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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)
Multipoint Measurement Tool (MMT)

Impedance Task (IMP)
T/S Parameter Laser Fitting (TSX)

Effective radiation area Sd

Scanning Vibrometer System (SCN)

 

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

Large Signal Identification (LSI Tweeter)
Large Signal Identification (LSI3)

 

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

Large Signal Identification (LSI Tweeter)
Large Signal Identification (LSI3)

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)

Rocking Mode Analysis (RMA)
Time Frequency Analysis (TFA)
Transfer Function Measurement (TRF PRO)

Air Leak Detection (ALD)
Equalization & Alignment (EQA)
Hi-2 Weighted Harmonic Distortion (Hi-2)
Meta Hearing Technology (MHT)
Sound Pressure Task (SPL)
Sound Pressure and Impedance Task (SPL-IMP)
Spectrogram 3 D Limits (3DL)

Air leakage noise localization
(position of modulated noise source)

 

Air Leak Stethoscope (ALS)

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

3D-Distortion Measurement (DIS)
Multi-Tone Measurement (MTON)
Scanning Vibrometer System (SCN)
Transfer Function Measurement (TRF)

Equalization & Alignment (EQA)
Spectrum Analysis (SAN)
Sound Pressure Task (SPL) 
Sound Pressure and Impedance Task (SPL-IMP)

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

Near Field Scanner (NFS)
3D-Polar Far-Field Measurement (POL)
Scanning Vibrometer System (SCN)
Transfer Function Measurement(TRF)

 

Sound power response

Near Field Scanner (NFS)
3D-Polar Far-Field Measurement (POL)
Scanning Vibrometer System (SCN)
Transfer Function Measurement (TRF)

 

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

Transfer Function Measurement (TRF)

Equalization & Alignment (EQA)
Spectrum Analysis (SAN) 
Sound Pressure Task (SPL) 
Sound Pressure and Impedance Task (SPL-IMP)

Group time delay response
(total, minimal phase)

Time Frequency Analysis (TFA)
Transfer Function Measurement (TRF)

 

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

Time Frequency Analysis (TFA)
Transfer Function Measurement (TRF)

Spectrogram 3 D Limits (3DL)

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

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

Equalization & Alignment (EQA)
Hi-2 Weighted Harmonic Distortion (Hi-2) 
Sound Pressure Task (SPL) 
Sound Pressure and Impedance Task (SPL-IMP)

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)

EAR

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

3D-Distortion Measurement (DIS)
Multi-Tone Measurement (MTON)

 

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

3D-Distortion Measurement (DIS)
Live Audio Analyzer (LAA)
Large Signal Identification (LSI)
Large Signal Identification (LSI3)
Multi-Tone Measurements (MTON)
Rocking Mode Analysis (RMA)
Transfer Function Measurement (TRF)

Dynamic Excursion Check and Control (DCX)
Motor + Suspension Check (MSC) 
T/S Parameter Laser Fitting (TSX)

Multi-tone distortion

Live Audio Analyzer (LAA)
Linear Parameter Measurement (LPM)
Multi-Tone Measurement (MTON)

 

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

Live Audio Analyzer (LAA)
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)
Live Audio Analyzer (LAA)
Large Signal Identification (LSI)
Power Testing (PWT)

 

Auralization

Live Audio Analyzer (LAA)
Simulation-Auralization (SIM-AUR)

Spectrum Analysis (SAN)
Sound Pressure Task (SPL) 
Sound Pressure and Impedance Task (SPL-IMP)

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)

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

 

3D (scanning geometry)

Scanning Vibrometer System (SCN)

 

Accumulated acceleration level (AAL)

Higher Modal Analysis (HMA)
Scanning Vibrometer System (SCN)

 

Decomposition into radial and circumferential mode

Scanning Vibrometer System (SCN)
Rocking Mode Analysis (RMA)

 

Rocking mode analysis

Scanning Vibrometer System (SCN)
Rocking Mode Analysis (RMA)