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I hope this is not off topic, and comes under the category: "usage of specific music software or hardware". I am new to this community but have used other communities before.

I am playing live at the weekend in a hall of small size, no more than 100 people. We will be using a mixer/amp combo, specifically the Yamaha EMX512SC. We have at our disposal x4 100w passive speakers which for the purpose of this question I am assuming they are all 8ohm.

I have researched that running speakers in series you half the impedance. With this in mind I am looking at the specifications for our mixer/amp combo and I am concerned that we are not safe to use it.

According to the Yamaha EMX512SC specifications:

Maximum output power: @4ohms 500W/ch
Maximum output power: @8ohms 370W/ch (100V model), 350W/ch (120V model), 320W/ch (220-240V model)

Yamaha EMX512SC has output 2 channels. Is it possible for me to safely run these x4 100w speakers, using series or parallel wiring?

Note: We only plan to use this equipment for vocals and keyboards only, as we plan to use our guitar/bass guitar amplifiers.

Update, after comments/answers.

Unfortunately I do not have exact model numbers for the speakers. Two of the speakers are carlsbro, they look exactly like the ones in this picture, but 100w not 150w.

Based on the answers so far, I am correct that this diagram would be suitable? enter image description here

End Result. We got to the venue and it was a lot smaller than what we had anticipated. After looking at both sets of speakers we found that one pair was actually 16ohms 100 watt. The other pair had no markings on at all except that they were 100w, so we still had mystery speakers in terms of ohms! These speakers however had accompanied the mixer/amp and they had been run together previously. We ending up going with just these speakers, each had their own channel.

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    In parallel you halve the impedance. In series you double it. Also, make sure you double check and verify the nominal impedance sir your speakers. It's important. – Todd Wilcox Feb 14 '17 at 12:53
  • @ToddWilcox I think this is your area of expertise. Would love to see your answer to the question when you have time to do it justice. – Rockin Cowboy Feb 14 '17 at 17:02
  • Can you clarify the exact model of the speakers? The "100W" spec does not give us much information, we need either a spec that is called the "program", "music", or "RMS" watts and ideally also the peak watts the speaker can handle. – Todd Wilcox Feb 14 '17 at 23:20
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Building a PA with mystery speakers is fraught with peril. The biggest question that faces you is: If you blow one or more of those speakers, who will care and how much will they care?

Speakers that are not well marked are usually the cheapest kind. So you're probably not risking a lot of value, unless there's some kind of sentimental value or just ownership that someone takes seriously.

Your real question is how to minimize the risks of using mystery speakers. Here's how:

  • Connect them in series, not parallel, to get the highest load impedance.
  • Make the left and right channels symmetrical. In other words, if you have two speakers of model A and two model B, make left A+B and right A+B, don't make left A+A and right B+B.
  • EQ out the lows. Don't send anything lower than 80 Hz or so, and if you can start rolling it off around 200 Hz, you'll be sending about 1/3 less power to the speakers in a less-important range (especially for vocals, which are usually king).
  • Your speakers probably can't reproduce much at all above 15 kHz. If you can cut that out, do that also.
  • Place the speakers and microphones to minimize feedback, which is one of your biggest dangers in many ways.
  • Get everything (especially the keyboards) plugged in and turned on before you even turn the PA on to prevent damaging pops. Turn the PA on last and off first. Talk to the keyboard player about how important this is and remind them before and right after the show.
  • Limit your last set of main output level controls to their halfway point at most, unless that's really not loud enough.
  • Use a compressor and/or limiter to tame dynamics - especially on the vocals.

When all is said and one, I predict you'll wish you had someone who knows what's what and a good set of monitors, but everyone's coming out to have a good time, so don't let it stress you too much.

  • the poor wording in the illustration in the question seems to imply that you can mix impedance on each A+B channel. My understanding is that this is not a good idea (?). – Yorik Feb 15 '17 at 21:40
  • @Yorik If you have to mix impedance, it should be done in series, not parallel. Another good reason to run mystery speakers in series. – Todd Wilcox Feb 15 '17 at 21:42
  • Absolutely - mixing in series is not an issue. In parallel, it is! – Doktor Mayhem Feb 15 '17 at 22:54
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    I took your advice, see updated question. We didn't need to risk running both sets of speakers in the end. I've learnt that you should really know what you're working with before the event. – Jack Pettinger Feb 20 '17 at 9:48
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The accepted and top-voted answer is just wrong. You state that you have an amplifier capable of serving 4Ohms of impedance, and (presumably equal) speakers of 8Ohms of impedance. You can wire two pairs of speakers in parallel, leading to a load of 2 times 4Ohm.

The accepted answer recommends wiring them in series, and using the combinations A+B and A+B in case you have different speakers. For different speakers, only connection in parallel leads to a defined response depending on the output voltage.

