Linear Parameter Measurement (LPM)

• 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.

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

Advantages
Simple technique
M_ms is measured primarily

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

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

Advantages
Simple technique
Cms is measured primarily

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

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

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

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