Mackie M800 Owner's Manual - Page 15

CONSTANT DIRECTIVITY SWITCH If you don't have constant directivity horns, you can leave this switch OFF. Compression drivers mounted on constantdirectivity horns require compensation in the form of a high-frequency boost, with its "knee" set somewhere between 2kHz and 6kHz. Until now, you'd have to resort to external crossovers or worse yet, graphic EQ modules. Both of these are fraught with limitations, not to mention adding cost, rack space requirements, and complexity to your system. The M•800 power amplifier eliminates the need for any of these external devices - it has the compensation circuitry already built in, and using it is a breeze. CD FREQUENCY Your compression drivers' spec sheet should have a suggested frequency for compensation boost. If so, just turn the CONSTANT DIRECTIVITY switch ON and set its knob to match that frequency. If your spec sheet doesn't have that information, you can simply adjust the frequency knob by ear, preferably using the same music as the actual performance (3.5kHz is a good place to start). 15dB 10dB 5dB CONSTANT DIRECTIVITY HORN EQ /AIR EQ 4.5k Hz OFF ON 2k Hz 6k Hz AIR EQ TYPICAL More on Constant Directivity Horns All high-frequency compression drivers have an inherent roll-off of about 6 dB per octave above about 3kHz. The exact frequency at which the roll-off occurs (called the mass breakpoint) depends on the materials used, the mass of the moving parts (diaphragm and voice coil) and the strength of the magnet. The CONSTANT DIRECTIVITY HORN EQ control on the M•800 compensates for this natural roll-off in the power response of the compression driver coupled to a CD horn, with the end result of flat-frequency response (constant) over a wide coverage angle (directivity). 0dB -5dB 20Hz 100Hz 1kHz Constant Directivity EQ 10kHz 20kHz Even if you don't have CD horns, you can use the CONSTANT DIRECTIVITY feature to enhance your EQ curve. By setting the frequency knob fully clockwise, you introduce a very high-frequency boost to the signal (above 6kHz). And in Mackie-land, this gentle boost has a name: AIR, as seen on our SR series of consoles. By boosting these high frequencies, AIR will breathe life into your mix, making cymbals brighter and vocals silkier. Speaking of Mackie SR consoles: If you use the AIR feature on an SR console as well as the AIR feature just described on the M•800, you may be overdoing it. You won't hyper-ventilate or anything, but it might cause your audience to experience ear fatigue from too much highfrequency content. Too much of a good thing, perhaps. 15