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Linear Parameter Measurement (LPM)

Features and Benefits

  • Identifies linear transducer model (Thiele / Small parameters)
  • Measures suspension creep
  • Single-step measurement with laser sensor
  • Two-step measurement with additional mass or test enclosure
  • Monitors signal to noise + distortion ratio (SNR+D) and noise floor
  • Automatic validity check
  • High reliability and reproducibility
  • Fast measurement

The Linear Parameter Measurement (LPM) module of the KLIPPEL Analyzer System is dedicated to identifying the electrical and mechanical small signal (Thiele/Small) parameters of electro-dynamical transducers with high accuracy. It is based on the electrical impedance by measuring the voltage and current at the speaker terminals. Enhanced by an optional laser displacement sensor, the identification does not require a second measurement and thus avoids common problems of the traditional two-step methods (e.g. added mass). An additional benefit of the displacement measurement is the identification the suspension creep parameters, resulting in better accuracy of the loudspeaker model at low frequencies. The LPM provides tools to identify and avoid typical problems such as poor signal to noise ratio and malfunction due to nonlinear effects of the driver or amplifier limiting.


KLIPPEL Analyzer 3

dB-Lab software

Power amplifier or KA3 Amplifier Card
Laser sensor (optional)
• PC
• It is recommended to use coating spray for micro-speakers and tweeters with transparent and shiny
  diaphragms. More information.

Added Mass Perturbation Technique

A second measurement is performed while a known mass Madd is added to the cone.

Simple technique
Mms is measured primarily

Cannot be applied to tweeter and microspeakers
Time consuming
Mechanical resistance or stiffness are assumed as frequency independent para

Test Box Perturbation Technique

A second measurement is performed while a known air stiffness Kair is added to the suspension.

Simple technique
Cms is measured primarily

Depends highly on precise value of effective radiation area Sd
Residual air volume (inside the transducer) cannot be considered
Requires sealed diaphragm
Cannot be used to measure mechanical mass without air load
Time consuming

Laser Technique

In addition to the voltage and current also the voice coil vibration (e.g. displacement) is measured by using an optical sensor.

Fast (one step technique)
Simple to use
BI is measured primarily
Most precise results
Can be applied to most transducers

Optical problems (angle, surface)
Coil displacement is not axial-symmetrical

Related Information

Other Modules of the R&D System
Large Signal Identification (LSI):
Linear Simulation (LSIM):
  Fast and comprehensive simulation of the linear transfer behavior of transducers and passive/active
  loudspeaker systems
Impedance Task (IMP):
  Linear Parameter Measurement (TS-Parameter)
T/S Parameter Laser Fitting (TSX) add-on for IMP:
  Thiele Small parameter identification with laser

Application Notes
AN 16 Multitone Distortion
AN 25 Maximizing LPM Accuracy

Literature and Papers
Fast and Accurate Linear Parameter Measurement


International Electrotechnical Commission
IEC 60268-5, IEC 60268-7, IEC 60268-22, IEC 62458, IEC 62459, IEC WD 63034

European Standards
BS EN 54-24

Audio Engineering Society

Institute of Electrical and Electronics Engineers
IEEE 269, IEEE 1206, IEEE 1329, IEEE 1652