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Voice coil temperature

Characteristics:

KLIPPEL R&D System

Variation of dc resistance Re versus time

 LSI, PWT

Increase of voice coil temperature ΔTv

 LSI, PWT, DIS

Heating and cooling curves

 LSI, PWT

The voice coil temperature can be monitored without using an additional sensor by measuring the dc resistance and considering the material properties of the voice coil. The dc resistance corresponds with the electrical impedance at very low frequencies. An additional pilot tone (1 – 4 Hz) has to be added to the stimulus (test signal or audio signal) to ensure a reliable measurement of the dc resistance which is not affected by the motional impedance and inductance of the coil. The short thermal time constants in small transducers (microspeaker, tweeter) require a fast method and dedicated signal processing to measure the dc resistance as fast as possible. 

KLIPPEL R&D SYSTEM (development)

Module

Comment

Large Signal Identification (LSI Woofer, LSI Tweeter, LSI Box)

LSI measures the dc resistance of the cold transducer in a special mode of the large identification process. A dc stimulus is generated by rectification of the ac signal at the power amplifier output using a diode in the DA hardware. This value of the initial dc resistance is used as a reference for calculating the increase of the temperature during the following measurement.  

Power Test (PWT)

PWT adds a pilot tone of 1 - 4 Hz of low amplitude to the excitation signal generated by the internal generator or to the external audio signal. Thus, the temperature can also be measured during an off-cycle when no regular stimulus is supplied to speaker. The power test provides an ultra-fast sampling of the voice coil temperature (100 ms) to measure the temperature variation at high temporal resolution.

3D Distortion Module (DIS)

DIS provides a special measurement (pilot tone at 130 Hz) which estimates the voice coil temperature at sufficient accuracy to protect the transducer under test.

Example:

Increase of voice coil temperature Tv and input power PRE dissipated in resistance RE versus measurement time during power testing using different kinds of music signals as stimulus.
Increase of voice coil temperature Tv and input power PRE dissipated in resistance RE versus measurement time during power testing using different kinds of music signals as stimulus.

Templates of KLIPPEL products

Name of the Template

Application

Thermal Parameters (woofer)

Analysis of heat transfer in woofers based on identified thermal woofer parameters

Thermal Parameters AN 18

Thermal Parameters measured by using PWT module according Application Note 18

Thermal Parameters AN 19

Thermal Parameters measured by using PWT module according Application Note 19

LSI Woofer Nonl.+Therm. Sp1

Nonlinear and thermal parameters of woofers with fs < 300 Hz at standard current sensor Sp1

LSI Woofer+Box Nonl. P Sp1

Nonlinear parameters of woofers operated in free air, sealed or vented enclosure with a resonance frequency fs < 300 Hz at standard current sensor Sp1

DIS Compression Out(in)

Output amplitude versus input amplitude at four frequencies

DIS Harmonics vs. Voltage

Harmonic distortion measurement versus amplitude

DIS SPL, Harm protected

Harmonic distortion measurement with protection

SIM Compression Out(In)

Output amplitude versus input amplitude at four frequencies using large signal parameters imported from LSI; Simulated results are comparable with DIS Compression Out(In).

SIM Therm. Analysis (1 tone)

Heat transfer based on thermal parameters imported from LSI using a single-tone stimulus

SIM Therm. Analysis (2 tone)

Heat transfer based on thermal parameters imported from LSI using a two-tone stimulus

PWT 8 Woofers Param. ID Noise

Parameter identification of woofers using internal test signal (no cycling, no stepping)

PWT EIA accelerated life test

Accelerated life testing according EIA 426 B A. 4 using any external signal to monitor temperature, power and resistance

PWT IEC Long term Voltage

Power test to determine long-term maximal voltage according IEC 60268-5 paragraph 17.3 without parameter measurement for one device monitoring voltage, resistance, temperature and power

PWT IEC Short term Voltage

Power test to determine short term maximal voltage according IEC 60268-5 paragraph 17.2 without parameter measurement applied to 1 DUT monitoring temperature, power and resistance

PWT Powtest (fast Temp.)

Power test for fast monitoring of temperature, power and resistance without parameter measurement using external continuous signal (noise) supplied to IN1

PWT Powtest EXT. GENER.

Power test for monitoring temperature, power and resistance using external continuous signal (noise) supplied to IN1

PWT Powtest LIMITS

Power test to find maximal input voltage, power and temperature limits without parameter measurement applied to 1 DUT

PWT Powtest MUSIC

Power test without parameter measurement monitoring temperature, power, voltage and resistance using any external signal

PWT Powtest SWEEP

Power test for measuring the thermal time constant of the voice coil using sweep signal with low crest factor

PWT Powtest TIME Const.

Power test for measuring time constant of voice coil using internal test signal with cycling (ON/OFF phase)

PWT Woofer Param. ID MUSIC

Parameter Identification of Woofers

using external test signal (no ON/OFF cycling, no stepping)

PWT Woofer param. ID NOISE

Parameter Identification of Woofers

using internal test signal (no ON/OFF cycling, no stepping)

Standards:

  • IEC Standard IEC 60268-5 Sound System Equipment, Part 5: Loudspeakers
  • AES2-1984 AES Recommended practice Specification of Loudspeaker Components Used in Professional Audio and Sound Reinforcement
  • CEA CEA-426-B Loudspeakers, Optimum Amplifier Power
  • EIA 426B Loudspeaker Power Rating Test CD provided by ALMA International


Papers and Preprints:

Y. Shen, “Accelerated Power Test Analysis Based on Loudspeaker Life Distribution,” presented at the 124th Convention of Audio Eng. Soc., May 2008, Preprint 7345.

W. Klippel, “Nonlinear Modeling of the Heat Transfer in Loudspeakers,” J. of Audio Eng. Soc. 52, Volume 1, 2004 January.

C. Zuccatti, “Thermal Parameters and Power Ratings of Loudspeakers,” J. of Audio Eng. Soc., Volume 38, No. 1, 2, 1990 January/February.

K. M. Pedersen, “Thermal Overload Protection of High Frequency Loudspeakers,” Report of Final Year Dissertation at Salford University.

Henricksen, “Heat Transfer Mechanisms in Loudspeakers: Analysis, Measurement and Design,” J. of Audio Eng. Soc., Volume 35, No. 10, 1987 October.