Linear Suspension Test (LST)
Optional Module for the KLIPPEL QC Framework
Features and Benefits
Hard- & software turn-key solution
- Ensure quality of final speaker at an early stage
- Ensure consistency and validity of production
- Interface between manufacturer and customer
- Test linear parameters like resonance frequency, Q-factor and stiffness/compliance
- Test mass and stiffness deviation from Golden Unit (LST Pro)
- Dynamic method in small signal domain according to IEC 62459
- Robust model-based resonator parameter fitting
- Fast and simple clamping
This software module and hardware accessory for the QC framework of the KLIPPEL Analyzer System is dedicated to the quality control of loudspeaker moving parts such as diaphragms, suspension parts (spiders, cones, surrounds) and passive radiators (drones). Round parts are quickly mounted on the measurement bench using a set of mounting parts (rings, cones). No time-consuming clamping is required. The built-in loudspeaker of the test bench drives the device under test (DUT) pneumatically in order to find the resonance frequency using a log sweep (chirp). Linear mechanical parameters like resonance frequency, stiffness/compliance (LST Lite) or relative mass and stiffness deviation (LST Pro) are measured using a laser sensor which may be enhanced by an additional microphone for improved accuracy. High test speed and simple clamping allow short test cycle times to go for 100% testing.
Spider Test (LST Lite)
A standard application of the LST Lite module is spider testing. For this application, the resonance frequency f0, the Q-factor and the effective stiffness k0 are measured.
Round spiders can be attached to the measurement bench using a subset of the modular ring set (optional). The cone for inner clamping is selected by the neck diameter of the spider. For this application, sound pressure measurement is optional but recommended for best accuracy (resonator parameter fitting). In order to measure the spider stiffness, the approximate moving mass (dominated by the inner mounting parts) must be entered.
Once the measurement bench is adjusted and the software properties are set, large batches of spiders can be tested with a very short cycle time. The test objects are only attached by gravity to minimize mounting time. For soft suspension parts, an additional upper clamping ring may be used.
18" Cone Test (LST Lite)
Testing large size objects with a diameter of more than 222 mm requires using the larger SPM test bench together with custom clamping rings.
The 18’’ cone in this example is attached to the test bench using a custom wooden ring which fits the rim diameter. The ring is attached to the SPM test bench using the provided standard clamps. For inner clamping, a suitable cone has been selected from the standard plastic cone set.
Testing large size objects requires a two-signal measurement method. The laser is used for displacement measurement while a microphone (not visible in the picture) is picking up the stimulating sound pressure inside of the SPM Bench. The resulting transfer function allows accurate measurement of the resonator parameters.
Headphone and Micro-Speaker Diaphragms, Tweeter Domes
Since most small and miniature speakers (e.g. micro-speaker, headphone) do not have spider, the diaphragm defines the compliance of the final driver. Testing the shaped, mostly thin foil parts is a difficult task. Furthermore, tweeter domes mostly exceed the frequency range limitations of the LST Bench. For such applications, the MSPM Bench extension may be attached to the LST Bench providing a smaller volume with a dedicated driver for excitation and a different clamping system. The DUT is mounted on a custom tray. For reproducible and defined conditions, gluing the DUT to the sample tray is recommended. Therefore, this application is rather recommended for sample testing than for 100% EOL check.
Passive Radiator Test (LST Pro)
For testing passive radiators, the LST Pro is recommended because both mass and stiffness deviation may vary in production. In addition to LST Lite results, there are two more measures. Mass deviation and stiffness deviation are based on a physical model and defined relative to a defined reference unit (“Golden Unit”). This unit may be selected according to R&D specifications or automatic golden unit selection based on a batch of reference units.
All subsequently measured devices are related to the reference unit. If the reference moving mass is known (e.g. from (M)SPM using added mass method), the parameter deviation can be monitored in absolute values or percent.
If the passive radiator is not round, a custom platform may be mounted on top of the LST Bench. The outer frame must be fixed for reproducible conditions (e.g. using clampers).
In case the ambient conditions (temperature/humidity) have changed over time, the limits may be calibrated using the golden unit. It should be kept under the same ambient conditions close to the test station.
Other Modules of the QC SYSTEM
• Motor + Suspension Check (MSC):
Fast measurement of voice coil offset and suspension asymmetry