There comes a time in every car audio enthusiast’s life where they have stared at their amplifier and subwoofer specs, puzzled about how to wire them together, how to manage the overall impedance load? What is impedance in the first place? Why does it matter? More important than that, what hits harder: 1 ohm or 4 ohm? Does impedance affect my tone?
Let’s dig into the often misunderstood and sometimes confusing world of impedance.
What is speakers impedance?
Impedance is a fairly straight forward concept. It refers to the opposition or resistance offered by an electric circuit to the flow of alternating current.
The impedance of a subwoofer coil is the amount of electrical resistance, or load, a subwoofer puts up against an amplifier’s output. It’s measured in ohm, and it’s symbolized by the Greek letter Omega: (Ω) for shorthand.
Subwoofers usually come in 2-ohm, 4-ohm, or 8-ohm configurations. A sub’s impedance is often found printed on the magnet, if you’re unsure of what you have.
When you’re building a car audio system, making sure your subwoofer’s power handling is perfectly matched to the amp’s top RMS output is a must, in the same way matching the impedance of your sub amp and sub is also a must.
You don’t want to buy a couple of subwoofers and an amplifier, only to find out that the latter can’t run the subs because wired together, their overall impedance would be too low for the amp to run without overheating and constantly turning off.
All pretty simple, right?
Well, there’s still so many misconceptions around the topic of impedance when it comes to amplifiers and subwoofers. The biggest of which is “What hits harder : 1 ohm or 4 ohm?”. Before answering this question, we should make certain things clear first.
Why does speaker impedance matter?
First and foremost, it’s worth mentioning that although car audio manufacturers label the impedance of most car speakers at 4-ohms, the impedance of a speaker is constantly changing with frequency. For example, at 45 hertz, the impedance of a speaker might be 8 ohms, while at 2,000 hertz, the impedance might be just 3 ohms.
The overall impedance of a driver is not a constant value, but can be represented as a dynamic profile that changes with frequency.
So, instead of stating the impedance for every frequency, speaker manufacturers state the “nominal” impedance (4-ohms is the standard impedance in car audio), which is a rough average impedance for speakers and amplifiers when driven within the part of the audio spectrum for which they are designed.
Speaker impedance is constantly fluctuating due to two main reasons:
- Resonance frequency — Resonance frequency refers the frequency below which a loudspeaker is increasingly unable to generate sound output for a given input signal. Every loudspeaker has a resonant frequency at which it moves freely once it is tapped or otherwise engaged. At that frequency the free movement of the driver generates what is known as “counter-electromotive force” which opposes the flow of supply voltage and creates a fairly steep impedance spike.
- Voice coil inductance — The second reason for impedance fluctuation is due to voice coil inductance at higher frequencies which also causes the impedance to rise up.
As we’ve stated above, speaker impedance determines the amount of wattage drawn from the amplifier. This means, the lower the impedance, the more current can flow.
And it goes without saying that a greater current requires an amp with ample power output. Another way of looking at it is to say the lower the impedance, the higher the load on the amp (and the harder it has to work).
A 4-ohm speaker for instance offers twice as much resistance as a 2-ohm speaker, resulting in half as much energy flowing through the speaker in the form of sound. As a result, an amp rated at 100 watts RMS at 8 ohm impedance load can deliver around 200 watts at 4 ohms impedance.
Almost all amps are stable at 4-ohm load. Most of them can drive 2-ohm loads on each channel, but not when the channels are bridged together. Few amplifiers are stable at 1 ohm load.
In a nutshell, these general relationships can be summarized as follows:
Low impedance → more current → greater load → increased power
High impedance → less current → smaller load → decreased power
Looking at the relationships above, it appears that the lower the speaker impedance, the more power output the amp delivers through that speaker. While this is true to an extent when the amplifier can not push out anymore current and power. At this point, either the amp fuse blows, or its protection circuit kicks in and switch the amp off to prevent it from blowing out or causing serious damage to other components in the system.
Having said that, it’s of paramount importance to avoid running an amplifier with a load impedance of less than the stated minimum (normally 4 ohms).
Why do I need to know about speaker impedance?
Well, you need to know about your speaker impedance for one simple reason, and that is to make sure the speaker impedance is within the range that the amp is designed for.
The capability of an amplifier must be considered before applying a load to it (hooking up a speaker). You don’t want to spend a ton of cash on a couple of subwoofers and an amplifier, to find out that your amp can’t run the subs because wired together, the impedance of your subs would be too low for the amp to run without overheating.
Wiring options change a sub’s impedance
It must be noted that a sub’s impedance is susceptible to change not only depending on the frequency but also depending on how the subs and their voice coils are wired together — in parallel or in series.
Series wiring means that the subwoofers are wired one after the other — a plus of one to a minus of another. When subwoofers are wired in series, you add their impedances together to find their total impedance. For example: two 2-ohm speakers wired in series have a total impedance of 4 ohms.
Parallel wiring means that the terminals of each subwoofer are connected to the same things — plus to plus, and minus to minus.
The total impedance of multiple subwoofers wired in parallel is equal to their impedance value divided by the total number of speakers. For example: Four 4-ohm speakers wired in parallel have a total impedance of 1 ohm.
Difference between 1 ohm and 4 ohm
Every speaker and subwoofer has a voice coil. This is the device that puts up the electrical resistance and performs the work. Its resisting property is what we refer to as impedance. The lower a speaker’s impedance, the easier it is for an amp to supply power to it.
So, technically speaking, the only difference between 1 ohm and 4 ohm is the amount of resistance a speaker’s voice coil applies to the audio current supplied by the amplifier.
Problems arise when the amp’s output meets very little resistance (low impedance) and it tries to push out more power than what it’s capable of. This is one of the main causes of overheating amps.
It should be made clear, however, that if you think that you can only connect an 4 ohm speaker to an 4 ohm amplifier, you are wrong. Perfectly matching the sub and amp is highly recommended for optimal results, but in theory a 4 ohm speaker can be paired up to a 1 ohm amplifier as well. Only then the loudspeaker wouldn’t be able to fully handle the amp’s full power output.
It’s the other way around, too, however, you should be very cautious with this. Connecting a 1-ohm speaker to an 4-ohm amplifier, will simply overtax the latter. Your amp will be overloaded and it might even blow out.
What hits harder 1 ohm or 4 ohm?
Technically speaking, a subwoofer rated at 1-ohm impedance load will hit harder and produce more output than a 4-ohm subwoofer, given similar input wattage, because the resistance is much lower.
|1 Ohm Sub||4 Ohm Sub|
|Produces a louder sound||Produces better sound quality|
|Expensive||Slightly cheap (for the most part)|
|Puts much strain on the amp||Better amp efficiency|