The LMS Test.Lab Array-based Holography and Focalization solution includes a number of unique and innovative techniques that increase localization accuracy and the applicable frequency range. For sound source localization, near-field
acoustic holography offers the best possible accuracy across the frequency spectrum as well as ample quantitative data for intensity and (partial) sound power contribution calculations.
The LMS Test.Lab Acoustic Source Localization
technology can be used in both stationary and non-stationary situations.
To localize sources, microphone measurements are usually taken along a plane in the near-field. Due to interference and other unwanted effects, the measured pressure will not reveal the real sources. To localize the real sources, very specific sound source localization processing is required. It is this processing that one finds in the LMS Test.Lab Array-based Holography and Focalization solution.
The upper frequency limit is determined by the distance between measurement points or microphones. To extend the upper frequency limit without additional measurements or higher channel counts, a focalization processing is applied. This is an economic and efficient way to double the upper frequency limit without any extra time or hardware investments.
Covering a complete object with microphones requires a significant investment in measurement hardware. To limit the investment, it is possible to measure in patches for either stationary or transient applications. The data from different runs is combined in a unique way so that a larger surface can be covered with less investment in measurement hardware.
To increase overall testing productivity , LMS also provides other techniques for sound source localization according to different required criteria such as frequency range, accuracy, cost and time pressure. The latest LMS sound intensity techniques include sound intensity (supporting pressure-pressure and pressure-velocity probes); high-definition acoustic cameras (a beam-forming solution combined with focalization) and acoustic holography (a holography solution combined with focalization.)
Engineers at International Automotive Components (IAC) – the largest acoustic materials supplier to the automotive industry – use the new LMS Test.Lab High Definition Acoustic Camera to identify noise sources in seconds compared to hours and days needed with traditional methods. Using this tool, engineers gain deeper insight into acoustic behavior and shorten turnaround times in lowering interior car noise for automakers around the world.
CETENA Ship Research Center uses LMS Test.Lab for a variety of standard – and not so standard maritime equipment testing. Everything from worst case scenario shock tests to the acoustic resonant frequency of a Murano chandelier on a mega-cruise ship is subject to the expert scrutiny of the CETENA testing team in Genoa, Italy. And this team counts on the powerful LMS testing solutions that can deliver results in minutes instead of days as billion-euro projects hang in the balance.
LMS Acoustic Holography performs a spatial transformation of sound fields – meaning that it takes a measurement of sound pressures along a certain plane and predicts what the readings would be anywhere else. This can be towards the nominal source (back propagation), towards the far field, or in any other direction or plane. Special techniques are available when working in complex multisource environments. Acoustic Holography is a powerful tool that helps to solve noise source identification and quantification problems. 
Finding out the exact source of a sound is a tough challenge for any acoustics engineer. Since the early 90’s, a number of methods, based on microphone arrays, have matured and are used throughout numerous industries. In general, the methods fall into three categories: near-field acoustic holography, beamforming, and inverse methods. Depending on the test object, the nature of the sound and the actual environment, engineers will have to select one method or the other. What that means for the near-field acoustic holography (NAH) technique is described in more detail below
