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Infrasound Measurement

Detection of Airborne and Structure-Borne Sound Transmission with Low-Frequency Sensors

On this page, you will find infrasound sensors and solutions for professional and semi-professional applications.
 
Our solutions are divided into two systems:
 
The first system consists of a Class 1 USB measurement microphone with an infrasound microphone capsule (from 1 Hz) and a standard microphone capsule (from 4 Hz).
 
The second system is based on our RogaDAQ2 2-channel USB data acquisition system, to which two low-frequency sensors can be connected.
 
The combination of the MP30-Infra infrasound measurement microphone and the highly sensitive KS48C accelerometer enables the simultaneous measurement of infrasound and structure-borne sound.
 
The highly sensitive MMS214 measurement microphone with low self-noise of 6.5 dBA and the KB12VD accelerometer with low background noise of less than 4 µg are ideally suited for measurements below the human hearing threshold, for example, for acoustic consultants.
 
To make optimal use of this sensor technology, we offer our professional NVH analysis software as well as the corresponding calibrators for measurement microphones and vibration sensors.
 
The software must, in particular, allow users to calibrate the sensors or input their sensitivities so that the sensors output values ​​in physical units such as sound pressure level or displacement.
In this presentation, I will show you how to measure hum and infrasound using a calibrated USB measurement microphone.
 
Data analysis is performed using the open-source software SCILab.
 
The script, user manual, and report template are provided free of charge by engineer Edwin Krasser.
The first class 1 WS2F-compliant infrasonic measurement microphone with USB interface on the market.
 
It is equipped with a pre-polarized 1/2” microphone capsule that has been specially developed for low-frequency applications and works in a linear range from 1 Hz to 20 kHz.
 
The iSV1611 USB microphone preamplifier is able to perform measurements in two different level ranges simultaneously.
 
The measurement of infrasound is possible with very low ambient noise from a level of 15 dBA.
 
The USB microphone preamplifier is designed for three different sampling rates: 48 kHz, 96 kHz and 192 kHz.
 
This allows the iSV1611 digital preamplifier to be combined with other microphone capsules, e.g. for ultrasound or high-level measurements.
 

Human Sound Perception and dB(A) Weighting of Sound Compared to Loudness in Sone

In this presentation, I illustrate the difference between standard A-weighted sound level measurement and loudness expressed in sones.
 
This demonstration clearly demonstrates that A-weighting is an outdated measurement standard dating back to the 1930s—a standard that is highly industry-friendly and does not adequately reflect human auditory perception.
Meaningful Psychoacoustic SI Units:
 
  • Loudness Level phon vers time
  • Loudness Level sone vers time
  • Sharpness acum vers time
  • Loudness Level phon vers speed
  • Loudness Level sone vers speed
  • Sharpness acum vers speed
  • Specific Loudness
  • Open Articulation index vers time
  • Open Articulation index vers speed
Since the 1970s, shortcomings in the dB(A) weighting system have been recognized, and psychoacoustic SI units—such as loudness (sone), bark, and sharpness—have been introduced.
 
Despite these findings, the industry insists on using dB(A) weighting, as it offers numerous advantages for their product development processes.
 
For instance, manufacturers of air-source heat pumps can—under the Federal Immission Control Act (BImSchG)—easily comply with the prescribed dB(A) limit values.
 
Disturbing low-frequency thrumming or acoustic beats—such as those clearly audible in this YouTube video—go undetected by A-weighting; consequently, in this specific example, the BImSchG obviously fails to serve the best interests of those adversely affected.

Our product list of suitable systems for infrasound and structure-borne sound measurements

MP30-Infra

Infrasound Microphone

Class 1 – WS2F – DIN IEC 61094-4

  • Sensitivity 50 mv/Pa
  • IEPE constant current supply 2-20 mA
  • Directional characteristic: omnidirectional
  • Frequency response: 0.5 Hz – 20 kHz (± 2 dB)
  • 0.5 Hz – 3.5 Hz: ± 2 dB
  • 3.5 Hz – 4 kHz: ± 0.5 dB
  • 4 kHz – 20 kHz: ± 2 dB
  • Acoustic noise floor 15 dB A-weighted
  • Measuring range 15 dB(A) to SPL peak (5% dist.) 135 dB

Structure-borne sound measurement in buildings

In this presentation, I will demonstrate how infrasound and low-frequency building vibrations can be measured using a seismic accelerometer.

The measured structure-borne sound source, with a frequency of 80 Hz * 60 seconds is a fan, with 4800 rpm, of a NAS located in the corner of a building.

Structural Dynamics Vibration Measurement System

Modal hammer – accelerometer Sensor DAQ
NVH-IMP software for FRF measurement
Vibration measurements on buildings - Structural vibrations - Building dynamics measurements & monitoring

Application areas include scientific research, industrial monitoring, and construction.

The modal hammer is connected to the first channel, and the accelerometer to the second channel, enabling structural investigations, for example, of bridge or building structures.

The measurement is performed using the NVH-IMP software, which is pre-configured for impact hammer test measurements with an FRF transfer function.

The sensor sensitivity of the modal hammer in N and the sensitivity of the accelerometer in m/s² are entered into the software before the test. The size of the sensors can vary depending on the object’s size and mass.

All important measurement results are displayed by the software. Double impacts are immediately visible.

Triaxial Seismic Accelerometer

triaxial low frequency accelerometer

KS48C-3 + 729 Tripod floor plate Set

The triaxial seismic accelerometer set is designed for measuring low-frequency vibrations. Its high sensitivity makes it ideal for a wide range of applications. 
 
The highly sensitive accelerometer has a measuring range of 6g and can therefore detect even the smallest vibrations. 

KS48C Specifications

  • High Sensitivity Accelerometer
  • Suitable for seismic measurements and structural investigations at low frequencies
  • Highly sensitive sensor system without internal amplification thus excellent resolution and lowest noise
  • Particularly good sensitivity/ mass ratio
  • IEPE voltage output
  • Frequency response 0.07 Hz – 4000 Hz (-3dB)
  • Sensitivity 1000 mV/g
  • Residual noise wide band; <14 µg RMS (0,5 – 10000 Hz)
  • Mass 165 grams
  • Measuring range ± 6 g
  • Robust design with M12 connector
  • Protection grade IP67 

KB12VD/01 + 729 Tripod floor plate Set

High Sensitivity Vibration Sensor Seismic Accelerometer

The seismic accelerometer set is designed to measure low-frequency vibrations. Its high sensitivity makes it ideal for a wide range of applications. 

The highly sensitive accelerometer has a measuring range of 10 V/g, allowing it to detect even the smallest vibrations. 

KB12VD Specifications

  • High Sensitivity Accelerometer
  • Suitable for seismic measurements and structural investigations at low frequencies
  • Highly sensitive sensor system without internal amplification thus excellent resolution and lowest noise
  • Particularly good sensitivity/ mass ratio
  • Air-damped resonance and overload protection by friction coupling
  • IEPE voltage output
  • Frequency response 0.05 Hz – 260 Hz
  • Sensitivity 10 000 mV/g
  • Mass 150 grams
  • Measuring range ± 0.6 g