CLIOwin 6.5 PCI User's Manual - Audiomatica Srl

Now things look much better and this is the almost anechoic response of the speaker.
Almost means that nothing comes for free. The low frequency part of the response
seams quite optimistic for such a little speaker. The price we paid in setting to 0 the
impulse tail is that we lost information on the lower part of the spectrum. The transition
frequency between meaningful and meaningless data is calculated as 1 divided by the
selected impulse length. In our case we selected a 6.8ms long impulse. 1/0.0068=147Hz
right? Wrong. We have the first 2 ms of the impulse, which is the time of sound flight
that does not carry any information. We could have selected the impulse as in Fig.10.18
without affecting the frequency response at all. Phase response would have been
greatly affected.
0.50
V
CLIO
0.40
0.30
0.20
0.100
0.00
-0.10
-0.20
-0.30
-0.40
-0.50
0.00 1.1 2.3 3.4 4.6 5.7 6.8 8.0 9.1 10 11
ms
Figure 10.18
The right calculation is 1/(0.0068-0.002)=208.33Hz. In our room the smallest
dimension is floor to ceiling. This is indeed the most frequent case. This dimension is
however 4m. The best location for the speaker would have been at 2m both from the
floor and the ceiling. The second consideration is microphone distance. The highest it
is, more is the useless part of the impulse you have to subtract. In practice we do not
encourage distance below 70cm for complete speaker measurement and you should
increase to 1m for bigger ones. However single driver measurement can take advantage
from a reduced distance.
Chapter 10 - MLS 95