Compression of Fundamental Components
Characteristics: | KLIPPEL R&D System |
|---|---|
Output amplitude versus input amplitude | DIS, SIM, MTON, TBM |
Thermal power compression | DIS, SIM, LSI3, PWT, MTON |
Nonlinear amplitude compression | DIS, SIM, MTON, TBM |
The SPL response of the fundamental component at high amplitudes differs from the response predicted by a linear model based on Thiele/Small parameters. The amplitude difference can be expressed by a compression factor in dB. The compression is caused by transducer nonlinearities and the increase of the resistance Re corresponding with the increased voice coil temperature due to dissipated electrical input power. Short-term and long-term measurements are recommended in standards to differentiate between the two mechanisms and to define the maximal acoustical output. Improving the linearity of a transducer usually requires a compromise in thermal power handling.
The figure to the left shows the amplitude of the voice coil displacement (fundamental component) versus terminal voltage. At low voltages (U < 2 Volt rms), there is almost a linear relationship between input and output amplitude as predicted by linear parameter modelling. At higher amplitudes, the nonlinearities in the motor and suspension system cause a soft limiting of the output amplitude which limits the maximal output but which also protects the voice coil former against bottoming at the back plate.
The figure to the left shows a short-term measurement by using the DIS module with a single-tone stimulus of 1s length. The voltage is increased in 3V steps but the measured acoustical fundamental is divided by the input amplitude. Therefore, all curves are identical as long as the system behaves linearly. At low frequencies, the loudspeaker nonlinearities reduce the acoustical output, but at the resonance frequency, the electrical damping due to force factor nonlinearity Bl(x) decreases and the loudspeaker produces 1 dB more output. At higher frequencies, the displacement is small and the fundamental component is not affected by loudspeaker nonlinearities.
The figure to the left shows the short-term measurement of the same loudspeaker, but the single-tone was replaced by a two-tone stimulus. The first tone f1=20 Hz represents a bass signal. The frequency of the second tone f2 is varied over the audio band. At higher voltages, the first tone generates high displacement and the loudspeaker nonlinearities reduce the output of the high-frequency tone f2 by 4 –10 dB at low and high frequencies. Only at the resonance the force factor nonlinearity Bl(x) reduces the electrical damping, and the acoustical output will be increased by 3 dB.
KLIPPEL R&D SYSTEM (development)
Module | Comment |
|---|---|
DIS module performs a steady-state distortion measurement using a single and two-tone signal and measures the amplitude of the fundamental and of the compression in dB. DIS stepwise increases the amplitude of the stimulus and protects the transducer under test if the voice coil temperature or the distortion exceed user defined limits. The pre-excitation time may be used to perform short-term or long-term measurements according to international standards. | |
SIM predicts the large signal performance considering the thermal and nonlinear parameters. It reveals the voice coil temperature and the maximal displacement which cause the compression of the fundamental and which limit the maximal acoustical output. | |
| Large Signal Identification (LSI3) | LSI3 measures the voice coil temperature and electrical input power of the device under test. From this information it also calculates the power compression in dB caused by the heating of the voice coil. |
| Power Testing (PWT) | |
| Multi-Tone Measurement (MTON) | MTON module allows the measurement of the compression by comparing the transfer function of the device under test (DUT) at different voltage values. Maximal compression and distortion, as well as maximal temperature increase can be defined to avoid the destruction of the DUT during the measurement. |
| Tone Burst Measurement (TBM) | TBM module runs band limited burst measurements versus input voltage and frequency and measures the distortion and the compression in dB. |
Templates of KLIPPEL products
Name of the Template | Application |
|---|---|
DIS Compression Out(in) | Output amplitude versus input amplitude at four frequencies |
DIS 3D Harmonics AN 9 | Harmonic distortions versus frequency and voltage according Application Note AN 9 |
