Bass traps because "small" listening rooms are dominated by bass peaks and nulls below the room's transition zone or Schroeder frequency which about 300-500Hz (which is only a difference of about 9-10 semitones).
Room size (and budget) may dictate what kind of bass traps to get. Resistive traps (GIK, RealTraps) need to be pulled into the room at least 6-7" which equates to one-quarter the wavelength of 500Hz to be effective. Otherwise Membrane traps (RPG) can be positioned right against the wall where sound pressure is maximized. The Resistive traps work best when sound movement is maximized (which is at the one-quarter wavelenght) whereas Resistive traps work best when sound pressure is maximized right against the wall.
Room size (and budget) may dictate what kind of bass traps to get. Resistive traps (GIK, RealTraps) need to be pulled into the room at least 6-7" which equates to one-quarter the wavelength of 500Hz to be effective. Otherwise Membrane traps (RPG) can be positioned right against the wall where sound pressure is maximized. The Resistive traps work best when sound movement is maximized (which is at the one-quarter wavelenght) whereas Resistive traps work best when sound pressure is maximized right against the wall.