Confused about speaker Ohm ratings, the word impedance, and what it all means? You’re in the right place!
In this article I’ll cover:
- What is an 8 ohm impedance speaker? What are 4 ohm, 2 ohm, and other speaker impedances?
- Impedance and Ohms meaning in speakers.
- Can I use an 8 ohm speaker with a 4 ohm amp? What about other speakers with higher or lower ohms?
- Do Ohms affect sound quality? What about speaker crossovers?
What is an 8 ohm impedance speaker? What are 4 ohm, 2 ohm, and others?
As it so happens, over many, many years some unregulated (not strict) standards have developed for the speaker impedances used in consumer electronics.
- 8 ohm speakers are used typically for home stereo systems, outdoor systems, and musical instrument amplifiers. Because home stereos have access to higher power supply voltages, a higher impedance speaker can be used to power speakers than say in a car.
- 4 ohm speakers are typically used for car stereo systems. Because vehicles have less voltage available than home stereos, they have to allow more current to flow instead in order to create more power. This is done by using a lower Ohms rating speaker (4 ohm, 2 ohm, and even 1 ohm sometimes).
- 2 ohm speakers are typically used for high-power car audio systems – mainly bass subwoofers. This has become more common in the last decade or so as amplifier technology has improved and prices have come down.
- Other impedances such as 16 ohms may be found in small electronic devices, older home stereos, and various other audio applications.
In essence, 8 ohm, 4 ohm, and 2 ohm speakers describe the general range of the speaker’s impedance and are some of the most commonly used. Speakers are never exactly 8 ohms or 4 ohms, for example.
They’re called “8”, “4” and so on because they’re approximately that amount. The Ohms rating for a speaker helps you match it with the electronics that can power it correctly without having to worry about small differences.
What does Ohms mean in speakers? What is speaker impedance?
When we talk about Ohms in speakers along with the word impedance, what we’re really talking about is the speaker’s total opposition to the flow of electrical current when connected to a stereo or amplifier.
When choosing a speaker the impedance, listed in units of measurement called Ohms, is used as a good approximate matching guideline for stereo equipment.
What does impedance mean exactly? When is an 8 ohm speaker not really 8 ohms?
This graph shows the actual impedance for an 8 ohm speaker measured and plotted on a graph over the range of audio frequencies. As you can see it’s not strictly 8 ohms – it changes wildly at times.
An 8 ohm rated speaker is only 8 ohms part of the time. That’s because a speaker’s impedance varies quite a bit because of real-world factors like resonance and inductance depending on the musical frequencies the speaker is playing at a given moment.
For example, an 8Ω speaker’s total Ohms (impedance load seen by a stereo) could be as low as 6 ohms, as high as 70 ohms at resonance, and approaching 12 ohms near high frequencies as shown in the graph pictured here.
A speaker’s resonant frequency is the frequency at which its magnet & voice coil assembly behave differently and isn’t fairly well controlled like at other frequencies. Because of that, the speaker “resonates” and as a result creates a much higher impedance that affects several factors related to sound in that brief range of frequencies.
This is usually taken into account by speaker manufacturers. They avoid using a speaker near this frequency to decrease problems with the sound and performance due to it.
Speaker coil inductance
Inductors are very useful electrical parts that take advantage of inductance. Inductance is a property of electrons flowing through a wire loop and the magnetic fields that form around it. Just like an inductor, speaker voice coils have magnetic fields created as electrical current flows through them. These fields acted in a way that provides an amount of “resistance” depending on the frequency.
Speaker impedance is the total sum of two things:
- The resistance of the long winding of wire making up the voice coil.
- A special magnetic property called inductance created when the wire is wound into a coil.
Most speakers use a traditional design with a voice coil made from a very long length of wire that’s tightly wound around a paper tube called a bobbin. When supplied power from a stereo or amplifier, magnetic fields create motion as they are attracted to or away from the speaker’s magnet. This moves the speaker cone and sound is created from the motion of air.
Speaker voice coils always have a certain amount of resistance (Ohms) from the wire itself that is part of what makes up speaker impedance. This is what you’ll measure when using a test meter across the speaker terminals.
Because of the physics property of inductance the same magnetic fields produce sound from a speaker also have an opposition to the flow of current, somewhat similar to the wire’s resistance. This also contributes a bit more to the total resistance which is called the impedance.
Can you measure speaker impedance?
When measuring the Ohms (resistance) of a speaker, you’re measuring the direct current (DC) resistance of the wire coil only – not impedance. However, it’s generally pretty close to the total average impedance.
When measuring “impedance” with a resistance tester for example you’re measuring the resistance of the coil wire, not the actual total impedance. That requires fancier equipment to do. However, knowing the DC resistance puts you in the ballpark as it’s usually very close.
What is better: 8 ohm or 4 ohm speakers? Are 2 ohm or 4 ohm speakers better?
8, 4, and 2 ohm speakers aren’t necessarily “better” than one another. It’s more accurate to say that the best speaker impedance depends on the system and electronics being used. The best impedance is the one that matches an amplifier, stereo, or crossover’s impedance spec correctly and delivers the best sound and power.
