A lot of audiophiles will tell you that the answer to this question is quite straightforward. Before we delve into this, I feel like there are a few questions we should answer first.
First of all, what is Ohm? This is the electrical resistance and conductance. One Ohm is equivalent to the resistance of a conductor hence the lower the number the less the resistance.
A key thing to note is that 8 ohm speakers on a 4 ohm system only need to be rated at half the output power of the amp. This means that a speaker rated at 8 ohms and max input of 50 watts is equal to a speaker rated at 4 ohms with a max input of 100 Watts.
Speakers, just like the outputs of amplifiers, have an impedance rating. Typically, 4-ohm speakers should be used with the 4-ohm speaker outputs of an amplifier, and 8-ohm speakers should be used with 8-ohm amplifier outputs.
This said, it is important to note that contrary to what a lot of us have always thought, 8 Ohm speakers are not always 8 Ohms. Actually, the number of times an 8 ohm rated speaker is actually 8 ohms are few. This is because the speaker’s impedance varies, depending on the frequencies the speaker is playing at any given moment. Sometimes an 8 ohm speaker might be 7 ohms, or at times 27 ohms, or even 64 ohms.
Subwoofers and speakers of all kinds have an impedance rating (in ohms), which shows the difficulty of the speaker to power. Low impedance efficiently allows the electric signal that is the music, to pass through the speaker. The majority of speakers have an ohm rating of 4, 6 or 8. Less expensive receivers can at times have issues driving low-impedance 4 Ohm speakers.
So to answer the key question here, Yes, it is very possible to mix 4ohm and 8ohm rated speakers together. Many receivers have the ability to handle 4 ohm speakers without overheating or shutting down when used within their limits. To ensure that you don’t exceed this limit, you should select the impedance switch to its highest setting while keeping the unit properly ventilated.
So how do you wire a 4 ohm speaker to 8 ohm?
If all your speakers have common impedance, just divide the common impedance by the total number of speakers you have. This will give you the net impedance. For example: Four 8 ohm speakers wired in parallel will have a net impedance of 2 ohms.
But that rating is just a precedent. If you are considering buying 6- or 8-ohm rated speakers, you have nothing to fret about as those speakers are optimally placed for amp matching.
However the story changes when it comes to 4-ohm speakers. These speakers often place higher demands on 6- or 8-ohm rated receivers and amps’ power reserves. You can prevent those receivers/amps from running into trouble with 4-ohm speakers, by ensuring that you play sounds at a moderate volume.
However, the receiver/amp’s protection circuits will most likely cushion you from any likely damage by shutting down the receiver or amp in case you play your movies or music at extremely high volume.
When in doubt about a 4 ohm speaker’s compatibility with a receiver, check with the speaker’s and/or receiver’s manufacturer. If your speakers are rated at 6- or 8-ohms, and most are, don’t worry about matching impedance with your receiver or amp.
Can I use the connection for Speaker B on my amp for my extra speakers?
As a general rule, you can’t. However you can with some speakers.
Most Hi-Fi stereo amplifiers have connections for Speaker A and Speaker B, which are usually in parallel, hence it would be just like connecting two speakers in parallel. The amp amp does however provide switches to turn each set on or off.
How do I calculate the impedance of multiple speakers?
If you have 2 speakers wired in series, then simply add their individual impedance together. For example: A 2 ohm speaker in series with a 8 ohms speaker: 2 + 8 = 10 ohms.
If you have 2 or more speakers in parallel and all the speakers are the same impedance, then divide that impedance by the number of speakers. For example: if you have four 8 ohm speakers, then 8 ÷ 4 = 2 ohms.
In case you have multiple speakers in parallel and all the speakers are not the same impedance, then using it is easier to use my Speakers in Parallel Calculator would be easier.
The above calculations are for connecting manufactured speakers boxes, and are not to be used when building your own speaker box and connecting two or more speakers in a cabinet using a crossover circuit.
A crossover splits the signal into different frequencies for each of the speakers hence making calculation for the total impedance complicated because impedance depends on frequency.
In a nutshell, while you can mix different ohm speakers you are more likely to get the best sound quality from speakers with equal ratings connected in twos, such as two 4-ohm speakers connected to speaker number 1 on the amp or receiver and two 2-ohm speakers hooked up to speaker number 2.
See? Speaker impedance is not as confusing as we deem it to be.