Microphone Characterization Testing for ECM and MEMS Design Validation

Microphone characterization testing verifies how accurately and consistently a microphone converts a known acoustic input into an electrical output. By measuring sensitivity, frequency response, self-noise, signal-to-noise ratio (SNR), total harmonic distortion (THD), and acoustic overload point (AOP), engineers can validate an ECM or MEMS microphone before committing it to a product design.

At PUI Audio, we use calibrated reference instruments, controlled acoustic environments, repeatable fixtures, and electroacoustic test systems to support product development, supplier qualification, design validation, root-cause analysis, and production quality assurance. That flexibility matters because our microphone portfolio includes electret condenser, analog MEMS, and digital MEMS technologies, each with distinct integration requirements.

What Does Microphone Characterization Measure?

A basic test asks: given a known sound pressure, what output does the microphone produce? A complete characterization answers several design questions:

SoundCheck supports frequency response, distortion, phase, maximum SPL, and other configurable electroacoustic measurements, making it useful from R&D through production.

Why Test at 94 dB SPL and 1 kHz?

Microphone sensitivity is commonly referenced to a 1 kHz tone at 94 dB SPL. That acoustic level corresponds to 1 pascal, providing a convenient reference for expressing analog sensitivity in mV/Pa or dBV/Pa and digital sensitivity in dBFS.

Calibration establishes a known baseline before the device under test (DUT) is measured. The broader principle is well established: IEC 61094-5 describes determining microphone pressure sensitivity by comparison with a microphone of known sensitivity.

A Controlled Microphone Test Setup

Our documented setup uses SoundCheck software, an audio analyzer or interface, a speaker, an acoustically isolated or anechoic test box, a calibrated reference microphone, a regulated power supply, the DUT, appropriate cables, and a repeatable fixture.

First, the reference microphone is fitted to an acoustic calibrator and calibrated at 94 dB SPL. It is then placed in the test box so the speaker output can be set and equalized. In the documented procedure, the calibration sweep runs from 10 Hz to 10 kHz, with the EQ response checked for adequate flatness and verification at 1 kHz against a ±3 dB acceptance criterion.

Only after the microphone and acoustic source are calibrated do we install the DUT. Position and orientation must remain consistent: the port, fixture geometry, nearby surfaces, and acoustic path can change the measured response. PUI Audio’s MEMS application guidance likewise explains that PCB placement, sound-hole position, and vibration paths can introduce noise or alter performance.

ECM vs. MEMS Electrical Configuration

The acoustic principle is the same for ECM and MEMS microphones, but their electrical interfaces are not.

ECM Test Setup

An ECM typically contains an internal FET that requires DC bias. In our documented setup, a 2.2 kΩ bias resistor supplies and limits current while converting the microphone’s changing current into a measurable voltage. However, 2.2 kΩ is a common test value, not a universal requirement. The microphone datasheet and target circuit should determine the supply voltage, load, polarity, and coupling arrangement.

MEMS Test Setup

An analog MEMS microphone generally uses a regulated supply, ground, and analog output without the external bias resistor used for an ECM. Digital MEMS devices require the interface appropriate to their architecture, such as pulse-density modulation (PDM) or I²S, including the specified clock, data, logic, and supply conditions. PUI Audio’s guide confirms that its digital MEMS microphones support PDM and I²S formats.

For either technology, we verify polarity, keep the acoustic port unobstructed, follow the datasheet, and reproduce the intended installation conditions as closely as practical.

From Calibration to a Repeatable Test Sequence

Once the hardware is calibrated and connected, the software controls acquisition, analysis, limits, and reporting. The documented procedure sets the input sensitivity to 1 V/Pa, saves the configuration, and runs the microphone sequence. A production-oriented workflow may also combine visual inspection with electroacoustic measurement, prompt the operator for dimensions such as height, length, and spacing, and generate a frequency-response profile.

Before accepting results, confirm that:

• The reference microphone and sound source are calibrated.
• The DUT uses the correct bias, supply, load, polarity, and digital interface.
• The fixture, microphone orientation, and acoustic-port path are repeatable.
• The software range, sensitivity, test level, and pass/fail limits are documented.
• The expected SPL range and installed enclosure conditions are represented.

A datasheet describes component performance under stated conditions; characterization shows how the selected microphone behaves in the actual measurement chain and product environment.

Build Better Microphone Data Into Your Design

Reliable microphone selection requires more than comparing headline specifications. It requires a controlled acoustic reference, the correct electrical interface, repeatable placement, and test limits connected to the application.

PUI Audio supports OEM teams with ECM, analog MEMS, and digital MEMS components plus application engineering and microphone test capability. Explore our microphone portfolio or meet with a PUI Audio engineer to discuss selection, integration, and validation for your next design.