How to measure room acoustics with REW

Guide

By Jeremy Screeton · Published October 14, 2026

If your system sounds boomy on some notes and thin on others, the room is usually the reason. Every room reinforces some bass frequencies and cancels others, and reflective surfaces smear detail. The good news is that you no longer have to guess. With a measurement microphone and the free Room EQ Wizard (REW), you can see exactly what your room is doing in about an hour.

This guide walks through the whole process for a first-timer: what to buy, how to connect it, how to run a sweep, which graphs matter, and how to turn results into action.

What you need

• REW. Free, cross-platform software for room and speaker measurement. Download it from the official site linked on our REW listing.
• A measurement microphone. The simplest route is a USB mic that ships with its own calibration file. miniDSP makes the widely used UMIK series, and Dayton Audio’s OmniMic is another calibrated option with its own software. XLR measurement mics also work but require an audio interface with phantom power.
• A mic stand so the microphone sits at ear height, pointing at the ceiling or at the speakers depending on which calibration file you use.
• A computer connected to your system by HDMI, USB DAC or analogue output, so REW can play test signals through your speakers.

Step 1: Set up REW and load the calibration file

Install REW, plug in the USB microphone, and open Preferences → Soundcard. Select your microphone as the input and the device that feeds your speakers as the output. Then open the Cal files tab and load the calibration file that came with your specific microphone (it is usually downloaded using the serial number). Many manufacturers supply two files: a 0° file for pointing the mic at the speaker and a 90° file for pointing it at the ceiling. The 90° file is the common choice for listening-position measurements because it treats sound arriving from different directions more evenly.

Step 2: Set a safe level

Turn your amplifier down before you start. In REW’s Measure dialog, use the Check levels button and raise volume gradually until the test signal is clearly audible over background noise, roughly the level of loud conversation. You do not need to be loud. Very high levels risk tweeters and can trigger rattles that distort the results. REW’s SPL meter can help you repeat the same level later.

Step 3: Take your first sweep

Place the mic where your head normally is. Measure one speaker at a time first: disconnect or mute the other channel, or choose a left-only output if your setup allows. Use a full-range sweep (REW defaults are a sensible start), click Start, and stay quiet while the sweep runs. Repeat for the other speaker, then measure both together. Name each measurement clearly, for example “L seat”, “R seat”, “L+R seat”.

Step 4: Read the frequency response

The SPL & Phase graph shows level versus frequency. Apply 1/6-octave smoothing to make it readable. What you are looking for:

• Bass peaks below about 200–300 Hz that stand several decibels above the average. These are typically room modes and are why certain notes boom.
• Deep, narrow dips in the bass. These are cancellations caused by the speaker, wall and listener positions. Adding EQ power to a null rarely works; moving the speaker or the seat often does.
• A dip in the low hundreds of hertz that changes when you move speakers toward or away from the front wall. This is often a boundary interference effect.
• The overall tilt. In-room response from most speakers falls gently toward high frequencies. A flat line at the seat is not the goal.

Step 5: Look at decay over time

Frequency response alone does not show how long the room keeps ringing. Open the Waterfall or Spectrogram view. Frequencies that keep sounding long after the rest have stopped are the modes you hear as one-note bass. The RT60 view estimates reverberation time across frequency; very long decay in the midrange and treble often means the room is lively and could benefit from absorption at first-reflection points, while long bass decay points to bass trapping.

Step 6: Average several positions before deciding

A single microphone position can mislead you, because bass varies dramatically over short distances. Take several measurements in a small area around your head (for example, a few inches left, right, forward and back), then use All SPL → Average the responses. Make decisions on the averaged curve. This is also how most room-correction systems, such as Dirac Live, approach calibration.

Turning results into improvements

1. Move things first

Placement is free and often the most powerful fix. Try moving the listening seat away from the exact midpoint of the room, since bass level at the room’s center is often affected by cancellation. Try speakers a little further from or closer to the front wall and re-measure after each change. Keep a log of each position and its measurement name.

2. Treat reflections and bass

Broadband absorption at the side-wall first-reflection points can tighten imaging. Thick panels and corner traps are the practical tools for bass decay; thin foam has little effect at low frequencies. Manufacturers such as GIK Acoustics, RealTraps, Primacoustic, Vicoustic and Artnovion publish product data and room-treatment advice worth reading before you buy. Re-measure after adding treatment to confirm it helped.

3. EQ the remaining bass peaks

REW’s EQ window can suggest filters to reduce peaks at the listening position, and can export them to many DSP devices and software players. Cut peaks rather than boosting dips, keep corrections mostly below the room’s transition region (often a few hundred hertz), and listen afterward. Dedicated room-correction products automate much of this, but understanding your own REW graphs makes it easier to judge what they are doing.

Common mistakes

• Forgetting the calibration file. Without it, the graph includes the microphone’s own errors.
• Measuring too loud or too quiet. Too loud risks damage and rattles; too quiet buries the sweep in noise.
• Chasing a flat line. A gently sloping in-room response usually sounds more natural than a ruler-flat one.
• Judging from one position. Average several.
• Using heavy smoothing to make problems disappear. Use smoothing to read trends, not to hide them.

Going further

Once you are comfortable, REW can also measure distortion, impulse response and individual speaker behavior. ARTA is another long-standing measurement suite for loudspeaker work, and Sengpiel Audio’s calculators are handy for wavelength and room-mode arithmetic. Browse more tools in our Room Setup and Reviews & Measurements categories.

Audio-Atlas is an informational directory; mentions are not endorsements. Check details with each manufacturer or business. See our editorial policy and affiliate disclosure.