You have run your first sweep in Room EQ Wizard, and the line leaps up and down through the bass. Every room does that. Once you know which parts belong to the room and which to the speakers, the graph becomes a to-do list.
What the line shows
The frequency response graph shows loudness in decibels from the deepest bass on the left to the highest treble on the right. It is never the speaker alone: it is the speaker plus every reflection from the room, so the same speaker measures differently at another seat.
Smoothing averages each point with its neighbours, from 1/1 octave, a few gentle hills, to 1/48 octave, every wiggle. Heavy smoothing hides the bass resonances you most need to see; Floyd Toole calls for high resolution in low-frequency room measurements. REW's help recommends its variable smoothing for responses you plan to equalise.
Below about 300 Hz, the room is in charge
In a home-sized room the bass is shaped by room modes, resonances between the room's walls, floor and ceiling. They show as tall peaks and deep, narrow dips that move when the microphone moves. Toole places the transition, or Schroeder, frequency, below which the room dominates, at roughly 200 to 300 Hz in typical domestic rooms; CEDIA/CTA-RP22, the recommended practice for immersive audio design, gives 150 to 500 Hz for small rooms.
A bass peak is usually a resonance that equalisation can cut. A deep, narrow dip is usually a cancellation: REW's help explains that no amount of EQ restores a true cancellation and that lifting sharp dips often gives poor results, and RP22 lists correcting a room null with amplitude filters among the jobs equalisation is generally not suitable for. Boosting one only wastes headroom; move the seat or the subwoofer instead. For scale, RP22 allows the response below the transition frequency at the main seat to stray from its target curve by at most ±5 dB at its first performance level and ±3 dB at its third, with 1/3-octave smoothing.
Cut the peaks. Move away from the dips.
Shape, decay and ringing
Higher up, judge the overall shape. Toole shows that highly rated loudspeakers in typically reflective rooms produce a curve that slopes gently down from bass to treble, and in double-blind tests by Sean Olive and colleagues, listeners adjusting bass and treble chose a balance close to it, though untrained listeners wanted more bass. He also warns that equalising the wiggles above the transition risks making a good loudspeaker worse.
The RT60 graph shows how long sound takes to fall by 60 dB in each band. RP22 repeats a longstanding guideline of 0.2 to 0.5 seconds for home cinemas: much longer harms speech clarity, much shorter sounds dead. REW's help notes that RT60 is not meaningful below a few hundred hertz in domestic rooms and points to the waterfall for the bass instead: a ridge that runs far back at one frequency is a resonance that keeps ringing.
Measure well, then read it again
Load the microphone's calibration file before you measure: REW subtracts it from every measurement taken after it is loaded. Measure at the main seat at ear height, with the microphone pointing as its calibration file assumes: miniDSP's UMIK-1, for example, comes with a 0° file for pointing at the speaker and a 90° file for pointing at the ceiling, which miniDSP recommends for surround measurements. Keep the sweep level and settings the same for a before and an after, and to compare timing between speakers and subwoofer use a timing reference, a loopback or an acoustic reference through a speaker with a tweeter.
Then open the file in the free REW Analyzer on this site. It runs in your browser and the file is not uploaded. It lists the biggest issues first, checks the measurement itself, tells you, once you give it the room's size, whether the lowest bass peaks and dips line up with a single predicted room mode, and overlays a before and an after, or several seats. If the bass is the trouble, our subwoofer integration guide takes it from there.
