Connecting Multiple Speakers to a PA SystemJuly 12, 2012 6:00 am Live Sound
In the simplest PA system setup possible, you would have a power amplifier with one speaker output connector and you would connect one speaker to it. Boom. Done. Some power amplifiers have two independent speaker output connectors. In this case you could connect one speaker to each connector. Again, boom. And twice the sound!
But what if you need to connect more than one speaker to a single speaker output connector on your power amplifier or powered mixer? If you have just a single speaker output, it would be nice to be able to connect two speakers to it, one for each side of the stage. Even if you have two independent speaker outputs available, you still might want to have an additional speaker or two further back in the audience, in addition to the two “mains” flanking the stage.
But where do we connect the additional speaker(s)?
The usual approach to this problem is to “daisy-chain” an additional speaker by connecting it directly to one of the existing speakers, as if we were “tapping off” some of that speaker’s signal to drive the added speaker, which we basically are. But what we are really doing is connecting the two speakers in parallel, and driving the combination with the power amplifier’s speaker output.
NOTE: This all assumes you are using a power amplifier to drive passive speakers in the classic manner. If you are using powered speakers, the rules for connecting multiple speakers are different. See your user manual for details.
If you check your speaker, you will probably find that it has two 1/4″ connectors on it. They may be labeled “Input” and “Output”, or they may have no labels at all, like the speakers my band uses. Inside the speaker, these two connectors are wired directly together, and both are connected to the speaker system inside the box.
Here’s a diagram that shows what is happening when we daisy-chain two speakers to a PA output. (The multiple drivers usually found inside the box are shown as a single speaker for clarity.)
(Click for a PDF version of the diagram)
The top part of the diagram shows the connections inside a typical PA speaker. (”Tip” and “Sleeve” refer to the parts of the 1/4″ connectors used.) The bottom part of the diagram shows that the two speakers end up connected in parallel (i.e. both connected directly to the PA speaker output) when you daisy-chain them by running a cable from the power amplifier to the first speaker and a second cable from the first speaker to the second speaker.
One consequence of daisy-chaining two speakers in this way is that the impedance presented to the PA speaker output is cut in half. This means that if each of two daisy-chained speakers is rated as having an impedance of 8 ohms (a typical value), the amplifier output will “see” a total load of 4 ohms. This is almost always OK (check your amplifier’s manual to be sure), but many amplifiers cannot handle impedances of less than 4 ohms. In this case, you should not try to daisy-chain a third 8-ohm speaker on the same output, as this would reduce the impedance to one-third of 8 ohms, or 2.66 ohms. This could be a “heavy” enough load to blow the amplifier, or at the very least a fuse!
Series Or Parallel?
One possible source of confusion here is the distinction between series and parallel speaker connections. In the diagram above, it is clear that daisy-chained speakers end up connected in parallel, since the “plus” terminals of both speakers are connected to one lead from the amplifier output and both “minus” terminals are connected to the other lead.
“But when we hook them up, we go from the amplifier to the first speaker, then from the first speaker to the second speaker. Doesn’t that mean they’re in series? It looks like a ’series’ of speakers to me.”
Well, no. In a series connection, the signal would come from the amplifier on one of the output leads and run through one of the speakers, then through the other speaker, then back to the amplifier on the other lead. (It would also present a 16-ohm “load” to the amplifier, since impedances add up in a series connection.) If you trace the signal flow in the diagram, you’ll see that that’s not what’s happening here.
Series connections are used in very large live-sound setups (e.g. in arenas) and within multiple-speaker cabinets, and for the same reason: a system containing many 8-ohm speakers must still present a total impedance of 8 ohms at the point where it is connected to the amplifier. To achieve this, a combination of series and parallel connections is used. For example, in a 4-speaker bass cab, two of the speakers might be wired in series (16 ohms) with the other two speakers also wired in series (16 ohms). Then the two pairs are wired in parallel, giving a total impedance at the connector of 8 ohms!Tags: Live Sound, PA system, Speakers -->