Crate Amplifiers LS1-131, LS3-231, LS2-215 manual Some Methods of Connection, Room Equalization

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

APPLICATIONS:

SOME METHODS OF CONNECTION (Continued):

Figure 8: In-Line Between a Mixer and Amplifier:

MIXER

(OR PREAMP)

	EQUALIZER
Output signal from	BALANCED OUTPUT
mixer/preamp	jack of equalizer
connects to	connects to INPUT
BALANCED INPUT	jack of power amplifier
jack of equalizer

POWER AMPLIFIER

SPEAKER OUTPUT jack of power amplifier connects to INPUT jack of speaker

APPLICATIONS:

ROOM EQUALIZATION:

Any sound system, whether it is a home stereo, a large sound reinforcement system, or recording studio moni- tors, will vary in its perceived reproduction depending on its environment; its room. When sound is produced, some frequencies are reflected and some are absorbed. This results in an uneven sound field. If speakers are placed in room corners or against walls, a large increase in the lower frequencies will occur. Some speakers are designed to use this increase to flatten their response. Other speakers, such as near field monitors and P.A. speakers, are designed to be flat in a free air environment (that is, having no external boundaries). These speakers, when placed in the wrong environment, will produce an increased low frequency response. An equalizer may be used to compensate for this condition.

By using a spectrum analyzer or Real Time Analyzer (RTA) and any of the Crate Pro Audio Live Sound equaliz- ers, a flat response can be obtained with precision and accuracy. This also may be achieved by ear, though not with the same accuracy, by using a favorite recording with which you are familiar.

Another means of achieving a flat response with your system is called “Feedback Tuning” or “Ringing the Room”. This method requires an omni-directional microphone with a very flat response to be placed in the listening area and connected to your system in an unequalized channel of your mixer. With your graphic EQ set flat, slowly turn the gain of your microphone up until a frequency starts to ring (WARNING! Be careful not the let this ring excessively or speaker damage may occur.) Pull down on the EQ slider that makes the ringing stop. Pull only a few dB, not all the way. Increase the system gain again, and another frequency will begin to feed back. Pull down on the corresponding slider again. Repeat this procedure three or four times only. After that, go to the sliders you have not yet moved and bring up their level until that frequency begins to feedback, then pull the slider down until the feedback just stops. Continue this procedure with each slider. This method takes a lot of practice and patience but it will adjust the response of your system to electronically compensate for the room. Additional equalization may be required at this point; the next section will explain.

FLETCHER-MUNSON EQUAL LOUDNESS CONTOURS:

The human ear does not hear all frequencies equally. For example, the ear is less sensitive to bass notes at lower levels than at higher levels. To compensate for this, additional equalization may be necessary to create a pleas- ing overall sound, even after a room has been EQ’d. A “preferred curve” is actually a series of boosting and cutting at various frequencies, depending on the overall performance level, so the ear perceives all frequencies at the same level. These curves are known as the Fletcher-Munson Equal Loudness Contours (see figure 9 on the following page). Notice that the amount of boosting changes with overall listening levels, since the ear hears lower frequencies better as the volume level increases.

After achieving an electronically flat response from your speakers in the room, use the Fletcher-Munson chart to adjust the contour according to the sound pressure level of the performance. These curves are intended to be used as guidelines only. Experimentation is always necessary to find your own “preferred” sound.

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