User`s manual

makes life harder even if more interesting. Deriving the principals T&S Parameters
from the five curves yields to Table 13.1
Fs Qms Qes Qts
+10dBu 69.244 3.105 0.609 0.5094
+5dBu 71.63 3.6461 0.6643 0.5619
0dBu 72.9912 3.986 0.695 0.5920
-5dBu 73.5429 4.1663 0.7147 .61
-10dBu 73.82 4.227 0.7218 0.6166
Table 13.1
Values from 0dBu to -10dBu are in optimum agreement and this sets the maximum
level to be used to 0dBu. Interestingly enough, Internal Mode is less sensitive to
output level. We will go further into this topic relying on CLIO being a complete and
powerful audio measuring system. Without changing connections we will use CLIO’s
FFT and Signal Generator to evaluate the distortion current at resonance at 10dBu.
Fig.13.5 shows the spectrum in this condition. The second harmonic is 56dB lower
than the fundamental, which is 0.158% distortion. Even at 10dBu we are easily in
the linear region of the loudspeaker motor. However what we have seen above,
clearly states 10dBu is quite a high level for this device.
Audiomatica Srl FFT 03/07/2001 12.22.50
CH A dBV 6.4kHz 16384 Rectangular File: impedancedistortion.fft
0.00 100 200 300 400 500 600 700 800 900 999Hz
-10.0
dBV
-30.0
-50.0
-70.0
-90.0
-110.0
CLIO
Figure 13.5
The reader could be tempted to determine the absolute quality of the device by
means of this procedure. While he or she may be right, a lot of experience is
needed. One important parameter, for reliable comparison among devices, is the
value, in VRMS, at the speaker terminals at resonance. It is shown from FFT as
-10dBV that is 0.316VRMS.
13.3.3 DEALING WITH ENVIRONMENTAL NOISE
The next problem in measuring loudspeaker impedance is noise. Transducers do
their job in both directions and noise will appear as voltage exactly where CLIO’s
input is connected. To evaluate the problem we deliberately produced a disturbance
by generating a 110Hz single tone causing 58 dBSPL at the speaker cone. We took
two impedance curves in this condition one with MLS the second with Sinusoidal.
184 13 MEASURING IMPEDANCE AND T&S PARAMETERS