Never mind, it is an important question, which materials suit best for low frequency absorption.
People measure the absorptivity (1 means 100% absorption) of all kinds of material like porous rubber to coconuts.
Let's check performance of tyical absorbers first:
I built some using flexCL cellulose, which is denser than glasswool or foam. Acoustic Fields/Dennis Foley use activated coal, which I had never considered.
There is a very good simulator on the net for diffuse sound
http://www.acousticmodelling.com/8layers/porous.php.
Corner absorbers are different from wall absorbers, the best material depends on the absorber thivkness: flexCL has a high flow resistivity 60000 kPa*s/m², so it works well on walls absorbers with ~100mm thickness, whereas in a corner with 400mm depth, foam with 10000 kPa*s/m² is more effective because sound is less reflected.
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Now let's look at AF's ACDA panel. It's 200mm to 300mm thick for aroumd $1000 per panel, filled with activated carbon (which is used normally in air or water filters).
The hypothesis is that it's effective at low frequency, bc the carbon adsorbs air/gases/water and therefore has high flow resistance.
Activated carbon can adsorb and desorb gas molecules onto and off its surface. Research has examined whether this sorption affects low frequency sound waves, with pressures typical of audible sound, interacting with granular activated carbon. Impedance tube measurements were undertaken examining...
pubmed.ncbi.nlm.nih.gov
BTW if this is the case, it would work best in dry air below 60% humidity.
And yes, there is research that activated carbon indeed does absorb low frequencies:
So does carbon actually work for absorption? Actually yes, Marin/Arenas in 2019 compared fiberglass and carbon and it showed a 2.5x improvement at low frequencies inside a resonator:
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And Travenas showed, that different porosity of the carbon pellets can change the result slightly.
So Acoustic Fields' claim could be scientifically legit and the images in the video could be real. Active Carbon pellets can absorb more at low frequencies in dry air. And with less impact on high frequencies in the room. If this is due to porousity or adsorption is not 100% clear, but doesn't really matter.
How much is it DIY?
If you want to build one, you can order a ton of activated carbon on Alibaba for $1000 and build 8 ACDA10". Or use the rest in your Britta water filter
Data on the acoustic performance:
Acoustic Fields provides a Riverbank lab measurement. It shows 33% of absorption for the 200mm panel at 33 to 50Hz, compared to my simulated 25% of cellulose of same thickness.
Above 65Hz absorption drops to 13%. So ACDA helps for deepest modes only.
Above 1kHz a normal porous absorber would be >90%, where ACDA would be still 13%.
Summary: this corresponds to a deep
bass trap: you can filter out lowest modes without impacting high frequencies. You can add a foam in front of it to absorb high frequencies as well. Interesting stuff, but too expensive vs my cellulose DIY solution.
Realistically, you need at least one wall of absirbers, so about 8 panels for $8400 and a ton of weight to carry.