What Size Amp Do I Need for Car Speakers?




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If you’re like most car drivers, you want to make sure your car speakers are blasting out your favourite tunes as loudly as possible.

But what size amp do you need for your car speakers, and how can you ensure you get the best sound quality? Let’s find out.

Generally, the RMS wattage of the amplifier should be equal to or greater than the RMS wattage of your car speakers. So if each speaker is rated for 100 watts RMS, you’ll need an amplifier that can deliver between 100W or 200W RMS per channel.

Tip: Overpowering the speakers is better than underpowering them.

If your amplifier is too powerful for the speakers, you can reduce the gain for weak speakers, but this won’t damage the speakers.

However, if you underpower the speakers, or worse, using an amplifier of a higher than speakers impedance, those can cause the amplifier to overheat and get damaged.

So it’s always better to choose an amplifier that can deliver more power than what your car speakers need.

For example, to experience the full potential of Focal ES KX2 K2, I had to connect them to the powerful Focal FPS 4.160 amplifier to allow them to play at their full potential, and the results are excellent. (links to Amazon if you would like to try them)

In the article below, I will guide you on what size amplifier you need for your car speakers.

Is an Amp Necessary for Car Speakers?

The amplifier is necessary for car speakers because your car stereo does not have enough power to drive the speakers properly.

Most car radios, even those aftermarket ones, have power in the range of 5-15W RMS per channel, with some rare cases where the RMS wattage goes over 18W per channel.

Focal ES 165 KX2 K2 Power 6-1/2" 2-Way Component Speaker System

The main reason for this is that the car stereos are made to be small and compact, and that’s why they use smaller transformers that can’t deliver enough power to the speakers.

Also, because most factory car speakers do not handle more than 5-10W RMS, higher power output from the serial stereo is unnecessary.

And this is where the external amplifiers come into play. Most car amplifiers today have power in the range of 50-500W RMS per channel, and some even go over 1000W RMS per channel.

So if you want your car speakers to sound loud and clear, you’ll need to use an aftermarket amplifier, and ideally, it would be made in AB class for speakers.

How Do I Know What Size Amp I Need for My Speakers?

The amplifier should be big enough to power the car speakers properly. If the amplifier is too small, it won’t be able to deliver enough power to the speakers, and they won’t sound as loud as they should.

The underpowering effect can be especially noticeable in one of two cases:

#1 Speakers With Low Sensitivity

Low speaker sensitivity is the main reason you may need to choose a stronger amplifier that can deliver more power than your car speakers need.

If your car speakers have low sensitivity, they’ll require more power to reach the same volume as a speaker with high sensitivity.

As you may know, the difference of just 3dB makes the speakers sound twice as loud. So, for example, the 90dB speakers will be twice as loud as the 87dB when powered by the same amplifier.

To gain another 3dB, you have to double the power of these speakers, but one thing you have to remember is that you cannot increase the power forever.

The reason is that the speakers are designed with the maximum SPL, so when this is crossed, the sound pressure will destroy the speaker, or in the best case, the voice coil will melt.

#2. Speakers With Lower Impedance Than Amplifiers

Impedance discrepancy is another situation where you’ll need an amplifier that can deliver more power than your car speakers need.

If the impedance of your car speakers is lower than the amplifier, the amplifier will have to work harder to deliver the same amount of power to the speakers. Unfortunately, in many cases, this causes the amplifiers to burn out due to overheating or shut down due to the clipping.

Focal FPX4.400SQ 4 x 70 @ 4ohms, Class AB

To avoid this issue, make sure you have the proper power supply for the speakers at the correct impedance.

If, on the other hand, the amplifier is too powerful, it won’t be a problem since you can always turn down the gain.

Of course, it does not mean that you can use a 600W per channel for a75W speakers, but the optimal is when the amplifier’s RMS wattage is equal to or double the RMS wattage of your car speakers.

For example, you need a min 120 W 4 ohms amplifier to power 120 W 4 ohms speakers, but at the same time, you will need a 240 W 4-ohm amplifier for 120 W 2-ohm speakers.

On the other hand, if you want to use a 2-ohm amplifier for those speakers, its power should be a minimum of 60 W RMS.

All the above amplifier values I show are per channel.


Picking a suitable amplifier for your car speakers is not as difficult as it may seem at first.

You just have to know the RMS power of your car speakers and choose an amplifier that can deliver at least the same amount of power.

Try to always match the amplifier with the speakers, not the other way round, because it is easier to find the amplifier for the specific speakers.

If you want to be on the safe side, choose an amplifier with a bit more power than what your car speakers need.

This way, you’ll ensure the amplifier can deliver enough power to the speakers, and you won’t have to worry about underpowering them.


Should Speakers Have More Watts Than Amp?

The speakers do not need to have more watts than the amplifier. In fact, it is recommended that you choose an amplifier that can deliver at least as much power as your car speakers need.

How Many Watts Do I Need for My Car Amplifier?

The size of the car amplifier you need will depend on the RMS power of your car speakers.

Make sure to choose an amplifier that can deliver at least as much power as your car speakers need, and try always to match the impedance of the amplifier with the speakers.

For example, if you have 100W 4-ohm speakers, it is best when the 4-ohm amplifier has between 100 and 150W of RMS wattage per channel.

How to Match 4 Ohm Amp With 2 Ohm Speakers?

If you want to match a 4-ohm amplifier with 2-ohm speakers, the amplifier should be able to deliver at least double the power of what the speakers need.

For example, if your 2-ohm speakers require 100W of power, choose a 4 ohm amplifier that can deliver at least 200W of power per channel, but make sure the amplifier is designed to work with a lower impedance.

How to Match 2 Ohm Amp With 4 Ohm Speakers?

If you want to match a 2-ohm amplifier with 4 ohm speakers, pick the amplifier with the power output between 0.5x to 1x the speakers’ RMS wattage.