CLIOwin 7 PCI User's Manual - Audiomatica

11.3 A BRIEF DESCRIPTION ON SETTINGS EFFECTS
11.3.1 STEPPED VS. NOT STEPPED
Although measuring speed increases, use of a “not stepped” sweep can adversely affect
measuring results in several circumstances. As an example that should make this clear,
let’s see what happens while measuring the impedance of a woofer in Internal or
Constant Current Mode. Please refer to Measuring Impedance for more information on
this topic. In both conditions the loudspeaker is driven from a high impedance source
and its damping is only mechanical. Fig.11.1 shows a 6" woofer, driven by a 100Ohm
output impedance generator delivering a sinusoidal burst 200ms long, at its resonance
frequency. When the excitation stops, the device continues to move, and therefore
produce back electromotive force (EMF) voltage for more than 50 ms. Something very
similar happens at start-up. In this situation, if CLIO is set in “not stepped” mode, it will
acquire this EMF together with the actual results.
0.200
CLIO
V
0.120
0.040
-0.040
-0.120
-0.200
0.00 50 100 150 200 250 300 350 400 ms 450 500
Figure 11.1
Fig.11.2 shows the same driver impedance taken both in stepped (black) and “not
stepped” mode (red). The “not stepped” curve is simply wrong. Conclusion: use always
stepped modeor the highest frequency resolution if the behavior of the device to be
measured is unknown.
25.0
CLIO
180.0
Ohm
Deg
20.0 108.0
15.0 36.0
10.0 -36.0
5.0 -108.0
0.0 -180.0
10 100 1k Hz
10k 20k
Figure 11.2
136 Chapter 11 - Sinusoidal