QSC Audio CX Series X. How Many Speakers?, …+25% for, watts, …approx. 1/4 watt, you need…

X. How Many Speakers?

How many loudspeakers can you connect to the distributed line? The amplifier itself determines the amount of audio power available to the line, and from that figure you must compensate for insertion loss in the speaker transformers and for headroom when you determine how much power is available

1.56watts for the speakers.

			…+25% for		For example, let’s suppose you have an amplifier rated at 500 watts into a 70-volt
			headroom.†		line, and your speaker transformers each have an insertion loss of 1 dB, which is
				1.25 watts	typical. The losses in the transformers mean that they will draw 25% more audio
		…approx. 1/4 watt
	more to compensate				power than they deliver to the speakers. For headroom, as mentioned before, you
		for transformer			add at least another 25% to the total amount of power drawn from the amplifier.
		insertion loss*		1 watt
					The additional 25% headroom is optional but highly recommended. It will allow
					for future additions to the system and reduce the stress on the power amplifier.
					1.25 x 1.25 = 1.5625
		For every watt put			So you’ll need at least about 56% more power than the total sum of the transformer
		into the speakers,			taps. The reciprocal of 1.5625 is .64, so conversely you can figure on allowing a
			you need…		maximum of 64% of the amplifier’s rated power for the loudspeakers. Therefore,
					the highest combination of transformer taps the 500-watt amplifier can drive
					satisfactorily is a sum of about 320 watts, e.g., 32 speakers each tapped at 10 watts,
					or 64 speakers tapped at 5 watts, etc.
					This table lists the recommended maximum load (sum of all speaker transformer
*assuming a typical insertion loss of 1dB
					power taps on one line) for the CX6T and CX12T amplifiers. These figures assume
†a good engineering practice
					a typical transformer insertion loss of about 1 dB.
						You can, of course, use different output configurations on
						the two amp channels if it’s not operating in bridged mono
						mode. For example, one channel of a CX12T could drive a
						70-volt line loaded at 320 watts while the other channel
						drives a 25-volt line, or even a direct loudspeaker.

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