Room acoustics is the condition of room shape, size and materials that influence the waveforms that reach your ears at your preferred listening chair. It is not just the waveforms from speakers that do. Room accoustics can alter the sounds from speakers so that what reaches your ears are totally different from what the speakers deliver. It is said that 50% of what you hear is shaped by your room accoustics. An otherwise excellent mix of amps and speakers can sound mediocre if not aweful under bad room accoustics. While an entry level system can sound gorgeous in an accoustically engineered room. (Like those Bose speakers in Bose showrooms.
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The object of room treatments is to minimize early boundary reflections that can smear or modulate the sounds from speakers and/or create standing waves. One can never totally eliminate these but room treaments can DECAY these early reverbs so they either don't reach your ears in time or get too weak to matter. Treating the room for better accoustics can dramatically improve the sounds you are getting from your current system.
Room treatments are often done for two sets of frequencies in the audio spectrum. One for the bass, or those below 180-200hz and another for the rest. Low frequencies with typical energies have no respect for absorbent or diffractive materials and are known to go through walls. (That's why you hear the bass most often from the neighbors' music, not the mids or highs) Bass frequencies produce standing waves depending entirely on room shape and size and are generally referred to as "room modes." Bass traps are about the only thing one needs to address these. Contrary to the name, bass traps don't trap bass, but diminish secondary bass signal reflection from creating standing waves that can create boominess in one freqeuncy while cancelling out some bass in another frequency so you get weak bass or none at your listening position. Try to google search on "room modes" I think
www.audioholics.com has great articles on this.
OTH, the rest of the frequencies respond well to absorbent materials like thick drapes and cushions to diminish early reflections. Rough wall surfaces can also help. Diffractive objects like venetian blinds, bookshelfs with differing book sizes (preferably with hardbound cloth covers) and figurines can also provide room treatments. But the more formal room treatments are your accoustic boards for ceilings and thick carpets. Audio engineers would know more about them.
The internet is a rich resource on this topic. Try googling the topic.
