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How to Choose a Car Amplifier for Speakers? Do I Need One?

There are many amplifiers out there with many different features: built-in crossovers, DSP, high and low-pass filters, tons of power, and more. It can be overwhelming to understand more when searching for the amplifier, especially if you only know how many watts your car speakers need.

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Luckily amplifiers are not that complicated to understand, so let me help you choose the right amp for your car speakers.

The right amplifier should have RMS power for each channel matching the RMS of each speaker. For example, four 100W speakers should be powered by a 400W amplifier. Another thing to define is the correct number of channels, depending on the number of speakers and subwoofers.

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This article will detail what an amplifier is and why you need one for your car audio system, describing its various benefits. Then I will show you how to match an amplifier with your speakers in terms of power, RMS and Peak watts, speaker efficiency, and if you have additional subwoofers.

Lastly, I will explain different scenarios depending on how many speakers you have, including a subwoofer and how many channels an amplifier can provide, and what additional features it can offer your speakers.

What is a car amplifier for?

Any amplifier, as the name suggests, amplifies a signal to a certain degree. In terms of audio both for home entertainment and car amplifiers, an amplifier will take a line-level audio signal and boost it so you can listen to the audio through your speakers at a set volume.

how to choose car amplifier for speakers

This is the only possible way that you are able to hear sound through your speakers.

An amplifier works on a technology that takes current and routes it through a tone of circuitry and components, and at the end, transistors take the current and power it through your speakers producing sound. 

What about a preamplifier? Can I use that?

A preamplifier is most definitely a type of amplifier because it does boost an audio signal; however, a preamplifier only boosts a low-level signal to line-level. The preamp then sends its signal to the amplifier, which can be boosted further and out through your speakers. 

For example, a preamp in a mixing desk will boost a microphone signal and then send it through to the stereo amplifier for further amplification. 

For car audio purposes, your stereo will send a signal to its preamplifier (this can be the radio signal, CD player, or smartphone). Then the preamp will send the signal to its built-in amplifier if it has one or out to the external aftermarket amplifier. Hence you can not just use a preamp for any sound whatsoever.

Why do I need a car amplifier for my speakers?

You might be wondering why you need an amplifier if your standard OEM factory stereo can play music without the need for one.

Head units do have an amplifier built into them; otherwise, you would not be able to hear your music because you need an amplifier to push a line-level signal through your speakers to create volume.

In fact, some high-end vehicles even come with factory-installed external amplifiers to power advanced sound systems.

However, if your car does not come with a powered OEM stereo amplifier, you may need to consider getting yourself an aftermarket one for these reasons. 

You get better sound quality from a car amplifier.

The most prominent feature of an amplifier is that you can increase volume without incurring any distortion.

If you enjoy cranking up the volume and you need to hold back because, at a certain volume level, all you hear is loud distortion, then an amplifier would suit you well. A professionally built aftermarket amplifier will produce clean, high-quality sound in addition to volume.

It can produce clean, high-quality sound due to the fact that it has no limitations when it is built, unlike the amplifier that has to be housed in your car stereo.

With proper components and distinctive design, it gives your speakers room to breathe, creating adequate headroom. This means that your speakers work less and at the same time produce better quality sound.

You get additional power for your aftermarket speakers.

Standard OEM factory speakers and amplifiers usually leave the assembly line having 10 to 15 watts of power unless, as I mentioned, it is some luxury car.

If you intend to purchase aftermarket speakers, their power and efficiency rating will be much higher than standard OEM factory speakers (in the hundreds and even thousands of watts).

The amplifier in your stereo will not have the power, not to mention the capability of handling aftermarket speakers.

There will be no clarity, no depth in the audio, no proper frequency response, and low volume. These are just a few problems you will be plagued with if you choose to run influential aftermarket speakers from your car stereo without an amplifier.

You are able to power a subwoofer.

If you plan on running a subwoofer, then you will need an amplifier without question.

Amplifiers nowadays have built-in crossovers that function as a high-pass filter allowing frequencies that only the subwoofer should receive. In addition to this, your car stereo that is pumping out 15 watts peak RMS will just not have the power to drive a subwoofer, which is hundreds of watts.

Not to mention that your stereo most probably does not have a dedicated subchannel or a crossover built into it.

This would mean if you actually do hook your subwoofer up to your stereo via a standard channel (not recommended), the sound that would follow would be detrimental to anyone who is listening.

How to match the car amp with the speakers?

Suppose you are looking to acquire an aftermarket amplifier and/or aftermarket speakers.

In that case, you definitely need to consider a couple of things before you jump onto Amazon and start throwing away your hard-earned money. 

Like other types of technology, speakers and amplifiers are built with a specific design in terms of power, impedance, frequency response, and a few other factors.

This means you can’t just go and purchase a set of aftermarket speakers and an amplifier, and away you go. In essence, they have to work together to simultaneously produce the best possible sound working in tandem with one another. 

Hence you should try and match your speakers and your amplifier in terms of power at least, but there are more factors to consider.

If you don’t, you could receive low quality, week sound, and conversely, you could blow your speakers if the power ratio of your amplifier and speakers are wrong.

Matching amplifiers to speakers in terms of power (wattage).

Amplifiers with too much power.

The main thing to note under this heading is your amplifier’s wattage should never exceed that of your speakers. For example, if you have a set of speakers that peak at 300 watts, then your amplifier should not exceed this maximum rating, or you will more than likely blow your speakers when you drive your speakers too loud. 

