Constant directivity switch, Cd frequency – MACKIE M800 User Manual

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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 men-
tion 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 DIREC-

TIVITY 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).

100

10k

20k

–5

Even if you don’t have CD horns, you can

use the

CONSTANT DIRECTIVITY feature to

enhance your EQ curve. By setting the fre-
quency 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 EQ

OFF ON

CONSTANT DIRECTIVITY

HORN EQ /AIR EQ

4.5k Hz

6k Hz

2k 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 oc-
tave above about 3kHz. The

exact frequency at which the roll-off occurs
(called the mass breakpoint) depends on the ma-
terials 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).