Airborne sound and structural vibrations are directly related. On one hand, because vibrating objects can emit airborne sound in the acoustically perceptible range (20 Hz to 20 kHz), and on the other hand because airborne sound can also be an excitation mechanism for structural vibrations. For this reason, the IDS has a broad portfolio of acoustic measurement technology, consisting of microphones, laser microphones and hydrophones. This enables us to measure sound pressures in the frequency range from 20 Hz to 1 MHz. The measurements can be carried out mobile or in our in-house acoustic chamber. The IDS also possesses an acoustic camera for the visual localization of acoustic sources.
Acoustic Camera
An acoustic camera is a measuring device for localizing sound sources. A microphone array is used to calculate the direction of sound propagation based on the phase relationship of the sound pressure levels at different microphones (holography or beamforming method). The built-in optical camera allows the noise source to be correlated with a video image. The IDS uses a camera from the manufacturer CAE SOFTWARE & SYSTEMS (Bionic M-112). This camera has 112 individual microphones and can locate noise sources with a frequency of 40 Hz to 24 kHz.
Optical Microphone
An optical or laser microphone enables the measurement of airborne sound up to the high ultrasonic range. In contrast to conventional microphones, it does not have a diaphragm membrane but is based on optical measurement of the sound waves. This allows a significantly higher bandwidth of the measuring range to be realized. The IDS is equipped with an ETA250 ULTRA optical microphone from the manufacturer XARION. This measuring device can cover a frequency range from 1 Hz to 1 MHz with a dynamic range of 100 dB.
Acoustic Chamber
A anechoic room enables representative acoustic measurements because the sound emitted by an object is largely absorbed by the room walls, the ceiling and possibly the floor of the room. As a result, free-field conditions prevail in the room, which is a necessary condition for carrying out sound power measurements. The IDS has a so-called anechoic chamber, i.e. all six sides of the room are lined with highly absorbent material. The floor consists of a steel grid. The dimensions of the room are 5.2 x 3.6 x 3.35 metres.
Microphones & Hydrophones
Microphones are well known and are suitable for measuring sound pressure levels in the air. Hydrophones, on the other hand, are microphones for underwater applications. Due to the different sound characteristic impedances of liquids and gases, hydrophones are constructed differently to microphones. Hydrophones are generally based on a pre-polarised piezoelectric hollow sphere, which is deformed by pressure fluctuations and generates surface charges. Microphones for metrological applications, on the other hand, usually operate according to the condenser principle with a membrane and a counter electrode. The IDS owns various microphones as well as hydrophones. We use microphones from the manufacturer PCB for our measurements. This makes it possible to cover a frequency range from 1 Hz to 70 kHz at sound pressure levels of up to 177 dB. Hydrophones from TELEDYNE RESON are used for applications in liquids. These offer a frequency range of up to 470 kHz or 800 kHz.
Acoustic Measurement Technology Equipment
- Acoustic camera Bionic M-112 from CAE SOFTWARE & SYSTEMS
- Various microphones from PCB
- Optical microphone ETA250 ULTRA from XARION
- Hydrophones from TELEDYNE (TC4038 und Tc4034)
- Acoustic chamber 5,2x3,6x3,35 m
