Bass traps - foam cushiony items from Amazon ok?

Erik, they are adjustable. They look like 2001 A Space Odyssey. A buddy has 12 of them, pretty interesting.. 24" tall and about 15" across. He wouldn't let me take one apart.. LOL Look like modified SonoTubes, but all fixed up..

A 16" x 48" SonoTube is 15-20.00 USD at Lowes or Home Depot.  I'm thinkin.. :-)

One tube inside the other with a slot cut about 2" wide on the inside one.
Top to bottom.  Fix a top to it out of plywood 1/2". Stand 1"slats upright on the lids in a star pattern, on the underside. Drill your 5 holes between the slats drop that top in the Sonotube. Silicone it in place.  Then slide it up and down for the control you want. Mark it, remove the inner tube dampen it with heavy fiberglass insulation and slide it back in place. The bottom the same way, just no holes.

On its side and use the bottom too (have to drill), 2 6 footers aught to do it, on their side of a room, holes either end slot facing out at a 45 degree angle..

It might need something like black hole for the inside tube liner add another 10-20.00 usd for something like a peal and stick..

I can make better ones for 200.00 for 3 or 4. The problem is the "I can make part", has just about wore me out.. LOL 400.00 tops for 4 NICE ones

Less paint or fabric covers. I think covering the tubes with mylar first and then with a porous speaker grill fabric..  The plywood lid would be easy to finish with a nice veneer add 10-100.00 per veneer, just depends how fancy you want it, ay? Bottom set them on spring packs if they are upright..

Regards

I tried building a variable helmholtz resonator once.  It didn't work out too well and didn't really do anything.  I found that tuned membrane bass traps worked a lot better.

Did you have enough to make a difference? Did you measure what peaks you wanted to tame.

They have to be tuned and with enough volume to effect the mode in that room.. A single or even 4 if 8 are needed still leave you without "ENOUGH" to treat the tones correctly..

It's a volume thing not a placement thing as "much as". Diffusion or absorption are different..  This works on canceling a certain peak or peaks.. The formulas are way over my head.. But I can read a mic sweep and see its effects on a given room.. Large will work, just fine smaller will not for BASS anyway..  Adjust the slot to change the frequency, pretty simple.  Just how much ugly can one put up with.. Starts looking like a Roman or Greek Temple.. Ahh that's the reasons for the columns.. LOL

Tuned the Temple..

I use pink fluffy 2’x2’x8’ superchunks in 3 possible corners of my room and the decay time is great, 20ms i think.....

start with trihedral corners

foam go good :0)