EEVblog 1745 - Continuity Tester Spectral Probing
Why It Matters
The video shows that firmware tweaks can alter audible alerts in ways not perceptibly beneficial, emphasizing the necessity of calibrated acoustic tools and proper test chambers for accurate product noise assessments.
Key Takeaways
- •New BM2257 firmware raises continuity tone to 2.7 kHz.
- •Actual measured tone frequency differs from spec, around 2.9 kHz.
- •New firmware tone is quieter, not louder as claimed.
- •Class‑1 sound level meter shows bunker noise floor near 33 dBA.
- •Accurate acoustic testing needs a dedicated low‑frequency isolation chamber.
Summary
Dave Jones (EEVblog) revisits the BM2257 multimeter, highlighting a firmware upgrade (v256) that shifts the continuity buzzer from the original 2.5 kHz to a claimed 2.7 kHz. To verify the change he employs Cry Sound’s class‑1 sound level meter and acoustic imaging kit in his underground bunker, aiming to capture the audible difference.
Measurements reveal the new firmware actually drives the buzzer at roughly 2.9 kHz, and the sound pressure level is lower than the older version—58.2 dBA versus 49 dBA at one meter—contradicting the manufacturer’s claim of increased loudness. The class‑1 meter also records a background noise floor of about 33 dBA, with noticeable low‑frequency rumble below 60 Hz that interferes with precise readings.
Jones notes, “they said it’s to make it a bit louder,” yet the data shows a softer tone and unexpected harmonics. He demonstrates the Cry Sound system’s capabilities—calibrated microphone, interchangeable capsules, FFT analysis, and selectable A, C, Z weightings—while exposing the bunker’s residual low‑frequency noise that hampers accurate acoustic testing.
The episode underscores the value of objective, calibrated acoustic measurement over anecdotal claims and illustrates the need for a dedicated low‑frequency isolation chamber when evaluating fan noise or other quiet devices. Engineers and hobbyists alike should consider both firmware impacts and proper test environments to ensure reliable product performance.
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