Choosing the appropriate speaker impedance means the difference between scratchy, muted sounds or strong and clear beats. As we all know, this difference is critical when blasting breakup tunes or enjoying a road trip singalong.
Of course, manufacturers design car stereos to account for speaker impedance. However, if you install an aftermarket sound system, you’re likely concerned about how to measure speaker impedance and how it will impact your system.
What Is Speaker Impedance?
Speaker impedance refers to how much a speaker resists an electrical current from an amplifier. Essentially, impedance causes the speaker to place a specific load on the amplifier because of the nature of an AC current. In a DC system, the same effect is also called resistance.
This load is higher or lower depending on the frequencies of the audio signal. If you have seen a sound table with an electrical display of frequencies, you’ll notice how they peak and plummet, even within a single song.
The changes in frequency cause changes in impedance. If this all sounds a bit complicated, it’s okay. There is a lot more to the physics of turning electrical current into sound waves. For now, let’s examine the basics of how speaker impedance functions.
How Speaker Impedance Works
Impedance affects how much current a speaker draws from an amplifier. The impedance is measured in ohms, a gauge of how much power the speaker requires to function.
Lower impedance means more current can flow from an amplifier to the speaker itself. Logically, since more current requires more power, the amplifier must work harder when the impedance is low. You might assume this is a good thing. However, the reality is a bit more complicated.
What is an Ohm?
Ohms measure electrical resistance in an electric circuit. The ohms change when there is a difference in the voltage from one end of the current to the other. The change happens when a current passes through a speaker and amplifier system.
Impedance and Voltage
Low speaker impedance causes a greater flow of electrical current. More current creates a higher load on an amplifier, which requires the amplifier to produce more power.
High impedance leads to less demand for electrical current. Less of demand causes a lower load on the amplifier, which requires it to draw less power.
In general, you can imagine an inverse relationship between speaker impedance and power (specifically, voltage).
However, other outside factors do influence this relationship. If you have ever attempted to play a speaker in freezing weather, you probably failed. Among other things, temperature impacts the relationship between voltage and impedance.
How Frequency Impacts Impedance
As the frequency changes, speaker impedance also changes. With music and vocals, frequency is constantly shifting, so impedance is also changing. If you have ever heard a speaker “blow,” what you likely experienced was the amplifier hitting its capacity.
However, this is uncommon because speakers are designed to shut off if they do hit capacity. For this reason, ohm ratings are listed on amplifiers.
Usually, these ratings fall between 4 and 8 ohms. A lower quality speaker, around 4 ohms, might struggle to keep up with a low impedance current.
A sound system will function best when the impedance is compatible with the amplifier’s range. Since the ohms vary, the listed ohms are generally a single number, even though it fluctuates.
People often mistakenly assume a higher ohm rating means a speaker will work better. However, while high volume requires higher ohms, this is not an issue unless you reach extremely high volume.
Does Speaker Impedance Matter?
It’s a common misconception that speaker impedance matters a lot when you are selecting speakers for personal use. It doesn’t. For any speaker at a reasonable volume, ohms are negligible.
The simplest way to conceptualize why this is the case is to picture impedance as a little goblin. Now, imagine a little 4-ohm rated goblin as needing to eat more power to perform. Another large goblin already needs much less to achieve the same results.
Moreover, as a speaker reaches higher ohms and requires less power, it must sacrifice some sound quality. If this were not the case, after all, no one would bother making “little goblins.”
Prioritizing Voltage over Impedance
Again, the power component is critical here. Power drives your entire sound system, so electrical current capacity is important when selecting best type of speakers for you. To power a speaker of 6 ohms, you need a consistent current of around 100 volts.
Fluctuations in a power current more commonly causes sound distortion than does issues with speaker impedance.
The Bottom Line
As long as you confirm that your system supports a steady voltage, an online chart calculator will confirm whether your power matches your speaker impedance.
For a car stereo, a 6-ohm amplifier rating is likely a good range for the volume and quality you hope to achieve.
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