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Multi-tone distortion

Characteristics:

KLIPPEL R&D System KLIPPEL QC System

Relative multi-tone distortion

 LPM  MTD

Distortion-noise-ratio

 LPM  MTD

A nonlinear system generates new spectral components which are not in the stimulus. In addition to harmonics, the fundamental components interact with each other and generate difference-tone and summed-tone components in the output signal which can easily be identified in a two-tone signal. Using a multi-tone stimulus, the number of distortion products rises quickly with the number of fundamental components, and order of the components can not be identified anymore. However, the multi-tone stimulus has similar properties like the pink noise, the organ tone or other audio signals, and the distortion can easily be separated from the fundamental components by using a FFT which is synchronous to the stimulus length.

KLIPPEL R&D SYSTEM (development)

Module

Comment

Linear Parameter Measurement (LPM)

LPM module uses a multi-tone complex as stimulus which may be used for distortion measurement in a separate microphone channel.

KLIPPEL QC SYSTEM (end-of-line testing)

Module

Comment

MTD (Multi-tone Distortion Task), preview

MTD uses a multi-tone stimulus to measure absolute and relative distortion in a very short time.

 

Example:

 

The figure above illustrates the interpretation of the multi-tone distortion measurement applied to a woofer system. The suspension generates distortion close to the resonance frequency fs. Force factor Bl(x) generates significant intermodulation throughout the audio band. The distortion generated by inductance nonlinearity L(x), L(i) and Doppler rise to higher frequencies.
The figure above illustrates the interpretation of the multi-tone distortion measurement applied to a woofer system. The suspension generates distortion close to the resonance frequency fs. Force factor Bl(x) generates significant intermodulation througho
The figure above shows the results of three different distortion measurements. The blue curve shows high values of harmonic distortion (THD in dB) at low frequencies where the displacement is high but decreases by 40 dB (below 1 %) at higher frequencies. A two-tone stimulus with a constant bass tone at 50 Hz generates significant intermodulation of the second tone anywhere in the audio band. The multi-tone stimulus is distributed over the full audio band generating smaller voice coil peak displacement and less intermodulation than the critical two-tone signal, but the distortion level is still 20 dB above the harmonics.
The figure above shows the results of three different distortion measurements. The blue curve shows high values of harmonic distortion (THD in dB) at low frequencies where the displacement is high but decreases by 40 dB (below 1 %) at higher frequencies.

Templates of KLIPPEL products

Name of the Template

Application

LPM multitone distortion SP1

Multi-tone distortion at high amplitudes (see Application Note AN 16) using standard current sensor 1

Diagnost. MIDRANGE Sp1

Comprehensive testing of midrange drivers with a resonance 30 Hz < fs < 200 Hz using standard current sensor 1

Diagnost. RUB&BUZZ Sp1

Batch of Rub & Buzz tests with increased voltage (applied to high power devices)

Diagnost. RUB & BUZZ Sp2

Batch of Rub & Buzz tests with increased voltage (applied to low power devices)

Diagnost. SUBWOOFER (Sp1)

Comprehensive testing of subwoofers with a resonance 10 Hz < fs < 70 Hz using standard current sensor 1

Diagnostics MICROSPEAKER Sp2

Comprehensive testing of microspeakers with a resonance 100 Hz < fs < 2 kHz using sensitive current sensor 2

Diagnostics TWEETER (Sp2)

Comprehensive testing of tweeters with a resonance 100 Hz < fs < 2 kHz using sensitive current sensor 2

Diagnostics VENTED BOX SP1

Comprehensive testing of vented box systems using standard current sensor 1

Diagnostics WOOFER (Sp1)

Comprehensive testing of subwoofers with a resonance 30 Hz < fs < 200 Hz using standard current sensor 1

Diagnostics WOOFER Sp1,2

Comprehensive testing of subwoofers with a resonance 30 Hz < fs < 200 Hz using current sensor 1 and 2

Standards:

  • IEC Standard IEC 60268-5 Sound System Equipment, Part 5: Loudspeakers
  • AES2-1984 AES Recommended practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement


Papers and Preprints:

W. Klippel, Tutorial “Loudspeaker Nonlinearities - Causes, Parameters, Symptoms,” J. of Audio Eng. Soc. 54, No. 10, pp. 907-939 (2006 Oct.).

E. Czerwinski, et al., “Multitone Testing of Sound System Components' Some Results and Conclusions, Part 2: Modeling and Application,” J. of Audio Eng. Soc. Volume 49, 2001 December, pp. 1181 – 1192.

S. Temme, et al., “A New Method for Measuring Distortion Using a Multitone Stimulus and Noncoherence,” J. of Audio Eng. Soc., Volume 56, 2008 March, pp. 176 – 188.  

W. Klippel, “Nonlinear Large-Signal Behavior of Electrodynamic Loudspeakers at Low Frequencies,” J. of Audio Eng. Soc., Volume 40, pp. 483-496 (1992).

A. Voishvillo, “Graphing, Interpretation, and Comparison of Results of Loudspeaker Nonlinear Distortion Measurements,” J. of Audio Eng. Soc., Volume 52, No. 4, pp. 332-357, April 2004.

W. Klippel, “Prediction of Speaker Performance at High Amplitudes,” presented at 111th Convention of the Audio Eng. Soc., 2001 September 21–24, New York, NY, USA.