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Comparison of Wired and Wireless (Bluetooth) Speaker Response

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This test sequence performs frequency response and distortion measurements of a Bluetooth speaker using both a wireless Bluetooth and wired stimuli; then compares the results. This sequence is configured for use with a Portland Tool & Die BTC-4149/4148 or BQC-4149/4148 Bluetooth interface.

Initially, the sequence prompts the operator to turn on the Bluetooth device under test and set it to pairing mode. BTC message steps will connect the Bluetooth device (operator selects the device from a list of detected Bluetooth devices) and connects Bluetooth audio. A 1 kHz test tone is transmitted, and if detected, the test sequence proceeds. A stepped sine sweep from 20 kHz to 100 Hz is played wirelessly to the Bluetooth speaker and measured via a calibrated reference mic.

Two post-processing steps convert the sampling rate and alignment of the response, then an analysis step calculates the frequency response and THD. The Bluetooth is disconnected, and the Bluetooth frequency response and THD curves are displayed on graphs. The operator is then prompted to connect the wired analog input into the Bluetooth speaker, and the same measurements are performed using the analog connection. Analog frequency response and THD curves are temporarily displayed on graphs, followed by graphs containing both Bluetooth and analog curves for comparison.

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Practical Impedance Measurement

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Author: Steve Temme
Loudspeaker impedance measurements are made for many reasons. In the R&D lab, these range from the simple task of identifying a speaker’s resonant frequency to more complex functions such as calculating the speaker’s Thiele-Small parameters. On the production line, impedance measurement is a key quality control parameter that verifies that the speaker’s motor properties are correct, that the magnet is charged correctly, the voice coil number of turns is correct and that the moving mass (cone and voice coil) is within specification.
There are two basic methods of making impedance measurements on loudspeakers, micro-speakers and headphones using sound card and software based systems. These are basic single channel measurements, and more complex, but more accurate, dual channel methods. Both methods are implemented in SoundCheck, and with some additional hardware these tests are simple to carry out.

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Advances in Impedance Measurement of Loudspeakers and Headphones

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Impedance measurement is often the sole electrical measurement in a battery of QC tests on loudspeakers and headphones. Two test methods are commonly used, single channel and dual channel. Dual Channel measurement offers greater accuracy as both the voltage across the speaker (or headphone) and the reference resistor are measured to calculate the impedance. Single Channel measurement methods are more commonly used on the production line because they only require one channel of a stereo soundcard, which leaves the other free for simultaneous acoustic
tests. They are less accurate, however, due to the test methods making assumptions of constant voltage or constant current. In this paper we discuss a novel electrical circuit that offers similar impedance measurement accuracy compared to complex dual channel measurement methods but using just one channel. This is expected to become popular for high throughput production line measurements where only one channel is available as the second channel of the typical soundcard is being used for simultaneous acoustic tests.

Authors: Steve Temme and Tony Scott
Presented at the 135th AES Conference, New York 2013

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Measurement of Harmonic Distortion Audibility Using A Simplified Psychoacoustic Model – Updated

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A perceptual method is proposed for measuring harmonic distortion audibility. This method is similar to the CLEAR (Cepstral Loudness Enhanced Algorithm for Rub & buzz) algorithm previously proposed by the authors as a means of detecting audible Rub & Buzz which is an extreme type of distortion[1,2]. Both methods are based on the Perceptual Evaluation of Audio Quality (PEAQ) standard[3]. In the present work, in order to estimate the audibility of regular harmonic distortion, additional psychoacoustic variables are added to the CLEAR algorithm. These variables are then combined using an artificial neural network approach to derive a metric that is indicative of the overall audible harmonic distortion. Experimental results on headphones are presented to justify the accuracy of the model.

Authors: Steve Temme, Pascal Brunet and Parastoo Qarabaqi
Presented at the 51st AES Conference, Helsinki, Finland, 2013

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Measurement of Harmonic Distortion Audibility Using A Simplified Psychoacoustic Model

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A perceptual method is proposed for measuring harmonic distortion audibility. This method is similar to the CLEAR (Cepstral Loudness Enhanced Algorithm for Rub & buzz) algorithm previously proposed by the authors as a means of detecting audible Rub & Buzz which is an extreme type of distortion[1,2]. Both methods are based on the Perceptual Evaluation of Audio Quality (PEAQ) standard[3]. In the present work, in order to estimate the audibility of regular harmonic distortion, additional psychoacoustic variables are added to the CLEAR algorithm. These variables are then combined using an artificial neural network approach to derive a metric that is indicative of the overall audible harmonic distortion. Experimental results on headphones are presented to justify the accuracy of the model.

Authors: Steve Temme, Pascal Brunet and Parastoo Qarabaqi
Presented at the 131th AES Convention, San Francisco, 2012

Full Paper

Automated Perceptual Rub & Buzz Distortion Measurement

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Author: Steve Temme.  Reprinted from the September 2011 issue of Voice Coil.

In this article, Steve Temme discusses Listen’s latest work on perceptual Rub & Buzz measurement.
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Are You Shipping Defective Loudspeakers to your Customers?

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Author: Steve Temme

Loudspeaker distortion is undesirable. The type and level of distortion, however, can greatly influence the perceived annoyance. In addition, identifying the type of distortion can also help pinpoint the mechanism or mechanisms in the loudspeaker that are causing the distortion. “Rub & Buzz” is a good example of a particularly annoying type of distortion that is very difficult to measure. Pinpointing the cause of the problem from the measurement is an even more difficult task. Understanding why this type of distortion is so annoying and how to measure it is critical in being able to properly test loudspeakers on the production line.
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Evaluation of Loudspeaker Performance at Low Frequencies

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Authors: Steve Temme and Christopher J Struck

Evaluation of loudspeaker performance at low frequencies is complicated by long wavelengths, room interaction and cabinet/baffle diffraction. Since low frequency measurements have traditionally required large, impractical testing environments, different techniques have been developed in an attempt to overcome this requirement. Anechoic chambers, outdoor measurements, half-space measurements, ground plane measurements, cepstral liftering, parametric modelling and near field techniques are compared with respect to accuracy, speed, bandwidth and practical implementation.
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Time Selective Measurements with a Logarithmically Swept Sine

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Author: Martin Rung

A time selective measurement of a frequency response is (directly or indirectly) based on a measurement of the impulse response, where a well-defined time window is applied to the impulse response. The frequency response is simply the Fourier transform of the impulse response. Time selective measurements are often used in electroacoustics to make simulated free-field measurements of transducers. This is to isolate the directly transmitted, “freefield” sound from reflections due to the surroundings. By using a time window applied to the impulse response, it is
possible to obtain results similar to those obtained in a non-echoic environment.
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