For another thing, even assuming equal speakers, wiring them in series gives you an impedance of 16Ohm rather than the 4Ohm the amplifier is rated for. Now output power is reduced along with the impedance, meaning that the 500W/ch amplifier will now already reach its maximum rated voltage at a 4th of its rated power, namely at 125W/ch. Beyond that, it will start clipping. Since it does that at a fourth of its rated maximum current, it will easily survive it. The tweeters of the speakers won't.

So it makes no sense at all to wire 8Ohm speaker pairs in a manner where you load a 4Ohm-rated amplifier with merely 16Ohm. Instead, put them in parallel and put the rated load of 4Ohm on the amplifier.

Another answer recommends verifying the impedance with an ohmmeter. Again, this is at best incomplete advice since the DC resistance is not the same as the AC impendance in audible range. As a rule of thumb, the DC resistance will typically be about 25% lower than the impedance, meaning that you'll measure something like 6Ohm for a speaker rated at 8Ohm of impedance, and 3Ohm for a speaker rated at 4Ohm.

Because of the frequency crossover, the DC resistance will only reflect the bass speaker's impedance far below its resonance frequency. Other speakers are blocked from DC.

  • Also note that there is no practical option in this sort of setup to run two speaker cabinets in series. Unless you make up custom cables, they will always be in parallel. – Laurence Payne Jan 18 '18 at 23:11
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Transistor amps aim to have an output impendance of 0Ohm (which means that their output voltage does not depend on the load as long as the load is within specifications). You have two channels each allowing a load impedance of 4Ohms. Putting different speakers even of equal specs in series is problematic since the voltage will not be distributed evenly. However, putting even different speakers in parallel is unproblematic since one speaker's voltage is not affected by the other (assuming good cabling, of course: every speaker should have its own cable to the amp). Now the laws of complex impendance mean that when the speakers don't have the same phase displacement at some frequency, the overall conductance might add up to be less than expected. Meaning that the overall impendance might be larger than expected, completely harmless for a solid-state amp.

So electrically you are good. Acoustically, different speakers might have different delays for different frequencies. This may be particularly noticeable if they have different crossover frequencies, different loudspeaker types, bass reflex pipes or delay lines or horns.

The best you can do here is to put them up with good distance. That way, most of the time people will getting predominantly the signal from a single speaker, and when not, the attenuation problems will be more due to the overall geometry rather than the specific speakers.

So in a nutshell: you are fine. Wire two speakers in parallel for each channel. If you have two different types of speakers, you wire two different types in parallel so that your two channels have one mixed pair each.

Note that "polarity" of speakers is usually only defined in relation to the respective other speaker of a pair. If you find that the result lacks a lot of bass in the center of the room or feels strange, it might be worth seeing what happens if you reverse polarity on one type of speaker. It might match the other better then.

Most of the fine points here apply when you have two different pairs. If you have 4 speakers of the same type, there is a lot less that can go less than optimal.

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If you are certain you have 8 Ohms impedance on each speaker, it is safe to connect a pair in parallel per channel, since the amplifier will see only 4 Ohms per channel.

For every case, be aware that your amplifier will retrieve more power than your speakers can handle. Do not reach its maximum capacity.

Make sure to check your actual impedance with an ohmmeter/multimeter and do not connect impedances lower than 4 Ohms (you will burn your amp)

  • Don't panic! The sort of amp we're discussing has pretty good protection. It won't explode even if a speaker output is completely shorted. – Laurence Payne Jan 18 '18 at 23:12
  • The wonders of engineering!... however using the right setup is always encouraged ;) – Alexis Jan 25 '18 at 23:54
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Whatever you do, don't ever connect different loudspeakers in series. That's because their frequency response is defined in respect to the voltage they are driven at, not the current.

As an extreme case, connecting a box with a piezo tweeter and a box with a ribbon tweeter in series will likely kill either a tweeter or the amp pretty fast. That's because one tweeter has mostly capacitive impedance, and the other has mostly indictive impedance, and they mostly cancel, leading to a total impedance that is actually less (in absolute terms) than either of the original impedances.

Only ever connect speakers of different type in parallel, and then in manner where their combined impedance does not become less than what the amplifier can support.

It's actually mostly unproblematic to connect somewhat lower total impedances than rated to an amplifier as long as you are not going to play the amplifier near to its limits. For example, an amplifier able to put out 50W at 8Ohm will with the same current be able to put out 25W at 4Ohm (this is not entirely accurate since the operating current is delivered at a less efficient output voltage than when the amplifier is used at specified impedance, but as a rule of thumb, it's a good first approximation).

Playing an amplifier to its limits, particularly a solid-state amp, is a real bad idea since it will likely kill the speakers pretty fast, in particular if they have separate tweeters. An amp that is maxing out will deliver a lot of high-energy high-frequency noise, with considerably more power than its specs.

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