The Bedrock BAC4 is a precision multi-level acoustic calibrator providing both 94 dB and 114 dB outputs at 1 kHz per IEC 60942 Class 1. It enables field calibration verification across two reference levels, supporting both pre- and post-session calibration checks at the two most commonly used calibration levels in professional acoustic measurement. The BAC4 is ideal for measurement campaigns spanning a wide dynamic range, laboratories with multiple instruments, and measurement professionals who want comprehensive calibration verification capability in a single portable device.
Providing two calibration levels allows verification that a sound level meter's response is linear across its operating range — not just at a single reference level. This is particularly relevant for Class 1 measurements submitted for regulatory or legal purposes, where the measurement record must demonstrate full traceability and linearity. The BAC4's 114 dB output is also useful for verifying that the instrument can correctly measure high-level industrial and machinery noise without clipping or non-linearity.
The BAC3 provides a single 94 dB output and is the more compact and affordable option for general-purpose field calibration. The BAC4 adds the 114 dB output level for more comprehensive verification. For most measurement professionals working in environmental noise and building acoustics, the BAC3 is sufficient. For industrial noise, machinery noise, and any work where the instrument operates near its upper measurement range, the BAC4's dual-level verification provides additional confidence.
Dual-level calibration verification is particularly important in these scenarios: (1) Industrial and machinery noise surveys — where instantaneous SPL levels often reach 100–120 dBA and verifying the instrument's performance at 114 dB confirms it will not saturate or behave non-linearly during the measurement. (2) Impact sound and impulsive noise measurements — short-duration high-level events such as impact noise testing per ISO 16283-2 or explosive event monitoring require confidence that the instrument is reading accurately at high levels. (3) Multi-instrument laboratory environments — where several instruments are calibrated routinely and dual-level checks are a built-in quality assurance procedure. For general environmental noise surveys where levels remain below 100 dBA, the BAC3's single 94 dB level is fully adequate.
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