CONSTANT DIRECTIVITY SWITCH

If you don’t have constant directivity horns, you can leave this switch OFF.

Compression drivers mounted on constant- directivity 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

0dB

–5dB

100Hz

1kHz

10kHz 20kHz

20Hz

Constant Directivity EQ

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 high- frequency content. Too much of a good thing, perhaps.

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 compres-

sion 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 (con- stant) over a wide coverage angle (directivity).

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