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Near Field Scanner System (NFS)

The Near-Field-Scanner 3D (NFS) offers a fully automated acoustic measurement of direct sound radiated from the source under test. The radiated sound is determined in any desired distance and angle in the 3D space outside the scanning surface. Directivity, sound power, SPL response and many more key figures are obtained for any kind of loudspeaker and audio system in near field applications (e.g. studio monitors, mobile devices) as well as far field applications (e.g. professional audio systems). Utilizing a minimum of measurement points, a comprehensive data set is generated containing the loudspeaker's high resolution, free field sound radiation in the near and far field.

•    SPL at any point in 3D space

•    Directivity in near / far field 
•    High angular resolution 
•    Balloon / polar plot
•    Power response
•    Non-moving loudspeaker 
•    Open export interface
•    Non-anechoic measurement
•    Fast measurement
•    Comprehensive radiation data set
•    Portable measurement equipment
•    Flexible dimensions
•    Negligible reflections from equipment
•    Applicable to large loudspeakers (500 kg)

Specification

Benefits over traditional far field measurements

  • Applicable to large loudspeakers 

    Due to non-moving loudspeaker, large Loudspeakers can be measured, being supported by a crane from ceiling.

  • Avoiding air diffraction problems for far field measurements  

    Far field measurements of large loudspeakers will require large anechoic chambers to ensure far field conditions.

    Such measurements suffer from diffraction problems caused by temperature differences in the air over distance  

    and time,  leading to high errors in the phase response in upper frequency bands.

    A temperature change of only 2°C will result in a phase error of 180 degree at 10kHz in 5m measurement   

    distance.

  • No anechoic room needed  

    Radiated sound can be separated from reflected sound of the room by using field separation technique

  • Higher accuracy than anechoic chamber measurement 

    No room correction curve needed below 100Hz.

  • Fast measurement

    Standard 3D acoustic measurements like sound power are done in less than 20 minutes for typical 2-way systems. 

  • High Signal-to-Noise-Ratio

    High sound pressure level in near field. Less critical ambient noise requirements

  • Comprehensive radiation data set 

    Radiation data set gained from near field measurement provides SPL at any point in 3D space. 

    Near and far field data is provided without the need of further measurements. 

  • Provides full 3D Near Field Data 

    Near field data is provided at any point outside the scanned surface. 

  • High angular resolution <1° with low number of points

    Angular resolution is not depending on number of measurement points 

    (Traditional far field measurements require 64800 measurement points for 1° Resolution) 

Measurement Method

Measurement

The Near-Field Scanner 3D uses a moving microphone to scan the sound pressure in the near field of a compact sound source such as a loudspeaker system or a transducer mounted in a baffle. The device under test (< 500 kg) does not move during the scanning process. The reflections in the non-anechoic environment are then consistent and can be monitored with our novel analysis software, which uses acoustical holography and field separation techniques to extract the direct sound and to reduce room reflections.

Multi-pole Expansion

The sound field generated by the source is reconstructed by a weighted sum of spherical harmonics and Hankel functions which are solutions of the wave equation. The weighting coefficients in this expansion represent the unique information found in the near-field scan while gaining a significant data reduction.

Field Extrapolation

The near-field data, measured at a high SNR, is the basis for predicting the direct sound at larger distances. This avoids diffraction problems of classical far-field measurements (non-homogeneous media).

Optional Module: Field Separation

Performing a measurement in a small or reverberant room, the influence of the room cannot be neglected. Windowing techniques can be applied for high frequencies but not for low frequencies.

The Input/Output Field Separation approach solves this issue, providing a separation of the radiated sound from the reflections and room resonances.
This method is useful for low frequencies (below 1 kHz) where windowing techniques cannot be applied. In such frequency bands, even in well-built anechoic rooms, room modes build up. 

Optional Module: Near Field Analysis

Near Field Analysis

The wave expansion provides the sound pressure at any point outside the scanning surface, which is required for assessing studio monitors, mobile phones and tablets as well as other personal audio devices where the near field properties are important. 

At each position around the DUT, key features like SPL Response, Spatial SPL distribution and Phase characteristics are visualized.

Optional Module: Far Field Phase Analysis

The Far Field Phase Analysis module provides an advanced far field analysis of the exact phase behavior of the sound source. Features like phase balloon, group delay and reconstructed impulse response visualize the sound field. 

 

EASE Interface

The module also includes an export interface for the complex response data. This interface supports common external software like EASE.

Requirements

  • Near Field Scanner
  • Distortion Analyzer 2
  • TRF - Transfer Function
  • Microphone
  • Power Amplifier
  • PC

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