How do I Connect Multiple Speakers to my HiFi Amplifier

I am often asked “How do I connect multiple speakers to my amplifier?” Before I answer, let’s define what we mean by the word “amplifier”. In a stereo “amp” there are two amplifiers – one for the left, and one for the right channel. That is, in the one amplifier box, there are two different amplifiers. In a home theatre amplifier with surround sound, there may be 5, 6, 9 or 11 amplifiers in the one “amplifier” box. For the purposes of this article, we are talking about connecting multiple speakers to a single amplifier only, that is, either the left or the right, or any single amplifier. Of course you can connect multiple speakers to both the left and right amp of a stereo – you just need to follow the principles twice, once for each amp.

Multiple Speakers on One Amplifier

Multiple speakers - Connecting two speakersBy adding an extra speaker to the output of an amplifier, you are adding to the load of the amplifier. That is, two speakers is double the load of one speaker. Most amplifiers can cope with a load of two speakers. Similar to a passenger on a small motor bike: add another passenger and the load the bike needs to carry is doubled, but most bikes will cope with two passengers.

However adding more than two speakers will normally overload the amplifier. Similar to the motor bike example: it can cope with two passengers, but starts to struggle with 3 or more passengers. Most modern amplifiers have some sort of limiting circuit to stop the amplifier working if it is overloaded. In some amplifiers, this involves blowing a fuse inside the amplifier. In other (more technical) amplifiers they will automatically turn off until you turn it back on with a load that is under its maximum safe load.

Amplifiers may cope with multiple speakers at low volumes,multiple speakers - bike example (400 x 267) but will have issues when running at high volume levels. Similar to the motor bike illustration: it may cope with 3 or 4 passengers while going slowly on a flat road, but it will struggle when asked to work harder (like go up a hill or go faster). To be safe, never overload your amplifier.

To understand the technical reason for this, I strongly encourage you to read through the technical explanation below. A good overview on this can be found in the video in the article on Understanding Speaker Impedance

If you just want to know how to wire two speakers to one amp, (4 speakers to a stereo) without switching or individual volume control, see the article on How to connect 2 speakers to 1 amplifier.

If you want speaker on/off or individual volume control, or you want more than two pair of speakers, (like three, four or more pairs) connected to your HiFi amplifier, see the article How to wire four speakers to one amplifier.

If you need to wire more than four pairs of speakers, particularly in a commercial installation, see the article on Distributed Speaker Systems.

Technical Explanation

In the specifications for a hifi amplifier might say Output: 100 watts @ 4 ohms

This is normally specifying the maximum power output of the amplifier and the minimum resistance in the speaker circuit. So in this case, the amplifier will produce 100 watts of power when run at full volume connected to a speaker load of  4 ohms. The ohms bit is our main concern. Ohms is a measurement of resistance. In the case of speakers, it is the measurement of how much resistance the speaker has in the circuit connected to the amplifier. Technically speaking, the resistance of speakers is called “impedance”, as the output of an amplifier is AC, and resistance in an AC circuit is called impedance.

To understand what all this means, we need to get technical and use some formulas. An explanation of these formulas can be found in the article The Dreaded Ohms Law. multiple speakers - ohms law We will use the summary table from that article. You don’t need to understand these formulas but we need to use them.

In our example, we know:

Power is 100 watts: P = 100

Impedance is 4 ohms: R = 4

So we can use the various formulas to calculate the output voltage(V) and current(I) of the amplifier.

Calculation of output voltage(V):

V=\sqrt{P\times R}=\sqrt{100\times 4}=\sqrt{400}= 20\ volts

Calculation of output current (I):

I=\sqrt{\frac{P}{R}} =\sqrt{\frac{100}{4}} =\sqrt{25} =5\ amps

So, from the specifications and a couple of calculations, we now know the following:

Power=100 watts Impedance (resistance) = 4 ohms Voltage = 20 volts Current = 5 amps

An equivalent circuit will help us visualise what is happening.

multiple speakers - connecting 1 4 ohm speaker

This illustrates the maximum capacities of the amplifier. With a load impedance (speaker) of 4 ohms, the amplifier needs to deliver 5 amps to produce the 100 watts of power. This amplifier will normally have some sort of limiting circuitry to limit the current output to no more than 5 amps. The reason being, all the electronics will be designed to deliver 5 amps. Therefore to avoid “blowing up” the output stage (and possibly the power supply), some form of current limiting is employed. The most simplest form of a current limiting circuit is a fuse. If a 5 amp fuse is placed in series with the output, then it would supply the current until the total current exceeds the 5 amps at which point it would “blow”.

