| An Introduction to Equalizers |
|
The Crate Pro Audio Live Sound Graphic Equalizers are available in two mounting configurations: a 1-3/4" single rack space (LS1-131/LS2-215) and a 3-1/2" double rack space (LS3-231). These equalizers are a perfect addition to any professional sound system, particularly the Crate Pro Audio systems. The Crate Pro Audio LS1-131/LS2-215/LS3-231 equalizers offer precision control of the audio spectrum.
The LS1-131 and LS3-231 provide 31 bands of equalization at standard ISO center frequencies, 1/3 octave apart. They cover the entire audio spectrum from 20Hz to 20kHz. This allows precision control and fine tuning of your audio system. (The LS3-231 offers two channels of 31 band equalizers.) The LS2-215 provides two channels of 15 band equalization at standard ISO center frequencies, 2/3 octave apart from 25Hz to 16kHz. All of the new Crate Pro Audio Live Sound Equalizers incorporate constant "Q" multiple-feedback bandpass filter sets for high resolution with minimal interaction between bands (see Figure 1 below) |
These filters have a relatively low "Q" thus preventing "ringing". Ringing occurs when a filter instantaneously receives an input signal and hangs on to the signal for a period of time after it has stopped (see Figure 2 below).
All three equalizers have a flat phase response (see Figure 3 below) for accurate sound reproduction with no coloration to your speaker system. This maintains pure stereo imaging without the "comb filter" effect. As your ear passes across the stereo plane of your system, the comb filter effect sounds like "peaks" and "nulls" in the response which can change the imaging dramatically.
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 amplifier 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 instruments. 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.