Mackie MR5 Owner's Manual - Page 8

MR5 PROTECTION CIRCUITS There are several protection mechanisms designed into the MR5 to safeguard the loudspeakers and amplifiers from inadvertent damage. CAUTION: The protection circuits are designed to prevent damage to the loudspeakers under reasonable and sensible conditions. Should you choose to ignore the warning signs (i.e., excessive distortion), you can still damage the speakers in the MR5 by overdriving them. Such damage is beyond the scope of the warranty. Overexcursion Protection A 12 dB/octave high-pass filter at 60 Hz just prior to the low-frequency amplifier prevents very low frequencies from being amplified. Excessive low-frequency energy below 60 Hz can damage the woofer by causing it to "bottom out," also known as overexcursion, which is equivalent to a mechanical form of clipping. Thermal Protection All amplifiers produce heat. The MR5 is designed to be efficient both electrically and thermally. • If for some reason the heatsink gets too hot, a thermal switch activates and turns off the amplifier. This protection operates independently for the low-frequency and high-frequency amplifiers. Therefore, it is possible for only the low frequency or high frequency amplifier to shut down while the other remains on. • When the heatsink cools down to a safe temperature, the thermal switch resets and normal operation resumes. • If the heatsink temperature again gets too hot, the shutdown process repeats. Should this happen, make sure that airflow to the rear of the cabinet is not restricted. If the ambient air temperature is very warm, try pointing a small fan toward the heatsink to increase the airflow through the ventilation holes. Integrated Magnetic Shielding Input Signal Wiring You should use high-quality, shielded cable to connect the signal source to the SIGNAL INPUT jack [1] on the MR5. • For balanced signals, foil shielded cables, such as Belden 8451, 8761, or 9501 are commonly used for studio wiring. • Microphone cables work well for the XLR input. • The better the shield, the better the immunity from externally induced noise (like EMI and RFI). Route the cable away from AC power cords and outlets. These are common sources for hum in an audio signal. Wall warts and line lumps are especially insidious hum inducers! You can purchase quality cables from your Mackie dealer. • In certain home theater applications, it may be necessary to connect the speaker outputs from a stereo receiver to the inputs of the MR5, if the receiver doesn't have preamp outputs or other line-level output connections. CAUTION: Do not attempt to connect a speaker output directly to the input of the MR5! Speaker levels are much higher than line levels and can damage the input circuitry in the MR5. You can, however, insert a speaker-level to line-level signal attenuator between the receiver's speaker output and the MR5's input. Your Mackie dealer may be able to help you find one, or you can build your own. CARE AND CLEANING Your Mackie Reference Studio Monitors will provide many years of reliable service if you follow these guidelines. • Avoid exposing the monitors to moisture. • Avoid exposure to extreme cold (below freezing tem- peratures). • Use a dry cloth to clean the cabinets. Only do this when the power is turned off. The MR5 contains drivers with large magnetic structures. The drivers' magnets are shielded to help prevent the magnetic field from radiating out into the environment and playing havoc with computer monitors or TV screens. Unshielded speakers can cause distortion in both the shape and color of the picture if placed too close to a CRT (cathode ray tube). If you have a particularly sensitive computer monitor or TV screen, it may be necessary to move the speakers a few inches away.  MR5