OK, let's see...
I took the two graphs and overlaid them in Paint, sliding the second one up several dB so the average levels matched. I haven't figured out a good way to change the dot colour in one graph so I can tell the curves apart more easily, but at least this gives an idea of what behavior is common and what is influenced by moving things around.
JohnK is spot on as usual about the peaks -- 30 feet gives you peaks around 19, 38, 57, 76, 95 and so on -- and the peaks are almost unchanged between the graphs, which makes sense. The 38 hz peak is almost 10 dB high, which might be noticeable -- having the EP500 ~7 feet from a wall might take that down a bit.
You have major suckout around 150 Hz, which might be an artifact of having the fronts of the M60s 2 feet from the back wall. You should be able to move that dip down by pulling the speakers further from the wall, but there aren't any convenient peaks to knock out that way. You could probably pull the 60s out another 2 feet and knock down the 75-80 Hz bump a bit if you had room.
It's possible that some absorbent material behind the 60s could help if you had something which worked at those frequencies (I'll look around). Maybe Mark's fat-ass dog.
There is also a dip around 250 Hz, which I'm guessing is the crossover frequency between woofs and mid on the 60s. I vaguely remember Ian or Alan telling us that moving the microphone up or down an inch in the anechoic chamber has a huge effect on the response around crossover frequencies, ie don't worry about it because it all averages out courtesy of room reflections.
One of the graphs steps up a few dB below 120 Hz, while the other steps up more like 80 or 90 Hz. I'm hoping the graph with the speakers set to large is the one which steps up at 120 [EDIT, I just confirmed that]. If so, then (a) your sub is set a few dB hotter than the mains, and (b) setting the speakers to "large" gives you a range of frequencies where both EP500 and M60s are active, so you get an extra few dB between 80 (where the 60s step down a couple of dB) and 120 (presumably where the EP500 crossover has pretty much zeroed the output).
Bottom line is that both are pretty good graphs. If you had a long sub cable, I would try the EP500 midway between the two positions you tried, ie 7 feet from the side wall, and see if that knocks down the 38 and 76 Hz peaks.
You could take the EP500 down a few dB to get rid of the step up at 80/120 Hz, but what the heck, it's a big boy and can probably handle the extra few dB just fine. [EDIT - I notice you measured the same SPL for sub as for the other speakers, so I'm guessing your meter may be reading a few dB low in the bass. The Radio Shack meter correction table on the SVS site says 2-3 dB through the upper subwoofer range, and 5-7 dB in the 20 to 30 Hz range, so you probably are set a few dB hot even though your graph says you are not. I wouldn't bother taking your subwoofer level down except as an experiment.
Again, this is a nice graph. Enjoy !
It's too bad you can't donate a couple of feet in one direction to Mark, maybe taking your room down to 27x30 or so. That would make your peaks a bit wider and lower, and would do the same for Mark's room -- right now he sorta has a cube full of Axioms ;(
Last edited by bridgman; 07/01/06 04:41 AM.