Remember, these are the maximum ratings of the amplifier. In practice, many speakers are made to have an impedance of 8 ohms. Therefore the equivalent circuit would be similar, but with a different impedance, therefore a different current as shown here:

I=\frac{V}{R} =\frac{20}{8} =2.5\ ampsmultiple speakers - connecting one 8 ohms speaker

The power output of the amplifier is also reduced:

P=\frac{V^2}{R}=\frac{20^2}{8}=\frac{400}{8}=50\ watts

In practice, because the speaker impedance is increased, the load is decreased and the amplifier is capable of outputting around 23 volts which gives a maximum power output of 70 watt @ 8 ohms.

The important principal is: the higher the speaker impedance, the less current required from the amplifier. Also, the lower the speaker impedance, the more current required from the amplifier.

OK, this is all very good, but what about connecting two or more speakers to the amplifier? Glad you ask, this is the fun bit. Let’s connect two 8 ohm speakers to the one amplifier.

multiple speakers - connecting 2 8 ohms speaker in parallel

You will notice that each speaker still draws 2.5 amps from the amplifier. So the combined load on the amplifier is now drawing a total of 5 amps (2 x 2.5=5). You may have noticed that this is the same current (and therefore the same total load) as one 4 ohm speaker. That’s right, two 8 ohm speakers in parallel is the same as one 4 ohm speaker. If you like, you can prove this using the formula for calculating resistances in parallel. If you’ve had enough formulas, just skip this and go to the next paragraph.

\frac{1}{R_{Total}}= \frac{1}{R_1}+\frac{1}{R_2}\ \ so\ \(\frac{1}{R_{Total}}= \frac{1}{8}+\frac{1}{8}=\frac{1}{4}\ \ therefore\ {R_{total}=4\ ohms

The good news is, this is within the specifications of the amplifier as we saw earlier. So, as long as the speakers both have an impedance of 8 ohms (or more), and the amplifier is rated for 4 ohms, then you can safely run the amplifier with two speakers.

Now what do think is going to happen if we are having a party in several rooms and need multiple speakers (like four speakers) connected to one amplifier on the stereo? The circuit would look like this:

multiple speakers - connecting four 8 ohm speakers

If the poor old amplifier can still hold the 20 volts, each speaker is still trying to draw 2.5 amps, meaning the total current draw from the amplifier is 10 amps – way above its specified capabilities. At this point, we hope it has a limit/protection circuit and has turned itself off, or at the very least the 5 amp protection fuse inside has blown. If there is no current limiting circuitry, then quickly turn the power off when you see the smoke rising from the amplifier.

For those who like the mathematical evidence rather than just the pictorial reasoning, the calculation of the total resistance looks like this:

\frac{1}{R_{Total}}= \frac{1}{R_1}+\frac{1}{R_2}+\frac{1}{R_3}+\frac{1}{R_4}\ \ so\ \ \(\frac{1}{R_{Total}}= \frac{1}{8}+\frac{1}{8}+\frac{1}{8}+\frac{1}{8}=\frac{1}{2}

therefore\ {R_{total}=2\ ohms

and then calculate the current:

I=\frac{V}{R} =\frac{20}{2} =10\ amps = smoke.

For an easy way to calculate the total impedance of speakers in parallel, try my simple Speakers in Parallel Calculator.

Keep in mind that changing the total load impedance of an amplifier will also increase or decrease the power output of the amplifier. See Multiple Speakers Change Amplifier Power for more details.

Also if the speakers each have a different impedance, then there will be different power levels available to each speaker. For more detail see How Multiple Speakers Share Power. 

Multiple Speaker Selector Switches

multiple speakers - 4 way speaker selectorThere are ways of connecting multiple speakers to a HiFi amplifier without causing damage, but not by simply connecting one speaker onto the other. For a detailed and practical outline of how to connect four or more pairs of speakers to a HiFi amplifier, see this article. The simple method (with the limitations listed in the other article) is to use a speaker selector switch. A 4 zone switch will allow up to 4 pairs of speakers to be connected to the one amplifier.

Please note, speaker selector switches are designed for multi-room installs in a home or small low power installs (like an office or cafe). They are generally suited for low power (under 100 watts) amplifiers. They should be not be considered in a commercial install or for use with high output power amplifiers.

