Tag Archive for: loose particles

Steve Temme Featured on THD Podcast (Part 2) – Transient Distortion and more

In the second of a 2-part series on the THD Podcast, Steve Temme continues his discussion about why its important for engineers to be able to correlate audio measurements to audibility. He demonstrates Listen’s latest transient distortion algorithm, which offers the unique ability to listen to the recorded waveform with the stimulus removed so that just the distortion artifacts can be heard. This aids understanding of the measurement and makes it very easy to set limits.

THD Podcast #92: Steve Temme discusses Transient Distortion Measurement (Loose Particles)

Additional Resources for Transient Distortion Measurement

All about the Transient Distortion measurement algorithm discussed in this Podcast.

More about SoundCheck’s audio measurement algorithms.

 

More about Steve Temme and the History of Listen, Inc.

SoundCheck Innovation Timeline – highlights of Listen’s product and algorithm introductions.

Reflections on Listen’s 25th Anniversary (2020) – Reprint of an article from Loudspeaker Industry Sourcebook.

 

About the THD Podcast

The Total Harmonic Discussion / the THD Podcast, hosted by Dave Lindberg and Simon Weston, is a weekly discussion on audio and headphone technologies and the people who bring the technology to market. All episodes can be found on its Youtube Channel, and it’s also available on Spotify, Amazon Music, iHeartRadio, Rumble, BitChute, Limited, Apple, and Google.

 

A New Method for Transient Distortion Detection

Transient distortion, or ‘loose particle’ measurement, is an important loudspeaker production line quality control metric that identifies and facilitates troubleshooting of manufacturing issues.

This paper introduces a new enhanced loose particle measurement technique that discriminates more accurately and reliably than current methods. This new method introduces ‘prominence’ after envelope detection, a new metric for audio measurements, that effectively isolates transient distortion in the presence of periodic distortion. This technique also offers the unique ability to listen to the isolated transient distortion waveform which makes it easier to set limits based on audibility and has widespread applications.

Authors: Steve Temme, Rahul Shakya and Jayant Datta, Listen, Inc.
Presented at 155th AES Conference (October 2023) New York, NY

Full Paper

 

Paper Introduction

Transient distortion, or ‘loose particle’ measurement, is a valuable quality control metric because it identifies non-periodic distortion, for example, rattling parts, separately from periodic distortion such as rubbing or buzzing parts. This facilitates troubleshooting of manufacturing issues. This paper introduces a new transient distortion measurement technique that is more accurate and reliable than current methods. In addition to improved performance, this new algorithm also aids understanding of the correlation between measurement results and audibility, since it is possible to isolate and listen to just the transient distortion artifacts. Although this analysis method was developed for measuring loose particles in loudspeaker drivers, it is also valuable for measuring rattling parts such as buttons, fasteners, and loose wires on various audio devices, and measuring impulsive distortion or Buzz, Squeak and Rattle (BSR) in automotive audio applications [1].

What is Transient Distortion? Why does it matter?

Transient distortion is caused by random clicking, popping, and other noises in the time domain. In a speaker or headphone driver, this might be caused by foreign particles such as glue or magnet fragments trapped in the gap behind the diaphragm or dust cap. In a device such as a smart speaker, transient distortion might come from a loose volume control button on the device that rattles when sound is played. In an automotive application, it could be characterized as buzz, squeak and rattle from loose wires, screws or fasteners in a car door that the loudspeaker is mounted in. In all cases, the sound is undesirable, so devices that exhibit such faults should be identified and rejected.

In the recorded time waveform, transient distortion faults appear as impulsive noises added on the stimulus wave. These impulses are not related to the frequency of the stimulus, but rather to the vibration caused by the displacement amplitude of the diaphragm. The transient distortion is more frequent and significant when the speaker is driven near or below its resonant frequency, where the displacement of the diaphragm is the greatest.

Although the sound – a random clicking, buzzing or popping noise – can sometimes sound similar to higher order harmonic distortion (Rub & Buzz), such defects are not clearly reflected in the frequency spectrum of the waveform. Figure 1 shows a waveform with transient distortion, and the corresponding frequency spectrum. The vertical black line represents the stimulus frequency and the orange broadband noise spectrum indicates the transient distortion. Transient distortion is best identified at the time the transients occur, unlike Rub & Buzz distortion which is best identified by the frequency at which it occurs [3].

The entire paper also covers:

Prior Measurement Methods

The new algorithm – comparison and results

Conclusions

Download paper

In addition to this paper, please also check out the Enhanced Loose Particles Webpage and our detailed video explanation of how this algorithm works.

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!

 

Evaluation of Audio Test Methods and Measurements for End-of-Line Automotive Loudspeaker Quality Control

In order to minimize costly warranty repairs, automotive manufacturers impose tight specifications and a “total quality” requirement on their part suppliers. At the same time, they also require low prices. This makes it important for automotive manufacturers to work with automotive loudspeaker suppliers to define reasonable specifications and tolerances, and to understand both how the loudspeaker manufacturers are testing and also how to implement their own measurements for incoming QC purposes.

Specifying and testing automotive loudspeakers can be tricky since loudspeakers are inherently nonlinear, time variant and affected by their working conditions & environment which can be change dramatically and rapidly in a vehicle. This paper examines the loudspeaker characteristics that can be measured, and discusses common pitfalls and how to avoid them on a loudspeaker production line. Several different audio test methods and measurements for end-of-the-line automotive speaker quality control are evaluated, and the most relevant ones identified. Speed, statistics, and full traceability are also discussed.

Authors: Steve Temme, Listen, Inc. and Viktor Dobos, Harman/Becker Automotive Systems Kft.
Presented at the 142nd AES Convention, Berlin, Germany

Full Paper