1GA16_1L.DOC
ROHDE & SCHWARZ
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5.4.3 Polarity Check by Comparison to Reference Sound Pressure Characteristic
This method uses the superposition of frequencies in the transition range of the crossover units. If one of
the loudspeakers is wrongly poled, some frequency components are cancelled and this is clearly reflected
by the frequency response of the sound pressure level (particularly when compared to that of the correctly
poled reference loudspeaker).
This method should be preferred for checking the polarity of tweeters and mid-range speakers.
5
5.5
.5 Distortion
Distortion
The UPD and UPL device software offers several functions for determining the distortion of a signal - and
thus also of the sound pressure produced by a loudspeaker. The following functions are available for
example:
•
THD for measuring the total harmonic distortion or any combination of discrete harmonics with or without
display of the harmonics line spectrum. This measurement function ignores the noise; for measuring the
2nd and 3rd order distortion in line with DIN IEC 268, part 5, d2 and d3 have to be selected.
•
THD+N with or without post-FFT of total signal,
•
FFT with or without zoom FFT for increasing the frequency resolution.
FIG 16 Distortion (THD) versus frequency
Although these measurement functions are directly accessible from the user interface, the most important
are also integrated at the application level and may be selected with the THD softkey (F9) at the main
level. At the next softkey levels different kinds of measurements can be selected:
•
THD TOTL (F6)
total distortion (all di)
•
THD d2 (F7)
2nd order distortion
•
THD d3 (F8)
3rd order distortion
•
THD+N (F9)
total distortion with noise
•
POST FFT (F10)
THD+N with display of total signal as post-FFT
•
ZOOM FFT (F11)
display of total signal with zoom factors from 2 to 128
Summary of Contents for UPD
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