Speaker selector switches can use various techniques to allow multiple speakers to be connected to the one amplifier, namely:

  • a series resistor (around 2½-5 ohms) to restrict the minimum impedance of the speakers circuit to this value. This simple series resistor is often marketed as “manual impedance protection” or simply “Protection”. They are normally good for lower powered amplifiers, and the resistor can get hot at high volume levels.
  • combining the different speakers in series and/or parallel to keep the overall impedance above 4 ohms.
  • matching impedance transformers – this is normally the best, but it is also the most expensive.

All these methods allow multiple speakers, but at a lower volume than using just one speaker. This is logical as the signal is being shared by more than just the one speaker. To see how the power is distributed by the different types of speaker selector switches, see my Speaker Selector Switch Simulator.

For a more detailed explanation and summary of the features of speaker selectors, see my Speaker Selector Switch Summary.

Instead of using a speaker selector switch to connect multiple speakers to your hifi amplifier you can use impedance matching volume controls, as outlined in the article on connecting four speakers.

Conclusion

Depending on the impedance of your speakers and the rating of your amplifier, you should be able to use two pairs of speakers connected to a HiFi amplifier. However, it is wise to use the example given above as a guide and use the figures in the specifications of your amplifier and speakers to calculate and know for sure what the outcome will be. Otherwise use a multiple speaker selector switch and/or impedance matching volume controls. The video in Understanding Speaker Impedance explains how speaker selectors help with impedance protection

For a practical discussion on how to simply wire just 2 pair of speakers to a stereo amplifier (4 speakers to a stereo amp), see my article on How to connect 2 speakers to 1 amplifier.

For more practical information of how to wire two, three, four or more speakers to one amplifier using speaker selector switches and volume controls, see this article.

Manymultiple speakers -download PDF practical examples of connecting multiple speakers to your HiFi have been discussed in the comments below. If, after reading these discussions, you still have a question please read the FAQs before submitting your question.

Thanks to James from Sydney, Australia who suggested this topic.

Please Note: During the Covid-19 pandemic I'm busy with a number of streaming projects, and have very limited time to attend to this website. I'm currently taking up to a week to answer questions. Sorry for any inconvenience.

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I am setting up audio in a room that is 15’ wide by 30 long’. I have a flat screen TV along the 15’ wall And a projector that projects to a screen at the end of the room; i.e. 90 degree to the wall where the TV is.. (Example: Sit in a chair facing TV to watch TV, to watch projector screen, pick up chair and turn 90 degrees to face projector screen) The projector screen has left/Right/Center speakers to the (Of course) Left Right and center of the screen. That works fine. The surround speakers are on stands… Read more »

Hi Geoff. I’m interested in option 2 as above with a similar setup except my setup is a square. I’d love to draw a diagram but I’ll describe it below. Basically in configuration 1 (watching TV on one wall) I have speakers 1-6. 1=FL, 2=FC, 3=FR, 4=RL, 5=RR and 6 is unused but is the FC in the second position. The sub would remain in place for both scenarios. In Scenario 2, by turning 90degrees to my right to watch the projector, spk1=RL, 2 is unused, 3=FL, 4=RR, 5=FR, 6=FC. I’d like a single 2 position switch or selector as… Read more »

Geoff, Many thanks for the quick response. I’ll get the multimeter out tonight and have a fiddle! Hopefully it’s as simple as only switching the +ve feeds. The reason(s) I haven’t gone down the relay route is a) simplicity and b) being even less sure about the wiring! I really ought to investigate relays but am only just getting into the hobby electronics again after a long time off! Just out of interest, would I not need a relay per amp output, so 5 of them and then an external low voltage power source to switch it? In response to… Read more »

Hi
I have a controller with only one rca output
So how could i connect it to several speakers? Just use an amp? And therefore, if i use will i be limited to use just 2 speakers?

I got an old pair of Magna Planar ribbon speakers that require an amplifier that has a minimum of 100 watts into a 2 ohm load. without going into car audio, can I safely wire a powered sub-woofer with 8 ohm resistance to each ribbon speaker to run the resistance up where my Onkyo amp can handle it? I burned up a couple of expensive amps years ago when these were my Dads speakers. I want to hook them up as the front speakers in a 5.1 system.

