Originally Posted by Mfusick
What is your general idea about your bass treatment strategy ? What were you planning on doing additionally (that is beyond what is done for these measurements)
Honestly, I was hoping that measurements like this set would inform what was needed for a treatment system. There is nothing going on here at all - just a sub in a room, with some (small amount) of assorted stuff laying around (tools and a couple boxes alongside the speakers). The biggest change I expect is from firing up all found subs (all four corners). The only other treatment I have actually planned is the helmholtz trap I am building from the "speaker stand" (seen in my post from 11/3 and in the video). I don't have a specific plan for EQ either. My processor (AVR) doesn't have any active EQ for the .1, so I apart from the XO setting in the AVR and the level settings in the amps, I don't have any options before I add equipment. I am happy to do that, but haven't worked out a plan - again, I was hoping to determine my needs first, then pick the equipment that would meet those needs.
My general feeling for strategy is that you start with positioning, then move on to passive treatment (absorption) and finish with EQ assuming adequate headroom. I have committed long ago to no more than four subs in four corners. The small size of the room makes a lot of passive treatment challenging, but that's why I have made arrangements for a helmholtz trap 40 inches tall, 8 feet wide (2/3 of the width of the room), and two feet deep (as deep as will fit behind the screen). I could add some additional absorption on the screen wall (and I will to some extent for sure - but maybe not for bass), but I don't think I can have anything meaningful for bass traps in any other places in the room. And for EQ I am flexible but have no current equipment.
My feeling looking at this set of plots is that the stuff below 50 Hz is going to change once I drive all four subs - but I'm not sure if it will be for the better. I know it's difficult to discern from the plots all overlapping like this, but I figured this was better than 14 individual images. The highest output between 20 and 50 Hz is measured nearest the corner. At 50 Hz, where the level measured was very similar at all positions, the highest levels were still measured in the corner, and the level came down smoothly as I moved toward the middle of the room. So you can look at the pattern of the plots and work out which one was in the corner and next closest and so on. There's something going on length-mode-wise around 30-40 Hz near the middle of the room. What's causing that? How should I expect it to change driving four subs? What if half of them are out of phase (for example)?
Hopefully, my helmholtz trap will help above 70-80 Hz. Obviously, there will be mains integration details to work out once I get there. To what extend should I expect my mains to mitigate those problems (mains are sealed f3 near 80Hz, flexible crossover, but assuming THX)?
I will need more measurements, I am sure. For instance, I feel confident that the spatial uniformity I see in these plots will not continue when I measure away from the side walls. Again, that will change once I start running subs on both sides of the room, but in what ways?
I guess I will work most of this out through trial and error eventually, but I am trying to get my head around what the actual modal resonances are - not what I think they should be based on a calculator. Once I get that straight in my head, I can start to make sense of what changes I can expect and get a better idea of what treatments I will need and what I can hope to gain from various EQ options.