What process did you use to integrate multiple subwoofers for 2 channel listening?

My conclusion based on the physics, principles, and actual personal experience is this whole "integration" thing is a distraction, a time waster, and interferes in people's understanding of what is really going on. 

After years and years of trying one sub, as well as searching around reading about and whenever possible actually hearing all kinds of solutions, I had totally given up. Good bass cannot be done. It is just too big a nut to crack. 

When I heard about DBA around 2 years ago I thought here we go again. This time however it turned out there was a doctoral thesis written on this very subject. Not some phony baloney doctoral thesis either like the one recently which is beyond a joke. No, this was a serious paper by a grad student who actually exhaustively measured bass levels in different rooms with all kinds of subs and placements.   

What he found was remarkable: the more subs the more modes and the smoother the response. He even worked out a formula showing the improvement each additional sub contributes to smoothing bass response.  

Then to top it all off everyone who actually tried this method raves about it.   

Along the way I also learned some very crucial psycho-acoustics. To wit, humans cannot localize very low frequencies. Not only that, it takes us a lot longer for those low frequencies to even register as being heard. Tests with headphones prove we cannot hear 20Hz at less than one full wave.   

One full wave at 20Hz is 1/20th of a second. Duh. But now I want you to really think about that. 1/20th of a second. Sound travels roughly 1ft per millisecond. These are all just facts. Highly encourage everyone don't take my word for it, look it up. 1ft per ms varies by atmospheric pressure but who cares, it is a nice round number and close enough for government work.  

1/20th of a second is 50 milliseconds which equates to 50 feet. You can also plug it into this calculator, which will tell you it is 56ft. http://www.mcsquared.com/wavelength.htm  Close enough. 

So then, how on Earth is it possible to "time align" or "integrate" or whatever you want to call it something that we not only cannot locate, but cannot even hear until it has traveled clear across the room and back? Riddle me that one, Batman! We can't. I really do hope this demolishes the "integrate" and "timing" hypotheses.   

Not holding my breath. 

Also not being one to stay stuck in mental ruts I pulled myself out of that one and built four subs. When I got them in the room they were plopped down near walls and corners pretty much wherever there was convenient space. I did try and have them be different distances from corners. But that was about it.  

When I turned them on straight away right off the bat immediately and without doing anything I heard the best bass I ever heard in my life, and by a long shot. Not even close.   

THAT is how I "integrated": with physics, science, and logic. Plop em down. That simple. 

When you have four or more. The fewer you have, the harder it gets. NOT because of anything to do with integration! Purely to do with the physical fact that fewer subs results in greater lumps, bigger peaks and dips, while more subs results in smaller lumps, smaller peaks and dips. With four subs you get incredibly full yet tight, deep, extended bass, effortlessly. Both effortless in how it sounds, as well as being effortless in what you have to do to get it: plop em down. Yes it really is that easy.   

Yada yada

Now, once you do have four subs in the room sure, you can work on getting their level dialed in. You can kill yourself trying all the different methods. Or you can set the crossover to about 80 and then adjust the volume levels. If you have something like the Dayton SA1000 then you can also use the one band EQ, bass boost, and or low cut filters to tweak things.  

I highly recommend doing all this by ear. Because, see Equal Loudness Contours. Meters measure equally regardless of volume. But our hearing changes dramatically with volume. So you can have it measure flat, but it will only sound flat at one volume level. Above that it will sound like too much bass, below that too little. So it is a trade off compromise situation. 

In my case, I made some pretty big swings early on, then within a few days got to where I was making smaller and smaller changes further and further apart.  

You can get more detailed about it but this really is all there is to it. Listen to a lot of different music over a long enough period of time and then make only a very tiny change. Because you will find some records will sound like there is no bass, the subs are doing nothing. This is the way it should always be. You do not ever want to feel like you are listening to subs. I sure don't. Read the comments. Most people don't even know there are 5 subs in the room until I point them out.

Tim, Noble100 used the crawl method. I tried that, you can do it, but read up and notice we all wind up with pretty much the same thing in the end. Then we all wind up making tiny incremental tweaks until finally at some point, done. 

you skipped the Phd paper on harmonics…….