Because they’re both the most popular types in the world I think it’s helpful to clarify a few things about 4 ohm vs 8 ohm speakers. That’s especially true for home stereo owners who aren’t clear on why they’re supposed to use 8 ohm speakers.
- You cannot use 4 ohms speakers with an 8 ohm compatible stereo or amplifier (typically home stereos). Using a lower impedance speaker than the stereo is rated for can cause it to run hot and even be permanently damaged!
- 8 ohm speakers can be used with a 4 ohm radio or amplifier. However, there’s a disadvantage to doing so that I’ll explain later.
- When using speaker crossovers, you cannot swap 4 or 8 ohm speakers as the crossover is designed to work only with the correct speaker load. Changing this causes the crossover frequency to change, affecting the sound.
Home stereos have an advantage over car stereos systems in that they have a much higher voltage supply available and don’t need large amounts of electrical current to deliver power. Car amplifiers can deliver huge amounts of power to 4 and 2 ohm speakers by using an internal power supply to generate higher voltages (often somewhere around 28V) for amplifying the speaker signal.
Otherwise it wouldn’t be possible to drive car speakers with tons of power and get boomy bass like many people enjoy from a 12V system.
When are 2 and 1 ohm speakers used?
Factory-installed amps sometimes use 2 or 1 ohm speakers to develop more power without spending the money on amplifier designs using an improved power source.
2 and even 1 ohm (yes, 1 ohm!) car audio speakers are rarely used except for car subwoofers and some special cases. Some factory-installed premium amplified car audio systems use lower impedance speakers. Bose and others are some good examples of this.
Car manufacturers “cheat” and avoid using a “real” car amplifier with an internal power supply as aftermarket products do to save money. They often use 2 or 1 ohm speakers to develop more power by delivering more current to the speaker in order to get a bit more power from the 12V supply available.
However, this brings other problems like not being compatible with standard 4 ohm speakers when it’s time to upgrade or replace faulty ones. They also can’t produce as much power as even a moderate power budget aftermarket amp that uses 4 ohm speakers can.
Do Ohms affect sound quality? Are higher ohms better for speakers?
Shown here is a graph comparing the power developed by 8 and 4 ohm speakers when connected to the same amplifier. As you can see, an 8 ohm speaker produces less power at the same output (volume) as a 4 ohm speaker. That’s because they need a higher voltage due to their higher impedance.
Speaker Ohms affects sound normally only under certain circumstances such as power (volume) and how they interact with crossovers. Higher ohms doesn’t mean better sound quality in the majority of cases.
You’ll get the best sound when using the right speaker impedance for a given application:
- Matching the correct speaker Ohms to a radio or amp for the best available power and volume.
- When using speaker crossovers.
1. Speaker power, volume, and how speaker Ohms matters
In the graph I posted above you can see what happens if an 8 ohm speaker is used in the place of a 4 ohm. What you’re seeing is:
- The power for the lower impedance speaker, at the same amplifier or stereo output level, is twice that of the 8 ohm speaker.
- The maximum power you’ll get for an 8 ohm speaker connected to a 4 ohm rated amp will always be lower than that of using a 4 ohm speaker.
What this all means is that using a 16Ω speaker in place of an 8Ω one, for example, has disadvantages in power loss and volume. There’s nothing to be gained from doing it. (Likewise the same principle for 8Ω and 4Ω speakers, too). For two otherwise identical speakers the sound quality itself will be the same – but one will have a lower volume.
Can I use an 8 ohm speaker with a 4 ohm amp?
While you can use higher impedance speakers with an amp or stereo if you like, it’s better to avoid it if you can. In some situations like when there’s plenty of power available from an amplifier, it’s less of a problem. However, using 8 ohm speakers in a 4 ohm car audio system for example isn’t desirable because power is often already hard to come by.
The stereo or amplifier will work fine but the maximum power output will be 1/2 of versus using 4 ohm speakers. Also, mixing and matching the two types means the speakers will be mismatched in volume output.
It’s best to properly match speaker impedances to stereos and amps for the best results.
2. Crossover shift and how speaker impedance matters
This diagram shows what crossover shift is and how speaker impedances affect how a crossover works. Changing the speaker Ohms load means the crossover frequency will shift and affect the sound.
Speaker crossovers work using capacitors and inductors that filter out sounds based on the speaker load they’re connected to. When you change the speaker impedance used you change the crossover frequency and the sound. Changing the crossover frequency like this is called “crossover shift.”
In other words, the range of sound that speakers will play will no longer be as intended. Bass speakers will often have to play midrange or treble sounds while tweeters may be exposed to midrange and bass – both very undesirable.
This can affect the sound quality in several ways:
- A “harsh” sound from woofers or midrange speakers. Tweeters may sound distorted and begin to “break up” at a lower volume than they used to.
- A “thin”, weak quality to the music.
- Gaps in the sound ranges you should be hearing.
Speaker crossovers should only be used with the speaker impedance they’re designed for or they won’t sound the same.
For example, using an 8 ohm home speaker crossover with a 4 ohm car speaker won’t work correctly. That’s because the part values were chosen for one impedance only. When you change that, it dramatically changes the crossover frequency and you can expect bad sound as a result.
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