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

International Electrotechnical Commission
CEA-2034 Standard Method of Measurement for In-Home Loudspeakers


Most relevant Measurements 

Modules of R&D SYSTEM

Modules of QC SYSTEM

Linear transducer parameters
(resonance frequency, Q factors, T/S, creep, inductance, tuning resonance and quality factor of the port)

Linear Parameter Measurement (LPM)
Large Signal Identification (LSI Box)

Impedance Task (IMP)
Motor + Suspension Check (MSC)

Nonlinear parameters

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

Motor + Suspension Check (MSC)

Electrical impedance

Linear Parameter Measurement (LPM)

Impedance Task (IMP)

Thermal parameters

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

 

Rub & Buzz and other irregular defects

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

Standard, Programmable System
Meta Hearing Technology (MHT)
Air Leak Detection (ALD)
Air Leakage Localization Module

On-axis SPL 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, Standard, Programmable System

Group time delay response
(total, minimal phase)

Transfer Function Measurement (TRF)

System task in Standard System

Phase response
(minimal-phase, excess-phase)

Transfer Function Measurement (TRF)

System task in 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)

 

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

Power Testing (PWT)

 

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

Power Testing  (PWT)

 

Nonlinear harmonic distortion
(THD, components)

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

Basic, Standard, Programmable System

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)

3D-Distortion Measurement (DIS)

 

Peak displacement
DC displacement

3D-Distortion Measurement (DIS)
Transfer Function Measurement (TRF)
Large Signal Identification (LSI)

 

Sinusoidal burst measurement

Transfer Function Measurement (TRF)

 

HI-2 distortion

3D-Distortion Measurement (DIS)

 

Multi-tone distortion

Linear Parameter Measurement (LPM)

Multi-tone task in Standard System

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

Transfer Function Measurement (TRF)

 

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

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

 

Coil temperature

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

 

Rated noise power

Power Testing (PWT)

 

Distortion generated by dominant nonlinearities
Bl(x), Cms(x), Le(x), Le(i) in reproduced audio signal

Auralization Module (AUR)
Large Signal Identification (LSI)
Power Testing (PWT)

 

Distributed mechanical parameters
(cone vibration, geometry)

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

 

Accumulated acceleration level (AAL)

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

 

Modal analysis and decomposition techniques to find
circumferential, radial components and rocking modes

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

 

Radiation analysis (sound pressure on-axis and off-axis, directivity index, sound power response)

Scanning Vibrometer System (SCN)
3D-Polar Far-Field Measurement (POL)

 

Auralization

Auralization Module (AUR)

 

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