CLIOwin 6.5 PCI User's Manual - Audiomatica Srl

10.4.4 PHASE & GROUP DELAY
We used the term "Frequency Response" to refer to graphics the kind of Fig.10.5 and
Fig.10.8. Frequency is in the x-axis in both figures. The units that respond to frequency,
y-axis, are Volt and Ohm, respectively. Both of them are complex quantities (have real
and imaginary part) and their magnitude is shown. Doing this we obtained a very
useful piece of information but we lost the original data (infinite numbers of different
real and imaginary part can lead to the same magnitude). How this information loss will
affect your life depends on what you are going to do with these graphs, or, better, which
was the original question you were trying to answer. Referring to Fig.10.5. A reasonable
question could have been: how much does "A" filter attenuate signal at 100Hz in respect
to 1kHz? You go trough the graph with the marker and answer 19.3dB. If you have the
IEC 651 norm you can go to the "A" filter specs and you will find this attenuation should
be 19.1dB +- 0.5dB for type 0 devices. End of your job. Lets now pose another question
referring to Fig.10.8: how much a 10kHz tone would be attenuated if we wire a 10 ohm
resistor in series with that woofer? We are simply not able to give the correct answer.
We need another piece of information, which is PHASE. Fig.10.19 is the same measure
of Fig.10.8 with phase curve overlaid. To obtain it we just stored the magnitude curve
and clicked on the phase button.
150.0
CLIO
180.0
Ohm
Deg
120.0 108.0
90.0 36.0
60.0 -36.0
30.0 -108.0
0.0 -180.0
20 Hz
100 1k 10k 20k
Figure 10.19
To acoustic devices the same principles applies. Fig.10.20 shows the magnitude
response of woofer and tweeter in a box without cross-over network.
110.0
CLIO
180.0
1.00
V
CLIO
dBSPL
Deg
0.80
100.0 108.0
0.60
0.40
90.0 36.0
0.20
0.00
80.0 -36.0
-0.20
-0.40
70.0 -108.0 -0.60
-0.80
60.0 -180.0 -1.00
0.00 20 Hz
100 1k 10k 20k
1.6 3.2 4.8 6.4 8.0 9.6 11 13 14 16
ms
Figure 10.20 and 10.21
The two measurements were taken from the same microphone position. Should we ask
ourselves which is the summed output we could not answer from the magnitude data
alone. Unfortunately acoustic phase is not so easy to handle as electric phase. We are
going to base our example on the tweeter, whose impulse response and window settings
are in Fig.10.21. Procedure for woofer would be exactly the same.
96 Chapter 10 - MLS