Typical Applications of the KLIPPEL endurance Test (KET)
When purchasing speaker systems, consumers expect them to have undergone rigorous quality testing to ensure longevity and performance. Therefore, loudspeaker developers and manufacturers should conduct service life tests to understand how their products behave over time and in various environmental conditions. This requires time-consuming long-term tests, which were previously limited in scope and control. KLIPPEL's multi-channel endurance tests provide a simple, effective and scalable solution for analyzing and evaluating passive audio systems and transducers (woofer, micro-speaker, headphones) over time. Conforming to international standards (e.g., IEC 60268-21), the Klippel Endurance Test (KET) offers long-term max SPL testing, accelerated life testing, destructive testing with death reports, and thermal stress testing. Loudspeaker designers and manufacturers should implement these tests for typical quality assurance applications, to receive valuable statistics for traceability of data and gain a detailed analysis basis for the development department.
There are different methods for simulating product life in a shorter time. These include varying stimulus conditions (level, bandwidth, signal, etc.) and environmental conditions (temperature, humidity, etc.) to stress the device more than normal. As an example, high-level stimuli with cooling-off phases can be used to determine the long-term maximum sound pressure level and uncover aging and fatigue issues. The Klippel Endurance Test monitors coil temperature, input power, and current to evaluate steady-state performance and the effects of stress. Testing the maximum performance limits of the device is critical to conscientiously and quickly detecting underperformance, gaining failure information, and protecting valuable prototypes. This can be achieved by gradually increasing the test level every 5 minutes by 1 dB steps up to a maximum level and stopping automatically if limits are exceeded or the device is damaged. High-resolution results are stored in a 100-second ring buffer for detailed failure analysis.
How can you perform continuous testing?
The main goal is to perform a test signal with constant power applied to the device(s) under test for a specified time (10, 100, or even 1000 hours) or according to standardized (IEC 60268-21 and 5) test schemes. KET constantly monitors coil and magnet temperature, input power and current to assess the steady-state performance and evaluate the impact of the stress applied. Environmental conditions may be altered throughout the test period (controlled by the KET sequence). The performance of the DUT shall be measured before and after the endurance test to evaluate the impact of the stress applied. For example, the most changes are typically related to suspension aging. KET manages parallel tests of up to 32 DUTs for fast, statistical failure rate analysis. » 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.
How can you perform accelerated life testing?
One typical accelerated live test (which is also used to determine the long-term maximum sound pressure level according to IEC 60268-21 cl. 18.4) combines is alternating high level high-level stimuli with resting (cooling down) phases. This test is also used to determine the long-term maximum sound pressure level according to IEC 60268-21 cl. 18.4. 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 (IEC 60268) for easy setup and use efficient every-day everyday operation. By the way: each KET channel can run individual setups and test schemes. » 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.
How can you perform destructive testing?
Most devices undergo thorough testing within their specified limits, but it's important to also test their maximum capabilities. Klippel Endurance Testing (KET) is a useful tool for determining the highest allowable power and coil temperature. The test automatically stops if the device is damaged or exceeds individual power, current, or temperature limits. The final 100 seconds of the test provide detailed information about the device's behavior during this crucial phase. » 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 logarithmic y-axis for power. The device under test, a small automotive woofer that is specified with a 12V max rms level, withstands more than twice that specified level for about 5 minutes. The coil temperature at the breakdown was measured at 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 be 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.
How can you perform a thermal stress test?
Thermal stress tests are part of environmental stress tests that can be performed or even combined by applying excessive heat, humidity, water, salt, or other aggressive chemicals to devices under test (DUT). Such tests prove the resistance of DUTs to tough environmental conditions that might appear in the final application. They are also part of accelerated live tests, which reveal aging and fatigue problems in a much shorter time than the actual product lifetime. » KET Example Data
Temperature Profile Test
A temperature sensor (red) measures the environmental temperature in a climate chamber while the voice coil temperature is plotted in brown. The test consists of 4 phases at room temperature, a heating phase, a freezing phase, and a resting phase, about 90 minutes each. Here the environmental heat and cold add additional thermal stress to the voice coil and the DUT, resulting in high coil temperature even at moderate excitation levels.
In this example, the external temperature sensor is automatically queried using an open API for any kind of sensor and included in result charts. Thus, other conditions using almost any digital sensor can be monitored and integrated into KET. Moreover, a software interface is available to control climate chambers or other instruments of torture for DUTs for automatic long-term tests with specific test profiles. As always after endurance testing, the compliance with expected behaviour shall be verified. Note that room temperature offset (20°C) was added to the measured coil temperature increase allowing comparison on an absolute scale.
KLIPPEL’s endurance test offers an individually adaptable test solution for long-term, performance, thermal and accelerated life tests. It individually monitors multiple devices under test with independent test signals/sequences and periodic status recording, which reduces the general measurement effort and, at the same time, provides highly precise results.The test also offers constant power testing for 10, 100, or even more hours. By utilizing budget-friendly smart amplifier hardware from Powersoft (Mezzo and Unica) that comes equipped with voltage and current sensing, the cost per test channel is significantly lowered. » Explore the capabilities of KET on your own and experiment with the complimentary example data.