Accredited Calibration of Microphones at ENMO Services

ISO 17025 acredited calibration lab

The ENMO Services laboratory is accredited according to ISO 17025. In 2018 and 2023, we proudly achieved our accreditation scope for sound level meters, sound calibrators, accelerometers, vibration calibrators, vibration meters, and force cells. Since July 2025, this scope has been expanded to include microphone calibrations, in accordance with IEC 61094-5 and IEC 61094-6. With this addition, we can support our customers even better and more efficiently in maintaining their measurement equipment. Various national guidelines emphasize that measuring instruments must be periodically verified through an accredited calibration, microphones included.

Which microphones do we calibrate?

Our laboratory is equipped to handle a wide range of microphone types and connections, including:

• 1/8 inch, 1/4 inch, 1/2 inch, and 1 inch microphones

• Traditional or CCLD connections

• Separate microphone capsules or microphones with preamplifiers

This versatility allows us to calibrate microphones of various brands and models under accreditation. Each calibration includes a fully compliant calibration certificate, clearly stating that the microphone meets its product specifications and remains within the specified tolerances.

What is checked during calibration?

A microphone unit can consist of only the microphone capsule, or the combination of a capsule and preamplifier. In acoustic terminology, these correspond to the open-circuit sensitivity and loaded sensitivity, respectively.

Microphone calibration consists of two main parts:

1. Determining the sensitivity at a reference frequency using an acoustic coupler (IEC 61094-5).

2. Measuring the frequency response using an actuator (IEC 61094-6).

These two steps are described in more detail below.

1. Determining the Reference Sensitivity

The first step involves entering the correct microphone parameters into the measurement system—such as nominal sensitivity, reference frequency, tolerance, connection type (LEMO or BNC), and environmental corrections. The reference sensitivity is measured using an acoustic coupler, optimized for 1/2 inch microphones (the most common size). The test microphone and a reference microphone (B&K 4180) are placed close together and exposed to the same acoustic signal. Using the insert-voltage technique, the influence of the preamplifier is determined and corrected where necessary. This allows precise determination of the open-circuit sensitivity. When a microphone and preamplifier are submitted as a combination, we refer to the loaded sensitivity. The final reference sensitivity is calculated under reference conditions—this is typically the value customers require for traceable measurements.

2. Measuring the frequency response

Beyond the reference frequency, it is important to understand how a microphone responds across different frequencies. For this purpose, an actuator is used—an electromagnetic device that excites the microphone diaphragm directly. Since the microphone grid is removed during this measurement, the result is known as the actuator response. Using well-established correction factors, this actuator response is converted into a sound-field response, for example, representing a free-field condition at 0° incidence. When the grid cannot be removed (for hermetically sealed microphones), the measurement is performed using the acoustic coupler instead. In such cases, the resulting curve is called the pressure response, as it is based on pressure excitation. If corrections cannot be applied, it is still possible to report the actuator or pressure-field response, allowing customers to perform trend analyses or monitor performance over time.

Calibration of microphone pairs

A microphone pair consists of two microphones used together, for example in a sound intensity probe.

After individual calibration, we verify that:

• the reference sensitivities are sufficiently close,

• the frequency responses are consistent, and

• the phase difference remains within required tolerances.

The phase is especially critical in intensity measurements, as phase deviations directly affect calculated results. For this purpose, we use a phase match coupler, designed to introduce no additional phase shifts. A reference microphone is not required here, as only the relative comparison between the two microphones is evaluated.

Reporting of results

Upon completion, each customer receives a comprehensive calibration report containing all relevant details, including:

• Customer and equipment information (serial numbers, type, date)

• Reference equipment used

• Environmental parameters

• Measurement results with associated tolerances and uncertainties

Measurement uncertainty is an essential part of ISO 17025 and contributes to the traceability and reliability of every calibration.

Reliable results with confidence

Thanks to these precise calibration procedures, you can be confident that your microphone or microphone pair performs reliably and within specification. Each calibration also includes a phase report—a parameter particularly important when microphones are used in pairs. With ENMO Services, you can continue your measurements with complete confidence, knowing that your equipment has been calibrated accurately and in full compliance with international standards.

<< Request your quote here for an accredited calibration of your microphone(s) >>