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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:

  • IEC Standard IEC 60268-5 Sound System Equipment, Part 5: Loudspeakers
  • IEC Standard IEC62458 Sound System Equipment – Electroacoustic Transducers - Measurement of Large Signal Parameters
  • AES2-1984 AES Recommended practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement
  • AES56-2008 AES standard on acoustics – Sound source modeling – Loudspeaker polar radiation measurement
  • 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

Motor + Suspension Check (MSC)

Nonlinear parameters

Large Signal Identification (LSI Box)

Power Test (PWT)

Motor + Suspension Check (MSC)

Electrical impedance

Linear Parameter Measurement (LPM)

Impedance task

Thermal parameters

Large Signal Identification (LSI Box)

Power Test (PWT)

 

Rub & Buzz and other irregular defects

Transfer Function Module (TRF PRO)

Standard, Programmable System

Meta-Hearing-Technology

Leak Detection Module

Air Leakage Localization Module

On-axis SPL amplitude response

(sensitivity, mean SPL, effective frequency range )

Transfer Function Module (TRF)

3D-Distortion Module (DIS)

Scanning Vibrometer Analysis Software (SCN)

Basic, Standard, Programmable System

Group time delay response

(total, minimal phase)

Transfer Function Module (TRF)

System task in Standard System

Phase response

(minimal-phase, excess-phase)

Transfer Function Module (TRF)

System task in Standard System

Directional characteristics

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

Scanning Vibrometer (SCN)

3D-Polar Radiation Measurement (POL)

Transfer Function Module (TRF)

 

Sound power response

Scanning Vibrometer (SCN)

3D-Polar Radiation Measurement (POL)

Transfer Function Module (TRF)

 

Input voltage

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

Power Test (PWT)

 

Input power

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

Power Test (PWT)

 

Nonlinear harmonic distortion

(THD, components)

Transfer Function Module (TRF)

3D-Distortion Module (DIS)

Basic, Standard, Programmable System

Intermodulation distortion (IMD)

3D-Distortion Module (DIS)

 

Amplitude intermodulation distortion (AMD)

(modulation of the fundamental)

3D-Distortion Module (DIS PRO)

 

Thermal and nonlinear compression

(fundamental, harmonics)

3D-Distortion Module (DIS)

 

Peak displacement

DC displacement

3D-Distortion Module (DIS)

Transfer Function Module (TRF)

Large Signal Identification (LSI)

 

Sinusoidal burst measurement

Transfer Function Module (TRF)

 

HI-2 distortion

3D-Distortion Module (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 Module (TRF)

 

Accelerated life test, power test

(durability, parameter variation)

Large Signal Identification (LSI BOX)

Power Test (PWT)

 

Coil temperature

3D-Distortion Module (DIS)

Large Signal Identification (LSI BOX)

Power Test (PWT)

 

Rated noise power

Power Test (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 Test (PWT)

 

Distributed mechanical parameters

(cone vibration, geometry)

Scanning Vibrometer (SCN)

 

Accumulated acceleration level (AAL)

Scanning Vibrometer (SCN)

 

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

Scanning Vibrometer (SCN)

 

Radiation analysis

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

Scanning Vibrometer (SCN)

3D-Polar Radiation Measurement (POL)

 

Auralization

Auralization Module (AUR)