Crate Amplifiers LS2-215, LS3-231, LS1-131 manual Low Cut Control

LS1-131/LS2-215/LS3-231Constant Q Graphic Equalizers

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.

Figure 4a: The Low Cut Control:

1dB
0dB
-1dB
-2dB
-3dB	10	15	40	150	250
-4dB
-5dB
-6dB
10Hz			100Hz		1k

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.

Figure 4b: The High Cut Control:

1dB
0dB
-1dB
-2dB
-3dB	3k	5k	10k	30k	40k
-4dB
-5dB
-6dB
1kHz			10kHz		50k

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.

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