Do I need an external mic for accurate phone measurements?
For awareness and everyday exposure tracking, no — a good app on the built-in mic gets within a few dB. For measurements you'd defend to anyone else, yes: NIOSH research found phone apps paired with calibrated external microphones matched professional meters within about ±1 dB.
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What the built-in mic gets you
Phone microphones are consistent enough — especially on iPhones, where models share tightly specified components — that well-calibrated apps land within a few dB of the truth at conversational-to-loud levels. NIOSH’s app testing showed the best iOS apps within about ±2 dB(A) in lab conditions on internal mics. For checking your gym class, your commute, or your kid’s concert, that’s all the accuracy the decision needs.
What an external mic changes
A calibrated external microphone (typically $15–100, plugging into Lightning/USB-C or the headset jack) replaces the weakest link in the chain. In the same NIOSH research, apps using calibrated external mics agreed with reference instruments within roughly ±1 dB — Type 2 meter territory. You also escape the phone’s voice-optimised mic placement and any residual OS processing on the built-in path.
When it’s worth it
- You take readings you’ll share with a landlord, venue, or employer and want them defensible-ish (a real Class 2 meter is still the standard for formal disputes).
- You measure quiet environments (below ~35 dB), where phone mic self-noise dominates.
- You measure loud events (above ~100 dB), where built-in mics start compressing the truth away.
When it isn’t
If the question is “should I wear earplugs here?” or “is the baby’s room quiet enough?”, the answer arrives just as reliably from the online meter or the built-in mic with Decibel Shield. Spend the money on good earplugs instead — they solve the problem the meter only describes.