Technical Resources
With over 100 combined years of audio measurement experience, our team has created a wealth of technical papers, sequences, articles and other useful information to assist you with your audio test needs. Please browse the collection below, or filter by type of resource.
Q&A with Steve Temme – Loudspeaker Industry Sourcebook 2022
Want to get to know Listen Founder and President, Steve Temme, a little better? Each year, Loudspeaker Industry Sourcebook features interviews with industry leaders in which they ask their opinions on current events, issues and trends in the audio industry. Read what Steve Temme had to say.
Full Article
Enhanced Perceptual Rub & Buzz Measurement for Testing Automotive Loudspeakers
Loudspeaker Rub & Buzz faults are a problem for automotive manufacturers as they sound harsh and immediately give the perception of poor quality. There are two places such faults can occur – during speaker manufacturing and installation of the speaker in the car. A buzzing loudspeaker in a car is disappointing to a customer and is costly to replace. It is also challenging for a service center to determine exactly where the buzzing is coming from and whether it is caused by a faulty loudspeaker or bad installation. Perceptual distortion measurements are often considered the holy grail of end-of-line testing because rejecting speakers with only audible faults increases yield. Although such measurements have been around since 2011, production line adoption has been slow because until now, sensitivity to background noise has made limit-setting challenging. In this paper, a new algorithm is introduced that uses advanced technology to reduce the impact of background noise on the measurement and offer more repeatable results. This facilitates limit setting on the production line and makes it a truly viable production line metric for increasing yield. This same metric may also be used for end-of-line automotive quality control tests. Results from various algorithms will be shown, and their correlation to subjective and other non-perceptual distortion metrics explained.
Authors: Steve Temme, Listen, Inc.
Presented at 2022 AES Automotive Conference, Dearborn, MI
End of Line Distortion Measurements
Steve Temme discusses the importance of detecting manufacturing-induced defects such as Rub & Buzz and Loose Particles during end-of-line testing, and explains the various algorithms that are used. He compares conventional and perceptual metrics for the measurement of Rub & Buzz, including Listen’s new enhanced Perceptual Rub & Buzz algorithm, and discusses why it can be beneficial to use both conventional and perceptual measurements in tandem.
Enhanced Perceptual Rub & Buzz Demo Sequence
This sequence demonstrates how SC20’s new enhanced Perceptual Rub & Buzz algorithm compares to normalized Rub & Buzz and subjective listening. Running this sequence on a batch of good and bad buzzing loudspeakers should help identify by measurement, audibly defective units and where to set production limits. Starting the sequence, the user is asked at what test level to play a stepped sine sweep (Stweep™) in 1/12th octaves, from 20 kHz to 50 Hz. The user is encouraged to try different test levels and change sweep parameters to find the optimum settings to catch buzzing loudspeakers. The loudspeaker is measured via two channels of the audio interface. A calibrated reference microphone is connected to one of the channels and an impedance reference built into the SC Amp or AmpConnect is connected to the other. A HarmonicTrak™ Analysis step analyzes the recorded waveform from the reference microphone, and displays both the enhanced Perceptual Rub & Buzz and normalized Rub & Buzz graphs.
Complete End-of-Line Speaker Test (includes ePRB)
This sequence is an example of the many types of tests that can be performed quickly and simultaneously on a loudspeaker production line. It includes perceptual distortion measurement with the new enhanced Perceptual Rub & Buzz algorithm. A stepped sine sweep (StweepTM) from 20 kHz to 50 Hz is played through the speaker and measured via two channels of the audio interface. A calibrated reference microphone is connected to one of the channels and an impedance reference built into the SC Amp or AmpConnect is connected to the other. A HarmonicTrak™ Analysis step analyzes the recorded waveform from the reference microphone, and outputs Frequency Response, THD, Normalized Rub & Buzz, Perceptual Rub & Buzz, Loose Particle Envelope and Polarity. A Post-Processing step calculates the Ave. Sensitivity from 100 – 10kHz. A second analysis step analyzes the waveform from the impedance reference and outputs a curve of impedance versus frequency. Another Post-Processing step performs a curve fit of the impedance curve and calculates the max impedance (Zmax), precise resonance frequency (f0), and the quality factor (Q) of the resonance peak. All measurements and parameter are tested against limits in Limit steps. All these test parameters can be adjusted accordingly.
The Evolution of Production Line Rub & Buzz Measurements
Steve Temme discusses the evolution of production line Rub & Buzz measurements in this April 2022 issue of AudioXpress. Starting with simultaneous analysis of higher order harmonics, he explains the progression of improvements including the greater accuracy offered by normalized distortion measurements, and progressing to the introduction of perceptual metrics. He covers the introduction of the first perceptual distortion algorithm introduced in 2011, and the newest enhancements to this which offer the repeatability necessary for successful end-of-line perceptual distortion measurement, where the reduction in false rejects and resulting higher yields add significant value to speaker and headphone manufacturers.
Measuring Hearing Protection Devices to ANSI S3.19-1974 Standard
This sequence is used to measure the NRR, or Noise Reduction Rating, of a hearing protection device to the ANSI S3.19-1974 standard. NRR is a numerical representation of the sound attenuation of a device. The sequence first measures the response spectrum of the unoccluded hearing protector test fixture, then makes a second measurement with the hearing protection DUT affixed. A signal generator virtual instrument generates the pink noise stimulus while an RTA virtual instrument simultaneously records the A and C weighted noise spectrums. The unoccluded and occluded measurements are analyzed with a series of post-processing steps according to the ANSI S3.19-1974 standard. The final display shows the NRR numerical value, RTA spectra of the left and right side of the unoccluded and occluded hearing test fixture, average attenuation level of the DUT, and the standard deviation of the DUT on the test fixture.
Microphone Polar Plot Substitution Method Using Outline ET250-3D
This sequence measures the directional response of a microphone and graphs the result as a polar plot. A log sweep stimulus is played from 100 Hz to 10 kHz at each angular increment, and the acquired waveform is analyzed using the Time Selective Response algorithm. This method allows the test to be performed in a non-anechoic environment by placing a window around the direct signal, eliminating the influence of reflections. Commands are sent automatically to the Outline ET250-3D turntable via an ethernet connection, instructing it to move in 10 degree increments after each measurement. The sequence measures the response every 10 degrees from 0 to 180 and mirrors the polar image, which simulates a full 360 degree polar and saves test time. The response at each angular increment is compared against the on-axis response to create a normalized curve. This removes the influence of the device’s frequency response and sensitivity, such that the polar plot only shows the directional response. The final display also contains a graph of the directivity index in decibels versus frequency.
