Complex sound measurements with a simple device!

Certain noises in our modern life can have detrimental effects on our hearing. To avoid such side effects, we must reduce the unwanted noise. But noise varies depending on the listening conditions and diffusion. Measurements and simulations help identify the root cause of an emanating source. However, noise testing is primarily carried out in laboratory conditions. But laboratory conditions are unrealistic, laboratory tests are restrictive, costly, and time-consuming.

In-situ on-site measurements allow an exposition to an actual situation.

The SonoCat is a multi-functional spherical microphone array. It consists of eight digital MEMS microphones located in a rigid sphere. They are used to collect all the acoustic data required for the calculation of the sound pressure level, the 3D sound intensity vector, and the sound absorption coefficient. The SonoCat is calibrated at a high standard and can be used to perform both point and scan measurements. For example, a point measurement can be used to measure the sound pressure or the 3D intensity vector to locate where a sound source is emitting. A scan measurement can provide the sound power of a machine or the average sound absorption of a surface.

The SonoCat is connected to a PC or a tablet with the SonoCat software where it can be used for monitoring, acquisition and analysis of the recorded sound field.

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Sound pressure level measurements

The Sonocat is a multi-purpose spherical microphone system that can measure sound pressure levels (SPL) in stationary sound fields.

Three common types of frequency weighting are provided to adjust the level according to the situation:

  • A-weighting: Frequency weighting based on the relative loudness perceived by the human ear at a sound loudness level of 40 phon.
  • C-weighting: Frequency weighting that is more appropriate for higher loudness levels.
  • Z-weighting: Frequency weighting at an equal level (0 dB) for all frequency bands (i.e. no frequency weighting).

The overall Sound Pressure Level is computed according to the IEC-61672-1 standard.

In-situ sound absorption measurements

All current methods to measure the sound absorption coefficient rely on assumptions for the global sound field impinging on the material under investigation. Measurements performed in the laboratory (such as impedance tube or reverberant room) are made in a controlled sound environment in which the sound field is known and predictable. However, outside the lab, the sound field can be difficult to control, unpredictable, and can vary depending on sound sources, for example. The capacity of a material to absorb sound depends on the source of the sound and its environment. Acoustic engineers know how much a material absorbs normal or random incident sound waves, measured in a laboratory, but not for oblique incident sound waves in situ for instance. In essence, acoustic engineers now lack the means to measure the effectiveness of the absorption materials where they are applied.

 

The sound absorption coefficient is defined as the ratio between the active and the incident sound power in relation to a surface. In classic measurements, the sound pressure and sound intensity are measured in a control sound field, with the assumption that the material under test will behave the same way in an anechoic environment and in-situ. This might not be the case. Instead of considering the global sound field the local plane-wave method takes the local sound field into consideration and assumes that the normal component of the sound field in each point can be described by an incident and a reflected plane wave. If we assume local plane waves near the surface, the effective in-situ absorption coefficient can be derived from sound field measurements. So we don’t need to take the equipment to a lab, we bring the measuring equipment to the actual sound field.

SonoCat Software

The SonoCat is user-friendly. It can be connected to any computer via USB where the software suite performs the measurements. A monitoring window displays the measured parameters in the frequency domain in real-time and precise measurements can be done with full control over the number of averages, FFT window, and overlap percentage. The recorded data is stored in a lossless compressed form and can be analyzed on the fly. The analyzed results are plotted in a GUI and can be exported as an image or text file.

SonoCat summarized:

  • Plug-and-play
  • Sound pressure level
  • Sound intensity level
  • Sound intensity direction
  • Sound absorption coefficient
  • Real-time monitoring
  • Data analyses on the fly
  • Compressed but lossless data storage

Click hier for more information on the SonoCat.