Transducer Nonlinearities (Curve Shape)
Characteristics: | KLIPPEL R&D System |
---|---|
Force factor Bl(x) versus displacement x | LSI3, PWT, SIM, AUR |
Mechanical compliance Cms(x) versus displacement x | LSI3, PWT, SIM, AUR, SPM, MSPM |
Mechanical stiffness Kms(x) versus displacement x | LSI3, PWT, SIM, AUR, SPM, MSPM |
Incremental stiffness Kinc(x) versus displacement x | LSI3, PWT |
Inductance L(x,i) versus displacement x and current i | LSI3, PWT, SIM, AUR |
Mechanical resistance Rms(v) versus velocity v | LSI3 |
Force-deflection curve F(x) | PPP, SPM, MSPM |
Nonlinearities inherent in the loudspeaker determine the large signal performance, such as the maximal output, signal distortion and stability. The nonlinearities can be represented by lumped elements having parameters which vary with the internal state signal (current, displacement, velocity, pressure) shown as red elements in the equivalent circuit below.
The IEC standard 62458 defines the dominant nonlinearities and static, quasi-static, incremental and full dynamic methods of measurements. Only the full dynamic measurement operates the transducer under normal operation conditions and is able to detect all relevant large signal parameters, such as force factor Bl(x), stiffness Kms(x), compliance Cmx(x), inductance L(x), Rms(v) versus displacement x, current i and voice coil velocity v.
The nonlinear parameters can be represented as a nonlinear curve, such as the instantaneous force factor value Bl(x) versus x, or as a power series expansion providing full information for numerical simulation and prediction within the loudspeaker design. Nonlinear parameters explain the generation of nonlinear distortion at high accuracy but are much easier to interpret than the result of a nonlinear distortion measurement.
Single-valued parameters are derived from the nonlinear characteristics. For example, the voice coil offset is a single-valued parameter derived from the symmetry point in the Bl(x) curve, expressed in mm. These values can be used for limit settings during the end-of-line testing and for the automatic control of the production process. Ultra-fast measurements and long-term monitoring of the loudspeaker nonlinearities can be accomplished using special test signals or ordinary audio signals.
KLIPPEL R&D SYSTEM (development)
Module | Comment |
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Large Signal Identification (LSI3)
| LSI3 measures the nonlinearities directly by using a nonlinear model adjusted adaptively to the device under test. A noise signal is used as stimulus, and the bandwidth is adjusted automatically to ensure the persistent excitation of the transducer. The permissible working range is automatically determined by using a protection system. An optional laser sensor may be used to check the orientation of the voice coil movement (coil in or out) and to calibrate the mechanical parameters. There are different versions of LSI3 dedicated to woofers, tweeters and loudspeaker systems (transducer mounted in enclosure). |
Programmable Post-Processing (PPP) | The PPP may be used to calculate the Force-deflection curve from the nonlinear stiffness curve coming from LSI3. There is a dedicated dB-Lab object template available. |
PWT also provides full identification of the woofer’s lumped parameters using an arbitrary stimulus (music). In contrast to the LSI, the voltage and the working range is determined by the user. | |
SPM measures the nonlinear stiffness and compliance of spiders, suspensions, drones and passive radiators. The user can specify the working range which is defined by the target displacement, and the SPM adjusts the stimulus automatically. | |
Micro Suspension Part Measurement (MSPM) | MSPM measures the moving mass, mechanical resistance as well as the nonlinear stiffness of micro suspension parts, usually used for micro speakers and headphones. The user can define the a working range which is defined by the target displacement, and the MSPM adjust the stimulus automatically. |
SIM requires the transducer nonlinearities as input to predict the large signal performance. A curve editor is provided to import the parameter from LSI or any other finite element design tool or to synthesize the curves manually. | |
