Crate Amplifiers LS1-131 - Manual (Page 5)

The LS1-131/LS3-231 both feature variable Low Cut and High Cut controls. The low cut control is not
only useful for subsonic filtering, but provides a wider range of control for low frequency “ringing” in some
sub-woofer systems and controls “wind” noises in microphones. This filter is extremely useful in using amplifi-
er power more efficiently. This is accomplished by eliminating inaudible subsonic frequencies below 30Hz
from reaching the system thus conserving power. Most full range P.A. enclosures do not produce frequencies
below 30Hz due to speaker limitations. This is typical for all enclosures of this type. Some of these enclosures
begin to roll-off at approximately 50Hz with a usable low frequency limit of about 35 to 40Hz (-10dB down).
These frequencies may be recovered by using an equalizer to boost the low frequencies to compensate for the
speaker’s roll-off. But frequencies below 30Hz may cause displacement-limited distortion, which is distortion
due to excessive movement of the speaker cone. Dial the Low Cut control to 30Hz and add a 12dB/octave
roll-off at that frequency. This will result in a noticeably cleaner sound. Figure 4a shows the rolloff curves for
this control at the frequencies shown on the front panel.
The High Cut control can be used to reduce high frequency noise in your source material (instruments,
recorded music, etc.) and can help achieve a more natural sound when reproducing some acoustic instru-
ments. Figure 4b shows the rolloff curves for this control at the frequencies shown on the front panel.
All units provide a Bypass switch which connects the input jacks directly to the output jacks. This is
extremely useful when troubleshooting or comparing your equalizer setting to the original signal. These
units also feature a “Range” switch. By pressing this switch, the “boost” and “cut” or control range changes
from ±12dB to ±6dB. This allows for greater accuracy. When using these equalizers with a Real Time or
Spectrum Analyzer, improved accuracy is important for fine tuning.
5
LS1-131/LS2-215/LS3-231 Constant Q Graphic Equalizers
Figure 4a: The Low Cut Control:
10Hz
-6dB
-5dB
-4dB
-3dB
-2dB
-1dB
0dB
1dB
100Hz 1k
10 15 40 150 250
Figure 4b: The High Cut Control:
1kHz
-6dB
-5dB
-4dB
-3dB
-2dB
-1dB
0dB
1dB
10kHz 50k
3k 5k 10k 30k 40k