Sound field mapping

Overview and introduction

In sound field mapping, the measured sound levels are visualized as a colour gradient over a photo of the measurement object, making it easy to see where the measurement object emits the most sound. In practice, three methods have proven effective for creating sound field maps. Sound field mapping using sound intensity measurements is carried out when there is a stationary acoustic problem. The sound intensities are measured one after the other at a large number of spatially precisely defined positions. In practice, positioning the SI probe is often very time-consuming. For this reason, we have developed software that automatically calculates these positions and displays them spatially using augmented reality glasses. Another method is acoustic near-field holography. This is mainly used when many sound sources are close together. However, it may also be the case that the sound has to be determined at a great distance from the sound source. Far-field methods using beamforming, which make use of acoustic cameras, are used for this purpose.

Lokalisierung des Schalls

Sound field mapping is a very efficient measurement method for quickly detecting acoustic problem areas. A sound field map usually displays the measured sound levels as a color gradient over a photo of the measured structure. This superimposed representation allows the acoustic weak points to be quickly identified. In the broadest sense, this representation is comparable to the contour lines on maps.

To create such maps, acoustic measurements must be carried out at a large number of precisely defined spatial positions. Interpolation between the measurement points is then carried out using various mathematical methods. The following figure shows an example of a sound field map above a PC workstation with 2 loudspeakers (only above the right-hand side for better clarity). This map quickly shows that most of the noise comes from the loudspeaker.

There are two main problems with conventional sound field mapping. Firstly, measuring the spatially precisely defined measurement positions is very time-consuming and secondly, only a two-dimensional representation of the sound field map over a photo of the measurement object is possible. For this reason, we have developed software that automatically calculates the measurement positions and displays them using augmented reality glasses. Once the measurement results have been entered, the sound field map is also automatically calculated and virtually superimposed over the measurement object. Thanks to the three-dimensional representation, the operator can now walk around the measurement object and see exactly where problem areas occur. The following graphic shows the differences between a conventional two-dimensional representation and a three-dimensional representation using augmented reality. 

Different methods for sound field mapping

Schallintensitätsmessung

If there is a stationary acoustic problem, the application of sound field mapping using a sound intensity probe is suitable. The sound intensities are measured one after the other at the defined positions. Appropriate software then overlays the measurement results graphically on an image, allowing the radiated sound power on this partial area to be determined. It is also possible to precisely quantify changes to the structure with a new measurement. Various measures can then be derived and evaluated from the results.

This method for sound field mapping places relatively low demands on the measurement technology, as it only requires two channels and an SI probe. On the other hand, however, the effort required to carry it out is somewhat higher.

Our patented augmented reality solution provides the exact measurement positions virtually through AR glasses. This shortens the time required to carry out such sound field mapping by up to 80 %.

Please do not hesitate to send us a message if you are interested in this procedure. We will be happy to help you.

Acoustic near field holography

With some measurement objects, there may be a large number of potential sound sources in a very confined space (e.g. an internal combustion engine). To ensure reliable localization of these sound sources, a very high spatial resolution is required. In practice, a sound pressure microphone array is used for this purpose. These mostly hand-held arrays are moved several times at a distance of 10-15 cm above the surface of the measurement object. The small distance is necessary so that they operate in the acoustic near field of the object.

The significant advantage of this method is that even closely spaced sound sources can be reliably separated and classified. However, the requirements for the measuring equipment are considerably higher (= higher costs) than for sound field mapping using sound intensity measurement. 

Far field method using beamforming

The far-field methods also work with a microphone array. However, the sound sources are determined using the effect of the time difference at a great distance from the sound source. This is done using beamforming calculations (method for determining the position of sources in wave fields).

In practice, the far-field method is carried out using so-called acoustic cameras. Such systems are very suitable for quickly detecting acoustic weak points. However, additional measuring equipment is also required here. Furthermore, it is difficult to quantify improvement measures with a new comparative measurement.

If you are undecided as to which of these methods you should choose in your specific case, we will be happy to advise you. We can also take over the sound field mapping of your measurement object for you.

Our services

  • Sound field mapping using a sound intensity probe
  • Sound field mapping by means of sound pressure measurement
  • Localization of unwanted sound sources
  • Assessment of acoustic measures on a specific structure
  • Easy interpretation of results
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