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Old 29th August 2017
Gear Guru
Holy Grail

Demetris here on GS offers a free calculator, predictor. It is fun, educational, and a bit of a reality check in terms of expectations.
But the behaviour of waves in a small room is extremely complex so any choice such as random or a single degree of incidence cannot deliver a realistic assessment. Also corner behaviour, which is mighty, is not factored in.
Lastly perhaps, the damped membrane effect of semi rigid fibre is not factored in.
So that calculator does well at encouraging the use of very thick light fibre, but doesn't recognise the usefulness of thin semi rigid traps straddling corners and so on. I am not sure that any calculator does or even could as the effects are quite complex. I mean how does one assess rigidity or frequency of resonance of a batt of 100KG fibre? Which afaik also varies a lot from sample to sample.

So overall, rather than looking to prediction, I suggest looking to tests and empirical evidence. The manufacturers of typical 100mm traps and larger have plenty of advertising showing good results. Many rooms are shown here before and after. The BBC R&D have come up with various LF solutions, including whole wall partitions of sheet steel, damped obviously. RPG and Renz manufacture 100mm thick traps, again involving steel, which are very effective around 70Hz.
There are softer membrane devices by RPG, Primacoustic, and afaik GIK.
PSI do an active powered trap.