How to Measure Frequency Response with Room EQ Wizard (REW)

This tutorial demonstrates how to measure and correct speaker frequency response using REW software combined with the UMIK-1 measurement microphone and Equalizer APO. The process involves calibrating the UMIK-1 with its serial number, configuring REW's sound card settings, taking multiple measurements at different positions around the listening area, averaging them for accuracy, and applying a house curve (modeled after Harman's preferred listening curve) to flatten the frequency response. The correction filters are then exported from REW and implemented in Equalizer APO to apply the EQ corrections to the audio system.

Overlay left and right speaker responses to ensure similar frequency characteristics. Apply corrections by selecting speaker, choosing 'Full Range Speaker' EQ type, setting target level, and adjusting 'Rise' parameter. Apply smoothing (1/6 octave) to reduce noise. Use 'Match Response to Target' to generate equalizer filters. Export filters as WAV files (32-bit float, 48 kHz) for left and right channels. Import these files into the audio system for playback correction.

This section covers importing EQ into MiniDSP and manual EQ adjustment. To import EQ: (1) Open the parametric EQ for the subwoofer, (2) Click Advanced to reveal import options, (3) Import the saved EQ file from Room EQ Wizard, (4) Link the EQ to other outputs (e.g., right sub) to apply the same EQ to multiple subs. Manual EQ adjustment involves: (1) Identifying problem frequencies (e.g., 58 Hz null), (2) Creating EQ bands in MiniDSP inputs tab, (3) Setting frequency, gain (e.g., +10 dB), and Q factor (e.g., 8 for sharp boost), (4) Applying EQ to all outputs, (5) Re-measuring to verify improvement. Multiple adjustments may be needed at different frequencies.

This video demonstrates how to improve speaker sound quality in any room by measuring speaker response using a calibrated microphone and software (Room EQ Wizard), then applying parametric equalization (PEQ) filters through a miniDSP device to correct frequency response irregularities caused by room acoustics, rather than purchasing new speakers or amplifiers.

Room correction data can be used to create EQ curves in the DAW that compensate for room acoustic issues. The speaker demonstrates how he recreated the room correction curve using ProQ4 filters, applying corrections to both left and right channels. The process involves scaling filter curves to match the room's frequency response deviations. The speaker demonstrates a musical example showing the difference between corrected and uncorrected playback: without correction, bass appears muddy and fatiguing, while with correction, the bass becomes clearer and more defined, and instruments achieve better separation and spatial placement.

Early reflection panels should be placed on side walls, ceiling, and front wall between monitors and listener, with total coverage not exceeding 20% of room surface area. Diffusers scatter sound energy in multiple directions while keeping energy in the room, eliminating standing waves without requiring excessive monitor power. Standing waves occur when sound waves reflect off parallel surfaces and interfere with incoming waves, creating peaks and nulls in frequency response. At low frequencies (below 100 Hz), these effects are highly audible. To identify problems, use a measurement microphone to play test tones at specific frequencies and find locations with the most significant reinforcement or cancellation. Membrane bass traps solve these issues using resonant panels that vibrate at specific frequencies to absorb sound energy, with resonant frequency calculated from panel mass and cavity depth.

Computational room acoustics simulation tests thousands of speaker, listener, and treatment combinations before construction. This approach optimizes wall positions and configurations impossible to test after building. Bass trapping is challenging because low-frequency wavelengths require specialized structural designs. Effective bass traps are tuned to specific frequencies and may require six to eight different trap types in a single room. Approximately 67% of acoustic treatments should be bass or lower mid-range traps because long wavelengths require more effort to absorb. The Schroeder frequency (~200 Hz in residential rooms) determines when individual mode treatment transitions to broadband absorption strategies.

Active bass traps are electronic devices that absorb low-frequency energy (15-160 Hz) by using a microphone to detect room resonances and drivers to dissipate that energy, providing an effective solution for controlling standing waves and decay times in small rooms where traditional passive bass traps (requiring quarter-wavelength depths of 2-3 meters) are impractical; optimal deployment typically requires 2-4 units placed strategically in corners where bass builds up, significantly improving mix clarity, stereo imaging, and overall sound intelligibility by eliminating the masking effect of prolonged low-end resonance.

