Clearing the air on limp-membrane absorbers

[MyPutzyRod]

There seems to be very little actual confirmation as to what really constitutes a limp membrane absorber.

Some of the most respected guys on here, Glenn and Ethan sell products that use proprietary membrane designs. My intent here is not to try to expose the secret sauce, but to expand upon their very clever and effective designs to the DIY realm.

Ethans density test I found to be eye opening in that 12 panels of 3 inch 705 FRK had excellent effects in a real room on real waterfall graphs. Not coefficients from a test chamber, but real simple waterfall graphs that showed great effects.

However, in his own traps, and in the GIK traps, the membrane is NOT bonded directly to the insulation. In the case of RealTraps, it is bonded to the fabric only, which allows it to move free of the insulation (or so I'm inferring). In this way it becomes a true membrane.

GIK and ReadyAcoustics on the other hand use proprietary fabric that in itself mimics the action of a membrane. Dubay of ready acoustics writes the following regarding whether their bass traps are membrane traps:

"No, and neither are other types of absorbers with material bonded to surface. (this is yet another piece of misinformation floated on the internet.)

Limp-mass absorbers feature a membrane that is not bonded to acoustical insulation and is free to move independently of the acoustic insulation. Though our Ready Acoustics fabric (when used with acoustical insulation) tests like a “membrane” it is not a membrane absorber in the acoustic science sense of the term."

These ideas have me pondering:
1) what can actually be labeled a limp membrane absorber?
2) is it better to bond a membrane (plastic, foil, kraft) to the fabric as opposed to directly on insulation?
3) does tight weave fabric create a "low pass filter" effect that is not actually absorbing more LF, but less HF, and thus adding more traps increases LF absorption without killing highs?
4) which tight weave fabrics if the above is true would exhibit such behavior?

[MyPutzyRod]

Uggh mods can this be moved to "bass traps", my apologies