Alternating current (AC) and direct current (DC) are differentiated by the direction that the electric charge flows. When using speakers, it’s important to understand the difference between these current types.
Are speakers AC or DC?
The straightforward answer to this question is that all speakers produce audio using AC. This AC power is provided by the amplifier. The amplifier itself runs on DC supply, but this is not directly supplied to the speakers. Therefore speakers are classed as being AC devices.
Like all audio-related questions, there’s plenty more to explore on this topic.
Understanding why speakers are AC devices is essential if you want to expand your knowledge of the differences between alternating currents and direct currents, and how they affect equipment.
In this detailed guide, I’ll answer all of your questions on the subject.
AC and DC Speakers Explained
Direct current, or DC as it is commonly labeled, describes the electrical charge’s flow which moves in a singular direction. Alternating current, or AC, describes an electrical charge which reverses its direction repeatedly.
Speakers come in two varieties – passive and active. The former type of speaker draws power from an external amplifier, which it is connected to using speaker wire. Active speakers, on the other hand, are all-in-one units that have an amplifier built-in.
Both passive and active speakers are classed as AC devices. This is because they receive the signal from the amplifier, and this is always AC rather than DC. The amplifier supplies the AC power to the speaker, which allows it to produce sound, whether it is of the passive or active variety.
- The confusion which surrounds this topic is mainly due to the fact that active speakers are plugged into the mains power, rather than being powered through speaker wire which comes from the amplifier.
It may seem logical that the power supplied to active speakers is of the DC variety. However, although active speakers receive power from the mains, they still have inbuilt amplifiers which boost the signal and prepare it for playback.
The power that comes from the inbuilt amplifier within an active speaker unit is AC – just like a passive speaker which receives power from an external amplifier. Amplifiers themselves do use DC power, but AC is used for the signal from the amp to the speaker.
What Happens If DC Power is Applied to Speakers?
Now that we’ve established that all speakers require AC power, you might be wondering what would happen if you were to apply DC power to them. In short – this should always be avoided as it could potentially be very harmful to your speakers.
All speakers include a device known as a voice coil, which is integral for generating sound. From an electrical standpoint, the voice coil is similar to a large inductor, due to the loops of wires it includes within a magnetic field.
It’s important to understand how inductors are impacted when different sound frequencies are played through the speakers. The impedance of the inductor varies as a result of the frequencies. This happens because the alternations of the current essentially increase the magnetic field in the voice coils.
When the current within the speaker oscillates at a faster rate due to the changes in frequency, this causes the voice coil (conductor) to have a higher impedance when higher frequencies are produced, compared to a lower impedance when low frequencies are produced.
- If you were to apply DC power to speakers, this will cause the voice coil to heat up significantly, which would likely cause damage to that component and possibly other components within the speaker.
This is because a fully functioning inductor when used with DC power has an impedance of zero – with no resistance whatsoever. This makes the inductor unsuitable for speakers.
Amplifiers supply a specific voltage to the speakers and maintain an adequate current for the voltage to be consistent concerning the speaker’s impedance.
Using DC power will cause the resistance to be lowered dramatically, which causes the voice coil to exert heat, thus potentially damaging the speaker.
The table below summarizes the differences between AC and DC.
|Alternating current||Direct current|
|Periodically reverses its direction||Flows steadily in one direction|
|Used for powering speakers||Used for powering amplifiers|
What Voltage Are Speakers?
Speakers come in many different shapes and sizes, and with vastly differing specifications. Therefore, there’s no one size fits all answer to the voltage that should be supplied to them.
Nevertheless, some general rules of thumb can be used to determine the ideal voltage of a set of speakers. As we’ve already established, the first thing that you need to ensure is that you are using AC to power the speakers, which comes from the amplifier.
The most important thing you need to do is check that the amplifier produces an appropriate wattage for your speakers.
If you are using active speakers, the built-in amplifier will be designed to do this. Passive speakers are used with an external amp, and therefore it’s important to check that the wattage matches up.
Truthfully, you don’t need to worry about the voltage too much. This is because voltage varies depending on other factors such as the volume of the sound source being played through the speakers.
For example, if you use volume control, this will cause the sound source to be scaled, and the amplifier will kick in to make the voltage consistent with the original audio signal. So when you turn up the volume to a desirable level, the amplifier will automatically change the voltage where necessary.
- It is vital that you make sure that the impedance of the speaker falls within the range of the amplifier.
This is most commonly 4ohms, or sometimes between 8 and 16 ohms. You can check this by analyzing the specs of the speakers and amplifiers on the manufacturer’s website or the manual that came with the devices.
Finally, another point to consider is that audio signals have varying peaks by nature. This ensures that they don’t cause the amplifier to continuously produce the same amounts of power.
Therefore it would be acceptable to use speakers listed as 25W with an amplifier listed as being 50W even when the volume is turned up to a fairly high level.
I have written an article on leaving powered speakers on. You can read it here.
How to Convert Speakers to DC
Although it’s advisable to use speakers with AC power, there is a way that you could theoretically convert them to DC.
- This should only be done if for some reason it’s not possible to simply use the speakers with an amplifier that will supply them with AC power.
Firstly, you’ll need to check the AC voltage of your speakers.
This can be done either by using a multimeter or by checking the specifications. It’s important to bear in mind that the voltage will fluctuate depending on the volume of the audio played through the speakers.
When you’ve got the general AC voltage of the speakers, you’ll need to do a simple equation to find the DC voltage.
Divide the AC voltage by the square root of two, and this will present you with the DC voltage.
You can input this equation into a calculator to ensure that you get the right answer. For example, if the speakers have an AC voltage of 60V, you would input 60/√(2) which would give you a DC voltage of 42.42 V.
It’s important to note that the DC output of the speakers will be lower than the answer to your calculation.
This is because the voltage of a current drops when it is connected to the speakers, so they never actually produce the full amount.
Once you’ve got the answer, you can then choose a DC power supply that matches up to the voltage required to power the speakers. Again, I would advise you to proceed with caution when doing this, as the speakers are designed solely to be used with AC power supplied by an amplifier.
You might not run into any issues by using this method, but there is a chance that the speakers will not perform well if they are used with DC power.
Also, because the voltage fluctuates, it isn’t easy to ensure that your calculations are one hundred percent accurate, so this should also be considered.
Check out this YouTube video that explains AC/ DC
Are microphones AC or DC?
Microphones output AC signals, which are known as analog audio signals. However, some microphones require DC power to work whilst others don’t require any power, depending on the variety.
Are audio signals always AC?
Audio signals are always alternating current electrical signals. In terms of strength, microphone signals are the weakest form of audio signals, while speaker signals produce the strongest AC voltages.
Can you use passive speakers with active speakers?
The most effective way to use passive and active speakers together is by linking them together using a mixer. The mixer would need two outputs, one of which would be sent to the active speakers and one to the passive speakers.