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Harmonic distortion

Characteristics:

KLIPPEL R&D System

KLIPPEL QC System

Total harmonic distortion (THD, THD+N)

TRF, DIS

QC Standard

Nth-order component versus frequency and/or amplitude

TRF, DIS

QC Standard

Hi-2 distortion (weighted low order harmonics)

DIS

Equivalent input distortion

TRF, DIS


Harmonic distortion components found in the output spectrum indicate nonlinearities inherent in the device under test. However, the measured distortion values depend on the spectral properties of the stimulus. Therefore, harmonic distortion measurements only provide a special symptom but not a comprehensive description of the nonlinear system. Intermodulation and other distortion components may have a higher impact on sound quality. The interpretation of the results of harmonic distortion measurements can be simplified by considering the particular physics of the device under test and psycho-acoustical processing in human hearing (e.g. masking effect). Recent progress in the nonlinear modelling of loudspeakers and other transducers explains how the force factor Bl(x), stiffness Kms(x) and other nonlinearities contribute to the harmonic distortion responses. The figure below illustrates this for a woofer:

KLIPPEL R&D SYSTEM (development)

Module

Comment

Transfer Function Module (TRF)

TRF provides a fast harmonic distortion analysis (THD and higher-order distortion components)  for all signals used for the transfer function measurement. 

3D Distortion Module (DIS)

DIS module performs a steady-state distortion measurement with user-defined pre-excitation time. DIS stepwise increases the amplitude of the stimulus and protects the transducer under test if the voice coil temperature or distortion exceed user defined limits. 

KLIPPEL QC SYSTEM (end-of-line testing)

Module

Comment

QC Standard: SPL Task; SPL+IMP Task System Task (Preview)

The Tasks measures 2nd-5th harmonics and THD using a sinusoidal chirp with sweep speed and amplitude profile which excites the loudspeaker persistently in the critical frequency range while performing an ultra-short measurement.

Example:

DIS module measures the harmonic distortion while changing frequency and amplitude of the excitation tone. The maximal value of the amplitude is determined automatically by the protection system provided by DIS (e.g. 10 % distortion value). The results are transferred to the mathematical post-processing tool (MAT) where the maximal SPL level for any percentage of THD (e.g. 1 %) is calculated.
DIS module measures the harmonic distortion while changing frequency and amplitude of the excitation tone. The maximal value of the amplitude is determined automatically by the protection system provided by DIS (e.g. 10 % distortion value). The results are transferred to the mathematical post-processing tool (MAT) where the maximal SPL level for any percentage of THD (e.g. 1 %) is calculated.
The figure above illustrates the calculation of the equivalent input distortion as performed by the TRF module. The harmonic distortion found in the sound pressure signal depends on the receiving point r and the properties of the particular transfer path H(f,r). TRF performs an inverse filtering and compensates for the post-shaping by H(f,r) which gives identical values of equivalent input distortion. This is always the case for motor and suspension nonlinearities generating the distortion in the one-dimensional signal path close to the input.
The figure above illustrates the calculation of the equivalent input distortion as performed by the TRF module. The harmonic distortion found in the sound pressure signal depends on the receiving point r and the properties of the particular transfer path H(f,r). TRF performs an inverse filtering and compensates for the post-shaping by H(f,r) which gives identical values of equivalent input distortion. This is always the case for motor and suspension nonlinearities generating the distortion in the one-dimensional signal path close to the input.

Templates of KLIPPEL products

Name of the Template

Application

Diagnost. MIDRANGE Sp1

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

Diagnost. RUB & BUZZ Sp2

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

EIA 7.4 Distortion

Distortion measurement according EIA-426-B 7.4 Section B - Distortion

Equivalent Input Dist. AN 20

Equivalent input distortion according Application Note AN 20

Hi-2 Dist. Automotive AN 7

Weighted harmonic distortion (blat distortion) used for Application Note AN 7

IEC 24.4 Harmonic Distortion

Characteristic harmonic distortion according IEC 60268-5 chapter 24.4

Max SPL Level THD at LIMIT

Maximal sound pressure level (SPL) for a given percentage of harmonic distortion (THD)

Xmax10 % distortion

Maximal peak displacement producing 10 % distortion

TRF Crest Harmonics (x,f)

Crest factor harmonic distortion versus displacement to find Rub & Buzz and other loudspeaker defects

TRF Equiv. Input Harm. (SPL)

Equivalent harmonic input distortion calculated by inverse filtering of the measured distortion

TRF Harmonics current (Sp1)

Harmonics of the current signal using standard sensor 1

TRF Peak harmonics, time domain

Peak value of higher-order harmonics in time domain for Rub & Buzz analysis

TRF rubb+buzz w/o Golden Unit

Rub & Buzz detection without "Golden Unit" according Application Note AN 22

TRF rubb+buzz with Golden Unit

Rub & Buzz detection with "Golden Unit" according Application Note AN 23

TRF SPL + harmonics

Standard measurement for fundamental component (SPL) and harmonic distortion

DIS 3D Harmonics AN 9

Harmonic distortions versus frequency and voltage according Application Note AN 9

DIS Harmonics vs. Voltage

Harmonic distortion measurement versus amplitude

DIS HI-2

Weighted harmonic distortion (blat distortion) used for Application Note AN 7

DIS SPL, Harm protected

Harmonic distortion measurement with protection

SIM closed box analysis

Maximal displacement, dc displacement, compression, SPL, distortion using large signal parameters imported from LSI BOX

SIM Equiv. Input Harmonics

Equivalent input harmonic distortion using large signal parameters imported from LSI; Simulated results are comparable with TRF Equiv. Input Harm. (SPL).

SIM vented box analysis

Maximal displacement, dc displacement, compression, SPL, harmonic distortion using large signal parameters imported from LSI BOX

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.).

W. Klippel, “Equivalent Input Distortion,” J. of Audio Eng. Soc. 52, No. 9, pp. 931-947 (2004 Sept.).

S. F. Temme, “How to Graph Distortion Measurements,” presented at the 94th Convention of Audio Eng. Soc., 1993 March 16-19, Berlin, Preprint 3602.

W. Klippel, “Assessment of Voice-Coil Peak Displacement Xmax,” J. of Audio Eng. Soc. 51, Heft 5, pp. 307 - 323 (2003 May).

W. Klippel, U. Seidel, “Measurement of Impulsive Distortion, Rub and Buzz and other Disturbances,” presented at the 114th Convention of the Audio Eng. Soc., 2003 March 22–25, Amsterdam, The Netherlands, Preprint 5734.

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.