Calibrating a microphone

This knowledgebase article explains how to accurately calibrate a measurement microphone (or a microphone under test) in SoundCheck.

1. Hardware Connections & Schematic

1. Connect the Microphone: Connect your microphone to one of the inputs on your audio interface. If your audio interface doesn't provide a required Mic Bias (such as IEPE/Voltage Bias) and Gain, you may require a separate microphone power supply (such as the Listen SoundConnect 2) before you connect to the interface.

   However, if using Listen Hardware (such as AmpConnect 621, Audio Connect 2, Audio Connect 8x8 and many others), the interface also provides the necessary Bias and Gain functionalities. However, if you are using the HATS ear simulators with LEMO connectors that require a polarization voltage of 200V, a separate mic power supply (such as SoundConnect 2) is required.

   These can be configured either from the front panel options or the HW configuration window.

   Go to Setup > Hardware > Listen Hardware Tab. Right-click on the Listen Hardware connected and select Assign Startup Default. The window looks similar to this where Mic Bias and Gain can be assigned to each Input on the interface.

2. 
3. Change the Mic Bias for your chosen input to either SCM or IEPE depending on your microphone type. Click Apply > OK

Physical Calibration Using an Acoustic Calibrator

To do this, you must use a standard acoustic calibrator (like a Brüel & Kjær Type 4231).

Step A: Configure the Calibration Editor

1. Open the Calibration Editor (Setup > Calibration) and select the Input tab.
2. Select your Input Signal Path (e.g., Reference Mic or DUT Mic).
3. Ensure the Input Hardware Channel is mapped to the correct HW input channel.
4. In the Input Calibrated Device drop-down, select your microphone file (e.g., SCM 3 Mic.dat). If this is a new microphone, select Add New Mic.
5. Set the Gain: To ensure the software accounts for the hardware gain perfectly, if you are using a Listen Hardware, use the Device and Channel dropdown to select the device and channel. This will auto-read and auto-populate the gain. If you are using third party HW interface, enter the Gain manually.
6. In the Calibration Sequence drop-down, select Microphone Calibration.

Step B: Run the Calibration Sequence

1. Click the Calibrate Device button.
2. A window will prompt you to select your acoustic calibrator from a drop-down list (e.g., B&K Type 4231). If yours is not listed, select Other Calibrator and manually enter its output level (typically 94 dB SPL) and frequency (typically 1000 Hz).
3. Select your microphone type from the second drop-down list.
4. Insert the microphone carefully into the acoustic calibrator and turn the calibrator ON.

5. 

6. Click Calibrate in the prompt window.
7. SoundCheck will measure the 1 kHz tone. The measured sensitivity will be displayed in mV/Pa. If it falls within the manufacturer's tolerance limits, it will display a green Passed message.
   • Note: If it fails, ensure your calibrator is turned on, the microphone is fully seated, and the frequency/level settings match your calibrator's specifications.
8. Click OK or press Enter to accept the calibration.
9. The sensitivity and "Last Cal. Date" are automatically updated in the Calibration Editor. Click Save to store this calibration to your system.

Your microphone is now calibrated.