Ohmic Audio

Measuring Frequency Response

Equipment: - Calibrated measurement microphone - Audio interface or USB microphone - REW or equivalent software - Reference amplifier (or use system amp with calibrated gain)

Procedure:

  1. Background noise floor: Measure noise with everything off. Must be ≥ 20 dB below the quietest test signal. If not, reduce noise sources or increase test level.

  2. Calibration sweep: Play a calibration signal from known flat source to verify microphone + software chain is flat.

  3. System sweep: Play log-swept sine from 20 Hz to 20 kHz. Record simultaneously. 512k or 1M FFT points for high frequency resolution.

  4. Averaging: 4–8 measurements averaged to reduce noise. Essential in noisy environments.

  5. Windowing (optional): Apply 10–20 ms gate window to remove room reflections for mid/high frequencies. See Chapter 4 section 4.3.

Standards reference:

IEC 60268-5: Loudspeakers — defines measurement conditions for speaker sensitivity, frequency response, impedance.

CEA-2010: Subwoofer output measurement standard. Defines allowable THD, frequency range.