Crate Amplifiers LS2-215, LS3-231 manual Fletcher-MunsonEqual Loudness Contours, Feedback Control

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

Figure 9: Fletcher-Munson Equal Loudness Contours:

	140
				LOUDNESS LEVEL IN PHONS
	120			120
				110
dB	100			100
IN
				90
LEVEL
	80			80
PRESSURE
				70
	60			60
SOUND				50
	40			40
				30
	20			20
				10
	0			0
	20	100	1000	10,000
			FREQUENCY IN Hz

200
20	2
2.0	PER CM
	DYNES
0.2	PRESSURE
0.02

0.002

0.000

FEEDBACK CONTROL:

Feedback can be a major problem in live sound reproduction. Feedback occurs when an outgoing signal finds its way back into the system via a microphone or a guitar pickup and gets re-amplified. The outgoing signal is the transmitter and the microphone or pickup is the receiver. The best and most effective way to eliminate feedback is to separate the transmitter from the receiver.

If this is not possible, then an equalizer with narrow bandwidth filters, such as the LS1-131 or LS3-231, is an effective alternative. To find the frequency at which the feedback is occurring, simply select the frequency you feel is the problem and move it to maximum “cut”. If the feedback doesn’t stop then return the control back to its original position and adjust another frequency until the feedback stops. Once you have isolated the feedback frequency, then move the control back towards its original position until the feedback occurs again then reduce the level down until it just stops. This process allows you to eliminate feedback problems without sacrificing overall level or frequency response.

CREATIVE OR ENHANCEMENT EQUALIZATION:

The graphic equalizer can also be a creative tool. The LS1-131, LS2-215 or LS3-231 may be used on individual instruments, vocals, signal processors, and recording equipment to shape or mold them to the exact sound you want. With vocals, the frequencies between 10kHz and 20kHz may be boosted to help separate syllables for greater clarity and distinction. The vocal range is from about 150Hz up to 4kHz. When speech intelligibility is your main concern, this frequency range is critical. Emphasis is typically greater around 4kHz, particularly in a highly reverber- ant environment.

Using your equalizer with a digital reverb gives you the ability to change the characteristics of the “room” or “hall” you’ve selected, offering greater versatility.

Your equalizer can also be used to make a “de-esser”. A “de-esser” is what it sounds like, a clever way to con- trol “S’s” in a speech or vocal performance. This will require a compressor with a trigger input. You must first split your vocal source into two output signals. The first vocal signal is simply sent to the input of the compressor. The sec- ond vocal signal is sent to the input of your equalizer. The output of the equalizer is sent to the “trigger” input of your compressor. The output of your compressor is sent back to a channel on your mixer. The de-esser is made by boost- ing the 6.3kHz control to the +12dB position and then adjusting the compressor threshold until the desired effect is reached, that is, when an “S” is pronounced then the signal will be reduced. Some other adjustments can also be made on your compressor with the “attack time”, “decay time” and the “compression ratio” to enhance the effect.

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