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Voice coil displacement

Characteristics:

KLIPPEL R&D SystemQC Standard
Transfer-function Hx(f)=X(f)/U(f) between voltage and displacementLPM, TRF, SCN
Linear parameters (Thiele-Small)LSI, LPM, PWT,SCN, SPM

QC Standard, MSC

Nonlinear parameters

LSI, SPM,PWT, DAMSC
Peak, rms and dc displacement

TRF, DIS, LPM, LSI, PWT, SPMDA

MSC
Rub & Buzz analysisTRF PRO

The direct measurement of the mechanical vibration by using a touch-less sensor is very important for designing, assessing and selecting transducers which are optimal in the final application. The measurement of the displacement by using laser triangulation sensor gives more relevant information than measuring velocity or acceleration. The dominant transducer nonlinearities limit the maximal peak displacement Xmax of the voice coil which is one of the most important single-valued characteristics describing the large signal performance and the maximal acoustical output at low frequencies. An asymmetrical shape of the loudspeaker nonlinearities generates a dc component in the voice coil displacement which cannot be detected in the differentiated signals (velocity, acceleration, sound pressure).

The figure above shows the amplitude of the voice coil displacement versus frequency. Below the resonance frequency, the nonlinearities of the transducer, such as the force factor Bl(x) and stiffness Kms(x), decrease the fundamental component below the value predicted by a linear model. The nonlinear compression can be measured by a laser sensor or predicted by using a large signal model and identified nonlinear parameters (SIM).
The figure above shows the amplitude of the voice coil displacement versus frequency. Below the resonance frequency, the nonlinearities of the transducer, such as the force factor Bl(x) and stiffness Kms(x), decrease the fundamental component below the va

KLIPPEL R&D SYSTEM (development)

Module

Comment

Transfer Function Module (TRF)

TRF measures the displacement transfer function Hx(f) at higher frequencies with sufficient SNR by using a shaped stimulus (emphasis by 10 dB/octave to higher frequencies).

Linear Parameter Measurement (LPM)

LPM measures the displacement of the voice coil by using a multi-tone signal which gives the best SNR and generates a minimum of nonlinear distortion. This is important for a reliable measurement of the Thiele-Small parameter without perturbation technique.    

3D Distortion Module (DIS)

DIS module measures peak, bottom, rms value and dc components via frequency and input voltage.

Scanning Vibrometer (SCN)

SCN provides the mean value of the voice coil displacement averaged over the circumference of the voice coil.

KLIPPEL QC SYSTEM (end-of-line testing)

Module

Comment

MSCMSC task predicts the voice coil displacement based on the measured voltage and current signal using an imported Bl(x=0).

Example:

The figure above shows the positive and negative peak of the voice coil displacement for a terminal voltage which is increased in equal steps. For a sinusoidal stimulus of 10 Volts below the resonance frequency (fs= 50 Hz) the fundamental component is under compression and the displacement is 8 dB below the linearly predicted value. Above resonance asymmetries in the loudspeaker generate a dc component which shifts the voice coil by 2 mm to the negative side.
The figure above shows the positive and negative peak of the voice coil displacement for a terminal voltage which is increased in equal steps. For a sinusoidal stimulus of 10 Volts below the resonance frequency (fs= 50 Hz) the fundamental component is und

Templates of KLIPPEL products

Name of the Template

Application

DIS X Fundamental, DC

Fundamental and DC component of displacement

TRF H(f)= X/voltage

Transfer function H(f)= displacement(f) / voltage(f)

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

DIS Motor stability

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

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

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 Motor Stability

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

SIM vented box analysis

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

SIM X Fundamental, DC

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

AUR auralization

Real-time auralization of the large signal performance

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:

  • AES2-1984 AES Recommended practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement



Papers and Preprints:

W. Klippel, et al., “Distributed Mechanical Parameters of Loudspeakers Part 1: Measurement,” J. of Audio Eng. Soc. 57, No. 9, pp. 500-511 (2009 Sept.).

W. Klippel, et al., “Distributed Mechanical Parameters of Loudspeakers Part 2: Diagnostics,” J. of Audio Eng. Soc. 57, No. 9, pp. 696-708 (2009 Sept.).

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

R. H. Small, “Closed-Box Loudspeaker Systems, Part I: Analysis,” J. Audio Eng. Soc., Volume 20, pp. 798 – 808 (1972 Dec.).