It is not possible to wire two 8 ohm speakers to equal 8 ohms. In other words, it is impossible to make two 8 ohm speakers into an 8 ohm load.
People ask this question because they want to wire two 8 ohm speakers in say a 2×12 cab so they will equal an 8-ohm load on the amp.
In this case, here are your options:
- You can wire one speaker by itself for 8 ohms
- You can wire both speakers in series for 16 ohms
- You can wire both speakers in parallel for 4 ohms.
To get a total output of 8 ohms, you can wire the two 8 ohm speakers in parallel for 4 ohms and then wire that in series with a small resistor (a 3 ohm and 5 ohm resistor) for a total off 8 ohms.
How To Get A 8 Ohms Load?
To get an 8 ohm load, you would need two 16 ohm speakers wired in parallel or two 4 ohm speakers wired in series.
This is because speakers can only be connected in one of two ways, series or parallel and neither way will result in 8 ohms from two 8 ohm speakers.
Let’s get into more detail to see why we have these results when two 8 ohm speakers are connected in both series and parallel:
Connecting Two 8 Ohm Speakers In Parallel
If you connect two 8 ohm speakers in parallel, they will give a total load impedance of 4 ohms. This will not work for you because 4 ohms will be too low for an amp designed for a minimum load of 8 ohms.
Here is how this is calculated:
When speakers are connected in parallel and have the same impedance (resistance), we simply divide the impedance by the number of speakers in parallel.
In this case, the calculation is:
8 ohms divided by 2 = 4 ohms
If you wire the speakers in parallel and your amp isn’t designed for 4 ohm speakers, that will not be quite dangerous since the load will be too low. However, most amplifiers without a built-in preamp or tuner can handle 4-ohm speakers.
Connecting Two 8 Ohm Speakers In Series
If you connect two 8 ohm speakers in series, you will get a total load impedance of 16 ohms.
This kind of setup will of course work with amps designed for a minimum load of 8 ohms.
The only issue is, the amp may not operate at full power, especially if it is designed for variable loads even higher than 16 ohms. However, this load will not damage your amp.
In any case, while you will be operating at less power, the speakers should sound just fine.
How To Wire Two 8 Ohm Speakers For Maximum Power
It is very important that you match your speaker’s load with your amplifier’s output impedance for a number of reasons:
- You will get maximum transfer of power from the amp to the speakers.
- You can damage your amp if you attach an incorrect load (speaker of an incorrect impedance). If you are unsure, it is best to go got a higher impendence speaker to help protect your amp.
If you are looking to achieve maximum power output your best bet is to just use a single 8 ohm speaker.
However, before you do that, you need to ensure that the 8ohm speaker can actually cope with the amplifier’s full power output.
What if you don’t want to use one speaker? What if you want to cover a wider area with your music?
Well, in that case, you will not achieve maximum power. It is a tradeoff, one speaker for a maximum power of two for a wider coverage area but lower overall power.
Use A Speaker Selector Switch
There are many ways to connect multiple speakers to an amplifier. However, if achieving maximum power is not your main goal, then you can use a speaker selector switch with a 5 ohm resistor in series. You can use a 3 ohm and 5 ohm resistor.
This setup allows you to add both speakers in parallel for a total impedance of 4 ohms. This is then wired in series with the small resistor that will give a total output of 8 ohms.
Here is the problem with this approach.
In this case, the resistors will serve no purpose than helping you achieve 8 ohms. the downside is that they will use half of the power from the amplifier and waste it as heat.
If you require maximum power output., this is definitely not the best way to go.
If you do this, however, the amplifier’s output power will be reduced by 3dB compared to using just one 8 ohm speaker. If you are connecting a subwoofer, you can use a subwoofer Y splitter cable to compensate for the 3dB loss.
Mixing Speakers Of Different Wattage
Maxing speaker of different wattage is very common and there is no problem doing so. You can mix different wattage rating speakers, but you need to remember that you can’t use more than double the power of the lowest rated speaker.
Remember, you cant just double up speakers for twice the impedance. The amp doesn’t know how to give the higher-rated speaker more power, so it just splits the power you have equally between the two.
As we have already established, it is not possible to connect two 8 ohm speakers to get a total output of 8 ohm.
The simplest way to get a total output of 8 ohms, is to wire the two 8 ohm speakers in parallel for 4 ohms and then wire that in series with a small resistor (a 3 ohm and 5 ohm resistor) for a total off 8 ohms.