jriggy]

I remember reading and seeing pics of your room on here years ago.
I am not qualified to answer your question other than to give my recent experience, that would lead me to (unscientificly) say use a membrane/range limiter... I recently redid the acoustic treatments in my room and one area was replacing the front corners of GIK Tri-traps with the larger Soffit-traps but with the added option of the range limiter membrane layer. Allowing the reflections to occur here had a positive affect to soundstaging and openness in high frequencies.

[JLM]

The GIK 244 flat panels come "full range/boardband" and "range limiter".  Both use air gaps between the Owens Corning 703 fiberglass and the back (1 1/2 inches on the "full range" and 1 11/16 inches on the "range limiter").  The "range limiter" panels have a solid panel (membrane) on the front side and are slightly more effective below 100 Hz while the "full range/broadband" panels are roughly 3 times as effective from 250 Hz on up. 

[Rob Babcock]

I think an air gap will broaden the absorption range a bit and help to absorb a bit more energy.

[Housteau]

I understand the caution needed to not overly dampen the room of the needed higher frequency reflections.  In fact very recently I had visited a friends room and enjoyed the added sparkle that his system had over mine.  It is a lively room though with a high efficiency horn system, a completely different animal than mine.  When I came home to listen I realized that his extra sparkle came at the price of having a reduced overall black level between and around the notes.  That black level as I call it is a hard one to properly define, but I find it very important in recreating that virtual soundstage.  A large part of that does come from reducing various power supply noise especially in digital transmission, but also with room acoustics. 

Still, I wanted to add some of that sparkle back into the room without sacrificing any of the attributes that I love about my room.  So I played around and rearranged some of my room treatments.  My speakers are dipoles.  I had a tall double stack of tube traps against the wall behind each one.  I pulled them out and set them to the outside of the bass columns reflective side out.  I also added in a 2' x 2' square of transparent corrugated plastic roofing sheet to cover part of an absorptive bass trap that is center on my front wall.  Those two small changes gave me back some of that sparkle without loosing any of my black level that I worked hard to achieve.



An interesting byproduct that I was not expecting was that the bass was also positively effected.  While already being all that I felt it should be, it became even more so.  I had considered adding an outer reflective barrier to my front broadband corner treatments.  All I would need to do is remove the outer 3' x 8' decorative screen and face the rigid fiberglass.  But, as you can see in the photo that the tube traps are already reflective side out and the bass towers reflect much of the rest anyway.  On a graph the differences in bass response measure to be very slight, but the the subjective feel is not so slight at all.  My program runs on an old computer with date and other issues.  So, please disregard the written data.  Also, this graph reflects my room setting for LP's with a 1.5 dB shelved rise below 85 Hz.



As far as the air gap goes I went back and reread some thoughts on that to remind me of why I originally did what I did.  I called it corner fill, but in different articles I see it referred to as the Superchunk method.  From what I have found it appears to still be the preferred method with the downside being only one of cost.