Subwoofer: room 16 x 18.5....

the Human Ear is fairly insensitive to Bass Distortion. Several % should be doable, if not more. I know there is research, but I'm scared to look it up. That same amount of distorion at 5 or 6khz would drive bats from the room.

EQ'ing a room may make a certain seating position a sweet spot, but Will Not effect room modes. They are a function of the geometry of the room and sub placement. Multiple subs will excite the room and produce, best case, complimentary peaks / nulls which will give reasonably flat response over a larger area. Also, I suspect slightly lower distortion at higher levels.

As for X-over frequency, I cross my Maggie 1.6s at about 40 to 45hz. Lower limit for the Maggies is about 40 or so? Maybe 36, depending on who you read. Anyway, I dial 'em in for a little overlap, so as the maggies drop away, The sub picks it up. I do NOT use test tones / meter since I'm nuts anyway and this would be just like trying to put out a fire with Gasoline. Like, how obsessive can I get?
Besides, there is an art to the science of SPL measurement and you'd probably also need someone to help you take the data. Multiple repeats, a spreadsheet and I've finally flipped. Sheesh, Science ain't easy!
I may be able to wring a little more performance out of my system if I were to hi-pass the Maggies at 60-70hz and the lo-pass the sub at maybe 50-60hz. I will probably NEVER find out, unless a few volunteers show up with a bunch of stuff and some Single Malt!

Also, from our 'for what it's worth' department, Somewhere above 80hz or so, you can begin to localize the sound, so you gotta be careful there, too. With my current setup, I simply can't find my sub.

Magfan says, "Measurements of subs, while a good thing doesn't cut it in a real room."

"Measurements of subs, like frequency response and max spl are near-meaningless."

"Measuring for location is more advantageous, but still a hassle. Room boundry situations make such measurements in the hands of most of us, me included, kind of dicey."

"I do NOT use test tones / meter since I'm nuts anyway and this would be just like trying to put out a fire with Gasoline. Like, how obsessive can I get?
Besides, there is an art to the science of SPL measurement and you'd probably also need someone to help you take the data. Multiple repeats, a spreadsheet and I've finally flipped. Sheesh, Science ain't easy!
I may be able to wring a little more performance out of my system if I were to hi-pass the Maggies at 60-70hz and the lo-pass the sub at maybe 50-60hz. I will probably NEVER find out, unless a few volunteers show up with a bunch of stuff and some Single Malt!"

I say, It is not difficult at all! Measurements do matter! Measurements are the reality! Doing it by a test tone and meter is a waste of time. You need a program designed for this. Fortunatly there is one, and its for FREE. It is the Room EQ Wizard from the Home Theatre Shack. All you need to do is to download the program and an a Radio Shack SPL meter. No more crawling on the ground for Magfan!
The science is easy, the results can be eye opening.
Magfan, try this and post the results here. There are lots of members who will give you plenty of opinions:) If you live anywhere near Connecticut I will bring the Scotch.

Bob

Thanks so much for the kind offer! Even though I am on the 'left' coast, feel free to drop in.
But, I must respectfully differ. One theme running thru many posts is that measurements DoNot matter. The fuse guys and some of the cable guys are good examples. Nobody has demonstrated a way to measure a fuse good/bad. So, too, the cable goes unmeasured except for the measures of resistance and Capacitance we are all familiar with...and yet! there is something more to it.
I can see myself (I know me!) going absolutely nuts with an SPL meter, test tones or even analysis software. Since in my professional life, I am a cleanroom technician for a semiconductor manufacturer, I am Very Familiar with experimental design, and the use of JUMP analysis software.
Nope, I'm going to leave it fun, just listen and treat those known defects of my room. My room, just for laughs, has 8 sides, is very unsymetrical and has an off center 12foot vaulted ceiling.
Now, if I had a certified / calibrated microphone..........