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KLIPPEL Endurance Test (KET)

Features and Benefits

  • Dedicated solution for long-term, power and accelerated life tests
  • Testing passive audio systems or any transducer
    (woofer, micro-speaker, headphones)
  • Monitors up to 32 DUTs simultaneously
  • Reveals the destruction process in detail
  • Stimulus shaping, cycling and stepping
  • User-defined failure limits
  • Monitors data of user-defined, external sensors (e.g., temperature & humidity)
  • Control peripheral devices (e.g., heating chambers)

KLIPPEL Endurance Test (KET) solution provides a simple-to-use, cost-efficient soft- and hardware solution to run multi-channel long-term, power, and accelerated life tests for typical quality assurance (QA) applications such as validation checks or type approvals. Test signals can be defined flexibly using predefined stimuli as well as arbitrary wave files. Level stepping and cycling are available for any signals. Each DUT is monitored individually. Failures can be automatically detected by checking against user-defined limits. Open and short circuits are detected by general limits; thus, a destroyed device is detected immediately. A “Death Report” reveals details of monitored states at the highest available rate for a limited time just before the failure was detected.

32 DUTs can be measured using one PC. Even a higher channel number up to max. 64 channels, depending on PC performance and Dante® Interfaces, is possible (see references). Each DUT test can be individually started, muted and terminated. Each DUT can have its own test signal and configuration. The current test status of all DUTs can be visualized in a dashboard. Status information can be easily accessed via any browser device in the network. Dante® technology is used for streaming data via a (wired) network connection.

KET follows our market-leading long-term testing solution Power Monitor 8 (PM8) with the Power Testing (PWT) module. Note that PM8 and PWT are deprecated. The following feature comparison compares our long-term test solutions and gives a general feature overview.

Feature Comparison

Feature KLIPPEL Endurance Test (KET) Power Test (PWT) - Deprecated
Max. Num DUTs 32 (64) 8 (using Power Monitor 8)
2 (using Distortion Analyzer)
Signals Voltage / Current
No Displacement
Voltage / Current (PM8)
+ Displacement (1 DUT only, DA2)
Sample Rate Up to 192 kHz (depends on Amp) 48 kHz
Sources Internal (predefined stimuli) Internal (predefined stimuli)
  External audio signal External audio signal
  Any wave file (PC playback),
length restricted
Bypass Mode (Analog input)
(Monitoring any amplifier output)
  Any stimulus generated by MTON -
Stimuli (internal) • Pink Noise
• White Noise
• Multi-tone
• Two-tone
• Chirp
• Pink Noise
• White Noise
• Two-tone
• Chirp
Voltage Control Of amplifier output voltage for any internal stimuli.
For Wave-Files:
• dBFS-mode
• Fixed rms mode
• Rms Normalized
For internal and external sources.

Not available for Bypass mode
Voltage Stepping Linear, Exponential, User defined Linear, Exponential
Intermittent Excitation Yes Yes
Stimulus Crest Factor User-defined (6 – 18 dB) User-defined (6 – 18 dB)
Filter for stimulus 6/12/24/48/∞ dB 6/12 dB
Sampling Interval 1s 1s for 1 DUT (Minimum)
8s for 8 DUTs (Minimum)
States U / I / P / R / T U / I / P / R / T / X (1 channel only)



  • dB-Lab
  • Dante® Interface
  • KET Dashboard



  • W. Klippel, “Nonlinear Modeling of the Heat Transfer in Loudspeakers,” J. of Audio Eng. Soc. 52, Volume 1, 2004 January.
  • Henricksen, “Heat Transfer Mechanisms in Loudspeakers: Analysis, Measurement, and Design,” J. of Audio Eng. Soc., Volume 35, No. 10, 1987 October.

Demo Videos

Introduction Video

The video shows an overview of the new power and endurance test solution made by KLIPPEL in general and in particular an introduction to the KET structure and benefits.

Video: KET Introduction

Getting Started Video

The video shows an introduction to how to prepare the hardware and install the required software (e.g., Dante Virtual Sound Card, Dante Controller, dB-Lab 212, KET-setup). 

Video: KET Getting Started


Continuous Testing

The simplest test is continuous playback of test stimuli for a defined duration. Monitoring power, temperature, voltage, and current reveals steady state performance for given environmental conditions. Thermal equilibrium may take hours to settle, especially for larger woofers. For mass production, regular statistical investigation of the fault rate may be required. KET eases this process considerably by using multi-channel tests and template-based setups applied to a given number of DUTs. » KET Example Data

Voltage and Current
Power amplifiers used for KET are voltage driven, thus, the actual voltage at amplifier output can be monitored and compared with the specified level in setup. Current and voltage are provided as rms and as peak values. Potential clipping or power compression can be checked in the chart Device Compression / Limiter.

Temperature, Input Power
The voice coil temperature is closely related to the real input power supplied to the transducer. Note the dual Y axis in the chart. Both state variables plotted versus measurement time give important information for defining admissible maximal input power. For a continuous playback test the steady state temperature for the given level can be assessed.

Accelerated Stress Test

Special profiles of excitation level and/or environmental conditions are used to accelerate the life cycle of a transducer. Fast changes in conditions stress the DUT and simulate a typical load scenario of product life in a much shorter time. One typical test (which is also used to determine the long-term maximum sound pressure level according to IEC 60268-21 cl. 18.4) is alternating high level with resting (cooling down). KET provides many options to alternate or step up/down the level for any kind of stimulus. Templates provide predefined setups according to international standards for easy setup and use.  » KET Example Data

Voltage Cycling
This test consists of 10 loops of a heating phase of 60 seconds at a maximum power level, followed by 120 seconds cooling phase with low or no input power. Arbitrary-level profiles are supported in KET.

Temperature, Input Power
After the cooling phase, the voice coil temperature quickly heats up, increasing the input resistance of the DUT and therefore reducing the input power within the On-phase.

Destructive Testing

To assess maximum permissible power and coil temperature, DUTs shall also be tested beyond their limits. This behavior is clearly outside the specification but reveals the headroom, a DUT provides to extreme conditions. » KET Example Data 

Temperature, Input Power
In this example, the test level is increased every 5 minutes by 1 dB steps up to a maximum test level of 25V / 45 W. Note the log power y-axis. The DUT is a small automotive woofer that is specified with a 12V max rms level. More than twice the specified level the DUT survives for about 5 minutes. The coil temperature was measured at the break down of about 250°C. Note, that the coil temperature is averaged over the coil, usually the outer parts of the coil are less cooled and may considerably hotter than the inner parts.

Death Report
A death report provides high-resolution data just before a detected failure. A ring buffer of 100 seconds length stores results at the highest available rate, here about 200ms. This may reveal the root causes for a malfunction. In this example, the coil suddenly broke and the resistance jumped up quickly causing an open circuit failure.


Thermal Stress Test

External sensors, such as temperature or humidity sensors, can provide sensor data to KET. A software interface (KET-Store) accepts data and meta information to be monitored in KET software. As a result, the robustness and temperature characteristics of the DUT can be monitored. » KET Example Data 

Temperature Profile Test
A temperature sensor (red) measures the environmental temperature in a climate chamber. The 4 phases (Room Temperature, Heating Phase, Freezing Phase and Resting Phase) are used in this example to investigate the robustness and temperature characteristics of the DUT. Note that an offset (20°C) was added to the measured coil temperature increase to allow a comparison on an absolute scale.