I'm brand new to GLM(just got my monitors/subs this week), so I'll probably be able to give a better answer in a few weeks, but for now, I would take
@echopraxia's advice more seriously than mine. He's likely got much more experience at this point.
I just signed up for and installed the
GLM 4 Beta today. Was really great to see that GLM 4 actually works on my new Macbook Pro, so no more having to use the old machine with a cracked screen
. I'm going through
this training course atm, which I would recommend you do too. You can skip most of the first video, as they mostly just go through Genelec's history(unless you want to hear that). The second video is more useful and walks you through the GLM setup process. Towards the end, they get into subwoofer integration, and it looks like you have the option to EQ the subs individually or as a whole. Based on what I saw, the phase alignment in GLM seems superior to Dirac Live 3.0. With GLM, you choose a sub and a monitor you wish to phase align, then it plays a bunch of quick start and stop noises to automatically phase align the two to within 15°.
***I think you can individually time align with Dirac Live as well, but it requires an AVR with stereo(or more) subwoofer outs. The way I'm using Dirac atm is all my subwoofers are in mono coming out of the first subwoofer out of my AVR. In this configuration, Dirac sees all 4 subs as one sub and just EQs the overall response and timing.
In terms of Dirac's vs GLM's actual correction ability? I have heard that Dirac is quite a bit more sophisticated in the types of EQ it can perform, which should theoretically lead to better sound quality, but I have nowhere near enough personal experience with GLM to say if that's true or not(yet). I will be experimenting with using Dirac vs using GLM vs using GLM + Dirac in the next few weeks.
Manually phase aligning subs with Dirac Bass Module(different than Dirac Bass Management, which isn't really available yet) is not super difficult, but it is time consuming. For me it was a lot of back and forth of making an adjustment, remeasuring with REW, repeat, repeat, etc. I would also take a look at
@QMuse's
guide for manually time aligning subwoofers to mains. Lots of good info in that thread.
Gun to my head?
Dirac + SVS has higher sound quality potential
GLM + Genelec subs will be easier to get good sound
SVS option is also cheaper, given you already have the subs.
Like I said in the beginning though, I have little to no experience with GLM, so my opinion is very subject to change as I learn more.