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Low-frequency drive units

Examples

 

 

Low-frequency drive unit
  • Woofer
  • Subwoofer

Application

 

 

  • Home
  • Automotive
  • Multimedia and professional

Particularities

Low frequency drive units are operated below and above the fundamental resonance frequency (usually below 500 Hz) by using a crossover with a low-pass characteristic. Most low frequency drive units contain a moving coil assembly using an electro-dynamical motor principle. 
The electrical, mechanical and thermal behavior of the drive unit at fundamental resonance frequencies can be described by 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 and circumferential modes
  • Intermodulation distortion caused by Le(x) and Bl(x)


Standards

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
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))

Large Signal Identification (LSI)
Large Signal Identification (LSI3)
Power Testing (PWT)

 

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

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

Motor + Suspension Check (MSC)

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

Large Signal Identification (LSI)
Power Testing (PWT)

 

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

3D Distortion Measurement (DIS Pro)
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)
Spectrogram 3D Limits (3DL)
Sound Pressure Task (SPL)
Sound Pressure and Impedance Task (SPL-IMP) 

Localization of irregular defects

 

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

 

Sound power response

Near Field Scanner (NFS)
Polar Far-Field Measurement (POL)  
Scanning Vibrometer System (SCN)

 

Phase response
(minimal-phase, excess-phase)

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)

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

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

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

Spectrogram 3D 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
(difference-tone and sum-tone IMD)

3D-Distortion Measurement (DIS)

 

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

3D-Distortion Measurement (DIS PRO)

EAR

Sinusoidal burst measurement

Tone Burst Measurement (TBM)
Transfer Function Measurement (TRF)

Sound Pressure Task (SPL)

Thermal and nonlinear compression
(fundamental, harmonics 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 Measurement (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)

HI-2 distortion

3D-Distortion Measurement (DIS Pro)

Hi-2 Weighted Harmonic Distortion (Hi-2)

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)

 

Voice coil temperature

3D-Distortion Measurement (DIS)
Live Audio Analyzer (LAA)
Large Signal Identification (LSI)
Large Signal Identification (LSI3)
Power Testing (PWT)

 

Distortion in reproduced audio signal
(contribution of Bl(x), Cms(x), Le(x), Le(i))

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

 

Auralization

Simulation-Auralization (SIM-AUR)

Spectrum Analysis (SAN) 
Sound Pressure Task (SPL)

3D-geometry scanning

Scanning Vibrometer System (SCN)

 

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

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

 

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

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

 

Accumulated acceleration level (AAL)

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

 

Decomposition into radial and circumferential mode 

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

 

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

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