What should my next studio purchase be?

It comes down to mass I would say. 2 Inch panels in the corners wont do anything for the lowend, probably more harm than good. I'd say a minimum of 6 inches of 703 or alike in all corners. Use the 2 inch for early reflections. I guarantee if you put 6 inch 703 in all corners the room will instantly sound more controlled in the low end. One thing people never mention though, It is important to like the sound of your room. Just because you fill all the corners and or make the room sound dead as hell doesn't mean it will be an enjoyable listening environment. I actually took down a lot of my thinner hi frequency absorbtion because the room didnt sound the way i liked.
 
Since I posted about acoustic treatment, I've been questioning my own. I have 4 inch floor to ceiling panels straddling all corners of my little room. That should be thick enough, right?
 
I've got panels hanging on my walls just now anyway. I'm planning on moving sometime next year, so when I move into that place, I'll do superchunks. Rockwool seems to be a bitch to get up here, anything else I could use in its place?
 
I really wouldn't focus on going crazy with panels if you're in a tiny ass room or dorm or something dude.

But if you're set on it- I went through IDI and bought SAFB batts and made 1x2s from 2x4s and printed online coupons and downloaded mobile apps for Joanns. 18 4" thick 2'x4' panels cost me about $250 and about 18 hours of labor. From the specs iirc the SAFB was more absorbent than OC703 and way cheaper.

But I have to side with LBTM as far as mixing in a small room. Almost pointless but if/when you move into a larger space you'll be covered. Pun intended. And it helps with vocal overdubs and acoustic guitar stuff. But seriously I'd get other stuff lol
 
I'm with LBTM here, the difference with acoustic treatment is noticeable, but won't make or break a mix from my experience. It certainly won't improve your bass tone like a decent bass will.

Also you will do precisely fuck all to your bass response in a tiny room with 4 inch absorbers in the corners. A bass trap made of 0C703 is a POROUS absorber meaning it works on the velocity component of a waveform (velocity is minimum against a wall because all the air particles are being squished into the wall, Pressure is maximum). To get effective results you'd have to space the rockwool from the wall. At 50Hz, quarter wavelength (when the wave has most velocity) is around 1.75 meters, which makes spacing totally impractical. I don't really understand why the superchunk is such a popular design. I've seen rooms absolutely stuffed with rockwool AGAINST THE WALL and the difference in frequency response is not all that great (waterfall plot is much improved however).

To the OP, I'd say cover your first reflection points with 4 inch rockwool panels, spaced as far from the wall as you can get (2 inches or more) but don't waste your time trying to improve bass response. Get some cans to monitor low end and spend the rest on a high quality bass and fuck tons of fresh strings!
 
Univerity Student? Buy good headphones.

/ srsly I don't get why people be hatin' on this solution so much. For 100 bucks you're gonna end up with a perfectly clear and precise sound for mixing, aswell as more definition and clarity for tracking. If you don't have the money to get uber-monitors and treatment, that should improve your mixes a lot.
Having small monitors and an untreated room is like having and old sportscar that breaks down a lot, it might be cool upon first sight, but one should probably stick with a hatchback he can actually afford.
Words of wisdom.

/ Even better, go the full way and record a band on headphones. Superlux had some really, really good ones for around 20 to 30 bucks, plug some of them in a mutli out and track people with it. At first they'll give you the stares, but than they'll be like "Shiat, I can actually hear what I'm playing, I suck :(". If you're used to your monitor setup for months and can pick out any little shit that's gone wrong, doesn't mean strangers can. Tracking guitars on Headphones -> maximum win, people will be on the edge of their arse because they can spot the little details themselves, haha.
 
Univerity Student? Buy good headphones.

/ srsly I don't get why people be hatin' on this solution so much. For 100 bucks you're gonna end up with a perfectly clear and precise sound for mixing, aswell as more definition and clarity for tracking. If you don't have the money to get uber-monitors and treatment, that should improve your mixes a lot.
Having small monitors and an untreated room is like having and old sportscar that breaks down a lot, it might be cool upon first sight, but one should probably stick with a hatchback he can actually afford.
Words of wisdom.

/ Even better, go the full way and record a band on headphones. Superlux had some really, really good ones for around 20 to 30 bucks, plug some of them in a mutli out and track people with it. At first they'll give you the stares, but than they'll be like "Shiat, I can actually hear what I'm playing, I suck :(". If you're used to your monitor setup for months and can pick out any little shit that's gone wrong, doesn't mean strangers can. Tracking guitars on Headphones -> maximum win, people will be on the edge of their arse because they can spot the little details themselves, haha.
This.