Fig. 12 Measured frequency response curves for EQ4
As can be seen in fig. 9 through fig. 12, there is a falloff of the zero amplitude curves below 50 Hz
and above 15 kHz. This is due to the subsonic/ultrasonic filters, which are always in operation (see
section 3.3).
3.4.2 Adjustment of the filter Q
The quality factor of the filters (filter Q
3
) can be set by positioning the yellow jumpers on the EQ PC
board. The corresponding connectors are labeled ‘Bandwidth’. There is a choice of three filter Qs:
•
Peak (Q = 12):
yellow jumper left
•
Normal (Q = 3):
yellow jumper center
•
Shelve (Q = 1,5):
yellow jumper right
The resulting characteristic curves are shown in fig. 13.
Fig. 13 Characteristic curves of the EQ filters with three different Q factors preset.
3.4.3 Filter gain
The filter gain for each EQ band is adjusted with the trimmers on the EQ card from -12 dB
(maximum attenuation) to +12dB (see fig. 9 through fig. 12).
3
see glossary in the appendix
