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High-frequency Drive Units

Examples

 

 

  • Tweeter
  • Horn compression driver

Applications

 

 

  • Home
  • Automotive
  • Multimedia and Professional

Particularities

High-frequency loudspeaker drive units are operated at higher frequencies by using a highpass of a crossover system. Most of the transducers use a moving-coil assembly based on the electro-dynamical transduction principle. At the resonance frequency (about 1 kHz) the radiator (soft or hard dome, diaphragm, membrane) vibrates as a rigid body, and the transfer behavior of the drive unit can be modeled by an 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 maximal acoustical output is limited by the heating of the coil, regular nonlinearities and irregular defects, such as Rub & Buzz.
Thermal parameters describe the heating of the coil, the heat transfer to the pole tips, magnet and ambience considering conduction and radiation. The dominant nonlinearities are the stiffness Kms(x) or compliance Cms(x) depending on the voice coil displacement x and the resistance Rms(v) varying with velocity v. 
This drive unit is usually operated at higher frequencies where bending waves and longitudinal waves are generated on the radiator. Distributed parameters are required to describe the vibration and radiation behavior and can be measured by laser scanning techniques. Modal analysis and other decomposition techniques reveal the modal density, loss factor of the material and radiation problems.


Critical Issues

  • Flat SPL response on-axis and off-axis in the far field
  • Maximal peak displacement limited by suspension nonlinearities
  • Heating of the coil and thermal power handling
  • Rocking modes causing voice coil rubbing
  • High local displacement on particular points on the diaphragm causing nonlinear distortion

Standards

Audio Engineering Society
AES2 Recommended practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement
AES56 Standard on acoustics – Sound source modelling – Loudspeaker polar radiation measurement

International Electrotechnical Commission
IEC 60268-5 Sound System Equipment, Part 5: Loudspeakers
IEC 62458 Sound System Equipment – Electroacoustic Transducers - Measurement of Large Signal Parameters


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 (IMP)
Motor + Suspension Check (MSC)

Effective radiation area Sd

Scanning Vibrometer System (SCN)
Transfer Function Measurement (TRF)

 

Loudspeaker nonlinearities
(Bl(x), Kms(x), L(x) , L(i), Rms(v))

Large Signal Identification (LSI Tweeter)

 

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

Motor + Suspension Check (MSC)

Thermal parameters
(resistances, time constant, capacities, air convection cooling)

Large Signal Identification (LSI Tweeter)
Power Testing (PWT)

 

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

Transfer Function Measurement (TRF PRO)
Rocking Mode Analysis (RMA)

Standard System
Meta Hearing Technology (MHT)
Air Leak Detection (ALD)

Air leakage noise localization
(position of modulated noise source)

 

Air Leak Detection (ALD)

On-axis sound pressure amplitude response
(sensitivity, mean SPL, effective frequency range)

Transfer Function Measurement (TRF)
3D-Distortion Measurement (DIS)
Scanning Vibrometer System (SCN)
Rocking Mode Analysis (RMA)
Higher Modal Analysis (HMA)

Basic System
Standard System

Directional characteristics
(directivity index, coverage angle, radiation angle, polar radiation measurement)

Scanning Vibrometer System (SCN)
3D-Polar Far-Field Measurement (POL)
Transfer Function Measurement(TRF)
Higher Modal Analysis (HMA)

 

Sound power response

Scanning Vibrometer System (SCN)
3D-Polar Far-Field Measurement (POL)
Transfer Function Measurement (TRF)
Higher Modal Analysis (HMA)

 

Phase response
(minimal-phase, excess-phase, polarity)

Transfer Function Measurement (TRF)

Basic System
Standard System

Group time delay response
(total, minimal phase)

Transfer Function Measurement (TRF)

Sound Pressure Task (SPL)
Sound Pressure and Impedance Task (SPL-IMP)

Time-frequency analysis (Wigner, cumulative decay spectrum, sonagraph, wavelet, …)

Transfer Function Measurement (TRF)

 

Nonlinear harmonic distortion
(THD, THD+N, components)

Transfer Function Measurement (TRF)
3D-Distortion Measurement (DIS)

Standard System

Equivalent harmonic input distortion

Transfer Function Measurement (TRF)

 

Intermodulation distortion (IMD)

3D-Distortion Measurement (DIS)

 

Amplitude intermodulation distortion (AMD)
(modulation of the fundamental)

3D-Distortion Measurement (DIS PRO)

 

Thermal and nonlinear compression
(fundamental, harmonics, dc displacement versus voltage)

3D-Distortion Measurement (DIS)

 

Voice coil displacement
(peak, bottom, dc component, Xmax)

3D-Distortion Measurement (DIS)
Transfer Function Measurement (TRF)
Large Signal Identification (LSI)
Rocking Mode Analysis (RMA)

 

Multi-tone distortion

Linear Parameter Measurement (LPM)
Multi-Tone Measurement (MTON)

 

Accelerated life test, power test
(durability, parameter variation, maximal input power)

Large Signal Identification (LSI)
Power Testing (PWT)

 

Coil temperature

3D-Distortion Measurement (DIS)
Large Signal Identification (LSI)
Power Testing (PWT)

 

Distortion generated by dominant nonlinearities

Bl(x), Cms(x), Le(x), Rms(v) in reproduced audio signal

Simulation-Auralization (SIM-AUR)
Large Signal Identification (LSI)
Power Testing (PWT)

 

Auralization

Simulation-Auralization (SIM-AUR)

 

Distributed mechanical parameters
(mechanical vibration scanned on radiator's surface )

Scanning Vibrometer System (SCN)
Rocking Mode Analysis (RMA)
Higher Modal Analysis (HMA)

 

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

Scanning Vibrometer System (SCN)
Rocking Mode Analysis (RMA)
Higher Modal Analysis (HMA)

 

Shape of the surface (scanning geometry)

Scanning Vibrometer System (SCN)

 

Accumulated acceleration level (AAL)

Scanning Vibrometer (SCN)
Rocking Mode Analysis (RMA)
Higher Modal Analysis (HMA)

 

Decomposition into radial and circumferential mode
(indicating rocking mode)

Scanning Vibrometer System (SCN)

 

3D-geometry scanning

Scanning Vibrometer System (SCN)

 

Rocking mode analysisScanning Vibrometer System (SCN)
Higher Modal Analysis (HMA)