I'm aware it's been discussed before, but often with a different title and initially another intention of the threat. It's not easy to find that information by searching and I think it would be beneficial for many to have one all gather thread. And perhaps also discuss this more in detail then what has been the case so fare. A few questions I have: 1. If I use pressure based absorbers rather then velocity absorbers in tri-corners to treat low frequencies. Does that imply that I will not be able to treat midbass and upper bass in that corner? And what will then the overall effect be compared to using porous materal? 2. What is the best way to combine the two? I understand that it depends on the room and speakers, but are there are general knowledge one can have as a starting point? 3. I see some are treating the room with only Helmholtz resonators (under 100 Hz) and diffusors (working from around 500 Hz). This should imply that the frequencies between approximately 100 Hz and 500 Hz are not dealt with. Isn't this a problem? 4. How vital is it to reduce the reverb time in all bass frequencies?