Colored Noise

An acoustic camera makes it possible to see loud sounds in color. DEKRA experts work with this highly innovative instrument to make noise sources visible, even in complex locations. The unwanted noises can then be specifically combated.

The acoustic camera creates colored sound maps over the real image. Photo: shutterstock - Evija F

For example, the camera can show the noise-intensive areas of a combined heat and power unit. Photo: shutterstock – Evija F

The new technology can be used wherever conventional measuring instruments do not provide accurate information about the relevant sound source. Imagine this in a similar way to a thermographic image, which reveals deficiencies in thermal insulation, except that here the areas with the same volume appear in the same color: from red for particularly loud to quiet blue.

The device with which DEKRA expert Ilja Richter locates the disturbers of the peace does not have much in common with a normal camera. It looks more like three black honeycombs, the so-called arrays. In the middle of each is a digital camera that images the noisy object, surrounded by 128 microphones that record the sound waves. Software calculates the sound field from the transit time differences and immediately displays it above the real image as a colored sound map. The loudest area in the image section is always displayed.

Software calculates the sound field and immediately displays it above the real image as a colored sound map. Photo: DEKRA

Software calculates the sound field and immediately displays it above the real image as a colored sound map. Photo: DEKRA

The actual set-up time of the camera is about 20 minutes, but the correct location must first be found. “Sometimes I only spend a short time on site, sometimes a whole day,” says Richter. Sometimes the problem is approached from the front, sometimes from the side from an elevated position, or from behind. “I have to work my way up there,” he explains. The recording itself then only takes a few seconds and captures all the relevant data.

In most cases, a clear cause can be seen on the coloured sound map directly on site, but depending on the client’s requirements, the expert usually takes the material with him to his office and evaluates it there manually. Until he has found a photo that shows exactly where the problem actually lies, a time-consuming single image observation is necessary. For customers who want to use the results in the form of videos or pictures, however, this process is indispensable.

In the listening business for almost 20 years

The acoustic camera detects the loudest machine even in a narrow, noisy room. Photo: DEKRA

The acoustic camera detects the loudest machine even in a narrow, noisy room. Photo: DEKRA

Richter has been in the listening business for almost 20 years and is therefore a professional in the detection of sound sources. “You are sensitized and hear differently than other people,” he says. But his trained ears and the conventional sound level meter still reach their limits in very difficult conditions. Then the acoustic camera comes into play because it detects the loudest machine even in a narrow, noisy room. “This was the case, for example, when it was necessary to find the loudest machines in a production hall with packaging machines in order to protect employees from noise,” says Richter.

For example, the camera can show the noise-intensive areas of an engine, a combined heat and power unit or a wind turbine. It is also very helpful when searching for acoustic leaks. For example, it has already been necessary to analyse and illustrate the inadequate soundproofing of a partition wall between two hotel rooms. This revealed that sockets had apparently been misplaced and that the mineral wool in the lightweight wall under investigation had not been installed over its entire surface. If recourse claims are to be asserted, a picture-acoustic representation can be very convincing.

As an accredited measurement centre for noise and acoustics in accordance with §§ 26, 29b BImSchG (Federal Noise Protection Law), DEKRA supports: noise emission measurements and forecasts, building and room acoustics, noise at the workplace as well as vibrations and oscillations.

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