Bass trapping - corners or walls?

Your room will have bass nodes at different frequencies and spots.  Some of these "room nodes" will be loaded on the left/right side walls.  Some will be loaded on the front/back walls.  Others can also be loaded on the floor/ceiling points.  However, putting bass traps in the tri-corners of the room (such as where floor meets back wall meets side wall) will treat all three types.  It's a good compromise unless you need to specifically treat a certain frequency more so (in my room there is 50hz node loaded on the side walls, so I put 50hz membrane bass traps on the side walls to help).

@handymann - try using 703FRK panels instead of normal 703.  The foil cover on the FRK will reflect the mids/highs and will not suck the life out of the room as much.  It will be a fine-line balancing act.  Too much FRK panels will create brighter and harsher highs.  Your normal 1" 703 panels will do absolutely nothing to treat the 30-150hz areas.  The FRK foil panels will actually work well in treating frequencies down to about 80-90 hz.  The foil cover on the FRK will act as a "membrane" and will resonate to the 80-150 frequencies.  The fiberglass behind the foil will absorb the energy from this resonation and you have a nice 80-150 bass trap.  Anything below 80hz really requires a tuned membrane type bass trap (such as the GIK Scopus traps).

your 19x21x10 room appears to have 3 significant nodes at 53hz, 56hz, and 59hz:

https://amcoustics.com/tools/amroc?l=21&w=19&h=10&ft=true&r60=0.6

An idea would be to contact GIK Acoustics and have them make some custom T55 Scopus bass traps (figure on about $1,000 for four traps).  Them put them in the four tri-corners of the back wall.  That should really help treat the 50-60 hz area.  You have two other nodes, 80hz that load on the front/back walls, and 88 hz that load on the left/right walls.  You can probably treat these with some 2" 703 FRK place in the rear corners maybe just on top of the Scopus on the floor. 

@handymann - alternatively, you can make your own tuned membrane bass traps.  Requires some woodworking (sealed box) and neoprene rubber sheets and some acoust-a-stuff.  I can help advise on design of this if you want.  I have made two sets of tuned membrane (one pair at 50hz and another pair at 63hz).  They are very effective and work better than any other broadband type bass trap.  The thick GIK soffit traps really don't do much here.  I have even tried Helmholtz resonator boxes and they didn't do much either.

I don't know enough about your 12" sheet metal tubes (which I assume are your DIY version of ASC).  I have no experience with ASC traps, so I can't comment.

I don't have any experience with Dennis Foley's product.  It might be good.  It could be another variation of tuned membrane, but he really doesn't say.  Keep in mind that they are $1,000+ each and are very huge.  They have a really large 16" depth (which means they are going to stick out in the room like a large footprint speaker).  They do have a very large 30x60 face, which would be good for low frequency capture.  If you have the money and the room to place them, they might work out well.  DIY tuned membrane panels at 55hz would be 6" to 7-1/2" deep depending on thickness of membrane (either 3/16" or 1/4").  You can build them as large as you want.  Mine are 24" x 36".  It is definitely an interesting design using dual damped front wall diaphragms and carbon damping.  Could work out very well.  Shipping will probably be very expensive (maybe 300-400 dollars each) because they are oversize and very heavy (I've read 150-225lbs each).

You would need 3 GIK Scopus traps ($750) to match the area of a Dennis Foley.  Or two of the 24x36 DIY panels.

My room is 11 feet wide, 17 feet long, 9 feet tall. I have:

6 - 2’x4’ 703 FRK panels (various corner edges)

2 - Rockboard 80 2' x 4' panels (on side wall for speaker SBIR)

2 - GIK Monster bass traps 2’x 4’ with Flexrange Limiter (back wall)

2 - 63 hz limp mass tuned membrane 2’ x 3’ (back wall at corners)

2 - 50 hz limp mass tuned membrane 2’ x 3’ (side wall at back corners)

The two 50hz limp mass tuned membrane seemed to make the biggest difference in bass response. I also did a measurement on this and this really improved the 40-60hz area where nothing else did (even the 63 hz panels).

It’s really just a gut feeling that the FRK performs better than the GIK Monster Flexrange. It could just be additive. However, I did definitely hear 90hz boost when I put up certain FRK panels (like the front wall/ceiling edge). If you play 90-150hz test tones, you can feel the foil on the FRK resonating. On the Monster Flexrange, it’s a very stiff and solid front board panel. It’s somewhere between cardboard and actual wood (stiff but flexable panel, probably 1/8" or 1/4" thick). You cannot feel it resonating as much as the FRK foil.

The idea on the Owens 703 FRK. The front foil will resonant/vibrate with sound pressure waves in the 90hz to 150hz area. The pressure will resonate/push the foil and the fiberglass behind will absorb that energy. The same general principle works for the limp mass bass traps, except the front panel is 1/8" or 1/4" neoprene rubber with a fairly empty cabinet (just 1" of loose acoust-a-stuff glued to the back wall to improve Q). The limp mass is also a very narrow band trap, where the 703 FRK works well beteen 90 and 300hz.

The Monster Flexrange does well and doesn’t absorb much mid/high frequency, so it does not suck the life out of a room as much as a full broadband trap. The Owens 703 FRK reflects a LOT more mids/highs than the Monster Flexrange. On four of the FRK panels, I have a towel covering about 30% of the panel because it actually reflects too much and the mids/highs became overly powerful. It’s a fine line tuning exercise.