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DC displacement – dynamic offset the voice coil

Characteristics:

KLIPPEL R&D System KLIPPEL QC System

DC displacement versus frequency

DIS  

DC displacement versus amplitude

DIS  

Asymmetrical probability function pdf

LSI, PWT
Peak-bottom value DIS, TRF, LSI, PWT, SPM MSC

Asymmetries in the motor and suspension nonlinearities generate a dc component in the voice coil displacement which can be detected by a laser sensor. The sign of the dc component has a high diagnostic value because it is directly related with the shape of the nonlinearity. For example, an asymmetrical stiffness characteristic generates a dc component which always shifts the coil to the softer side of the suspension. An asymmetrical force factor characteristic may cause a significant dc component for excitation frequencies above resonance in the same order of magnitude as the fundamental. DC displacement generated by a poor suspension system may spoil the performance of an expensive motor structure because a dynamic voice coil offset produces audible intermodulation distortion.

The figure above illustrates the typical frequency of the dc displacement caused by an asymmetrical shape of nonlinear stiffness Kms(x), nonlinear force factor Bl(x) and nonlinear inductance L(x).
The figure above illustrates the typical frequency of the dc displacement caused by an asymmetrical shape of nonlinear stiffness Kms(x), nonlinear force factor Bl(x) and nonlinear inductance L(x).

KLIPPEL R&D SYSTEM (development)

Module

Comment

Transfer Function Module (TRF)

TRF reveals the dc component in the waveform of the displacement and in the Rub & Buzz analysis (instantaneous distortion 3D plot).

Large Signal Identification (LSI)

LSI predicts the dc displacement generated by a pink noise stimulus by using the nonlinear large signal model and the identified loudspeaker parameters. The predicted value can be compared with the value measured independently by using a laser sensor. 

Power Test (PWT)

PWT provides similar features like the LSI but may be used to monitor the dc component of multiple devices under test using ordinary audio signals.

Hardware

Displacement Meter of the Distortion Analyzer Hardware (DA)

The stand-alone operation mode of the DA measures the peak, bottom, dc component of the displacement using a laser sensor. This is a simple way for assessing the dc component in loudspeakers reproducing any signal.  

3D Distortion Module (DIS)

DIS module measures the steady-state response of the dc component versus frequency at different excitation levels. 

KLIPPEL QC SYSTEM (end-of-line testing)

Module

Comment

MSC (Motor Suspension Check)

MSC calculates the dc component using the large signal model and the identified nonlinear parameters in ultra short time (< 1s).It dispenses with a laser sensor.

 

Example:

 

The figure above shows the result of the motor stability check where the dc displacement is measured by a sinusoidal tone above the resonance frequency (1.5 fs). Increasing the terminal voltage, the dc displacement in the example approximately equals the amplitude of the ac component.
The figure above shows the result of the motor stability check where the dc displacement is measured by a sinusoidal tone above the resonance frequency (1.5 fs). Increasing the terminal voltage, the dc displacement in the example approximately equals the
The figure above shows the displacement probability density function pdf as measured by the LSI revealing an asymmetrical shape which is obvious by comparing the curve with the blue curve represented by the mirrored pdf. Since the voltage signal has a symmetrical pdf, the dc component shifts the coil to the positive side away from the rest position.
The figure above shows the displacement probability density function pdf as measured by the LSI revealing an asymmetrical shape which is obvious by comparing the curve with the blue curve represented by the mirrored pdf. Since the voltage signal has a sym

Templates of KLIPPEL products

Name of the Template

Application

DIS Motor stability

Checking motor stability at frequency 1.5 fs (where Xdc is maximal) according Application Note AN 14

DIS X Fundamental, DC

Fundamental and DC component of displacement

SIM X Fundamental, DC

Maximal displacement, dc displacement, compression using large signal parameters imported from LSI; Results are comparable with DIS X Fundamental, DC.

SIM Motor Stability

Checking motor stability according Application Note AN 14; Simulated results are comparable with DIS Motor stability.

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

Separate suspension

Separated stiffness of surround and spider according to Application Note AN 2

SPM Suspension Part

Nonlinear stiffness of spiders and smaller cones based on ONE-SIGNAL Method

LSI Tweeter Nonlin. Para Sp2

Tweeters with fs > 400 Hz at sensitive current sensor 2

LSI Headphone Nonlin. P. Sp2

Nonlinear parameters of headphones with fs < 300 Hz at sensitive current sensor 2

LSI Woofer Nonl. P. Sp1

Nonlinear parameters of woofers with fs < 300 Hz at standard current sensor 1

LSI Woofer Nonl.+Therm. Sp1

Nonlinear and thermal parameters of woofers with fs < 300 Hz at standard current sensor Sp1

LSI Woofer+Box Nonl. P Sp1

Nonlinear parameters of woofers operated in free air, sealed or vented enclosure with a resonance frequency fs < 300 Hz at standard current sensor Sp1

LSI Microspeaker Nonl. P. Sp2

Nonlinear parameters of microspeakers with fs > 300 Hz at sensitive current sensor 2

TRF Crest Harmonics (x,f)

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

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

DIS Compliance Asymmetry AN 15

Checking for asymmetries caused by compliance according Application Note AN 15

SIM closed box analysis

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

SIM Compression Out(In)

Output amplitude versus input amplitude at four frequencies using large signal parameters imported from LSI; Simulated results are comparable with DIS Compression Out(In).

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

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

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.