ACOUSTICS AND VIBRATION

A Chamber

Introduction

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Acoustic is essentially a vibration energy that propagates in a transmission medium such as air. Acoustics and vibration are interrelated and these mechanical phenomena often have great impact in our daily lives, from listening of music to vehicle vibrations.

Measurement and monitoring of sound and vibration is critical in many industry sectors such as aerospace, construction, automobile, electronics, manufacturing and healthcare, as it has great impact on quality of products and services; performance and reliability of equipment; health and safety of the people.

Latest News

NMC is expanding the acoustics metrology area to primary microphone calibration based on pressure-field reciprocity method. A secondary acoustic system based on free-field measurements will also be established.

MEASUREMENT STANDARDS AND DISSEMINATION

The Acoustics & Vibration (AV) Laboratory develops, maintains and disseminates acoustics, ultrasound and vibration related national measurement standards in Singapore. Beyond measurement traceability dissemination, these measurement standards open up opportunities for local and overseas sensing instrument developers and manufacturers to understand their device performance through comprehensive characterization. The acoustics and vibration metrology at NMC can be broken down into four areas namely airborne acoustics, underwater acoustics, ultrasound and vibration. These standards are derived from four base units which are ampere, metre, kilogram and second.

Airborne Acoustics

Sound measurements in air are performed in the frequency range from 20 Hz to 20 kHz. Sound pressure level (decibel [dB]) is realised using laboratory microphones in a reciprocity calibration arrangement, according to the international standard IEC 61094-2.

Services provided:

  • Calibration of Laboratory Standard (LSP) Microphones based on IEC 61094-2 Standard
  • Calibration of measuring microphones based on IEC 61094-6 Standard.
  • Calibration of acoustic calibrators and pistonphones based on IEC 60942 Standard.
  • Calibration of sound level meters and sound measuring instruments based on IEC 61672-3 Standard.
  • Calibration of Octave-band Filters based on IEC 61260 Standard.

Underwater acoustics

Sound measurements in water cover the frequency range from 30 Hz to 2 kHz. The underwater hydrophone calibration standard is realised based on Section 14 of IEC 60565:2006 using a vibrating water column. The hydrophone calibration is done through comparison with a reference hydrophone where both units are subjected to the same hydrodynamic pressure field in the water column.

Services provided:

  • Underwater calibration of hydrophones in the frequency range from 30 Hz to 2000 Hz.
  • Airborne calibration of hydrophones at the frequency of 250 Hz for selected models.

Vibration

The primary vibration standard is realised according to ISO 16063-11, using laser interferometry as an absolute reference. Standard Reference Accelerometers are calibrated against the primary standard. NMC is able to calibrate vibration transducers in the frequency range from 0.1 Hz to 350 kHz.

Services provided:

  • Calibration of vibration measuring instruments.
  • Determination of charge sensitivities for signal conditioners.
  • Determination of voltage gain sensitivities for power supply couplers.
  • Measurement of output acceleration of calibration exciters.

Ultrasound

Air-borne and structure-borne ultrasound has been widely used for non-destructive testing (NDT) such as inspection and maintenance of machine parts and structures. NMC is conducting related R&D to establish the metrological traceability for such applications.

TRAINING COURSES

training courses

These trainings also act as a platform to educate scientists and engineers working in the field on the fundamentals of acoustics and vibration metrology, and the importance of measurement comparability and traceability for international recognition of measurement and test results. 

Trainings conducted in the past:

  • Airborne acoustic measurement and calibration
  • Vibration measurement techniques

INTERNATIONAL COMPARISONS

To ensure the unbroken metrological traceability chain, the AV lab participated in several international comparisons in both the acoustics and vibration domains. NMC is currently the observer in the Consultative Committee for Acoustics, Ultrasound and Vibration (CCAUV) and also the active member in the Asia Pacific Metrology Programme (APMP) Technical Committee for Acoustics, Ultrasound and Vibration (TCAUV). 

International comparisons:

  • APMP.AUV.A-K3 Comparison of ½-inch laboratory standard microphone calibrations
  • CCAUV.V-K3 Comparison of acceleration complex sensitivity
  • CCAUV.V-k5 Primary calibration of magnitude and phase of the complex sensitivity of accelerometers from 10 Hz to 20 kHz
  • APMP.AUV.A-K5 Comparison of 1-inch laboratory standard microphone calibrations (2021, upcoming)

RESEARCH PROJECTS

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The AV Laboratory also carries out R&D and consultancy for industry and other stakeholders to develop and apply acoustics and vibration measurement techniques for various applications.

Some of the projects in AV laboratory:

  • Natural gas transmission pipeline leakage detection
  • MEMS microphone characterisation
  • Sub-nano meter vibration measurement for multi-terabit-per-inch-square hard disk drive

INTERESTING STORIES

accoustic and vibration introduction

How loud is too loud?

Noise-induced hearing damage is related to the duration and volume of exposure. It is suggested that the noise dosage should be less than 85 dB A-weighting for continuous 8 hours a day.

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