Frequency-Normalized THD Test Sequence

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This sequence measures both conventional Total Harmonic Distortion (THD) and Normalized THD to provide a more accurate representation of a device’s nonlinear behavior. A stimulus is played through the device under test and recorded via a calibrated reference microphone and amplifier signal paths. Conventional THD compares each harmonic to the fundamental at the stimulus frequency, which can cause distortion results to be influenced by the device’s frequency response roll-off. Normalized THD instead compares each harmonic to the fundamental at its measured frequency before plotting the result at the stimulus frequency, removing the effect of linear response variations. Both methods can be displayed and analyzed within the same step, allowing direct comparison of traditional and normalized distortion results.

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Polar Plot (MDT-4000 Turntable – LAN)

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Final Display for the Polar Plot (MDT-4000 Turntable - LAN) sequence

This sequence measures the polar response of a loudspeaker in both the vertical and horizontal dimensions using a polar plot. It is designed to work with the Portland Tool & Die MDT-4000 turntable and has all the necessary commands to automatically rotate it via a Local Area Network (LAN) connection. The sequence uses a log sweep stimulus with the Time Selective Response algorithm so that the measurements can be run in a non-anechoic environment. Note that the time window needs to be adapted to the user’s measurement space.

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Maximum Sound Pressure Level of a Full-Range Loudspeaker (ANSI/CTA 2034-A 2015)

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Figure 1 - Final display results - ANSI/CTA 2034-A 2015

This test sequence determines the maximum output capability of an in-home full-range loudspeaker system to the ANSI/CTA 2034-A 2015 standard. This standard uses shaped noise bursts and limits to measure the maximum output of a speaker. This sequence automates what is typically a time-consuming manual process minimizing test time and reducing the possibility of operator error.

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Soundbar Measurement over HDMI Connection

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Soundbar Measurement - screenshot of final displaySoundbar measurement over HDMI is simple in  SoundCheck as the WASAPI driver option allows easy connection to the device under test via HDMI.  This test sequence is not exclusive to soundbars; it can be used to make audio measurements on any audio device that accepts audio over HDMI (e.g. TV, computer monitor, home theater speakers, etc.)

The sequence itself is quite simple, containing 4 steps: Stimulus, Acquisition, Analysis and Display. Frequency response, THD, Rub & Buzz and ePRB are shown on the final display. More important are the instructions for configuring your SoundCheck system’s Hardware and Calibration to support the HDMI connected device.

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Loudspeaker Diaphragm Displacement Measurement Using a Laser

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Laser Displacement Measurement final screenshotThis pre-written test sequence demonstrates how to use a laser and SoundCheck to measure the peak (max and min) displacement of a loudspeaker diaphragm. SoundCheck is easily configured to include a laser signal path, making it simple to correlate diaphragm displacement with electrical impedance and audio artifacts.

In this laser displacement measurement, the user is prompted to enter parameters including test level, start and stop Frequency and stimulus frequency resolution. The sequence then plays the Start Frequency through the DUT and records the resulting diaphragm motion with the laser. Post-processing functions create maximum and minimum curves across the frequency range and display them on a graph.

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ANSI/CEA 2010-B 2014 Sequence for Subwoofer Maximum SPL

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This sequence measures the maximum peak SPL of a subwoofer according to ANSI/CEA 12010-B 2014. In this test, 1/3 octave band limited tone bursts are presented to the subwoofer across a 3 octave range from 20 Hz to 160 Hz. At each frequency, the stimulus level is increased in +3 dB increments until the harmonic (and non-harmonic) distortion and noise (HD+N) exceeds the specified threshold. The level is then decreased by 3 dB and the test continues with level increments of +1 dB until the HD+N threshold is again exceeded. The peak SPL of the fundamental at the last passing test level is recorded and the sequence continues to the next frequency. Peak SPL values are weighted according to the power spectrum defined in the standard and the Average Weighted SPL and final Broadband Peak SPL calculated as specified.

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Polar Plot (MDT-4000 Turntable) Sequence

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This sequence measures the polar response of a loudspeaker in both the vertical and horizontal dimensions. It is designed to work with the Portland Tool & Die MDT-4000 turntable, and has all the necessary commands to automatically rotate it via RS-232. The sequence uses a log sweep stimulus with the Time Selective Response algorithm so that the measurements can be run in a non-anechoic environment. Note that the time window needs to be adapted to the user’s measurement space.

The sequence plays the stimulus and measures at 10 degree increments from 0 to 180 degrees. This process is repeated with the speaker positioned horizontally. The two results are mirrored to display full 360 degree polar plots for each axis. A directivity index curve is also calculated for each axis and is displayed at the end of the test.

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Loose Particles Sequence

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This sequence demonstrates how to use SoundCheck to detect loose particle defects in loudspeakers. Loose particles typically reveal themselves as randomly spaced impulses, so they may not be detected when performing frequency based measurements such as THD, even though they can be clearly heard as undesirable artifacts. The loose particle algorithm, which is an available function in all analysis algorithms, analyzes a time waveform to detect these impulses. The user sets a customized threshold level for detection.

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Complete Test Sequence

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The purpose of this sequence is to perform a full suite of basic measurements for a loudspeaker. A 500 mV stepped sine sweep 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 is connected to the other.

A HarmonicTrak™ analysis step analyzes the recorded waveform from the reference microphone, and outputs frequency response, THD, Rub & Buzz, and various harmonic curves. A second analysis step analyzes the waveform from the impedance reference and outputs a curve of impedance versus frequency. A post processing step is used to estimate the characteristics of the impedance curve and calculates the max impedance, resonance frequency, and the Q of the resonance peak.

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Measuring Loudspeaker Maximum Linear Sound Levels Using Noise to the AES75-2022 Standard

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The AES75-2022 standard details a procedure for measuring maximum linear sound levels of a loudspeaker system or driver using a test signal called M-Noise. This is a complex procedure with many repetitive steps, which makes it time consuming to implement manually. This sequence automates the entire process, accelerating test time, minimizing operator intervention, and ensuring accurate and objective test results.

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ABOUT LISTEN INC

Listen is a global leader in audio measurement and analysis, with over 30 years’ experience developing innovative test methods and algorithms. SoundCheck, our powerful software-based audio analyzer, pairs with our test interfaces, precision microphones, and accessories to offer a complete solution for testing loudspeakers, headphones, microphones, smart devices, communication systems, hearing aids, automotive audio, and more. Trusted by engineers worldwide, Listen delivers the accuracy and flexibility essential for modern audio testing, from the R&D lab to the production line.

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