For most rooms, the calibrated internal iPhone microphone is all you need. But there are situations where an external microphone gives you a cleaner signal — and AcousticCheck (Plus) supports several ways of connecting one.

When an external mic is worth it

  • Very large rooms with long reverberation tails, where the internal mic’s noise floor truncates the decay.
  • Very quiet or very dead rooms, where you need more dynamic range than the built-in front end provides.
  • Low-frequency work below ~80 Hz, where the internal mic’s response falls off.

Supported connections

  • Lightning / USB-C measurement mics — plug-and-play; the app detects the input automatically.
  • XLR microphones via an audio interface — Plus supports common USB audio interfaces. Connect the interface, select it as the input in the measurement settings, and set the gain so a clap peaks around −12 dBFS.
  • Bluetooth microphones — supported, but be aware that many Bluetooth audio profiles compress the signal. Use a mic that advertises a measurement or “raw” mode where possible.

Calibration — external mics bypass the built-in device calibration tables. If your mic ships with a calibration file, keep its sensitivity value at hand; you can enter it in the input settings. Without it, relative measurements (before/after comparisons) remain reliable, absolute levels less so.

Speaker vs. microphone

Don’t confuse the two upgrade paths: for the sweep method you need an external speaker (any decent Bluetooth speaker works), while the microphone upgrade is about the receiving side. In big rooms you’ll usually want both.