Tag Archive for: loudspeaker

Loudspeaker Diaphragm Displacement Measurement Using a Laser

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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Polar Plot (MDT-4000 Turntable) Sequence

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

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

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

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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Polar Plot (Linear X Turntable) Loudspeaker Sequence

This sequence measures the polar response of a loudspeaker in both the vertical and horizontal dimensions. It is designed to work with the Linear X 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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Complete End-of-Line Speaker Test (includes ePRB and eLP)

This sequence is an example of the many types of tests that can be performed quickly and simultaneously on a loudspeaker production line. A stepped sine sweep (StweepTM) from 20 kHz to 50 Hz is played through the speaker under test 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 (ePRB), Loose Particle Prominence and Threshold (eLP) and Polarity. A Post-Processing step calculates the Average Sensitivity from 100 – 10kHz. A second Analysis step analyzes the recorded waveform from the impedance reference and outputs a curve of impedance versus frequency. A 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 parameters are tested against limits in Limit steps. All these limits can be adjusted to suit your own DUT.

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Basic Loudspeaker Testing Seminar

This introductory seminar is aimed at anyone new to audio measurement, specifically loudspeaker testing. It begins with an introduction to the basic design of a loudspeaker, including how a typical loudspeaker works. Various loudspeaker measurements are explained, such as frequency response, distortion, sensitivity, phase/polarity and impedance, and how they might offer indications as to potential defects in a speaker. Typical test configurations for both R&D and end-of-line production test are shown. A complete speaker test is demonstrated, using SoundCheck and our free Loudspeaker complete test sequence. This includes setting up software and hardware, calibrating and configuring the test (e.g. setting pass/fail limits) and a discussion of the results.

Basic Loudspeaker Testing demonstrations include:

  • Anatomy of loudspeaker design
  • How a loudspeaker works
  • Loudspeaker test setup with SoundCheck
  • Considerations when testing a loudspeaker in an R&D versus production environment
  • Critical measurements like frequency response, sensitivity, phase, polarity, impedance, and distortion

Presenters: Les Quindipan
Duration: 22 Mins

Basic Loudspeaker Testing measurement resources

Complete End-of-Line Speaker Test: This free test sequence performs a full suite of basic measurements for a loudspeaker, featuring our two new perceptual distortion metrics. ePRB, or enhanced Perceptual Rub & Buzz is used to detect and differentiate audible distortion from total distortion. eLP, or enhanced Loose Particles, performs transient distortion measurements even in the presence of background noise.

More about Basic Loudspeaker Measurement

Johan Segeborn’s video “How Does A Speaker Work?” is an excellent reference for loudspeaker behavior.

How to Measure Free Field Speaker Response without an Anechoic Chamber

Did you knowSimulated Free field measurement you can make free-field measurements without an anechoic chamber? In the March 2021 issue of VoiceCoil, Steve Temme explains his unique method for achieving this. The article explains how the ‘splice’ method results in a full range frequency response from a combination of near-field and windowed far-field measurement, and compares the results with anechoic chamber measurements and the manufacturer’s published response curve.

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