Typical Applications of KLIPPEL QC SYSTEM

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.

Passive system test is almost identical to coax driver test with tweeter mounted on top of a woofer in one housing and exploits the two channel capability of the Production Analyzer hardware. Internal switches allow to test 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.

Active systems having internal power amplifiers are connected directly to the XLR outputs. In this example the satellites are passive and hence can be tested also 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.

The first speaker multiplexers (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).

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. Thanks to the complete two channel architecture of the Production Analyzer hardware the test environments can be switched automatically (speaker, microphone). An optional ambient noise microphone can be used to ensure Production Noise Immunity.

Using this hardware setup shown above the following test steps can be executed in a sequence:

1st Step: Full band sweep at low or medium level 
This test assesses the regular performance of the headphone under "normal" operation condition. Acoustical (response, distortion…) as well as electrical criteria (impedance, T/S parameter) are tested in this step. 

2nd Step: Full band sweep at high level 
This test is required over the full audio bandwidth to guarantee the operation under critical conditions. Most important acoustical checks are Rub & Buzz, Loose Particles, THD, 2nd, 3rd harmonic and attenuation of headphone signal to outside microphone (Leakage).

3rd Step: Attenuation of external noise to the ear position 
This test requires a simulated head as provided by HATS from B&K, Head Acoustics and measures the frequency response from 20Hz to 20kHz by using an external signal generated by an active loudspeaker system. The free field response of the active loudspeaker can be compensated to assess the real attenuation curve vs. frequency in dB. All tests are performed separately for left and right channel.

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 parallely while the measurement chamber guarantees proper ambient noise attenuation for maximal measurement sensitivity.