User`s manual

11.4 A BRIEF DESCRIPTION ON SETTINGS EFFECTS
11.4.1 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.
Audiomatica Srl FFT 28/06/2001 17.30.53
CH A dBV 6.4kHz 4096 Rectangular File: sin2.fft
0.00 50 100 150 200 250 300 350 400 450 500ms
0.200
V
0.120
0.040
-0.040
-0.120
-0.200
CL IO
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 mode or the highest frequency resolution if the behavior of the
device to be measured is unknown.
Audiomatica Srl Sinusoidal 28/06/2001 17.13.49
CH A Ohm Unsmoothed Stepped Delay [ms]: 0.000 Dist Rise [dB]: 30.00 File:
10 100 1k 10k 20k10 Hz
25.0
Ohm
180.0
Deg
20.0 108.0
15.0 36.0
10.0 -36.0
5.0 -108.0
0.0 -180.0
CLIO
Figure 11.2
146 11 SINUSOIDAL