Laboratory notes
We are not going to publish another article explaining what sound absorption is. Anyone can get that answer in seconds now. What cannot be produced without doing the physical work is what we actually observe in the rooms — so that is what goes here.
The air gap changes your absorption more than the material does
The same absorber measured Type A and Type E-200 gives two very different low-frequency curves. Both are correct. Only one matches how your product is installed.
ASTM or ISO for transmission loss testing in Thailand?
STC and Rw are not the same number and do not convert reliably. Which one you need is decided by your destination market, not by the laboratory.
What calibration drift actually looks like
Instruments rarely fail suddenly. They drift quietly, and every measurement made in between is wrong by an amount nobody notices.