The Nor848B Acoustic Camera is a module-based approach that gives the user both portability and superior resolution for a wide range of measurement situations. The array dish is based on a hexagonal shape for combining several tiles to create larger and more capable systems as needed.
The Nor848B Acoustic Camera is a module-based approach that gives the user both portability and superior resolution for a wide range of measurement situations. The array dish is based on a hexagonal shape for combining several tiles to create larger and more capable systems as needed.
Acoustic beamforming arrays, commonly known as acoustic cameras, enable the user to visualize different sound sources at different frequencies and source strengths. The resolution and ability to resolve sound sources spaced closely apart, and at lower frequencies, are mainly decided by the overall size and number of microphones of the equipment being used.
Although image manipulation and deconvolution techniques on the beamformed results might give added resolution, in practice the properties of the array still influence the results. This size versus resolution criteria is the crux of the acoustic camera market. The Nor848B answers the need for a small, lightweight, and portable acoustic camera while offering excellent resolution and the option to configure for low-frequency measurement with additional Hextiles.
With a single Hextile, the user has a small, portable and lightweight acoustic camera that can be used for a wide range of measurement situations. The Hextile-based acoustic camera needs only a single USB cable for both power and data transfer – no extra battery cable needed. The array is made from robust and lightweight aluminium, has 128 MEMS microphones, and is less than 3 kg in weight while having a maximum diameter of 46 cm. The low frequency limit for the Hextile is 410 Hz.
For users that require better resolution both in lower frequencies and overall, three single Hextiles can be combined to a larger Multitile system, consisting of 384 microphones with a maximum diameter of 96 cm. The low frequency limit for the Multitile is 220 Hz.
For special low-frequency applications below 500Hz, it is also possible to utilize the Multitile in the low-frequency configuration as the Multitile (LF mode). By placing the individual Hextiles further away, the maximum diameter of the complete array system is increased to 1.46 m, making it ideal for low-frequency measurements. The Multitile (LF mode) is for low-frequency measurements below 1 kHz, with a lowest frequency limit of 120 Hz.
Connection: USB
Microphones: 128 MEMS microphones
Max sound level: 120 dB
Min sound level (system): 9 dBA
SNR per microphone: 65 dBA
SNR array (system): 82 dBA
Audio sampling rate: 44.1 kHz
Camera resolution: 2592 x 1944
Opening angle: 105°
Frame rate: 15 FPS
Operating temperature range: -40 to +85
Per microphone (flat): 100 Hz – 20 kHz
Per microphone: -26 +/-3dBFS/Pa @1 kHz 94 dB
Spatial sensitivity Hextile: 410 Hz – 20 kHz
Spatial sensititivy Multitile: 220 Hz – 20 kHz
Spatial sensititivy Multitile (LF mode): 120 Hz – 1 kHz
Dimension Hextile: 41 cm x 48 cm, Ø 48 cm
Dimension Multitile: 83 cm x 84 cm, Ø 96 cm
Dimension Multitile (LF mode): 126 cm x 121 cm, Ø 146 cm
Weight Hextile: < 3 kg
Weight Multitile: < 10 kg
Material: Aluminium
Power consumption: < 3 W
The biggest improvement when going from a single Hextile to the two different Multitile configurations is best demonstrated on a low frequency source. Shown below are the results from recordings on a single omnidirectional noise source emitting pink noise, with the color plot being calculated when the input signals are filtered at 500 Hz. This provides a direct comparison of the low frequency capability of the different arrays.
At the top are the different array configurations used for the recordings, with a 128 element Hextile, a 384 element Multitile, and a 384 element Multitile (LF mode). The diameters of the array configurations are 46 cm, 96 cm, and 1.46 m respectively.
The second rows show the beampattern for the different array configurations at 500 Hz and 3 dB dynamic range. As the overall array size increases, the beampattern gets more narrow, thus giving better resolution.
Finally, the color plot results from the three different array configurations recorded from a real noise source are shown with 3dB dynamic. The improvement in terms of resolution and pin-pointing the source is clearly visible when using a larger array size.
User friendliness and ease of use have always been at the forefront of the software design strategy.
We want the user to be able to get results quickly, and start analyzing recordings easily rather than the measurement set up or configuration of parameters. Live view of measurements combined with an intuitive software interface enables users without prior experience to make measurements within the first five minutes after powering the device.
The feature that sets the software apart from our competitors is the virtual microphone. The virtual microphone allows the user to filter out all audio signals from outside the chosen listening point. With this tool the user can listen to a specific location in the live or recorded video monitor to gain more insight in to the measurement area. This feature will especially come in handy when the camera is being used in noisy and complex environments where other noise sources might make it difficult to distinguish which sound source is producing the undesired noise.
In addition to live plotting and directive listening, it is also possible to record and analyze measurements at a later time. The raw signal from all microphones are saved, and all parameters such as frequency selection, time selection and so on can be changed in post-processing. This means that a recording can be done without selecting the optimal parameters during the measurement, since these can be changed when analyzing the recording. Recording measurements with the Nor848B is only a matter of pointing the array roughly towards the area of interest and pressing record. All analysis and changes of parameters can be done in post-processing such as directive listening, graphical overlay of sources, spectrogram, FFT analysis and so on.
Sometimes sources may be closely spaced apart, or a strong noise source in the area of interest is interfering with the recording and impairing the image quality. Often this will be seen as either a single large source, or the source of interest will be completely shadowed by the stronger source. Seen in the image below is a situation where two equally strong sources are positioned close to one another, and the resulting colour plot will display a single large source. In such situations the acoustic eraser feature may prove valuable. This function will add a red circle to the screen that can be dragged to any point, and remove the source from that point. This is highly effective when several noise sources are present. As seen on the pictures the acoustic eraser completely removes the source where the suppress point button is positioned. The virtual microphone can further be positioned on the source of interest.
Especially in automotive applications RPM measurements may give vital information. The acoustic camera software has the possibility to display frequency content as a function of RPM by using the order analysis function.
In the spectrogram window, frequency as a function of RPM is plotted. It is further possible to select a square in the spectrogram window to isolate interesting events. By pressing the “apply” button on the selection, the RPM and frequency limits in the main view window automatically change to the limits set by the selection in the spectrogram. The user may find an interesting sound event in the spectrogram, and automatically get the corresponding color plotting of the event chosen.
The Nor848B Acoustic Camera is a module-based approach that gives the user both portability and superior resolution for a wide range of measurement situations. The array dish is based on a hexagonal shape for combining several tiles to create larger and more capable systems as needed.
