I hear what you're saying dannut. The level of understanding and self education of acoustics is obviously going to vary by individual. Personally, I don't have the interest to get to the level of Dennis, draganfyr, localhost etc. That being said, take my experience here as an example of what some others may be going through.....
I decided to construct a HT over two years ago with no pre-existing education on audio theory, sound isolation etc. Only construction and electrical background. My last receiver was bought in the 80's!
As I started digesting more here, I came to the conclusion that sound isolation was important in my situation, and of course I wanted a good audio experience as well, but certainly no intent to have a THX certified theater.
As natural progression over the course of 2+ years, I began soaking up what "general" and more specific information is offered here. I would think that anyone investing in such a project will be reading and absorbing this information as much as their time and level of interest permits them, to hopefully achieve a goal that THEY are happy with.
In my case, as example of "general concepts" surrounding bass trapping, I constructed front and rear corner traps, as well as doing what I could with my riser. The results of that turned out pretty good (in my opinion, black line) as measured following (actually, most recent Audyssey is even better);
My room currently sounds "good" to me. I have good bass response, I don't detect a muddy sound field, comb filtering etc. but I am under the impression that with some simple measurements I will most likely find some sources needing treated which may further enhance my audio.
Now on to first reflections, which is where I'm currently at. The opinions on treatment methods, materials etc. seem to go on and on and quite frankly I'm not sure that I want to further investigate the merits of using QRD vs. diffusion vs. absorption etc. What I want to do is measure, determine any issues via ETC. and either someone will comment with a recommended solution, or I will eventually figure it out on my own. My current plan is to just absorb it away.
So what's the point of all this?
1) I believe there are indeed general guidelines which can be applied "generally" and there are some which cannot.
2) Certainly, knowledge is power, but there will always be varying degrees presented here.
3) A person CAN measure without being a subject matter expert, interpretation and correct resolution can be another matter entirely.
4) I APPRECIATE the feedback that the "more audio astute" here provide to those of us who are not in a similar position.