If you have a surround sound home theater system, you may consider running 4 ohms and 8 ohms speakers together. As an example, you may want to use 4-ohm speakers for the speakers in the front, center and, the sides and 8-ohm speakers at the rear.
Speaker Power
It is important to note that people often want to add speakers to an amplifier to increase power. Adding speakers to your amplifier will in most cases reduce the power in a speaker. Many people have the misconception that adding a speaker rated at 50 watts to another 50 watts rated speaker will give them 100 watts of power.
Two speakers rated at 50 watts each will potentially give you 100 watts of power however, If the amplifier is rated to only deliver a maximum of 50 watts of power then that is the maximum power it will deliver irrespective of the power capacity of the speakers.
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Amplifier Power
The total effective resistance of an electrical current (impedance) of a speaker can change the power output of an amplifier. It could either half or double the power output capacity depending on the impedance that can be affected by whether the speakers are wired in series or parallel.
A low impedance efficiently allows the electrical signal (music) to pass through the speaker. It must be noted however that if the impedance is lower than the minimum impedance level set for the amplifier there is a danger of the amplifier overheating.
What is Ohm
The first thing you need to understand is what is Ohm? An ohm is a measurement of electrical resistance. Described as a mathematical equation I (current) = V (voltage) / R (resistance).
According to Ohms Law. The value of resistance of a conductor is a ratio of the voltage (potential difference between the end of a conductor) to the amount of current running through it. Therefore the lower the ohm value the lower the resistance. 4 ohms resistance is much lower than 8 ohms resistance.
Electrical currents prefer to flow through conductors with lower electrical resistance. If 2 speakers of 4 and 8 ohms are wired to two different amplifiers with the same input value of, for example, 50 watts, more current will flow through the 4-ohm speaker than the 8-ohm speaker.
8-ohm speakers used with a 4-ohm output only need to be rated at half the output power of the amplifier. This means that a speaker rated at 8 ohms and a maximum input of 50 watts is equal to a speaker rated at 4 ohms with a maximum input of 100 watts.
8-ohm speakers do not permanently have a resistance of 8 ohms. A speaker impedance varies depending on the frequency the speaker is playing at, at any given time. Sometimes a speaker may be 7 ohms and at other times could be as high as 27 ohms.
More power is therefore required to drive speakers with lower ohms ratings. Connecting an 8-ohm and a 4-ohm speaker to the same amplifier will alter the load depending on how they are connected. If the overall impedance of the combined speakers is too low the amplifier can be overloaded.
Every amplifier has a minimum load impedance. It is important to remember never to connect a speaker or a combination of speakers whose impedance or resulting impedance is below the minimum impedance load of the amplifier.
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Can 4 ohms and 8 ohms speakers be used together.?
The answer is yes but there are various factors and parameters to be considered and applied to achieve maximum audio efficiency and to ensure that you do not overload the amplifier.
- You need to confirm the specifications for your amplifier to determine the minimum impedance load that your amplifier can cope with.
- You have to realize that when you connect two or more speakers of differing ohms the overall impedance will alter depending on the number of speakers and the way that the speakers are connected.
- There are 2 ways to connect speakers. In-parallel or in-series. When the speakers are connected in In-parallel the impedance drops. When speakers are connected In-series the overall impedance increases.
- Matching the power ratings of the speakers to the amplifier’s power capabilities is also advisable.
Wiring and Calculating Impedance Using 4 ohm and 8 ohm Speakers
- Series Connection – In this mode of connection the total impedance level increases due to the speakers being connected end to end. If you are connecting 4ohm and 8ohm speakers the two speakers will yield a total impedance of 12 ohms as the total impedance in any series connection of resistors is simply the sum of the two resistors.
Total Impedance = 8ohms + 4ohms = 12ohms
When wiring speakers in series join the positive polarity of the amplifier to the positive terminal of the 4-ohm speaker. Then join the negative polarity of the amplifier to the negative terminal of the 8-ohm speaker. Once this is done the remaining two opposite polarities from each speaker cable are conjoined together.
- Parallel Connection – When connected in parallel the total impedance reduces. For parallel connections, you multiply the value of the two resistors and divide that by the sum of the two resistors. So, when connected in parallel the 4-ohm and 8-ohm speakers will produce an effective total load of 2 .667 ohms which is too low as most hi-fidelity systems are designed to have an impedance of 4 ohms or more that will provide and maintain a good quality of sound. Parallel Connection is recommended for speakers with an impedance value of 8 ohms that will give you a total impedance of four.
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Total Impedance = 8 ohms * 4 ohms / 8 ohms + 4ohms = 2.667 ohms
When wiring the speakers in parallel due to one amplifier being used for both speakers the outputs of the amplifiers will be directly connected to the speakers. Your amplifier will have two positive and, two negative wires. Connect one positive and one negative wire to the + and – terminals on your 4-ohm speaker. Connect the other positive and negative wires from the amplifier to the + and – terminals on the 8-ohm speaker.
Conclusion
Yes, you can use a 4 Ohm and 8 Ohm, speaker together if you connect the two speakers (in series). This will protect your amplifier from potentially being overloaded due to the impedance being too low. Parallel connection is not advised unless you connect two speakers of 8 Ohms that will give you an acceptable impedance of 4 Ohms.
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