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Typical Applications of KLIPPEL QC SYSTEM

Driver Test Setup

The basic setup for testing single drivers comprises the Production Analyzer hardware, power amplifier, microphone(s) and a computer. In most cases the DUT and the near field microphone is mounted into a test box providing some protection against ambient noise. However, complete noise immunity cannot be obtained by simple passive shielding.

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QC System - Interactive Demo Tour
AN 45 - Optimal QC Setup for Fixed Time
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AN 48 - Yield Statistics

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Passive System Test Setup

The Passive system test is almost identical to the coax driver test, with the tweeter mounted on top of a woofer in one housing, and it exploits the two channel capability of the Production Analyzer hardware. Internal switches allow for testing the system channels separately as well as in combination without using external hardware. 
A starting switch (robust footswitch) and temperature and humidity sensor are included as options in this setup. Note that access to the speaker terminals must be provided for individual testing. Crossovers can also be measured using KLIPPEL QC System if in- and output are accessible.

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Active 2.1 System with Electrical and Acoustical Testing

Active systems having internal power amplifiers are connected directly to the XLR outputs. In this example the satellites are passive and hence can also be tested electrically (impedance, T/S and large signal parameters). The total acoustical output is assessed by using a near-field microphone. The second microphone located in the far field detects the ambient noise.

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Demo Video - Active 2.1 System Testing 
AN 64 - Housing Ground Check

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5.1 System with Electrical and Acoustical Testing. Analog or Digital (USB) Interface of DUT

The first speaker multiplexer (1 out of 8) is used for selecting one or two speaker channels from the amplifier output at the subwoofer. The selected channels are fed via the voltage and current sensors in the production analyzer via the second multiplexer to the speakers under test. All the remaining speakers are switched off. Both multiplexers are controlled by the same binary GPIO pins of the Production Analyzer
The third multiplexer is used for selecting the microphones using different GPIO pins. Thus the selection of the microphones is completely independent of the selection of the speakers. The ambient noise microphone always monitors the far field sound pressure. Although the 5.1 system in the application is connected to the analogue output of the PA, it can also be operated using a digital audio interface (e.g. USB).

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Microphone Test Setup

Testing microphones using a reference speaker and enclosure is also a straigthforward application for KLIPPEL QC. Microphones can be connected via IEPE or XLR line input to the Production Analyzer hardware.

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Alternate Test Setup

This test setup provides a cost efficient solution. Two lines with identical DUTs can be tested by using one KLIPPEL QC System only. One DUT can be mounted / dismounted while the other is tested. Due to the multi-channel capabilities of the KLIPPEL Analyzer, the test environments can be switched automatically (speaker, microphone). An optional ambient noise microphone can be used to ensure Production Noise Immunity

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Headphone Testing

The quality of earphones, headphones or headsets depends on many factors. In R&D, important design parameters are specified by several standards. Measurements with ear simulators provide defined load conditions and specied frequency responses. However, performing such tests can be a challenging and time-consuming task that requires experience and careful handling in order to obtain meaningful and reproducible results.

In quality control, other requirements like simple handling, speed, stability, robustness against ambient noise and reproducibility are much more important in order to pursue the ultimate goal of distinguishing good from bad units reliably. The most important test parameters are the frequency response and the matching between left and right channel. Furthermore, excessive harmonic distortion shall be reliably detected as well as any disturbing rattling and buzzing noises, even if operated at high level. Additionally, the functionality of signal processing features like ANC (active noise control) need a quick verification.

Application Note 73 specifically focuses on the aspects of QC testing for testing passive, digital (USB) and wireless (Bluetooth) headphones and headsets using dedicated headphone test stands by GRAS. The stated information can be transferred to other devices like earphones or hearing aids.

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AN 73 QC Headphone Testing
Demo Video - Headphone Testing

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Leak Detection for Large Subwoofer

Detecting air leaks in large speaker systems with only one microphone leads to physical problems due to shadowing of high frequency leak noise. Locating multiple microphones around the device under test solves this problem by measuring the speaker from different sides and thus covering the whole surface. The four test microphones are switched by a signal multiplexer for sequential measurement. An additional far-field microphone always monitors ambient noise in parallel while the measurement chamber guarantees proper ambient noise attenuation for maximal measurement sensitivity.

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