Tapco pmn manual Do The Math Ohms, Loads, and Such, Appendix B Technical Info

Appendix B: Technical Info

Do The Math: Ohms, Loads, and Such

An ohm is a unit of resistance — the more ohms,

the more resistance (or, more accurately in this case, impedance). The more the resistance, the less the power.

If you’re dealing with just one speaker (or cabinet) per output, the load in ohms is usually printed on it somewhere. That’s your load, usually 8 ohms or 4 ohms.

If you’re driving an assortment of speakers, things can get complicated. There are two basic ways of linking multiple loads (or speakers in this case): series and parallel.

Since series connections are not normally used in PA applications, we’ll concentrate on the parallel connection. Parallel means that the positive amp output connects to the positive terminals of all the speakers, and the negative amp output connects to the negative terminals of all the speakers. If one

speaker fails in a parallel configuration, the others will still work.

Calculating parallel loads is easy, as long as each speaker has the same value — just divide the value by the number of speakers. For instance, four 8-ohm speakers, connected in parallel, will equal 2 ohms (8/4 = 2). If the loads are not all the same, the formula gets a little more complicated, but nothing that you can’t do with a simple calculator.

ZT =					1
				1		1
	1		+		+		+ . . .
				Z2
		Z1				Z3

Using this formula, an 8-ohm speaker and a 4- ohm speaker, connected in parallel, will equal 2.7 ohms. Remember that the Juice amplifiers require 2 ohms or greater per channel in Stereo or Mono mode, and 4 ohms or greater in Bridge mode.

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