Alright then, let's use our room simulator to do some simulatin' on a subwoofer. I just go with the default values, but you can assume a couple of things, like your speakers and subs are going to be ported (unless they're super expensive they're likely to be ported), and it's best to have overlapping frequences (i.e. your crossover frequency should be higher than the lowest frequencies your mains can reproduce), according to Geddes. Let's add one against the front wall right in the center, that should work yeah?
INTERESTING. We've shrunk that null at 108Hz and moved it down below 100, and also have brought up our 30Hz considerably, but it's not perfect. What if we try inverting the sub's polarity?
Well, that didn't work. Wait, didn't both Tatz and Geddes say something about corner-loading?
Front-corner subwoofer positioning will offer the largest piece of clay to work with as you experiment with the high- and low-pass crossovers, frequency settings and subwoofer volume.
and here's Geddes:
1) If there are corners, then one sub should probably go in a corner. Corners have the unique characteristic of see all of the modes. But using two corners is not an effective use of two subs because the symmetrical situation makes these two sources less statistically independent. A less symmetrical location for the second sub would be better.
2) One of the subs should be relatively close to the mains, but not too close. Ideal here might be to locate the first sub close to the mains, but back in a corner, if in fact the mains are pulled out slightly from the wall behind them, as they should be.
3) The rest of the subs locations become far less important if the first two points above are adhered to.
Alright, so let's flip that polarity back and stick it in a corner, what do we get?
Ooh, baby. YES. Look at that marvelous low end. Yes, there is still some weirdness at about 90Hz and 120Hz, but this is overall much better. Say, what happens if we leave it there and flip the sub polarity once again?
YOU HAVE GOT TO BE KIDDING ME, HOT DAMN. All we did was flip the polarity!? Why does that work? Remember, because now we are making that room resonate
in our favor instead of against us. Now, it's important to note that
your experience here is not likely to go as smoothly and you will not KNOW if this has worked without measuring.. But if you don't want to go as far as measuring with a microphone and repeating, etc, this is going to be your M.O. - place, listen, flip sub polarity, compare. But take it from me and Carl and Earl - start in a front corner and also remember that since most subs are side-firing rather than down-firing, you will have four different positions to try, each with two polarity positions -
generally, firing at one of the walls will give you best results. Find some music that you know intimately and see if you can hear everything you know is in there. You can also try some slow sine wave sweeps and see if you notice any particular frequencies dropping out, or jumping out as the frequency rises.
Just for shits and giggles, though, let's at least finish out this particular detour and see what is predicted with a second subwoofer. Flipping the polarity back to its original position but still in the corner with the first sub, let's add another one (asymmetrically, mind you), and move it around until we find a position that seems to work pretty well:
Okay, not terrible. We've fixed some of that weirdness at 90 and 120, but still feels like it could be better. What if we invert the polarity on sub #2 only?
MUCH better, again. Now, is it as good as the first time we put one sub in the corner and flipped the polarity on it? Not really, but remember that everything we've done with the subs here is
a simulation, and every room is going to behave differently, which means that you are going to have to move your subs around and try different combinations of positioning and polarity until it falls into place. You will have better real world results with two subwoofers, truly. And if you've made it this far you should really get that measurement microphone because it will make this process much easier. But, the REQ Wizard room simulator feature is super useful for giving you some very decent starting points. So just remember:
I'll probably do another section on best practices when running sweeps and measuring with REQ Wizard at some point, but if you've made it this far you've probably got the acumen to figure that out. Lots of tutorials on that part elsewhere on the web. Good luck!
FURTHER READING
Setting up Multiple Subs, by Earl Geddes.
https://drive.google.com/file/d/0BxgUOG ... hMtesY_V9Q
Why Multple Subwoofers in Sound Reproduction?
https://mehlau.net/audio/multisub_geddes/
Two Great Articles on Multple Subwoofers.
http://seriousaudioblog.blogspot.com/20 ... tiple.html