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I've seen arrays of passive speaker boxes (high output passive professional PA speakers) that were connected to each other and only the last (or first) one was connected to the power amplifier (a very high power amplifier in that case). The speaker cabiners had the sockets labelled IN and OUT, which means they had been designed for this sort of connection.

The question: I wonder whether the same setup - multiple speakers hooked on single amp output - is possible with standard consumer home audio systems (as my Cantons dont't have the OUT connectors). I'm only interested in the technical aspects, not in how the fidelity may degrade (I only use coat hangers to connect my speakers).

I'm not very well educated in this field, so I'd like to provide some of reasoning I'd already done, in case there is something to correct in there, too. I understand that one should never connect a speaker box of impedance lower than that for which the amplifier is designed (so you can connect 8 Ohm speaker to 4 Ohm rated amp but not the other way around). I'd count that impedance behaves quite like resistance in that, that if I connect the speakers in parallel, I'd end up with half total impedance and would need a 4 Ohm rated amp for a pair of 8 Ohm rated speakers. With three of them, I'd be down to 2,5 Ohm rated amp for 8 Ohm speaker boxes. With speakers connected in series, I'd need an amp power rated roughly equal to the speaker power ratings combined but won't need to worry about the impedance (as long as the speakers are same or higher impedance than amp rating). For simplicity, I use sets of same speakers (make, model, power rating, impedance) here because that is what interests me. My amps are D-class.

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  • \$\begingroup\$ Your speakers can be seen just as inductances, so you can put two of them at your outputs; depending of if you do it serial or parallel and how your amplifier works, you might be able to create some magic smoke. \$\endgroup\$
    – PlasmaHH
    Commented Jul 20, 2015 at 9:06
  • \$\begingroup\$ Your question revolves around the PA speaker example in the first paragraph but there is no detail to decide if these devices were just fed a signal and this signal was daisy chained thru to the other speakers with each speaker having an internal amplifier. That makes a big difference. \$\endgroup\$
    – Andy aka
    Commented Jul 20, 2015 at 9:11
  • \$\begingroup\$ @Andyaka Thanks for the hint. I though I made it clear (with the power amp on the end) - because everything is pretty clear in one's head. I'll edit the question. \$\endgroup\$
    – Pavel
    Commented Jul 20, 2015 at 9:35
  • \$\begingroup\$ @PlasmaHH Well, if that's so simple, thank you for your comment - if you turn it into answer, I'll be happy to accept it. \$\endgroup\$
    – Pavel
    Commented Jul 20, 2015 at 9:40
  • \$\begingroup\$ To all downvoters: I'd appreciate if you left a comment as to what is wrong with this question. \$\endgroup\$
    – Pavel
    Commented Jul 20, 2015 at 13:50

1 Answer 1

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Yes, you are correct, you should not connect a speaker (or speakers) whose total impedance is less than the rated amplifier output. If the equivalent speaker impedance is higher than the amplifier output (e.g. connecting an 8 Ω speaker to an 4 Ω amplifier output). then the output will not be as loud as it could be

If you are connecting up more than one speaker to an amplifier, then you can create a network of parallel and series speaker connections to keep the impedance equal to or higher than the amplifier output.

enter image description here

In large installations, such as a sports arena where there may be hundreds of speakers, that's not what they do. Instead they use a "high-impedance constant voltage" distribution scheme:

enter image description here

A transformer at the power-amplifier output steps up the voltage to approximately 70.7V at full power. Each speaker has a step-down transformer that matches the 70.7V line to each speaker's impedance. Each of the step-down transformers are wired in parallel, making it trivial to add or remove speakers on the system.

Another advantage of this type of system, is the 70.7V line reduces power loss due to cable heating. That's because the speaker cable carries the audio signal as a low current. Therefore you can use smaller-gauge speaker cable or a very long cable.

The disadvantage of this scheme are the extra transformers needed; however it is possible to get both amplifiers (like the one below) and speakers that already included the needed step-up/step-down transfers.

enter image description here

The 25V output shown next to the 70V one is an older standard. You may also see 100V systems.

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  • \$\begingroup\$ Thank you for your answer! The network of parallel and serial connection is just what I was wondering about. I'll wait some courtesy hours before I mark the accepted answer. \$\endgroup\$
    – Pavel
    Commented Jul 20, 2015 at 13:29

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