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100 Things #15: Loose Particle Detection for Identifying Transducer Manufacturing Defects

Loose Particle Detection is a technique for analyzing random transient distortion in the time domain. It is an important measurement for end of line transducer QC as it identifies manufacturing defects caused by foreign particles such as glue or magnet fragments trapped in the gap behind the diaphragm or dust cap. This algorithm This differs from Rub & Buzz measurements which analyze the higher order harmonics in the frequency domain to detect periodic distortion.

Note: This video was made in 2022 and highlights Listen’s original Loose Particle Algorithm. This was updated in the 2023 release of SoundCheck (Version 21) to the new Enhanced Loose Particle Algorithm. While the principal of time-domain analysis remains, the new algorithm utilizes a new metric, Prominence, to offer results that better correlate to audibility. Check out the information on the new algorithm listed in the links below.

Loose Particle Detection for Transient Distortion Analysis

Learn more about SoundCheck’s Loose Particles (transient distortion) analysis

Watch the new 100 Things video introducing the updated 2023 version of this algorithm.

Watch the video introduction to Enhanced Loose Particles – Listen’s newest Loose Particle Detection Algorithm.

Read about the Enhanced Loose Particles algorithm.

Read the AES paper published about this new algorithm for transient distortion detection.

 

Video Script: Loose Particle Detection for Identifying Transducer Manufacturing Defects

SoundCheck’s unique Loose Particle Detection Algorithm analyzes random transient distortion in the time domain. This identifies manufacturing defects caused by foreign particles such as glue or magnet fragments trapped in the gap behind the diaphragm or dust cap –  otherwise known as ‘crap in the gap’. Although this algorithm has been in SoundCheck since 2005, I’m always surprised how few people are aware of it, since it’s so valuable for improving manufacturing yield.

Let’s first look at the types of distortion we see on the production line. Conventional Rub & Buzz measurements analyze periodic distortion by looking at higher order harmonics in the frequency domain. These usually indicate a rubbing voicecoil or similar. However, with loose particles, analysis in the frequency domain does not yield useful information.

Loose particle analysis examines transient distortion in the time domain. This identifies random clicking, popping or rattling noises made by particles trapped behind the diaphragm or dust cap.  We can visualize this by looking at both the time and frequency analysis of the signal together. Here, in the frequency domain, you can see the periodic distortion, in other words, Rub & Buzz. And here, in the time domain, you can see the random transients, or loose particles.

Let’s take a closer look at the algorithm.

Loose particle detection uses a swept sine stimulus and time-envelope analysis of the waveform response to capture the transients. Detection thresholds are set for the magnitude, duration, and number of transients to quantify their level and number over time. Limits and filters are applied to separate device transients from background noise. Fine tuning with these tools customizes the algorithm for your product and manufacturing environment.

Measuring the different types of distortion enables rapid troubleshooting and correction of manufacturing problems, and SoundCheck is the only production line measurement system that can accurately distinguish between periodic and random transients.

Loose particle detection is also useful for identifying loose or rattling components such buttons, keyboards, wires and fasteners. In the digital domain, it can catch Bluetooth dropouts, clipping and other digital signal processing artifacts. This functionality is available in all editions of SoundCheck – check it out!