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Фрагмент инструкции
4-1-3. MON. CONTROLS. Most groups like to hear their voices in the monitors; some also like to hear certain instruments as well (keyboard, acoustic guitar, and so forth). A good initial MON. control setting is 5 (straight up). Assuming that the various vocalists use similar miking techniques and sing at similar volumes, the levels appearing in the monitor mix should be fairly matched. Further adjustments can be made as needed. 4-1-4. CHANNEL TONE CONTROLS. Most vocal, keyboard, and other full range signals are best left flat (controls at 0, or straight up). For signals having a great deal of low frequency content, such as drums and bass guitars, the LOW control should initially be backed off slightly (rotated to the left) from the 0 position to reduce boominess. Naturally, all controls should be set to achieve the most pleasing sounds, but the settings listed above should help in achieving good results quickly. In general, extreme settings cause the sound to be unnatural and should be avoided. 4-1-5. GRAPHIC EQUALIZER. Start out with equalizer set “flat” (O dB). On the SR mixers, the 63 Hz control may be set initially 3 to 6 dB below the center position, since excessive low frequencies rob power from the rest of the system and low-end feedback can damage loudspeakers. 4-2. USING THE GRAPHIC EQUALIZER TO ELIMINATE ACOUSTIC FEEDBACK. 4-2-1. THE CAUSE OF ACOUSTIC FEEDBACK. Acoustic feedback in a sound system is the result of coupling between the speakers and microphones. The microphones will always pick up a certain amount of signal from the speakers; how much they pick up depends on the room acoustics, the frequency response of the microphones and speakers, and the mic and speaker placement. If the received signal is amplified enough (in the mixer and power amplifier), the speakers will continue to produce the signal, and the characteristic howl of acoustic feedback will begin. This feedback will occur at the frequency which receives the largest amount of gain from the sound system (including the room). If the signal can be attenuated at that frequency, more gain can be added to the rest of the signal frequencies before feedback occurs. This is the primary role of an equalizer in a sound system. 4-2-2. TYPICAL PROCEDURE FOR ROOM EQUALIZATION. 1. Set up your entire sound system the way it will be used, including all auxiliary equipment, and adjust it the way you would normally use it. If feedback occurs during setup, reduce the gain of the mixer with the MAIN and MONITOR level controls. Follow the procedure outlined in the paragraphs below, first for the main system and then for the monitors (assuming you are using an equalizer in your monitor system, which is highly recommended). 2. Set the controls on the GRAPHIC EQUALIZER to the “flat” position, indicated as “0 dB” on the panel. 3. Slowly increase the output level (using the appropriate level control) until the sound system is on the threshold of feedback - a ringing sound will occur when you tap on the microphones. 4. Slowly attenuate the Equalizer control which has the greatest effect on reducing the ringing. This will take some trial and error - the first ringing usually occurs between 1 kHz and 4 kHz. Continue until the ringing has stopped. 5. Again, slowly increase the output level control until the system is on the verge of feeding back. Adjust the equalizer to remove the potential feedback. Continue this procedure until you have achieved sufficient gain for your application or until the equalizer becomes ineffective at removing the ringing. It is best to back off the gain once maximum gain before feedback has been established. Avoid extreme settings or settings which require a large amount of cut in the middle frequency bands, as such settings impair intelligibility. 6. “Fine tune” the equalizer settings as the performance progresses to achieve the best overall sound from the system. 4-3. CORDS AND CABLES. 4-3-1. MICROPHONE CORDS. On the SR mixers, use balanced two-conductor shielded cable for all long runs. Balanced systems are capable of rejecting noise introduced from such sources as cash registers, electric motors and triac-controlled lights. If a balanced cable is connected to an unbalanced output (e.g., a keyboard mixer output) or microphone, use a balancing transformer close to the unbalanced device. This ensures maximum common-mode noise rejection for the entire system. If you have no choice and must use unbalanced cables, use the shortest cables possible and keep them away from AC power mains, lighting cables and speaker wires. If you want the quietest system possible, you should follow these rules with balanced lines as well. 4-3-2. SPEAKER CABLES. Use two conductor zip cord to connect the amplifier outputs to your speakers. The gauge of the wire is important; wire that is too light in gauge consumes power (the power from the amplifier heats up the wire for your particular situation). To calculate your speaker impedance, use Figure 3. 4-4. ...
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