What the built-in mic can do
The iPhone’s microphone is reasonably flat through the midrange. For sweeps across 180 Hz–4 kHz, RT60 estimates, and spotting obvious peaks and dips, it is already enough — exactly Acouvero’s quick-check range. “Does my room have a problem?” is a question you can answer for free.
Where the built-in mic falls short
Three limits. Low frequencies: phone mics roll off below roughly 100 Hz with no calibration data, and that is exactly where room modes live. Absolute level: without SPL calibration you see relative level only — you cannot say “this seat measures 85 dB”. Consistency: different iPhone models have different microphones, so cross-device comparisons are meaningless.
UMIK-1 vs UMIK-2
Both are miniDSP’s class-compliant USB measurement mics: plug-and-play, each shipped with an individually measured calibration file. The UMIK-1 is the long-time default: 48 kHz is more than enough for room work, and it costs far less. The UMIK-2 raises the sample-rate ceiling, lowers the noise floor and moves to USB-C — worth the premium if you also do high-resolution work; for room correction alone, the UMIK-1 is enough.
The calibration file is the point
What makes a measurement mic is not the hardware but its individual calibration file — a per-frequency correction table. Acouvero imports REW/UMIK-style files (use the 90° version for room work) and binds calibration to the input port, so swapping mics never applies the wrong curve; every measurement stores a snapshot of the calibration used, so later changes can’t rewrite history. A one-time 94 dB calibrator step turns relative readings into absolute SPL.
How Acouvero uses them
Plug in a USB mic and it appears in the input picker; unplug and it falls back to the built-in mic. The built-in mic records at 44.1 kHz, the UMIK-1 at its native 48 kHz. Our advice: run a quick check with the built-in mic first, and only shop for a mic if your problems turn out to live in the low end — many people discover that what they actually need is absorption panels, not a microphone.