April 6, 2019

How to Choose an Amplifier for your Car Speakers – A Practical Guide

Why use an amplifier

In simple terms, an amplifier or amp as it referred to, amplifies or boosts the volume and animates the music. Cars have audio systems which use built-in amps. However, these amps do a less than satisfactory job. When you try to increase the volume and notice plenty of distortion, it is possible that the in-built amp is underpowered and creating such distortion. Also, amps do not bring out the details in the music that were present when the music was produced. Irrespective of whether your music is blaring or low to allow conversation, an amp will bring definition to the sound. Road trips are no fun when the music in the car sounds flat and dull. As far as routine driving is concerned, traffic woes are enough to make it a tedious chore; a bland and uninspiring sound in the background only adds to the gloom. These inadequacies in your audio system can be eliminated by using an amp to get a real unadulterated sound experience will enrich your senses and lift your mood. 

Here are the specific benefits that an amp offers

Elevated sound

An amp provides you with a clean source of power that can drive speakers with no strain. The advantage with an external power amp is that it is not constricted by space which is not the case with a built-in amp. Thus, you can make the music sound sharp irrespective of whether the volume is high or low.

Powering after-market speakers

If you have upgraded your speakers, then using the in-built system will be a disservice to your speakers. After-market speakers or other components will demand more power for best output hence using an amp becomes mandatory.

Powering the subwoofer

If you have added a subwoofer to your audio system to get deeper bass, then an external amp is necessary to drive the extra power to your subwoofer.

With a multitude of choices available, which amp is the right one for you? When you purchase an amp, there are 3 key factors you need to consider. These factors will guide you on how to choose an amplifier for car speakers.


You will need 1 channel for every speaker that needs to be amplified. A mono amp can power your subwoofer too in case you have added it to the audio system. Amplifiers are distinguished into different classes by certain industry standards. These are class A, class B, class A/B and class D. Each class has its pros and cons. A class D amp is efficient and uses less power when amplifying a subwoofer.

There are amp units having 2, 4 or 6 channels and they offer a great deal of versatility. You may use a 2 channel amp to power 2 subwoofers or 2 coaxial speakers. Coaxial speakers are also known as full range speakers. They are easily available in the market and used by OEM and audio enthusiasts. 

Buying the right amp depends on the needs you have. Many people do not prefer to use the rear speakers. They like a stronger front and in such a case, a 2 channel amp will be the best option as only one pair of speakers need to be powered up.
However, if you like wholesome sound in the rear and like to maintain front-to-back fade option, a 4 channel amp is the way to go.


The output of most factory car stereos is limited to 10 watts RMS per channel. That is nowhere near to getting a top-notch audio experience in your car. Addition of an amp would be a step in the right direction.

Familiarize yourself with the term RMS (root mean term) value. This is a power rating you will find in the product specification of every speaker. Underpowered speakers will not deliver the best sound in your audio system. It is common for people to purchase the speakers first and then buy the right amp to power up the speakers. Your amp should be able to drive 75-150 percent of your speaker’s RMS. This is a good way of determining which amp is appropriate for you depending on your speakers’ specs.

Some folks opt for a factory system upgrade which will include the right amp and other equipment that is custom-designed for their vehicle. However, this could set you back financially. Another cheaper way to revamp your audio system is by getting a slick 4 channel amp to boost the front and back speakers.

Car type

Another important element in choosing the right amp is your car type and its interiors. If you drive a compact or hatchback, an amp with 50 watts RMS per channel will do the job. It is capable of drowning out the road noises and adding the fizz to your sound. Speakers having a top rating of 35 watts concerning the RMS will complement this well. For bigger cars or even, if you want a louder sound in a smaller car, RMS per channel of 75 watts is needed. Speakers having a top rating of 50 watts concerning the RMS will deliver an impactful sound.

For a hair-on-its-end experience in your car, 100 watts RMS is the magic number to look for in your amp. Speakers having a top rating of 75 watts concerning the RMS will our ears if that's what you expect from your music.

System compatibility & Subwoofer requirements

When you are starting, it is advisable to buy a head unit which has preamp outputs and an amp with line level inputs meaning an amp which has a strong output signal or which feeds on a very strong input signal. If you already have a head unit but without preamp outputs, then an amp with speaker level inputs will be needed.

It is difficult to boost the bass sound amongst all the sound components. A dedicated subwoofer amplifier can solve this problem. Mono amps or 1 channel amps are made for this specific reason, to work with subwoofers.

They work with a range of impedances. Also, they have specific filters and tone controls to enhance bass. Impedance is a measure to check the ease with which sound waves spread through a medium. Hence, a lower impedance speaker will need more power. For instance, a 2ohm speaker will extract more power as compared to an 8ohm speaker.

Some people bridge 2 channel and 4 channel amps for added power to the subwoofer. However, they might encounter a problem with this arrangement - an inability to handle the subwoofer’s low impedance and an overheated system.

As a music buff, your desire is for the bass to blend into the sound and complement the rest of the audio system. If you go by certain established standards you are most likely to get the best output. You must match the RMS power of your subwoofer with the power of the basic amplifier in your car. Normally the basic amplifiers power range should be between 75% and 150% of the desired power from the subwoofer. Suppose that you want 500 watts (RMS) of juice from your subwoofer. Here, your basic amplifier should have a power range between 375 watts (RMS) and 750 watts (RMS). If you want to install two subwoofers each with 500 watts (RMS), then your basic amplifier should have a power range between 750 watts and 1500 watts (RMS). 

If your subwoofer is a high power one, the existing amplifier must have a high power range. The lower the power of your subwoofer, the lower is the power range requirement from your basic amplifier. 

Match the impedance

Don’t forget to match the impedance. Incorrect impedance matching could overheat both your basic amplifier and your subwoofer – generally a bad idea! Subwoofers typically come either with a 2ohm or 4ohm impedance. If your basic amplifier has a 4ohm impedance, then you can connect a 4ohm impedance subwoofer. You could also connect two 2ohm subwoofers to the 4ohm basic amplifier. What happens if you have a cool dual voice coil subwoofer? They often come in two types: the coils are wired in parallel or they are wired in series. If they are wired in parallel, and each coil has a 4ohm impedance, then the subwoofer presents a 2ohm impedance to the basic amplifier – then your basic amplifier needs to have a 2ohm impedance for good matching. If the subwoofer coils are in series, there is an 8ohm impedance implying that your basic amplifier must also have an 8ohm impedance for good matching.

In addition to the power and impedance considerations, it is important to know that amps rarely come with all the necessary wiring you will need to connect them. Wiring kits, speaker wires, capacitor, battery terminals, hardware for power distribution etc. will need to be purchased separately. You should also remember the location you would like to install the hardware and accompanying wires. Installing an amp need not be a hard task. It is of utmost importance to take key measurements when you go to purchase the amp. Some people prefer to install it under one of the seats. Other common locations are in the trunk or firewall on the passenger side. Now, you should be ready to choose to perfect amp for your car.

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