Hey, I think I'm doing the same thing you are. And I wouldn't be embarrassed, those instruction might make sense to an acoustician or audiophile, but if you are like me, a simple musician who enjoys recording, WAY too much.
I came here looking for a step by step when I saw your post and I'll tell you what I did and really improved my room, though I'm not sure it's entirely correct, maybe just lucky.
I bought the RS SPL, the digital one and hooked its RCA output to one of my my Soundcard inputs, which I assume provides info to REW when it's metering that input.
I set the SPL up as directed, at head level 20 degrees to get both monitors equally.
In REW I went into the settings, in the Soundcard tab I set the top output slot to the soundcard hooked to my monitors (a Delta 66 in my case) despite the directions saying not to, then set the top input to the Deltas inputs where I had the cable from the SPL going. I set the levels section to use main speakers instead of subwoofers, tuned on the SPL to 80, then hit measure and listened to noise. It took a bit of fiddling but I eventually had the SPL sending back a signal to the input, which shows on the meter, though a pretty low signal until I cranked the monitors pretty high. The SPL was showing like 86db and I thought I was supposed to be setting levels to 75db, per the instructions, but that didn't give me enough signal going back to REW (the software told me this at some point, it wants somewhere between -24db and -8db I think). I think I adjusted the Sweep Level to do this.
The other thing I did in settings is go to mic/meter section and, after downloading the .cal file for my SPL meter, browsing to it and getting it loaded up. Check the c Weighing and be sure the SPL has this option selected too.
Then back to the main page, I just hit Measure, checked the levels (I think this is where I was told to go back and raise the input level, which a may or may not have done correctly). Then I hit start measuring. It was a very fast sweeping signal, and it was done. It gave my a curve I assume represents the SPL at every frequency it measures.
THEN, using that result, which is shown on the left with a date and time. In the Target Settings on the left of the screen I set Speaker type to Full Range, and I think I set target level to the same number as my SPL was reading when I took the measurements. In filter task I didn't change anything and hit Find Peaks which gave me a list that told me where the peaks were in the acoustics of my room, and how many decibels over a flat response for each of those frequencies (ion my case it gave me 4). I knew my room had a crazy spike somewhere and it showed up right away, I think at 120hz it was 17db over the target.
So, having this info, I went into my DAW and created an EQ preset to put into the main output channels to compensate for the room's resonances for use when I'm monitoring with my speakers, basically cutting the frequencies exactly the amount REW showed were out of whack. When I tried it out I was pretty amazed at how much better it sounded and how much clearer.
Now, this is how I did it. But I would say this is more of a question response than an instructional one, because I'm wondering if I did it right. The crazy hookups the instructions show seem to be for a much more complex set of measurements than would be necessary for "tuning" a recording room. I can't even figure out what all that splitting and cabling is for, it seems like measuring the resonances of a room are more straight-forward. On the other hand, it seems like what I did, the actual measuring and analyzing, was way to simple. A very quick sweep, that's it? Also, I don't think I measured the full range, just up to 200hz, but then maybe that doesn't really matter much. I'm going to poke around a bit more, maybe there are other tests.
And I would really like to see another test having done the EQ correction, maybe to fine tune a little, but can't figure out how that would happen without an external EQ which I don't have.
anyway, I hope this helps, and I hope someone will let me know if I did this right after all. Cheers.
