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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.
- 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)
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
IEC62458 Sound System Equipment – Electroacoustic Transducers - Measurement of Large Signal Parameters