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AP detects the rub & buzz defects

AP detects the rub & buzz defects
Rub and buzz examples

AP detects the rub & buzz defects

With the release of the v6.1 update, Audio Precision has added new measurement results, options and test signals to establish APx500 audio measurement software as “the best solution for production testing of loudspeakers, headphone drivers and microphones”.

For speaker driver developers, APx software now offers the broadest set of methodologies available in the detection of rub and buzz defects. Rub and buzz commonly refers to possible manufacturing defects that make undesirable noises during speaker operation. In addition to air leaks, the most common defect categories are rub-related noises when the speaker cone is off-centre and mechanically rubs when it moves to create sound, and buzz defects when loose particulate matter such as chipped magnet material or glue become trapped in the gap between the speaker’s voice coil and the cone.

Rub and buzz defects are not necessarily detectable by traditional audio measurements. Several different rub and buzz detection methodologies have been developed using high-pass tracking filters, distortion-oriented methods that focus only on high-order harmonics and techniques applying human hearing-based algorithms to the distortion signal. No single method has achieved uniform adoption in the industry.

Previously available in APx software, the v6.1 update uses high-pass tracking filters to remove the fundamental signal and detect defects as excursions in the residual waveform’s crest factor or peak ratio. SoneTrac is a Bose-developed improvement to rub and buzz that filters the residual signal and ratios it to the RMS of the total signal to reduce the noisiness of the measurement result. A High-Order Harmonic Distortion (HOHD) uses the Total Harmonic Distortion (THD) ratio but only of harmonics above the 10th, 10–35, 20–200, etc. that account for frequency masking effects. Rub and buzz loudness applies a psycho-acoustic loudness model to the residual signal to calculate the perceived level of the rub and buzz based on well-established models of the human perception of sound.

To support the addition of the HOHD and rub and buzz loudness measurements, AP has introduced the Fast Sweep signal with v6.1. Fast Sweep is an extremely fast-stepped frequency sweep with no input or output ranging between steps and continuous transition between steps to minimise transient effects. In addition, v6.1 allows an instant switch between IEC and IEEE THD calculation modes for harmonic distortion results that normalise harmonic distortion results when testing loudspeakers. All acquired waveform, impulse response or cross-correlation results can be saved to .wav files as a sequence step in automated measurement sequences.

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