Yes no need for a MiniDSP for this. If you can use HDMI with REW (as I do without any driver with my Mac) it is the simplest way.
Here is a simple method to time and phase align one sub with two bass managed front speakers (but of course there are many possible variants of this, but this is the one requiring the fewest number of measurements IMO):
1) Make sure you have measured the distance to the tweeters of both front speakers with a laser and set that distance in your processor (you could use timing ref for that too but I think it is not necessary as this will be more than accurate enough). Also set the distance to the sub to some approximate number, it will be changed shortly… Don't forget to press "Save"
2) Set the sub size and crossovers to about 2x the usual (so in my case 200Hz since my XO is usually 100Hz). That will very likely include the *fastest* impulse from most subs including the XO band. Don't forget to press "Save"
Place the mike exactly in the MLP.
3) Turn off/mute/disconnect the right speaker, select "use timing reference" and use the LEFT channel (left speaker tweeter) as the timing reference. Play a sweep to the sub through the RIGHT channel from 30-200Hz (assuming the RIGHT channel is bass managed to that sub, if not select the LFE channel or whatever that will output a sweep in your sub).
4) Press "info" on the measurement you just did (but it is also visible in the measurement panel to the left of the screen). You will see numbers for the delay (in ms and distance + or -) based on the initial rise of the impulse of the sub.
Add that negative or positive distance to your sub original distance measurement. The resulting distance will most likely be a bit "short", corresponding to the VERY first impulse from your sub, and perhaps at above the normal XO frequency. That is probably not the optimal distance (it is too short to blend well with the speakers at your usual XO). Confirm the distance by running (3) one more time: now the delay should be within a few cm (it is not 100% accurate, so do not expect 0cm). No point in getting stuck here. Go to (5).
5) Now we will try to optimize the blend/remove phase cancellations between sub and speakers: First set your usual XO and sub size (In my case sub size = 200Hz, XO= 100Hz, i.e., sub size = 2x the XO). We will run 3 measurements from 20-500Hz in BOTH speakers, the SUB, and with both speakers + sub, with the XO activated. That sweep will cover the whole XO region by at least a couple of octaves on both sides (assuming an XO for 80-120Hz). Don’t worry, your speakers and subs will be safe because of the XO.
6) Turn off (I have active speakers;-) both front speakers and run a sweep in the sub (e.g., through the BOTH hdmi channel) from 20-500Hz with the XO activated. Call that measurement SUB.
7) Turn on both front speakers and turn off the sub. Run a sweep from 20-500Hz through the "BOTH" channel (i.e. output in both speakers but not the sub). Call that measurement SPEAKERS.
8) Turn on both front speakers and turn on the sub. Run a sweep from 20-500Hz through the "BOTH" channel (i.e. output in both speakers including the sub). Call that measurement TOTAL
9) Plot those three graphs on “all SPL” or “overlay”. Probably, at some places within the XO band (at least one octave), there will be some cancellations between the sub and main. You can see that by comparing the amplitude response of TOTAL with SUB and SPEAKERS. The TOTAL should be no less than either SUB or SPEAKERS anywhere, and hopefully higher right on the XO frequency. If it is a several dB less at some places (it probably is), try to adjust the distance of the sub
UP incrementally by 10cm increments. Repeat the TOTAL measurement (see 8) and call that new measurement TOTAL+10cm.
10) Repeat (9) for 10cm, 20cm, 30cm, 40cm, .. (Also you may want to try -10cm, -20cm- -30 cm but I doubt it will work)… You will soon see a trend where the cancellation gets smaller or larger and moves up or down in frequency. Choose the sub distance that results in the “highest overall SPL” ie. the smallest cancellation in the most critical XO region (say, from 60 – 120Hz). But I would put some more weight at reducing cancellations in the lower frequencies within the XO band to preserve as much headroom as you can. At this point you can, if you like, also look at the actual impulse graphs, phase of each speaker vs sub at different frequencies etc to help guide the tweaking. But that is “intermediate level”. This was “basic” level.
11) Done. Run RP and let it fix all the rest. Measure the result with REW. It should look good. And sound good J
Caveats: Of course, this is a very basic approach and I cannot guarantee that it will ALWAYS work, although in the simple case of one sub and two speakers it should in 8 out of 10 cases… With more complex setups e.g. stereo front subs and LFE subs, it is a lot more complicated, but still possible to just extrapolate from the above description. But with multiple subs you have to decide if you want to align the subs first, and then with the speakers etc. You can also decide to measure each pair of sub and speaker individually, instead of just “BOTH” as I have outlined here. Or even more “clever” stuff. Note also that sometimes I have seen that the initial rise of the impulse can be WAY off from the peak impulse, and that difference can vary between subs, and phase can vary a lot between subs. Then it is time to read and experiment... and the basic approach may not work. I cannot list all the options and I am still learning and trying to understand how to deal with that myself ;-)
cheers, Erik