AcoustiCam AFD7001

AcoustiCam AFD7001
Quickly and effectively locate and analyse sound sources

The AcoustiCam sound field holography system combines the AFD7001 software developed on the SMT basis and the TORNADO measurement hardware including a microphone array.

The functionality of AcoustiCam is based on the signal processing of the simultaneously captured phase-exact sound pressure levels from the individual microphones. Mathematically the algorithm replicates a concave mirror which scans the examined sound field using the time-of-travel method.

During measurement the microphone array sequentially focusses any point in space in front of the array by variation of the calculated amplitude and phase correction terms. Thus an image of the sound pressure distribution is created in a single plane without mechanically moving the array.

The separation of sound sources according to location and frequency depends on the microphone geometry selected for the AcoustiCam. Any sound situation may be represented as a coloured, two-dimensional, absolute sound pressure distribution. For visualization of the sound situation the localization result may be superimposed onto a photograph of the examined object.

We offer a number of different array geometries with detachable 1/4“ ICP microphones optimized for various applications:

  • Single circle with 32 microphones (500 Hz to 20 kHz)
  • Double circle with 32 microphones (500 Hz to 20 kHz)
  • Inline array with 32 microphones for preemptive measurements
  • foldable star array with 30 microphones (200 Hz to 20 kHz)
  • detachable star array with 30 microphones (1 kHz bsi 20 kHz)

Compared to alternative concepts the solution we offer presents various benefits:

  • The data acquisition hardware may be used for other measurements as well.
  • The system allows uninterrupted data capturing on HDD with 32 channels for 8 hours.
  • The measuring hardware may be fully supplied from buffer batteries enabling mains-independent operation.
  • The system allows variable array geometries to match your requirements.
  • The low-cost solution features high accuracy.

Results:

  • Sound pressure distribution as a coloured map superimposed onto a photograph
  • Triggered time domain data on all channels
  • Transmission functions between all channels
  • Listening-in at one point of the image
Orthogonal beamforming
This novel AcoustiCam algorithm is based on the separation of the localization result into uncorrelated, i.e. independent sound sources. These involve different source mechanisms, which may also result in highly varying sound emission levels. Orthogonal beamforming provides separate representation of the individual sound sources. Subsequently, this allows separate localization of not only the highest-level main sound sources, but also of the lower-level masked sound sources. Neither muffling of certain areas nor performing several measurements is necessary. This method increases the signal-to-noise ratio to more than 25dB, compared to the 10 ... 15dB for conventional methods.
Source analysis
The AcoustiCam measurement system is able to analyse individual sound sources by determining the source-characteristic sound pressure spectra for a specific point. Even under unfavourable acoustic conditions (e. g. in a wind tunnel) existing sound sources may be localized reliably. There is no need to use special acoustic rooms.
Boundary layer array
Use of this so called boundary layer microphone array results in the cancellation of the sound emitted from behind the microphone array. Therefore no special acoustic rooms are required for the measurements, and any microphone geometry my be used. Special low-cost microphones are permanently integrated into the array.
Ring array
The considerably lighter ring array, compared to the boundary layer array, operates with 32 microphones mounted on a metal tube ring for common tripod attachment. This system uses COTS measuring microphones with ICP supply and BNC connectors. The microphones allow easy snap-on mounting and can be used in different measurement set-ups. A tripod with rollers and a swivelling head allows easy positioning.
Angle of view
As with an optical system deformation of the object image occurs when the angle between the object direction and the camera orientation increases. In the acoustic far field these deformations are negligible up to a maximum recommended angle of view of ±30°. The larger the dimensions of the examined object are, the larger the distance between the microphone array and the object has to be.
The AcoustiCam measurement system is based on the near field beamforming algorithm. This also allows a measurement in close proximity to the examined object, since the maximum recommended angle of view increases when the distance to the object decreases. The minimum permissible distance to the object is 0.25m.
This means that smaller objects may be placed very close to the microphone array, while larger objects need a greater distance for optimal depiction. That leaves virtually no restrictions to the use of AcoustiCam with respect to the size of the examined object.
Spatial resolution
Depending on the type of microphone array used various resolutions are available. Apart from the geometrical arrangement of the microphone, the spatial resolution of the system depends on the frequency and the distance of the sound source to be localized. The higher the frequency is, i. e. the shorter the wavelength, the higher the spatial resolution of the array is.

Versions and options

AcoustiCam AFD7001 versions and options
Order no. Description
982400.0Ring Array 32ch (500 Hz ... 10 kHz)
982407.4Star Array 30ch (200Hz...10kHz)
999999.5Line Array 30ch (200Hz...12kHz)
801276.6Option: Pass-By

Software

AFD7001 software

  • Stationary sound sources (sound sources with a fixed location and quasi-stationary source signal)
  • Non-stationary sound sources (moving sound sources / sound sources with a transient source signal)
Utilization of traditional and novel beam-forming algorithms in the
  • Time domain (e. g. pass-by for objects moving at a constant speed)
  • Frequency domain (e. g. orthogonal beam forming for individual location of independent sound sources, elimination of the channel noise to increase signal-to-noise ratio)
Sound source characterization
  • Image of the sound situation as coloured, two-dimensional absolute map of the sound pressure level
  • Visualization of the sound situation by superimposing the map onto a photo of the test object (integrated camera, generation of individual images or image sequences / videos)
  • Generation and auralization of the source signal (listen in)
  • Identification of the sound pressure level spectra and local sound pressure level profiles
  • Evaluation of trigger signals
  • Support of arbitrary microphone arrangements
Analysis modes
  • Continuous location of sources (live mode)
  • Unrestricted recording time (streaming)
  • Unlimited analysis runs through post-processing with variable calculation parameters without the need of a new measurement (e. g. selection of algorithms, subsequent disabling and weighting of individual channels)
  • Import of external time data from earlier microphone array measurements (ASCII format)
  • Export of calculated results as graphics, animated graphics or in ASCII format

Technical specifications

General technical specifications of AcoustiCam AFD 7001 (with ring 32)
Microphones 32 x 1/4" IEPE microphones (SMB connector)
Microphone arrangement Numerically optimized double-ring microphone arrangement
Diameter 1.3m
Frequency range 500Hz ... 10kHz
Minimum distance to test object ca. 25cm
Object size Unrestricted
Maximum angle of view 60°
Spatial resolution 28cm @ 1kHz, 14cm @ 2kHz, 7cm @ 4kHz, 3cm @ 8kHz
Signal-to-noise ratio 12dB @ 1kHz, 12dB @ 2kHz, 12dB @ 4kHz, 12dB @ 8kHz
Front-end Tornado_32D
Microphone calibration Via centric point sound source or 1/4" calibrator

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