bass traps..which wall first

when using bass traps (any kind for this question/answer) which wall should be the priority, the rear corners behind the speaker, to the corners behind the listener? Can 2 different ones be used "safely" for example can you use 4' tall traps behind speakers, and 2' behind listener and vice versa?
Behind the speakers first.

Yes you can use different sizes for the front and back.
Behind the speaker,in the corners, I prefer something soft and wideband. Then, behind the listener, membrane traps for deeper bass. Both can be combined if you're going DIY.
The first corner reflections would be from the corner closest to the speakers, obviously enough. So the front corners should be treated first.

Using different size traps allows you to trap different frequencies so that's not a bad idea. It would be good to determine what your problem frequencies are likely to be first, then choose a trap size for that frequency.
what are your thoughts on accoustical solutions traps up front (the 4' tall foam ones) and Aurelen Lenrd bass traps in rear (2' tall)
Auralex Lenrd traps in the front and rear corners, each 2 foot tall stacked in threes to create 6 foot stacks in the corners, works very well for me. A rug and some furniture and I'm done. I wouldn't want to lose some of the remaining ambience in the room.
I have some rock wool (8lb) four inches thick on the diagonal of the corners behind the speakers. I could not believe the difference it made. I highly reccomend it, especially if you have squarish room dimensions. I haven't personally tried all four corners, but if I could I would definitely do that as well. The other thing to think about is the first reflection from the ceiling. If you have speakers with good dispersion in the tweeter, you should put some damping in high frequencies on the ceiling, in my opinion. Ambience is good, first reflections are bad, again in my opinion.
what are your thoughts on accoustical solutions traps up front (the 4' tall foam ones) and Aurelen Lenrd bass traps in rear (2' tall)

I'd be inclinded to go for the MEGA LENRD's (or equivalent size) if you plan only a total of 12 linear feet of coverage in the corners (4' + 4' + 2' + 2')
im unfamiliar with the MEGA does it differ from regular lenrd's?. would 2 pr of regular lenrds be better? i just not a fan of the "look" of any product in the i fugured the 2' ones would be best solution
My understanding is that the MEGA LENRD are bigger. Size counts!

The MegaLENRD Bass Trap (Low-End Node Reduction Device) is extremely effective at smoothing out low frequency room nodes and is just a bigger version of the original best-selling bass trap. At twice the width (extending 24" along each wall, not 12" like the standard LENRD,) the bass trap is substantial enough to handle low-frequency problems in rooms of any size and is the only broadband absorber effective below 50Hz.
Foam is NOT a bass trap, unless it's 4' thick. Cotton, compressed fiberglass (703/705) or mineral wool are denser and wideband but become less effective below 200Hz. Even the commercially available membrane traps are limited due to shipping size and weight. A bass trap that works well to 50 Hz would be substantial and a wall in itself.
so then Ngjockey, what do you suggest? do you use any room treatments? you act as if all the current bass trap sold today are ineffective
That's not what I meant. You were asking about bass traps and foam just doesn't work for bass. It's mostly air but it works fine for mid to high frequencies and would be the choice for reducing highs without affecting lower mids. Denser material absorb lower frequencies and more of the upper frequencies for the same thickness. Well, concrete might be going too far but lead is used in the walls of many studios. Membrane panels (such as Realtraps) tend to be narrow band (100 to 300 Hz, optimal).

My only suggestion is to use the right material and type for your room and needs. However, Ready Acoustics bags seem like a bargain for general use and rigid fiberglass insulation can be found in the yellow pages.

I have built several membrane bass traps, including a couple that double as amp stands with granite tops. The 4' by 2' panels I built aren't very effective at 50 Hz either. For that, they should be about 8X4 and use thicker membranes. Not really practical for my transient nature. Moving 350 lb speakers is bad enough. I have also used custom futon pads (cotton only) and helped build tube and panel traps with compressed FG and mineral wool. Built some artsy diffusors for a friend in need too.

Here's an example: Get a section of 2" bedding/furniture low-density foam, large enough to wrap around your ears and then fold up a pair of jeans about the same thickness for the same purpose. Listen to your stereo with both and compare for yourself.
I think Ngjockey is just pointing out that you can't expect too much (if anything) from broadband bass traps (foam or otherwise) below 100Hz unless you increase your coverage/thickness significantly.