Geoff My living room and kitchen is side by side, divided by a fireplace. I listen to music in either the living room or the kitchen, but rarely in both places at the same time. I want to hook up 3 speakers, where the middle speaker is used in both zones. The speakers is Bowers & Wilkins CM8 and the impedance is 8 ohm. I wish to control the zones by the amplifier and not by a separate speaker switch. The amplifier NAD C375BEE is a stereo amplifier 2 x 150W, 4-8 ohm, and speaker selection A/B and A+B. As… Read more »

Geoff Yes I guess it is a rather unusual solution. I’ve searched the internet for many hours and didn’t find any information regarding this specific setup. Posting in a couple of forums gave me 2 yea’s and one nay, – not a good basis to lean on. Then I ran into your great site and decided to ask for your opinion. Also thanks for the advice on just wiring A to B. It’ so logical but a little psychological barrier, for me as a novice, to “short” these terminals directly. Thanks a lot for your help and for sharing your… Read more »

hi Mr Geoff, I have a Sony amplifier,the minimum impedance at spkr output is 6 ohms, if I connect 2 spkrs in parallel, the total impedance the amp sees is 4 ohms, if I connect 2 wire wound resistors, 1 ohm each, in series between amp out and speakers, will it total 6 ohms??? will the resistors act as impedance, instead of ohms. Thanks very much.

Thanks Geoff for the response, I used to be a electronic tech many years ago. Anyway I do have wire wound 1 ohm resistors I bought at frys elect, they are 25 watts, I don’t run the speakers too loud since I live in a apt. I just wanted to be sure it would work, I don’t have to spend all that $$$$ for a resistor speaker selector box, since I am only running a polk tower spkr, connected in parallel with a bose bookshelf spkr. I all ready know about connecting the 2 spkrs in series, that will bring… Read more »

I have a house with a Niles speaker system wired through the whole house. there are 8 zones each zone has a Niles vcs 2d volume control( 60 watt max) which splits off to a pair of Niles HD6 125 watt speakers. what do i need to run this system and im under a budget but want good sound? Sound Selector and or Receiver ?

i have found some 8 Zone sound selectors with impedance matching that should work. but not to sure on what kind of an amp, can you suggest something? does it matter how many channels it has?and is it ok if its more than 100 watts per channel?

Dear Geoff, I have been reading your articles and I have learned a lot about sound systems that I didnt know before . My question is about choosing the right amplifier as I have purchased already the speakers for my cars sound system , I have in my possession in total 6 speakers. 2× 400watt 4ohm heavy duty tweeters ( lanzar optibt38) 2× 600watt 8ohm 8″ midrange speakers (lanzar vmrn85) 2× 800wayt 3ohm 8″ midbass speakers (lanzar opti8mi) I really dont know witch amplifier is the right one and what specs I should look for, my plan was to purchase… Read more »

Hi Geoff, I have two systems running into a Niles SVC-4 speaker selector with a pair of Pioneer CS-77A’s (65 watts 8 ohms), a pair of CS-A500’s (50 watts 8 ohms) and a pair of CS-52T’s (20 watts 4 ohms). The first system (“A”) is powered by a Pioneer SA-8500 amp (60 watts per ch. @ 8 ohms or 75 watts at 4 ohms). The second system (“B”) is powered by a Carver CM-1090 amp (100 watts @ 8 ohms or 150 ohms @ 4 ohms). I usually run all three pairs of Pioneers together. The Niles has a “protection… Read more »

Hi Geoff, Through the Pioneer amp “A”, I run a tuner, turntable, RTR, 8 track and cassette deck. The Carver amp “B”, has a tuner, turntable, CDR, MP3, cassette deck and video. The Niles SVC-4 is capable of handling 2 amplifiers and 4 pairs of speakers. So, when I want to play a certain system, I power on the amplifier I want to use, say “B”, then on the SVC-4 I just select the switch for amp “B” and any combination of speakers I wish to listen to; I switch on the circuit protector if more than 2 pair are… Read more »

Hi Geoff Great web page, very well explained. I guess I am contacting you as more of a re-assurance than anything else (a second opinion if you like). I simply want to add 4 ceiling speakers to my home cinema set up. The amp has 2 separate circuits for 2 separate zones (its a DENON 1310) and I currently have a 5.1 system connected to the main zone which is zone A each at 90W; no worries there. I want to add the additional 4 x 8 ohm ceiling speakers into the dining area and connect to zone B which… Read more »

Wow u are the best… I need to know more about all this things, please help me…. I’m dong sound at church in Vic Falls…..