Amplifiers with too little power.

If you have an amplifier that does not have enough power to drive your speakers, the amplifier will clip the audio signals’ frequency ranges that it cannot produce, and this will be heard through your speakers by clipping.

Behind the scenes, the amplifier produces DC current in those instances of clipping, which is detrimental for your speakers, especially tweeters. 

This intern causes them to deteriorate with time and could also cause the voice coil in your speakers to get damaged. 

How to determine the correct power for your speakers and amplifier.

This is straightforward. All you need to do is match the RMW watts of both your amplifier and your speakers. Do take note that RMS and peak watts are very different, and you should not ever try to match peak watts.

You can consider RMS watts to be the average handling capability of your speakers on a day to day basis. In contrast, peak watts refers to how much power your speakers can handle in an instance and not continuously.

For example, if an amplifier has 300 watts RMS, it will produce good constant power at this level for a sustained period of time. It can still go louder, probably to 600 watts peak, however that spike can be devastating to the speakers with 300 watt RMS, but only 400 watts peak.

Many people make mistakes when going out and purchasing a set of speakers with a peak of 300 watts and think it is the same as their amplifier.

This is incorrect, and in reality happens, that the speakers’ RMS watts are only 150 watts (you generally halve the peak watts to get RMS watts). 

So make sure that you match your amplifier and speakers to each other accordingly and match up the correct watts, either RMS or Peak. 

What about speaker efficiency?

Speaker efficiency relates to how well a speaker performs with a small amount of power. In essence, you could have a 200-watt speaker with high efficiency that outperforms a 300 watt at the same volume level (it will be louder).

This means you could have a lower-powered amplifier that produces a clear, loud sound without the need to purchase an additional amplifier.

For example, you could have a 100-watt amplifier powering a speaker that is 150 watts, and it would sound better than a system based on 150watts. Although this may seem contradictory to the section where amplifiers with not enough power can also damage your speakers, this would only apply to amplifiers that are severely short on power handling capability, such as a 25-watt amplifier with 200-watt speakers.

This is definitely an avenue to pursue because high efficient speakers will also offer better overall sound quality. Speakers with a high-efficiency rating are considered to be 90db and above. 

How many channels does my amplifier need?

When car amplifiers were first introduced, they came out with two channels. Back in the early 90s’, this was enough, and I still have my first amplifier – Mac Audio 2×120 watt (with 2×80 watt RMS).

However, in today’s world, the standard of quality has changed, and so has our perception of good quality sound. 

With that in mind, an amplifier should have at least four channels (two channels for the front speakers and two channels for the back speakers). 

What if I have a subwoofer?

With a subwoofer, you can go further and get the amplifier with the 5th channel.

If you are a true audiophile and serious about sound, then a separate subwoofer channel is necessary. Similar to home entertainment surround-sound systems, car amplifiers usually have a 5.1 or 7.1 feature.

Point 1 means that there is a dedicated subwoofer channel however, in the case of the car amplifier, it is not based on surround sound

Car amplifiers with five channels have a dedicated channel for the subwoofer, and that channel will come with a built-in crossover. This means if you have a subwoofer, an amplifier with a dedicated subchannel and crossover will only power your subwoofer with the correct frequencies, which you will be able to adjust to tweak it just right.

In addition to that, the subwoofer channel may come with a certain amount of power that differs from the regular speaker channels because a subwoofer needs a tremendous amount of energy to drive it.

Let’s go back to the crossover that is built into the amplifier. You have to understand that some subwoofers may come with a built-in passive crossover, and hence you do not need one in your amplifier; however, this in most cases can just be bypassed if your subwoofer does, in fact, have a built-in passive crossover. 

Can I have one amplifier for all car speakers?

In most cases, yes. However, this will not be enough in vehicles with more than four speakers and more than one subwoofer.

Furthermore, car amplifiers are mostly built and based around a five-channel principle, which would only include two sets of speakers (front and back) and one subwoofer.

You do get car amplifiers with six channels, which also feature high and low-pass filters on them (this means they have a built-in crossover for both high and low frequencies).

However, this is the maximum amount of channels you are most likely to find on a car amplifier. 

If you have more than two sets of speakers and more than two subwoofers, the next step is to purchase additional amplifiers and route your car audio system accordingly.

Furthermore, you also get amplifiers built specifically for regular car speakers or specifically for subwoofers. Hence you could get separate amplifiers that drive only your subwoofers and then only your Speakers. 


If you want decent sound in terms of volume, clarity, depth, and more, you should opt to purchase an aftermarket amplifier, especially if you have already purchased a pair of aftermarket speakers.

A standard car stereo only puts out about 10 to 15 watts RMS. If you have speakers that are 100 watts and above, the stereo will not only not be able to provide it with enough power but will, in fact, slowly damage it to a point where they are broken (possibly for good).

There are many factors to consider when trying to match up your speakers with your amplifier, and the main thing to note is that the amplifier should not have too much power and not have too little energy (it should be just right like Goldilocks and the three bears).

After that, you need to correctly match your amplifier and speakers with the correct watts (both should match by RMS and not Peak watts).

Finally, you have to consider how many speakers you have and if you have a subwoofer because amplifiers come with many different channel variations, including ones dedicated explicitly to subwoofers that offer a high pass filter and built-in crossover.

Other than that, if you want more than two sets of speakers and two subwoofers, you would have to opt in to getting more than one amplifier and reworking your car audio system setup.