SIM-AUR simulates the large signal performance of transducers and loudspeaker systems, and allows to auralize the nonlinear distortion. The parameters may either be imported from a LSI measurement or SIM simulation, or fictious driver parameters may be used. |
Templates of KLIPPEL products
Name of the Template | Application |
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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 |
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) |
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 |
Equivalent Input Dist. AN 20 | Equivalent input distortion according Application Note AN 20 |
Force - Deflection Curve | Using the results from LSI, the force -deflection curve is calculated. |
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 |
SIM closed box analysis | Maximal displacement, dc displacement, compression, SPL, distortion using large signal parameters imported from LSI BOX |
SIM vented box analysis | Maximal displacement, dc displacement, compression, SPL, harmonic distortion using large signal parameters imported from LSI BOX |
PWT 8 Woofers Param. ID Noise | Parameter identification of woofers using internal test signal (no cycling, no stepping) |
PWT Woofer Param. ID MUSIC | Parameter Identification of Woofers using external test signal (no ON/OFF cycling, no stepping) |
PWT Woofer param. ID NOISE | Parameter Identification of Woofers using internal test signal (no ON/OFF cycling, no stepping) |
AUR auralization | Real-time auralization of the large signal performance |
Application Notes
AN 1 Optimal Voice Coil Rest Position
AN 2 Separating Spider and Surround
AN 3 Adjusting the Mechanical Suspension
AN 5 Displacement Limits due to Driver Nonlinearities
AN 15 Checking for Compliance Asymmetry
AN 21 Reduce Distortion by Shifting Voice Coil
AN 24 Measuring Telecommunication Drivers
AN 26 Nonlinear Stiffness of Suspension Parts
Standards
Audio Engineering Society
AES2 Recommended practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement
International Electrotechnical Commission
IEC 60268-5 Sound System Equipment, Part 5: Loudspeakers
IEC 62458 Sound System Equipment – Electroacoustic Transducers - Measurement of Large Signal Parameters
IEC 62459 Sound System Equipment – Electroacoustic Transducers – Measurement of Suspension Parts
Other Related Tests
Typical Test Objects
Papers and Preprints
“Loudspeaker Nonlinearities. Causes, Parameters, Symptoms”
“Loudspeaker Nonlinearities. Causes, Parameters, Symptoms” (Know-How Poster)
“Assessing the Large Signal Performance of Loudspeakers”
“Large Signal Performance of Tweeters”
“Measurement of Large Signal Parameters”
W. Klippel, “Dynamic Measurement of Loudspeaker Suspension Parts,” J. of Audio Eng. Soc. 55, No. 6, pp. 443-459 (2007 June).
D. Clark, “Precision Measurement of Loudspeaker Parameters,“ J. of Audio Eng. Soc., Volume 45, pp. 129 – 140, (1997 March).
W. Klippel, “Measurement of Large-Signal Parameters of Electro-dynamic Transducer,” presented at the 107th Convention of the Audio Eng. Soc., New York, September 24-27, 1999, Preprint 5008.
M. Dodd, et al., “Voice Coil Impedance as a Function of Frequency and Displacement,” presented at the 117th Convention of the Audio Eng. Soc., 2004 October 28–31, San Francisco, CA, USA.
W. Klippel, et al. “Fast Measurement of Motor and Suspension Nonlinearities in Loudspeaker Manufacturing,” presented at the 127th Convention of the Audio Eng. Soc., 2009 October 9-12, New York, NY, USA.
R. H. Small, “Assessment of Nonlinearity in Loudspeakers Motors,” in IREECON Int. Convention Digest (1979 Aug.), pp. 78-80.
A. J. M. Kaizer, “Modeling of the Nonlinear Response of an Electrodynamic Loudspeaker by a Volterra Series Expansion,” J. of Audio Eng. Soc., Volume 35, pp. 421-433 (1987 June).
W. Klippel, “Dynamical Measurement of Non-Linear Parameters of Electro-dynamical Loudspeakers and their Interpretation”, J. of Audio Eng. Soc. 30 (12), pp. 944 - 955, (1990).
M. Knudsen, et al., “Determination of Loudspeaker Driver parameters Using a System Identification Technique,” J. of Audio Eng. Soc., Volume 37, No. 9.
W. Klippel, “Nonlinear Modeling of the Heat Transfer in Loudspeakers,” J. of Audio Eng. Soc. 52, Volume 1, 2004 January.