KIRCHNER ATB 805 Handbook
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Contents
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32The pictures show the analyser measurements of the M-PN and MLS signals. Both signals are adeterministic noise (a frequency mix). The M-PN signal shows a pink noise. Practically all 1/3octave bars have the same amplitude. The drop in the low frequency range is not to be takeninto consideration for measurements. The MLS signal tends to comply with white noise. This iseasily audible when testing. The high frequencies have extremely high amplitude and the lowfrequencies are contained in the signal with –45dB. In opposition to 1/3 octave analysis the MLSsignal appears after testing through the correlation with a straight frequency characteristic. Acorrelation has the following functions:The loudspeaker is steered with the MLS signal shown above. If the loudspeaker has forexample a linear frequency characteristic then the microphone used will record the same signal.It is changed into a digital signal within the measuring instrument. This signal as well as the MLSsignal is withheld in the computer in digital form. During the correlation both signals arecompared. The result (frequency characteristic) consists of a picture of the differences. If bothsignals are the same (in the case of the linear loudspeaker) the result is a straight line. If theloudspeaker does not transmit the low frequency range very well, then the difference betweenthe signal measured and the output signal are pictured as a drop in the frequency characteristic.That the MLS signal is not suitable for testing is proved by the following:The loudspeaker is steered with the MLS signal. The energy distribution of the MLS the exactopposite of the music signal; in the high is a lot and in the low range nearly no energy.The results of this are:1. The extremely high energy of the high frequencies overload the high tones, so that apart of the frequency characteristic measured consists of dynamic compression anddistortion. The result is that one of the music transmission frequency characteristicscannot be measured.2. Because of the very small signals in the low frequency range an exact andreproducible measurement is nearly impossible. This leads to the need for at least 10measurements with the MLS signal before an exact result (with adaptive windows)can be expected.The M-PN Signal owns a steady energy distribution. It does not overload the high tones and hasenough signal amplitude in the low frequency range. Each measurement is reliable (evenwithout an average mean).7.3 THE RBLOW, RBMID AND RBHIGH SIGNALThe RB Signal is for the IMD, intermodulation distortion measurement. We give it the nameSignal 13. The Signal 13 is for nonlinear distortion measurement.Wolfgang Klippel, Germany, describes the distortion from nonlinear systems.The basic for this measurement is a generator signal with consist of two sine waves. The signalis modulated at the nonlinear transfer response of the system under test. The result is the THDand the IMD spectrum.The Signal 13 is for the quality control in the speaker industry. It is used for the Rub&bussmeasurement to test the mechanical quality of the speaker. In production line the speakers tendto have defects. These defects are cone displacement, rubbing voice coil and loose particles.The defect speaker produces an unwanted noise. An analysis of the noise shows short time andmagnitude distortion. In former time the noise was tested with a THD measurement withanalysing the energy of a high-order harmonics group. These are K13, K14,……..K20. For a realtest there is the need of a non-static signal. Therefore, the newer systems used a sine-sweep ora combination of step and sine. The measurement with these signals has a problem with thesurrounding noise. Therefore, the Signal 13 was developed from the Kirchner elektronikcompany. The signal consisting of the heterodyne of two sine waves with the ratio of 1:1,3. This |
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