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Passive Loudspeaker Systems

Examples


  • Drive units with crossover in enclosure

Applications

 

 

  • Home
  • Automotive
  • Multimedia and Professional

Particularities

Passive loudspeaker systems use an external power amplifier and are usually operated over the entire audio band. The transfer behavior of each drive unit (woofer, midrange, tweeter) can be described by an equivalent network model using lumped elements which are valid at the corresponding resonance frequency. 
The linear, nonlinear and thermal parameters of the model can be measured by using a new identification technique monitoring voltage and current at the loudspeaker terminals only. In addition to the mechanical and electrical parameters of drive units (see tweeter, woofer), there are a few acoustical parameters describing the port resonance of a vented enclosure, nonlinear resistance of the air in the port and the ratio of the air and suspension compliances. 
Small leakages in the enclosure which do not affect the electrical input impedance may cause audible air noise. This can be detected more reliably by using a sensitive noise demodulation technique. Parasitic vibration of the grill, handle or any other part of the enclosure may cause impulsive distortion similar to the irregular Rub & Buzz defects found in the drive unit. 
The sound pressure response on-axis and off-axis, sound power response and other directivity characteristics can be measured in the near field under arbitrary conditions or in the far field under anechoic condition. The acoustical characteristics can also be predicted by FEA and BEA using the mechanical distributed parameters of the loudspeaker drive units measured by a laser scanning technique and the geometry of the enclosure. 
Thermal model and the parameters valid for a single drive unit measured in free air may describe approximately the coil temperature and the cooling process in vented box systems. If the drive unit is mounted in a sealed enclosure, the thermal resistance Rtm describing the heat transfer between magnet and ambience is much higher than in free air.


Design Challenges

  • Optimal selection of drive units (woofer, tweeter)
  • Optimal design of the vented enclosure (alignment, port noise)
  • Crossover design and time alignment
  • Thermal power handling

Most Important Characteristics

  • SPL frequency response (1 m, 1 W on-axis)
  • Mean SPL in a effective frequency range (1m, 1W on-axis)
  • Long-term maximal input power
  • Maximal short-term sound pressure level (SPL) in stated frequency band (1s, 1m, on-axis)
  • Maximal long-term SPL in stated frequency band (1 min, 1m, on-axis)
  • Impedance curve (rated impedance)
  • Total harmonic distortion
  • Intermodulation distortion
  • Impulsive distortion (Rub & Buzz) at maximal short-term SPL in stated band
  • Sound power response or directivity index

Critical Issues

  • Rub & Buzz, loose partials in the drive unit
  • Parasitic vibration of the grill
  • Air leakage noise
  • Hard limiting of the suspension (large values of weighted harmonics HI-2 distortion)
  • Excessive modulation distortion (motor instability, Bl(x) and L(x) asymmetries)
  • Acoustical cancellation effects (negative directivity index)


Standards

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

Consumer Electronics Association
CEA-2034 Standard Method of Measurement for In-Home Loudspeakers

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)

Multi-Tone Distortion Task (MTD)

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)

 

Input voltage (rated noise voltage, short-term maximum voltage, long-term maximum power)

Live Audio Analyzer (LAA)
Multi-Tone Measurement (MTON)
Power Testing (PWT)

Multi-Tone Distortion Task (MTD)
Input power (rated noise voltage, short-term maximum voltage, long-term maximum power)Live Audio Analyzer (LAA) 
Multi-Tone Measurement (MTON)
Power Testing (PWT)
Multi-Tone Distortion Task (MTD)

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)

Multi-Tone Distortion Task (MTD)

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)

Multi-Tone Distortion Task (MTD)

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)

Multi-Tone Distortion Task (MTD)

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)

 

Rated noise powerLive Audio Analyzer (LAA)
Multi-Tone Measurement (MTON)
Power Testing (PWT)
Multi-Tone Distortion Task (MTD)

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)