Head and torso simulator (short: HATS), which is used to conduct audio tests

Acoustic Testing

Acoustic testing and measurements for telecommunications, emergency call systems and Amazon Alexa

For years, testing audio equipment with acoustic measurements was part of approval testing for mobile phones. Over the past years, the field of application of these tests has expanded. Audio tests are now also required for the approval of voice or emergency call assistance systems.

All accreditations
All accreditations

Implementation of audio tests

We are accredited to test audio equipment devices and the respective voice quality. Within the scope of our services, we specialize, among other things, in testing the acoustic quality assessment of mobile devices. Depending on the requirements, the acoustic tests are performed with test head couplers or the so-called “HATS” (head and torso simulators) as well as professional microphones and audio sources. In addition, we test the operability and quality of the voice functions of the head units and emergency call assistance systems in the vehicle for the automotive industry – with the aid of specially designed measuring systems.



When speech systems and technology are used in a wide variety of devices, speech quality in particular is a necessary feature for high-quality products. A large number of institutions, committees and associations therefore define standards and specifications for the quality of voice transmission to telecommunications products connected to the mobile network.

In our audio laboratories, we test a wide variety of products for their audio quality and thus support manufacturers in obtaining approval of the devices by various institutions:

  • various international network operators
  • GCF and PTCRB
  • Regulatory bodies for the marketing authorisation of the device
Hand pressing an auto emergency button

Emergency call systems

For some years now, the use of emergency assistance systems in vehicles of various classes has been mandatory in many countries and regions of the world (e.g. eCall, ERA-GLONASS).

For the automotive industry we test the operability and quality of the voice functions of head units and emergency assistance systems in vehicles. These tests are usually the basis for the market approval of the emergency call systems.


Information on eCall certification

Information on ERA-GLONASS certification

Logo of the Amazon voice service Amazon Alexa, whose devices must pass the Amazon Alexa Self-Test

Amazon Alexa

When using Alexa, Amazon’s cloud-based voice service, customers expect a high quality and consistent experience on all Alexa built-in devices. To support this experience, Amazon has implemented a mandatory testing process for device manufacturers who wish to market products with the Alexa Built-in Badge.

We support manufacturers of products with the Amazon Alexa feature by providing the official self-test services.

More Information on the Amazon Alexa Certification


Our audio laboratories

We conduct acoustic testing services in our laboratories in Essen and Milpitas (Silicon Valley). Thanks to technically excellent equipment we can test a wide range of devices.

Accreditations in detail


German Accreditation Body (DAkkS)

Our laboratories in Duesseldorf and Essen are accredited by the DAkkS in accordance with DIN ISO 17025 to perform a wide range of audio tests.

Detailed information on the scope of accreditation for our audio laboratories in Germany can be found on our accreditation overview.



Our laboratory in the USA holds the DIN EN ISO 17025 accreditation of the A2LA for audio services and can therefore also offer accredited test services in the field of audio.

Detailed information on the scope of accreditation for our audio laboratories in Germany can be found on our accreditation overview.


Expertise Audio testing

What are the measures of acoustic testing?

  • Sound velocity
    It tells us how fast the sound propagates in a medium. The speed of sound depends on temperature – at room temperature (20 degrees Celsius), for example, it is 343 meters per second.
  • Sound power
    It describes the total sound energy emitted by a sound source per unit of time.
  • Sound intensity
    The technical term stands for the sound power that passes through a sound absorbing surface per unit area.
  • Sound pressure level
    The sound pressure level is a ratio, formed from the reference sound pressure (hearing threshold) and the instantaneous sound pressure.
  • Sound power level
    It describes the noise generated by a product under operating conditions, for example.
  • Averaging level
    Because the sound pressure level is not constant for many sound processes, but varies over time, they are often combined into a single value: the temporal average or average level.
  • Rating level
    It can be used to consider subjective assessments of different types of noise pollution. For this purpose, the average level for the assessment period is often used. In addition, there may be surcharges for impulsiveness, tone and rest periods. The rating level is used, for example, for comparison with the immission guide values.

Which measuring methods are used for audio tests?

The following three methods are used in audio tests: the enveloping surface method, the reverberation chamber method and the comparative sound source method.

  • Enveloping surface method
    This is the most frequently used procedure, because I usually apply it directly at the location of the machines and devices to be tested. It involves measuring the sound power emitted by a noise source by measuring at numerous points on an imaginary enveloping or measuring surface that encloses the source.
  • Reverberation chamber method
    The basis for this method is the fact that the sound power radiated into the room by a noise source must be as great as that absorbed by the room’s boundary surfaces. Thus the sound power can be determined from the absorbed sound energy, calculated from the average sound pressure level of the room and its sound absorption capacity.
  • Comparison sound source method
    In it the sound power is determined by comparing the noise source to be investigated with a reference sound source. For this purpose, the sound pressure levels of both sound sources are recorded at several measuring points and averaged. In practice, this method is rarely used – the basic prerequisite is that a reference sound source and its exact sound power are known.

Are you interested in more details on this topic or are you looking for answers to urgent questions? Please contact us. Benefit from our expert support for all challenges regarding the market approval of your products.



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