Acoustic treatment is anything added to a room to change its acoustic properties. It is divided into two categories: absorption (reducing reflected energy) and diffusion (scattering reflections to reduce flutter echo while maintaining some acoustic 'life' in the space).
Absorption panels are the most common treatment. Made from dense porous materials — mineral wool (rockwool, Owens Corning 703), rigid fiberglass, or open-cell foam — they convert sound energy to heat through friction. Panels covering 20–30% of wall surface area significantly improve a room's acoustic quality.
Bass traps address low-frequency buildup in corners where room modes concentrate. Because bass wavelengths are long (a 100 Hz wave is 11.3 feet long), bass traps need to be thick — 4 inches or more — to be effective. Corner placement maximizes their effectiveness.
Diffusers scatter sound in many directions instead of absorbing it, preventing echo while keeping some natural room sound. They are used on rear walls in mixing environments and recording booths to avoid a completely dead, unnatural acoustic.
For home recording, the most cost-effective approach is: treat first reflection points (the walls to your sides when facing your monitors), place bass traps in corners, and position your microphone away from parallel walls.