Mackie M1200/M1400 owner manual AMP Mode, More on Constant Directivity Horns

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).

15dB

10dB

5dB

0dB

–5dB	100Hz	1kHz	10kHz 20kHz
20Hz

Constant Directivity EQ

Wait, there’s more: If you don’t have con- stant directivity horns, you can forget all this, and leave the switch OFF.

Or, better yet, you can use this 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 boost- ing these high frequencies, AIR will breathe life into your mix, making cymbals brighter and vocals silkier.

Speaking of Mackie SR consoles: If you use both the AIR feature on an SR console as well as the AIR feature just described on the M•1200/M•1400, you may be overdoing it. You won’t hyperventilate 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.

More on Constant Directivity Horns

Back in the early ’70s, radial horns were the common mechanism for reproducing high frequencies. Radial

horns had a serious problem, though. The high frequencies tended to beam straight ahead, so if you moved

away from front and center (off-axis), the bril- liance and sizzle quickly diminished to a muffled blur. Constant Directivity horns were designed to spread the higher frequencies evenly throughout the horn’s dispersion pattern.

This was accomplished by using a smaller opening to the horn, using straight sidewalls in both the horizontal and vertical planes (radial horns typically have curved vertical sections that cause beaming), and providing a flare at the mouth of the horn to disperse the mid to high frequencies.

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•1200/M•1400 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) with a wide coverage angle (directivity).

AMP MODE

This three-way switch, along with the OUT- PUT APPLICATION’s three-way switch, determines what kind of amplifier you want the M•1200/M•1400 to be.

1CHANNEL / BRIDGE / MONO

LOW CUT	INPUT
FILTER
TYPICAL	BALANCED
	OR
35 Hz	UNBALANCED
	STAGE
	MONITOR

AMP MODE

STEREO	MONO	BRIDGE
TYPICAL

INPUT

BALANCED

OR

UNBALANCED

CHANNEL 2

LOW CUT

FILTER

TYPICAL

35 Hz

STAGE

MONITOR

100 Hz OUTPUT APPLICATION 100 Hz

OFF	170 Hz		FULL		SUB		OFF	170 Hz
			RANGE		WOOFER
	CONSTANT DIRECTIVITY		LIMITER (CH1 & CH2)		FREQUENCY		CONSTANT DIRECTIVITY
	HORN EQ/AIR EQ						HORN EQ/AIR EQ
			STEREO
4.5 kHz					125Hz		4.5k Hz
		ON	TYPICAL			ON
2k Hz	5.6k Hz		ON	OFF	63Hz		2k Hz	5.6k Hz
	AIR EQ	OFF				OFF		AIR EQ
		TYPICAL				TYPICAL
			THRU			THRU

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