QSC CMX Serie Mode D'emploi page 6

Input Filter
What it is
The low-frequency (LF) filter rolls off signals below either 30 Hz or 50 Hz
cone motion, making more power available for the speakers' rated frequency range.
The filter settings for each channel are controlled individually through the DIP switch settings shown in
(Figure 5), a 5 Hz roll off protects against DC or deep sub-audio inputs.
When to use it (or not)
As a rule, your speakers will sound better with proper filtering. Unless you already have filtering in a preceding device, match the setting to the low
frequency rating of your speakers. Vented (bass reflex, ported, etc.) speakers are especially sensitive to cone over-excursion at frequencies below their
rated limit.
The 50 Hz filter works well with most compact full-range speakers, and has a slight boost at 100 Hz for greater fullness. The 30 Hz filter is intended for
subwoofers and large full-range cabinets. The "off" position should be used only for applications such as studio playback monitoring, where you need
to know if there are unwanted sub-audio signals present in your mix.
– Figure 4 –
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(Figure 6 and
5
7). This improves bass performance by limiting sub-audio
(Figure 4). When the filter is turned off
– Figure 5 –
– Figure 6 –
– Figure 7 –