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Mechanical Actuators

Low-frequency drive unit

Examples:

shaker, exciter

Applications:

home, automotive, multimedia and professional

 

Particularities:

 

Mechanical actuators convert the electrical input signal into a mechanical excitation force and may be used in combination with a separate radiator (e.g. panel) in distributed mode loudspeakers and active control application for noise and vibration cancellation. These transducers are operated below and above the fundamental resonance frequency (usually below 500 Hz) using inertial drive technology. Most actuators contain a moving coil assembly based on electro-dynamical motor principle. The electrical, mechanical and thermal behavior of the drive unit at fundamental resonance frequencies can be described by the equivalent network comprising lumped elements with linear and nonlinear parameters. The linear parameters comprise the Thiele-Small parameters, visco-elastic parameters (creep factor) and electrical parameters describing the lossy inductance at higher frequencies. The dominant nonlinearities are the force factor Bl(x), stiffness Kms(x) or compliance Cms(x) and inductance L(x) versus displacement x and the inductance L(i) varying with the input current i. Thermal parameters describe the heating of the coil, the heat transfer to the pole tips, magnet and ambience considering conduction, radiation and convection cooling.

 

Critical issues:

  • Maximal peak displacement
  • High dc displacement (coil is shifted out of the gap)
  • Motor instability (bifurcation, jumping effect)
  • Thermal power handling
  • Rocking modes
  • Intermodulation distortion caused by Le(x) and Bl(x)

 

Standards:

  • IEC Standard IEC 60268-5 Sound System Equipment, Part 5: Loudspeakers
  • IEC Standard IEC62458 Sound System Equipment – Electroacoustic Transducers - Measurement of Large Signal Parameters
  • AES2-1984 AES Recommended practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement

 

 

Most relevant Measurements 

Modules of R&D SYSTEM

Modules of QC SYSTEM

Linear lumped parameters

(resonance frequency, Q-factors, Thiele/Small, creep, inductance)

Linear Parameter Measurement (LPM)

Impedance task

Motor + Suspension Check (MSC)

Linear lumped parameters

(resonance frequency, Q-factors, Thiele/Small, creep, inductance)

Linear Parameter Measurement (LPM)

Impedance task

Motor + Suspension Check (MSC)

Loudspeaker nonlinearities

(Bl(x), Kms(x), L(x) , L(i))

Large Signal Identification (LSI)

Power Test (PWT)

 

Single-valued nonlinear parameters
(Xmax , XBl , XC , Voice coil offset Xoffset , Suspension asymmetry AKms)

 

Motor + Suspension Check (MSC)

Thermal parameters

(thermal resistances, time constants, capacities, air convection parameter)

Large Signal Identification (LSI)

Power Test (PWT)

 

Irregular loudspeaker defects

(Rub & Buzz, loose particles, wire beat, bottoming, air leakage noise)

Transfer Function Module (TRF PRO)

Standard, Programmable System

Meta-Hearing-Technology

Leak Detection Module

 

Air leakage noise localization

(position of modulated noise source)

 

Air Leakage Localization Module

Sound power response

Scanning Vibrometer (SCN)

3D-Polar Radiation Measurement (POL)

Transfer Function Module (TRF)

 

Phase response

(minimal-phase, excess-phase)

Transfer Function Module (TRF)

 

Group time delay response

(total, minimal phase)

Transfer Function Module (TRF)

System task in Standard System

Time-frequency analysis

(Wigner, cumulative decay spectrum, sonagraph, wavelet, …)

Transfer Function Module (TRF)

 

Nonlinear harmonic distortion

(THD, THD+N, components)

Transfer Function Module (TRF)

3D-Distortion Module (DIS)

Basic, Standard, Programmable System

Equivalent Harmonic Input Distortion

Transfer Function Module (TRF)

 

Intermodulation distortion

(difference-tone and sum-tone IMD)

3D-Distortion Module (DIS)

 

Amplitude intermodulation distortion (AMD)

(modulation of the fundamental)

3D-Distortion Module (DIS PRO)

 

Sinusoidal burst measurement

Transfer Function Module (TRF)

 

Thermal and nonlinear compression

(fundamental, harmonics versus voltage)

3D-Distortion Module (DIS)

 

Voice coil displacement

(peak, bottom, dc component, Xmax)

3D-Distortion Module (DIS)

Transfer Function Module (TRF)

Large Signal Identification (LSI)

 

HI-2 distortion

3D-Distortion Module (DIS)

 

Multi-tone distortion

Linear Parameter Measurement (LPM)

Multi-tone task in Standard System

Accelerated life test, power test

(durability, parameter variation, maximal input power)

Large Signal Identification (LSI)

Power Test (PWT)

 

Voice coil temperature

3D-Distortion Module (DIS)

Large Signal Identification (LSI)

Power Test (PWT)

 

Distortion in reproduced audio signal

(contribution of Bl(x), Cms(x), Le(x), Le(i))

Auralization Module (AUR)

Large Signal Identification (LSI)

Power Test (PWT)

 

Auralization

Auralization Module (AUR)

 

Distributed mechanical parameters

(mechanical vibration scanned on radiator's surface)

Scanning Vibrometer (SCN)

 

Modal analysis

(natural frequencies, shape of modal vibration, modal loss factor)

Scanning Vibrometer (SCN)

 

Accumulated acceleration level (AAL)

Scanning Vibrometer (SCN)

 

Decomposition into radial and circumferential mode (indicating rocking mode)

Scanning Vibrometer (SCN)