You don't need to do much. Speakers are far enough from walls and the room is big enough that the reflections are delayed enough so they won't compromise legibility of the direct sound from the speaker. Reflected sound that is delayed longer than 25mS is thought to be mostly benign, "reverb"
But too loud or too long midrange reverb is disconnected in time from the original sound, so it is non-linear and counts as noise. Too loud of a noise floor interferes with perception of low level direct sound. If you listen to music with large dynamic range then too much reverb can be a problem. High noise floor means you have to turn up colume to hear soft parts, then it's too loud in the loud parts. Depends on your music compressed/uncompressed, how critical you are about hearing accurate tone, etc. Fortunately, excessive midrange echo is easily tamed with carpet, drapes, furniture, or 1-2" thick absorption panels or amplitude diffusion on ceiling or wall reflection points. If you like the room to have quiet as possible noise floor, or a dead sounding room, then consider reducing the size of the listening area with thin faux walls, or free-standing wall panels like they use in recording studios.
Wood construction attics are one layer of wood, and maybe sheetrock, so bass goes through that easily, so your bass response is probably excellent. If you hear any problems come back for specific recommendations.
A thick rug in front of speakers helps to cut down the midrange floor bounce.
Enjoy!
