Mackie M1400/M1400i Owner's Manual - Page 24

The extension cord used to supply power to the "amp rack" should have a third wire safety ground to avoid presenting a safety hazard. We also recommend using a cord that has conductors large enough to avoid severely limiting the amplifier's ability to supply high currents on transients. Power amplifiers can have momentary peak current requirements many times above the nominal average current draw. According to Ohm's Law, the greater the resistance of the linecord, the more input power is lost between the AC outlet and the power amplifier (across the linecord). And to further aggravate the matter, this relationship is nonlinear. The amount of power lost across the linecord increases exponentially as the current demand increases. So if the current demand doubles momentarily because of an exceptionally loud bass note, the amount of AC input power lost across the linecord increases four times. You can see that it is very important to keep the resistance of the linecord to a minimum. That's why we recommend using a heavy gauge extension cord (like 14 gauge or bigger). Remember, wire gets thicker as the gauge number gets smaller (10 gauge is thicker than 14 gauge). AC Power Distribution In order to minimize ground loops, the safety grounds for all the outlets should be connected to a common ("star") grounding point, and the distance between the outlets and the common grounding point should be as short as possible. If lighting is used in a show, it is preferable to power the lights from a different AC circuit than the one powering the audio equipment. This will help minimize noise from the lights coupling into the audio (particularly if SCRs are used). INPUT WIRING Use a high-quality 3-conductor shielded cable to connect the signal between the signal source (mixing console, equalizer, etc.) and the balanced inputs to the amplifier. If you're using the unbalanced inputs, use a high-quality 2-conductor shielded cable. Your Mackie Dealer can recommend a suitable cable for your application. OUTPUT WIRING Use heavy gauge, stranded wire for connecting speakers to the M•1400/M•1400i amplifier's SPEAKER OUTPUT terminals. As the distance between the amplifier and the speakers increases, the thickness of the wire should also increase. Speaker wire has resistance, and when electricity passes through a resistor, power is lost. The thicker the wire, the less resistance it offers, and the more power actually gets to the speakers. The thickness of wire is rated in gauges. Use the chart below to determine the correct gauge of wire to use according to the distance between the speakers and the amplifier, and the impedance of the load the amplifier is driving. This ensures that the power lost across the speaker wire is less than 0.5 dB. Wire Length Up to 25 ft. Up to 40 ft. Up to 60 ft. Up to 100 ft. Up to 150 ft. Up to 250 ft. Load Impedance 2Ω 4Ω 8Ω 2Ω 4Ω 8Ω 2Ω 4Ω 8Ω 2Ω 4Ω 8Ω 2Ω 4Ω 8Ω 2Ω 4Ω 8Ω Gauge of Wire 14 gauge 16 gauge 18 gauge 12 gauge 14 gauge 18 gauge 10 gauge 12 gauge 16 gauge 8 gauge 10 gauge 14 gauge 6 gauge 8 gauge 12 gauge 4 gauge 6 gauge 10 gauge 24