Fabric has to be open weave to work. I wish canvas could work since WAF would be way much less a concern.
I have been using canvas art to tweak first reflections for many years. It does seem to do "something" beneficial. As to whether it is good in absolute terms, I'm not sure. But I can tell the imaging is not as good without the paintings, and that is good enough for me. Not to mention they look great.
How about hanging rugs, tapestries or quilts instead of the canvas? Canvas may be OK, but I would think that once they are painted and the paint dries hard, you are just going to have a somewhat reflective surface in front of your acoustic material.
You may also be about to hang some attractive curtain rods and a could of nice ceiling to floor length curtains that match your decor.
Thanks for the thought Reubent. I've thought of all options, and only quilts and canvas art fit my applications. Art on canvas look nicer than on quilts although the latter are a more suitable material. I suppose it is not feasible to place absorption panels behind canvas after all. But canvas may have a slight absorption qualities "in comparison" with bare wall. I do not need massive amount of absorption for my front wall (since I already have them at the side walls), so a nice canvas art may still do the trick if I cannot find an equally nice design on quilts.
The change in absorption from canvas paint is going to be frequency dependent. Higher frequencies may be reflected where they were previously absorbed. However, painted canvas is not near as stiff as drywall, plaster or paneling. To the extent that soundwaves strike the surface and pass through or physically vibrate the canvas there will be some deadening action at lower frequencies, though it may not be the same amount as before.
In short any change is likely to be a fairly complex model that will not be given to yes/no answers. You might try temporarily hanging some painted canvas in the various areas you were thinking of painting and just listen. Who knows, you might prefer the results.
A layer of painted canvas isn't soundproof, so there will be some effect to have panels behind painting VS not. It won't be the same response the panel was designed for, but it should be better than the painting on a bare wall.
You could also size the panel bigger than the paintin to sort of highlight it, or use some sort of standoff to space the painting off of the panel slightly.
Thinking that in a movie theater, the center speaker is behind the screen. If you look closely at the screen material, you will see that it is perforated with fine holes.
Similarly there are a lot of banner and billboard surface materials (media) that are perforated for one reason or another. If you could source one of these and then print on it with an inkjet (which has no mass unlike paints applied with brushes and palette knives) you might have something that both looks and sounds good.
Might look in the yellow pages for companies specializing in interior design applications as well as companies specializing in large scale printing...
Then stretch the final piece over a frame filled with your sound absorbing material. You would probably want a deeper frame (stretcher bar) then normal so you can get more masterial in.
Also do a search for John Risch here and on Audio Asylum. He's done a lot of great posts on DIY projects like this and may have already solved this problem.
I am sure a cost effective solution is out there - sorry I can't point you any more precisely.
After reading the previous posts something came to mind...
In brief : we all know how difficult it is to keep sound from sneaking out from our rooms through openings....
Maybe we can use this to our benefit here.
Consider installing the sound panels in the wall and "float" in front of them the paintings leaving an opening. Chances are that the sound will sneak to the absorbing panel and maybe you can get something closer to the panel alone than directly covered with the canvas. What are your thoughts about this?
I get your idea about leaving an opening between the absorption panels and the canvas painting. The painting cannot be framed in this case and furthermore the gap between the wall and painting may sacrifice aesthetics. Also, I am not too sure if the sound is able to sneak into the panels effectively as the opening/gap needs to be quite large. I'll see how it goes. Thanks for the thought.
Ryder, Some things to consider ......
You can absorb soundwaves - the density and composition of the materiel will determine what waves can be absorbed.
It is easier to absorb high frequencies, which have short wave lengths, and its easier to diffuse reflections with short wave lengths as well.
For example a rough surface on a canvas painting will effectively act as diffusor for very short wave lengths (high frequencies) which might be as effective for your purposes as anything else. But a painted canvas will not absorb any more frequencies than a bare wall which will not absorb or diffuse much of anything but is still preferable to glass which will absorbe and diffuse nothing. Painted canvas will not diffuse lower frequencies at all, but if your problem is first reflection points that might not be a problem as you are frequently just trying to control the high frequencies, an excess of which can cause a blurring (distortion) and a sense of brightness.
Using a cloth such as one having a heavy burlap weave will absorb very high frequencies and diffuse lower frequencies (thats why you should leave your speaker grills off your speakers if you want to hear your tweeters full potential).
Its all relative and, unlike a lot of audio that is not, it is based on hard science, not subjective. To effectively treat a room you must find the 'problems' than need attention and then figure out what materiels will work for you.
But to answer your question directly, IMHO a canvas painting will not absorb any high frequencies (except for those in a bat's range) and will effective diffuse only higher frequencies in the audio spectrum. Better than nothing and a hell of a lot better looking that audio acoustic panels! :-)
I haven't done anything at the moment but will most likely use some nice acoustically transparent fabric(thinking of quilts) to cover some absorption panels. The bare panels do bring some positive listening experience in my room.
I also have plans for some HQ diffusors at the side walls in between the speakers and the back wall but unfortunately do not have much space left to accomodate them due to existing panels on both walls.