Acoustic Damping Behind Speakers?

My speakers are placed about 3.5 feet from the wall behind them, which is just drywall. I get a funny echo from the wall and have been using the cushions from the sofa as dampers, which actually work fairly well. I can't imagine why, but my wife does not think this is an ideal solution, so I'm looking into some sound deadening options.

I was looking at Acoustimac panels, which are reasonable at about $50 each. Does anyone have any other favorite - and reasonably priced - products?

Also, at this point I'm only contemplating using two, placed directly behind the speakers. It would be difficult to get any more past 'she who must be obeyed'. Would this be sufficient? The room has a lot of stuffed furniture in it.

I purchased panels from this company when Sal was a member of AudioGon a few years back.

The panels are very nice and can be mounted vertical or horizontal and have a zipper so that the cover can be removed and washed if needed.
I've used ASC sound panels for years. I have 4 and they are highly effective.

I think they come in boxes of 8 which maybe more than you want...
A good cheap way out is to place 3 of the acoustic ceiling tiles (2x4') available at Lowes/Home depot spread evenly on wall behind your speakers.
I did this for a friend of mine a couple of years ago, and he still has them up.
I think they stop reflections more than anything, but it is a cheap fix, and doesn't look too bad (he has the white ones on a white wall).
Definately gave some improvement to his room.
I like ATS Acoustic panels. They are relatively inexpensive and come in a variety of fabrics. They also sell on ebay which is where I made my first purchase with them.
You can also Wall hang a nice looking Rug behind the speakers and it will not only look good but also do the job as needed..I use antique Pakistan rug on the wall behind my speakers and it works very well...
In 1979 we had the entire wall covered in cardboard eggcrates behind the double Advents. I don't know if it really sounded better or not but people knew we were serious when they walked in. We were blowin' our brains out to Supertramp and Michael Jackson.
Yes, must be tried. I have the Furutech acoustical free standing panels. They work well. Also, putting round units in the front corners should be tried. The latter can be found in most exercise equipment stores and cost less then $25 for a three foot log.
I use these products in my dedicated audio room in North Carolina.

They are very nice to deal with and the products look and work great. I was initially going to use Room Tunes or GIK tuning materials, but liked that Acoustics First did custom color at reasonable prices. The items were very easy to install, and look and sound great. It's nice that the wife likes the look of the product in her house too.....

I came across them by accident, but am glad I found them. Reasonable cost and nice folks too!!!
Fiberglass acoustic panels are readily available in most metro areas in 2'x4' panels, 2",3" & 4" thick. The 4" are under $20/sheet here. They can be covered by any cloth you desire...
The Acousticmac panels work very well for me. I use to bass versions behind the speakers and two "midrange", light thinner panels for side reflections. They also appear to be a bargain compared with others I have seen. I recommend them.
You can use a large thick backdrop (fabric).
They are heavy, that is why they are great at reducing virtually all tendencies of flutter echo and bass mumble.
You can use a wire and tension (device), torque this hard to hold the backdrop. They are avaible in many colours. It takes no space from floor, since it's close to wall and hang like an ordinary curtain.
addition to above post, you can use GIK Acoustics 242 or 244 (on stands or wall mounted) also. 244 reduce more bass/ lower mid, than 242, since it's thicker.
How about a couple large plants (artificial?) as diffusion? It works behind my panels.

I still listen to Supertramp's Crime of the Century.....and am probably down to no more than 20 active brain cells.
I have some of the same issues in my room and am strongly considering some of Furutech's panels. I would like the Acoustic Revive panels also but they are too expensive and sure seem identical to Furutech's. I have tried many of their products and they all have been impressive so I am guessing the panels are the real deal. They certainly get impressive remarks in the press/forums.

My first introduction to high end was a guy down the block who use to sell weed in the late 70's early 80's. He had an array of Phase Linear, SAE and the like and Magnapan Tympani's. We would sit in his basement for hours and hours and Crime of the Century was a go to record. That experience led to my obsession that has evolved into audio insanity. I guess it could have been the chemicals too.

Problem - It sounds like you're hearing flutter echo at the listening position that is attenuated when you place cushions on the front wall.

Constraints - WAF, cost, minimal visual impact

Possible Solutions - Flutter echos are most easily heard in the >1kHz frequency range which is easily dealt with. To kill a flutter echo you will need to treat one (or both) of the two parallel wall surfaces, which in your case could be the front and/or back wall. I'd also stay away from adding more absorption as you already have plenty with carpeting and lots of stuffed furniture - adding more absorption will move you closer to a dead sounding room and likely something to avoid. So, here are some suggestions that use diffusion or reflection:

(1.) Add texture to the wall's surface to break up the flutter echos with say a shelf with books or assorted nick nacks on it. This option should pass all contraints.

(2.) Add bass traps with a minimum of 4"-6" depth with a 6" air space behind it BUT WITH a hard surface that faces into the room so as to avoid mid/high freq absorption. Place it in the corners where all room modes accummulate. You can take a 1/8" thick piece of plywood and stain it to match the room and curve it to create a polyfuser (or sometimes called a hemi-cylindrical) diffuser. Or take a 16" or 24" diameter Sonotube used for creating concrete posts and cut it in half to make a 180degree arc and stuff the interior with fibreglass. Cover the curved surface with wood veneer that comes with glue on its back side which is easily applied with a hot iron. Stain or polyurethane the wood veneer to match your room's interior and it'll look like art or an architectural column of sorts. Should pass the cost constraint and depending on taste may also pass the WAF and visual test.

(3.) you could use a diffuser like a QRD or Skyline that when finished in nice wood and stained could look like art work and possibly pass the WAF test. While these do offer some low freq absorption they aren't bass traps so if you want the benefits of bass traps similar to the polyfuser idea above then you might consider building a 'bench' beneath and between the 2 front windows and putting fiberglass in garbage bags (to prevent breathing in air born fibres) in its interior and using 1/8" wood to allow low frequencies to pass through it to the fiberglass.

I'd stay away from using plants as a diffuser - while their irregular shape seems like a good way to scatter sound, the thin leaves can only affect tiny wavelengths of very high frequencies so they aren't effective, unless you're a bat! You could stick a plant in front of something else to help hide the thing behind it, but for diffusion plants can't offer effectiveness over a broad enough freq spectrum.

So to sum up, I'd suggest breaking up the wall's flat surface with diffusion (skyline, QRD, hemi-cylindrical) and adding bass traps but with a hard enough surface to avoid more MH/HF absorption. Hope this is of some help . . .