Calibration vs. Verification: Why Unregulated Calibrators Drift by 1.3 dB (Center 326 vs. AZ8930 & B&K 4231 Teardown)

Our lab teardown reveals a critical difference between sound level calibrators: While the Center 326 (Art. 7002) and B&K 4231 feature an internal feedback reference microphone that actively regulates pressure to 94.0 dB regardless of cavity volume, ultra-budget calibrators like the AZ8930 are unregulated and can deviate by up to 1.3 dB across different microphone geometries.

Brüel & Kjaer 4231 Reference Microphone Inside — 1. B&K 4231 (Class 1): Internal 200V reference microphone (±0.2 dB).

Center 326 Calibrator with feedback loop inside — 2. Center 326 (Class 2, Art. 7002): Actively regulated via internal reference microphone (±0.5 dB).

AZ8930 Calibrator inside without reference mic — 3. AZ8930 (Budget, Art. 7007): Digital design WITHOUT feedback reference microphone (unregulated!).

Combined with our CNC-machined 1/2” adapter (Art. 7157), the Center 326 provides rock-solid field calibration for the Bedrock SM50.

Calibration vs. Verification: Why Unregulated Calibrators Drift by 1.3 dB (Center 326 vs. AZ8930 & B&K 4231 Teardown)

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