I have a pair of Genelec 8020Bs that I bought for mixing and they sound absolutely great on jazz combos, rock bands, chamber groups, etc. Particularly the phantom center image-- really out of this world. But I could hear them struggling with the bass on Beethoven's 7th. It's got me thinking about a sub for them. Genelec recommends the 7050B. Does anyone have experience with different subs in this context?
For mixing purpose you
must get a sub IMHO, otherwise you cannot hear what's going on below 50-60 Hz (if something is missing or too loud).
If you want to hear as loud as possible with the Genelecs than stay with 7050B (or C) as recommended by Genelec. If unsure you can ask the Genelec support, as I did when I bought a sub to be used for my K&H O300D in 2006:
The O300D has similar SPL features as the Genelec 8050 and the recommended sub for the 8050 was the 7070 which was too big (and too expensive). I asked the support if the 7070 was really required for use in a 50 square meter living room as part of a home stereo system. The answer was that if I don't want to play at very high SPL the 7060B would suffice - and they were right. I've never had a aproblem with the sub, neither playing music nor movies with heavy sub effects. But although I like deep bass I'm no bass fanatic and prefer the bass to be neutral and not overblown.
Therefore it could be possible that a sub smaller than the 7050 is sufficient, but it depends on your application.
OTOH is could also be possible that you need a bigger sub, maybe for a big multi channel system:
A colleague of mine uses a Genelec 7060B with 5 Genelec 8020 in a 5.1 multichannel system. He bought it after listening to my 2.1 system. He listened to this combination as well as Genelecs 8020 and JBL LSR2325P in place of the O300D and decided for the Genelecs (the JBLs were too hifi and the O300D much too expensive). He is very satisfied with his system.
Another colleague also listened to my 2.1 system (both with O300D and Genelec 8020). He liked them both but preferred the O300D and finally bought a pair of Neumann KH420 (wow!) but no sub.
To make the point: in both cases listening to the 8020 alone (without sub) in the big living room was quite a surprise for both colleagues, but increasing the volume made clear that the 8020s are not made for big rooms. Adding the sub changed that significantly and the sub integrated well with the sats (although they did not match the ease with which the O300D played). So I can recommend a 7060B as sub for the 8020 but I fear it might beis overkill.