Mackie M800 APPENDIX C: Bi-ampingand Tri-amping, Biamplified System with Active Crossover

APPENDIX C: Bi-amping and Tri-amping

Most speaker systems in use today are of the two-way or three-way variety. Cone speakers are good at reproducing low and mid-range fre- quencies, but not high frequencies. Likewise, compression drivers are good at reproducing high frequencies, but definitely not low fre- quencies. This is why two-way, three-way, and even four-way speaker systems were developed

—to improve the efficiency of each individual driver by requiring it to reproduce only the fre- quencies that it reproduces best.

One method of accomplishing this is through the use of a passive crossover network between the amplifier and the speaker(s). Often the passive crossover is built into the cabinet along with the various drivers. The crossover divides the high-level speaker signal into frequency bands, which are then directed to the appropriate driver. There are some drawbacks to this method, however. The pas- sive crossover adds reactance to the load that

the amplifier sees, which can affect the damp- ing. Power is wasted as heat across the resistors in the crossover, reducing the amount of amplifier power available to the drivers themselves.

Biamplified and triamplified systems use separate power amplifiers to power each individual low-frequency and high-frequency driver. An electronic crossover (a.k.a. active crossover) is located between the signal source and the power amplifier. The advantages of this method include 1) increased headroom available from each amplifier, since they’re amplifying only a portion of the entire audio spectrum; 2) improved damping factor because the amplifier output is connected directly to the driver; 3) improved efficiency because there are no passive resistors to dissipate heat; and 4) flexibility to choose the optimum crossover frequency and crossover slope for the individual drivers in the system.

			FR SERIES
	POWER AMPLIFIER
		(STEREO MODE)
FROM SIGNAL SOURCE	CH 1		CH 1	+
(MACKIE MIXING CONSOLE)	IN		OUT	–
FROM SIGNAL SOURCE	CH 2		CH 2 –
(MACKIE MIXING CONSOLE)	IN		OUT +

TWO-WAY SPEAKER CABINET

	HIGH-LEVEL	HIGH FREQUENCIES
	PASSIVE
		TO TWEETER
	CROSSOVER
		LOW FREQUENCIES
		TO WOOFER
TWO-WAY SPEAKER CABINET
	HIGH-LEVEL	HIGH FREQUENCIES
	PASSIVE
		TO TWEETER
	CROSSOVER
		LOW FREQUENCIES
		TO WOOFER

Passive Crossover System

FR SERIES

FROM SIGNAL SOURCE

POWER AMPLIFIER

(MACKIE MIXING CONSOLE)

(STEREO MODE)

TO HIGH-FREQUENCY

CH 1

+

TWEET

LOW-LEVEL

AMPLIFIER

INPUT

CH 1

3-WAY ACTIVE

OUT

–

CROSSOVER

TO MID-FREQUENCY

CH 2

CH 2 –

INPUT

AMPLIFIER

OUT +

MID

FR SERIES

POWER AMPLIFIER

(BRIDGE MODE)

TO LOW-FREQUENCY

CH 1

+

INPUT

CH 1

AMPLIFIER

OUT

–

WOOF

FR SERIES

CH 2 –

FROM SIGNAL SOURCE

POWER AMPLIFIER

OUT +

(MACKIE MIXING CONSOLE)

TO HIGH-FREQUENCY

CH 1

(STEREO MODE)

TWEET

+

INPUT

CH 1

LOW-LEVEL

AMPLIFIER

Triamplified System with Active Crossover

2-WAY ACTIVE

OUT –

CROSSOVER

TO LOW-FREQUENCY

CH 2

CH 2 –

INPUT

AMPLIFIER

OUT +

WOOF

Biamplified System with Active Crossover

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