APPENDIX E: Technical Info
DO THE MATH: OHMS, LOADS AND SUCH
Remember: As the load gets “heavier,” its value in ohms goes down. For instance, a
Since you’re in the biz (or you are now, since you just bought an amp), you probably own a volt/ohm meter (or DVM, for Digital Volt Meter). It’s an indispensable tool for anyone working with speakers and such. If you don’t own a meter, go out and get one right now — we’ll wait.
If you’re just dealing with one speaker (or cabinet) per output, the load in ohms will be printed on it somewhere. That’s your load. You can confirm this with the volt/ohm meter you just bought — set it for ohms, set it for the lowest range (unless it’s an autoranging meter) and measure across the speaker termi- nals. It may not agree exactly; a speaker rated at eight ohms may read between 5 and 7 ohms. (If it’s a
If you’re driving an assortment of speakers (or cabinets), things can get complicated. There are two basic ways of linking multiple loads (speakers in this case): series and parallel.
“Series” means that the positive amp output connects to the first speaker’s positive termi- nal, the first speaker’s negative terminal connects to the second speaker’s positive ter- minal, the second speaker’s negative terminal goes to the third, and so on, until the chain ends at the amp’s negative output. Series con- nections are not normally used in PA applications because it ruins the amplifier’s ability to damp (control) the speakers.
Doing load calculations with series configu- rations is easy — just add the loads. For instance, four
“Parallel” means that the positive amp out- put connects to the positive terminals of all the speakers, and the negative amp output con- nects to the negative terminals of all the speakers. If one speaker fails in a parallel con- figuration, the others will still work, but the load will change. That lets you breathe a little easier (the show will go on), except that you may have a dead speaker and not even know it.
Calculating parallel loads is also easy, as long as each speaker has the same value — just divide the value by the number of speak- ers. For instance, four
(8 / 4 = 2). If the loads aren’t all the same, the formula gets a little more complicated, but nothing that you can’t do with a simple calculator.
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There are other, more complicated configu- rations, like
•As a load gets “heavier,” its impedance in ohms decreases.
•The lower the impedance (ohms), the higher the power: The M•1200 has 600 watts (per side) with a
•Do not connect a load of under 2 ohms (in STEREO and MONO mode) or 4 ohms (in BRIDGE mode).
•Never plug amplifier outputs into any- thing except speakers (unless you have an outboard box designed to accept speaker levels).
•Never play good music through bad speak- ers. You may, however, play bad music through good speakers (but only on
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