DIS 3D Intermodulation AN8 | Intermodulation distortions versus frequency and voltage according Application Note AN 8 |
DIS Harmonics vs. Voltage | Harmonic distortion measurement versus amplitude |
DIS X Fundamental, DC | Fundamental and DC component of displacement |
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). |
Diagnost. MIDRANGE Sp1 | Comprehensive testing of midrange drivers with a resonance 30 Hz < fs < 200 Hz using standard current sensor 1 |
Diagnost. SUBWOOFER (Sp1) | Comprehensive testing of subwoofers with a resonance 10 Hz < fs < 70 Hz using standard current sensor 1 |
Diagnostics MICROSPEAKER Sp2 | Comprehensive testing of microspeakers with a resonance 100 Hz < fs < 2 kHz using sensitive current sensor 2 |
Diagnostics TWEETER (Sp2) | Comprehensive testing of tweeters with a resonance 100 Hz < fs < 2 kHz using sensitive current sensor 2 |
Diagnostics VENTED BOX SP1 | Comprehensive testing of vented box systems using standard current sensor 1 |
Diagnostics WOOFER (Sp1) | Comprehensive testing of subwoofers with a resonance 30 Hz < fs < 200 Hz using standard current sensor 1 |
Diagnostics WOOFER Sp1,2 | Comprehensive testing of subwoofers with a resonance 30 Hz < fs < 200 Hz using current sensor 1 and 2 |
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 Tweeter Nonlin. Para Sp2 | Tweeters with fs > 400 Hz at sensitive current sensor 2 |
LSI Headphone Nonlin. P. Sp2 | Nonlinear parameters of headphones with fs < 300 Hz at sensitive current sensor 2 |
LSI Woofer Nonl. P. Sp1 | Nonlinear parameters of woofers with fs < 300 Hz at standard current sensor 1 |
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 |
LSI Microspeaker Nonl. P. Sp2 | Nonlinear parameters of microspeakers with fs > 300 Hz at sensitive current sensor 2 |
TRF Equiv. Input Harm. (SPL) | Equivalent harmonic input distortion calculated by inverse filtering of the measured distortion |
SIM Equiv. Input Harmonics | Equivalent input harmonic distortion using large signal parameters imported from LSI; Simulated results are comparable with TRF Equiv. Input Harm. (SPL). |
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 |
SIM X Fundamental, DC | Maximal displacement, dc displacement, compression using large signal parameters imported from LSI; Results are comparable with DIS X Fundamental, DC. |
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) |
| MTON Short term ampl. comp. @ OUT1; IEC 60268-21 | Short term amplitude compression according IEC 60268-21 using output OUT1 |
| MTON Short term ampl. comp. @ SP1; IEC 60268-21 | Short term amplitude compression according IEC 60268-21 using output SP1 |
| MTON Long term ampl. comp. @ OUT1; IEC 60268-21 | Long term amplitude compression according IEC 60268-21 using output OUT1 |
| MTON Long term ampl. comp. @ SP1; IEC 60268-21 | Long term amplitude compression according IEC 60268-21 using output SP1 |
| TBM ANSI/CEA2010A | Maximum SPL measurement according to Standard ANSI/CEA-2010-A |
| TBM ANSI/CEA2010B | Maximum usable Sound Pressure Level - Peak measurement according to Standard ANSI/CEA-2010-B |
| TBM ANSI/CEA2034 | On-Axis Maximum Sound Pressure Level - Peak measurement according to Standard ANSI/CEA-2034 |
Application Notes
AN 4 Measurement of Peak Displacement Xmax (performance-based method)
AN 12 Causes for Amplitude Compression
AN 18 Thermal Parameter Measurement
AN 19 Air Convention Cooling of Loudspeakers
AN 20 Equivalent Harmonic Distortion
AN 24 Measuring Telecommunication Drivers
AN 41 Measurement at defined terminal voltage
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
Other Related Tests
Rub & Buzz and impulsive distortion
DC displacement – dynamic offset the voice coil
Separated loudspeaker distortion
Harmonic distortion
Multi-tone distortion
Intermodulation distortion
Air leakage noise
Auralization
Transducer nonlinearities (curve shape)
Single-valued nonlinear parameters
Thermal analysis and heat transfer
Voice coil temperature
Typical Test Objects
Papers and Preprints
W. Klippel, Tutorial “Loudspeaker Nonlinearities - Causes, Parameters, Symptoms,” J. of Audio Eng. Soc. 54, No. 10, pp. 907-939 (2006 Oct.).
W. Klippel, “Assessment of Voice-Coil Peak Displacement Xmax,” J. of Audio Eng. Soc. 51, Heft 5, pp. 307 - 323 (2003 May).
W. Klippel, “Nonlinear Large-Signal Behavior of Electrodynamic Loudspeakers at Low Frequencies,” J. of Audio Eng. Soc., Volume 40, pp. 483-496 (1992).
W. Klippel, “Prediction of Speaker Performance at High Amplitudes,” presented at 111th Convention of the Audio Eng. Soc., 2001 September 21–24, New York, NY, USA.
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.