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Novel acoustic camera addresses price vs. performance dilemma

25.08.2020

Acoustic cameras are widely regarded as powerful tools for the localization of unwanted noise in products and processes. Engineers from product development, manufacturing and maintenance who are blessed with having access to such technology, appreciate the added value of visual information for implementing highly effective technical solutions. In addition, engineering managers and product marketers value avoiding costly trial and error as well as securing timely product launches due to increased predictability during product development, respectively.

The dilemma

Unlike thermal imaging cameras, acoustic cameras have not experienced comparable penetration into the equipment portfolio of engineering departments so far, especially in small to medium sized companies. One of the reasons lies in the properties of industrial sound emissions which are typically low frequency sounds by nature. In such a situation, a microphone array system with a diameter of at least one meter is typically required in order to reliably separate multiple sound sources. Considering the acquisition cost of such equipment in the range of 40k€+ combined with required expert know-how may result in a customer’s decision to refrain from purchasing. Over the last couple of years, the trend towards mobile acoustic cameras fueled hopes of having access to sound imaging devices at a more acceptable price. Yet, mobile systems with a diameter of about 30cm are just not capable of delivering the required image quality for typical industrial applications. Bottom line: we cannot outsmart physics easily and size simply matters. 

Introducing a novel method of sound imaging

For this reason, Seven Bel has tasked itself with developing a novel acoustic camera which delivers high image quality for industrial applications and offers superb usability and mobility at an affordable price. The enabling technology is a compact rotating sound scanner with a few state-of-the-art digital microphones. Fine spatial sampling of the sound field over a disc with a diameter of up to 1.32 meters results in acoustic images with excellent spatial resolution and dynamic range which drives confidence in the implementation of technical solutions, see Figure 1.

          

The benefit of scanning a large area can be easily seen from performing the following challenging experiment which is encountered in the testing of drivetrains and engines, see Figure 2. Three loudspeakers are excited with white noise, two of which coherently. The selected frequency band is 2000Hz +/- 115Hz and a dynamic range of 15dB is chosen. The center loudspeaker’s gain is +10dB vs. the outer loudspeakers. The large scanner with a diameter of 1.32m (left image) resolves the right and left speakers sitting 10dB below the center speaker and shows nice separation of sound sources, while the small scanner with a diameter of 0.5m (left image) clearly struggles with identifying the three sources. Yet, the smaller scanner is particularly useful for measuring medium to high frequency sound events in confined spaces.    

The sound scanner together with the user’s mobile device and Seven Bel’s number crunching cloud infrastructure in the background create a compact high-performance measurement system for the fast analysis of acoustic problems. The developers at Seven Bel paid special attention to designing a massively simplified workflow for measuring and analyzing acoustic images. Automatically generated reports can be easily shared with colleagues, partners or clients.

The technology has already been successfully demonstrated with products and processes from various industries ranging from automotive to transportation, home appliances and machinery construction.

Use cases

The design of enclosures for machining centers constitutes a particularly challenging task for mechanical engineers. Manufacturers must not only meet corresponding regulatory limits but also increasingly consider the fact that an optimal work environment for the machine operators is guaranteed. Acoustic images support engineers during the development phase in understanding, for instance, the time averaged local sound radiation during a machining process. These insights allow them to build machine housings which are optimal with respect to cost and acoustic effectiveness. In certain cases, sound is not coming from where it is initially expected. Grinding the edges of glass plates in glass processing centers leads to critical excitations of eigenfrequencies and eigenmodes of the material being processed. Sound may then not only come from the location where the grinding takes place. Instead, the glass plate being processed acts as a loudspeaker and may dominantly radiate sound from the opposite edge, see Figure 3. It is exactly this sort of insights which gives engineers the confidence to take the right measures when implementing designs for optimal sound reduction.  

Another interesting application can be found in the field of automotive engineering where engineers from vehicle simulation and testing are involved in reconciling simulation models with actual measurement data. Figure 4 shows a motorcycle operated under full load on a roller dynamometer. Engineers are particularly interested in confirming the exact location of sound radiation from the clutch cover in order to update material and geometry parameters in simulation models and thus, drive design optimizations.    

Seven Bel is currently gearing up for introducing their P50 and P132 sound scanners on the  market. The team is eager to learn more about new potential applications. So, contact us today at sevenbel.com and request a product demo.