Audio Tuning w/ Room EQ Wizard

Download & Install: Room EQ Wizard (REW)

Preferences

  • Output: System audio output feeding the PA (verify no OS EQ or processing)
  • Input: UMIK-1 USB Microphone
  • Calibration: 90-degree calibration file loaded
  • Sweep Level: –12 dBFS

Measurement Process

  1. Set up reference microphone:

    • Orientation: 90 degrees (vertical)
    • Height: Ear level
    • Location: Primary listening area

  2. Open the following REW tools:

    • SPL Meter
    • Signal Generator (Noise tab)
    • Levels Meter

  3. Turn down the PA system first, then connect the REW audio output to the system input.

  4. In the Signal Generator:

    • Select Pink Noise
    • Level: –12 dBFS
    • Press Play

  5. Slowly raise the PA system level until the SPL Meter reads:

    • 76–80 dB(C)
    • Confirm no clipping on the Levels Meter

  6. Stop playback and close:

    • Signal Generator
    • SPL Meter
    • Levels Meter

Measurement Sweeps

  1. Click Measure (top left) to open the Measurements Window and configure:

    • Type: SPL
    • Method: Sweep
    • Length: 512k
    • Iterations: 2
    • Frequency Range:
      • Preferred: 20–18,000 Hz
      • Optional: 15–20,000 Hz
    • Level: –12 dBFS
    • Output: Line Out
    • Measure channels separately when possible:
      • Left only
      • Right only
      • Left + Right (summed)

  2. Press Start to begin the sweep and capture measurements.

Analysis & Interpretation

1. SPL Response

  • Graph smoothing: 1/6 octave
  • Shows frequencies that are over- or under-emphasized at the listening position
  • Optional: Enable Phase display to examine crossover behavior
  • Target response:
    • Broad trends within ±5 dB
    • Avoid correcting narrow dips (often position-dependent nulls)

2. Waterfall (Decay)

  • Displays decay time of frequencies (“ringing” or lingering energy)
  • Recommended focus for auditorium tuning:
    • Frequency limits: 20–300 Hz
    • Window: ~30 ms
    • Time range: 300–500 ms
  • Look for:
    • Low-frequency energy lingering >250 ms
    • Improvements after delay or crossover adjustments

3. Spectrogram

  • Top-down view of frequency decay over time
  • Color scale: SPL
  • Axis: Time (decay) vs frequency
  • Useful for:
    • Visualizing low-frequency buildup
    • Comparing before/after system changes

Multiple Measurement Positions

  • Repeat measurements at additional listener locations:
    • 1 position: 1/2 back, center
    • 1 position: 2/3 back, center
    • 1 position: 2/3 back, slight left/right

Use multiple positions to identify consistent trends.
Act on broad peaks seen across measurements, not isolated nulls.

Notes & Best Practices

  • Always complete speaker aiming and delay alignment before applying EQ.
  • Use EQ only to address broad, repeatable response issues.
  • Save and archive:
  • REW measurement files
  • Before/after screenshots (SPL, Waterfall, Spectrogram)
  • Document why changes were made, not just what was changed.