t.akustik SA-P80 6pcs set

I bought these acoustic foam panels to act as the front layer in a set of DIY acoustic absorbtion panels. If you simply glue them to the wall you'll really only succeed in taming the mid- and high-frequencies, and this is rarely going to make your room sound better in isolation; in fact, it usually yields a "boxy" acoustic which is pretty unpleasant. However, as part of a wider-spectrum approach to treatment they can work really well. I built a series of wall absorbers lined with thick acoustic rockwool and felt, and fronted with these foam panels (which made them look very smart); and also used them to cover the front apertures of three bass trap units which I've got hidden away under the desks in my studio. The overall acoustic of the room is vastly improved; just be aware that you'll probably want to employ these alongside, rather than instead of, some other strategies like bass traps and dispersion units.
If you're interested in building your own acoustic traps and panels, you'll save a lot of money overall and be able to tailor the treatment to the shape and character of your own room; I'd really recommend Googling for Sound On Sound magazine's articles on acoustic treatment, which is what I followed in tackling my own studio.