Microtech Gefell News – Sound Power Hemispheres for sound power measurements according to ISO 3744 and ISO 3745

Internationally, manufacturers of all sound-emitting industrial and consumer goods devices are increasingly required by law to record and comply with the entire chain of human and environmentally relevant sound emissions.

At the same time, consumer-oriented sound design is becoming increasingly important in product development, e.g. designing corporate and brand product sounds in the field of e-mobility in the automotive sector.

The two sides of the same coin – Noise reduction and Sound creation

The reduction of unwanted noise emissions from a vehicle is not only regulated by law, but is also a special concern for the manufacturer of premium products.

However, noise reduction is only one side of the coin. Sound production is equally important for comfort and, above all, for safety.

After a long time of investigation now we are living in the century of e-mobility. Noise emission is as low as never was possible in the time of combustion engines, both gas and diesel.

But low noise emission is dangerous, especially for pedestrians. Legislators in mostly countries demand a minimum noise in the speed-range up to 20km/h and in reverse mode (European directive no.540/2014). These systems are called AVAS (Acoustic Vehicle Alerting Systems) and are obligatory since 1^st of July 2019 in electrical, hybrid-electrical and fuel cell cars.

High-grade sound – a key factor for the development of electrical mobility and more

The necessary analyses can only be carried out using powerful measuring and testing technology.

So-called enveloping surface methods are essential here, which enable measurements on measurement objects placed under a dome by means of sound power hemispheres, among other things.

The sound power emitted by a noise source is measured at defined, statistically uniformly distributed measuring points on a dome-shaped measuring surface enclosing the source. The microphone/sensor positioning is done according to sound power standards.

Microtech Gefell`s new  Sound Power Hemispheres allows sound-power measurements regarding these standards 3744 and 3745. It is a hemispherical microphone arrangement which can be installed with 6 or 12 bars and which allows to use 10 or 20 pieces of high standard measurement microphones conform to standard DIN IEC 61094-4.

The same microphone arrangement can be used, e.g., in a perfect application to record the sound of components of electrical vehicles. Another application for sound investigation of acoustical components by using of hemispherical microphone arrangements is measurement of tire noise. While engine and gearbox noise have been important parts in the “combustion era”, tire noise is more and more important with electrical cars and motorbikes. That part of noise emission was covered by the higher noise of the traditional elements. There are existing special tire noise test benches, where moving tires are installed on a separately driving roller dynamometer, surrounded from a microphone-hemisphere.

The new sound power hemisphers SLH 212/112 from Gefell are  a universal, i.e. "one for all" solutions for a wide range of measurement tasks, including the optional selection of suitable sensors from other manufacturers.

A unique feature in terms of flexibility is the possibility to cover all relevant frequency ranges (DIN EN ISO 3745:2017-10 / "General case").

Synergies from MTG’s development of 3D measurement microphone arrays for time-delay based 3-dimensional recordings were helpful in the design and construction.

Outstanding features of all new MTG-SLH-Models are user-optimised design, increased precision, extended functionality, application range and flexibility.

Hemisphere design and construction are based on special, laser-cut, flat, sound-optimised light metal rail profiles, highly stable connecting elements as well as freely adjustable microphon brackets, not only for MTG sensors.

The innovative design ensures optimal, stable sensor positioning, cost-effective, simplified mounting and measurement procedures, and, last but not least,  reproducible measurement data in accordance with international standards.

New features include horizontally running connecting floor braces, vibration-damping ground stability pads and the additional stabilising horizontally and diagonally running tension cable bracing device, important e.g. for SLH-use on test benches with clamping fields in the automotive sector.

A standard-compliant, geometrically exact alignment to the centre is possible without the use of additional measuring/adjustment equipment.

The SLH are available in two different sizes for the buildup of hemispherical microphone arrays with radii of one or two meters for up to 20 microphone positions each. Depending on the measurement task, the sound power hemispheres can be supplied with standard measurement microphones, particularly low-noise measurement microphones or measurement microphones for harsh environments.

The SLH variants at a glance:

• SLH 112 (1m radius, 12 bars)
  • SLH 212 (2m radius, 12 bars)
  • SLH 16 (1m radius, 6 bars)
  • SLH 26 (2m radius, 6 bars)