Panel absorbers are flat, picture-sized panels mounted horizontally on walls, tuned to specific frequencies causing booming. They're easy to install but must be custom-made for exact problem frequencies. You need to know you have a problem at, say, 68 Hz before ordering. They don't help with bass range issues as effectively as physical distance changes. Start with simple solutions like hanging curtains before investing in professional-grade devices.

Plants can be used as acoustic diffusers to reduce first-order reflections from the tweeter, with energy diffused on both sides to extend the sound stage further back. For rooms with concrete floors, walls, and ceilings, acoustic treatment is essential. A single carpet placed from the front of the speakers to the listening position can help reduce reflections. Bass traps are essential for room corners, especially in square rooms, to prevent bass buildup and standing waves. For rooms without a TV, place diffusers on the back wall at equal distances from the center; for rooms with a TV, place diffusers on the opposite wall. Standard diffuser sizes are approximately 80cm x 60cm, with larger rooms requiring larger diffusers. Absorbers should be placed 30-50cm away from diffusers.

Below 200 Hz, room acoustics dominates sound reproduction regardless of speaker quality. Bass wavelengths are extremely long (20 Hz = 56 ft, 40 Hz = 28 ft, 80 Hz = 14 ft), causing waves to bounce off surfaces and create standing waves with fixed peak and null patterns. These patterns cause subjective issues: peaks create boomy, ringing sounds while nulls cause bass notes to disappear. EQ effectively fixes peaks by reducing ringing and decay time (minimum phase behavior), but cannot fix nulls where waves actively cancel each other. Research by Harman demonstrates that multiple well-placed subwoofers dramatically smooth bass response more effectively than single subs. Four subs at different locations can approach solving room mode problems entirely by averaging out peak and null patterns. However, subs must be in different locations—stacking them in corners provides more output but identical room mode patterns. Small micro subs fail at this approach due to insufficient headroom. Practical considerations include subs compact enough for unconventional placements (corners, mid-wall, behind listening position) and wireless/daisy-chaining capabilities for easier installation.

For consistent subwoofer crossover alignment without acoustic measurement tools, combine pre-alignment delay values from manufacturer guides (such as L-Acoustics) with geometric delay calculated by dividing the distance difference between speakers by the speed of sound (1130 ft/s), then sum both values to achieve proper phase alignment and sound summation through the audience plane.

Multi-subwoofer systems require careful time alignment and phase control for seamless bass integration. Receivers under $1000 offer limited parallel outputs; higher-end models ($1000+) provide independent outputs enabling better calibration. Advanced users employ miniDSP devices offering four outputs with independent delay, level, and EQ controls. Time alignment addresses distance-based timing differences, while phase controls (preferably variable beyond 0/180 degrees) refine integration further. Phase manipulation can eliminate suckouts unresolvable through distance alone, such as 60-80 Hz dips. Both delay settings and phase controls constitute essential tools for achieving optimal bass integration across multiple subwoofers.

Advanced customization provides unprecedented control over the DSP chain: selecting target curves from library or loading custom curves, configuring crossover search ranges to constrain optimization, applying volume leveling using ISO 226 equal-loudness contours, enabling MEMO filtering for multi-speaker phase manipulation, configuring double bass LFE mode for bass extraction, locking subwoofer polarity during optimization, adding custom filters via REW EQ, applying frequency-dependent and multi-time windowing, adding all-pass phase correction filters (Q=0.71 recommended), and configuring bass shakers with specialized curves extending below 20Hz. Proper target curves should be flat above 6Hz to 20kHz with zero dB at 1000Hz reference point. Multi-subwoofer optimization requires sequential steps: align all speakers to target curve first, align each subwoofer individually, then optimize all subs together considering interactions. Newer AVRs support 18m distance adjustment while older models have shorter limits. Automated optimization may fail 30% of time with Dolby-enabled systems, requiring manual time alignment with keyboard precision for ceiling reflection correction. The system provides visual feedback showing predicted versus actual responses after applying custom filters.