I'd like to know more about the RPG Modex series myself. Particularly if they work as advertised for low frequencies. I've only encountered a few other products designed this way. The GIK Acoustics T40, T70 and T100 and MSR Springtrap are the only ones I know of.
There aren't many with facilities certified to test below 100Hz using the established ASTM C423 methods. The official results will simply stop at the lowest certified band, although they will provide the bass readings with an attached list of caveats. Many manufacturers won't include this information since it's unreliable (no known error tolerances, for example).
And I have a bone to pick with Acoustic Fields.
Acoustic Fields tutorials are unreliable, and at best inconsistent. It's a polite way of saying that they are the equivalent of cable companies and the like for audiophiles interested in acoustical treatments. They have a forum and Dennis responds personally to emails, but in both cases the messages are brief and cryptic. Same goes for their marketing materials: a lot of disorganized information, just educational enough to get you interested, but not enough to put together an informed buying decision.
Take the attached single-page RAL report for the ACDA-10 broadband/membrane trap. Total absorption for 8 units placed flat on the ground (which is called A mounting) averages to around 10 Sabins across the entire frequency range, and 17 for 100Hz and below. The full RAL report will contain the entire testing procedure, including pictures and other figures. One of the common items is total absorption per unit, which for the ACDA-10 roughly translates to 1.25 Sabins broadband, and 2.125 Sabins for sub-100Hz bass. This is disappointing. Broadband traps can easily perform at 10—20 Sabins per unit for the midrange. I don't know what the equivalent would be for bass traps.
Keep in mind that Acoustic Fields advertises the ACDA-10
to target the 30Hz—200Hz range and charges a minimum of $1050 USD. Each 27"x48"x8" unit is 137 pounds! Compare that to the report for the attached GIK T100 membrane trap ($190 USD, half the height and only 24 pounds). Looking at 100Hz, which is the T100's resonant frequency, you have:
- GIK T100: 6.98 Sabins per unit
- ACDA-10: 1.77 Sabins per unit
You may wonder if the comparison is fair given that the T100 report shows J mounting. J mounting indicates that something unusual or atypical was done. There is no associated standard, as there is for A mounting (flat on the ground) or E mounting (like A, but with brackets that hold up the tested unit, typically with 400mm spacing, and skirting around the resulting air gap to prevent absorption by the back of the tested unit). In the case of the T100, J mounting was described as wall mounted and no air gap. So all in all largely similar.
Acoustic Fields is likely going for low-level but linear absorption. As is, you'd have to cover the ceiling and every wall with these traps to make an appreciable difference. But even then the actual effectiveness is hard to guage since they don't post before/after acoustic results for their studio or listening room builds. The activated charcoal used for the trap interiors will also likely saturate over time with humidity.
It would be much cheaper, simpler and more effective to use targeted absorption with a number of different trap types.