How to choose your car amplifier Subwoofer or speakers: the complete guide
RMS power, impedance, number of channels, wiring and power supply: discover how to choose an amplifier suited to your speakers or subwoofer and how to install it correctly.
A powerful amp is not enough: it must above all be suited to your needs
When you are starting out in Car Audio,
choosing an amplifier can quickly become complicated.
Manufacturers talk about watts, RMS, ohms,
channels, Class D, bridging...
Yet, a few pieces of information are enough
to make a sensible choice.
In this guide, we will see how to correctly match
an amplifier to
a subwoofer, a component kit, or speakers,
then how to plan the necessary power supply and wiring.
Look at the RMS power, not the MAX power
The first piece of information to look at is the RMS power.
This is the value you should use to compare the power rating of your speakers or subwoofer with the power delivered by the amplifier.
MAX, Peak, or similar values are not the main values to use when sizing your system. Compare the RMS ratings.
Look for an amplifier capable of delivering power consistent with these 1000 W RMS at the impedance your subwoofer will actually be wired to.
Should you get a more powerful amplifier?
It is possible to use an amplifier slightly more powerful than the rated RMS power of the speaker or subwoofer, provided the system is correctly sized and used.
This can help maintain a power reserve without constantly pushing the amplifier to its limits.
For a 1000 W RMS subwoofer, an amplifier capable of delivering around 1000 to 1200 W RMS at the correct impedance can make a sensible match depending on the equipment used.
But you should not consider "+10 or +20%" as a mandatory rule.
The manufacturer's recommendations, the speaker's power rating, the type of use, and the installation must always be taken into account.
Power AND impedance must match
Saying that an amplifier produces 1000 W RMS is not enough.
You must always know at what impedance this power is available.
For example, an amplifier can deliver:
500 W RMS at 4 Ω
800 W RMS at 2 Ω
1200 W RMS at 1 Ω
The same amplifier can therefore deliver very different power depending on the impedance used.
Simply understanding ohms
The impedance of a speaker or subwoofer is expressed in ohms (Ω).
You will commonly find models in 1 Ω, 2 Ω, or 4 Ω. Subwoofers can also have multiple coils.
The subwoofer has a single coil. Example: 4 Ω.
The subwoofer has two coils. Example: D2 = two 2 Ω coils.
Wiring the coils in series or in parallel allows you to obtain different final impedances.
If an amplifier is rated stable
down to 1 Ω,
this does not mean it can operate
at 0.5 Ω.
An impedance that is too low can lead to
overheating, protection mode
or damage to the amplifier.
Choosing an amp for a subwoofer
To power a subwoofer, a monoblock amplifier is very often used.
To choose the right model, mainly check:
- The RMS power of the subwoofer.
- The number of coils.
- The impedance of each coil.
- The final impedance of the wiring.
- The RMS power of the amplifier at this impedance.
- The minimum impedance supported by the amplifier.
With both coils wired in parallel,
the final load will be 1 Ω.
You will therefore need to look at the power
the amplifier is capable of delivering
at 1 Ω.
Choosing an amp for speakers
For speakers or a component kit, the reasoning is similar, but you must also look at the number of channels.
For example, look for an amplifier
capable of delivering power close
to this value per channel at 4 Ω.
You should not compare the total power
of the amplifier with the power
of a single speaker.
Power per channel is important
Let's take an amplifier rated 4 × 100 W RMS at 4 Ω.
This means it can deliver up to 100 W RMS on each of its four channels under the conditions specified by the manufacturer.
To power four speakers, you therefore look at the power available per channel, and not simply the sum of all the power.
Can you bridge an amplifier?
Some 2 or 4 channel amplifiers allow you to combine two channels to power a single load.
This is what is called bridged or Bridge mode.
This solution can notably be used to power a subwoofer with certain multichannel amplifiers.
The minimum impedance allowed in bridged mode
may be different from that allowed
when each channel operates separately.
Always consult the amplifier's
manual before making the connection.
Choosing the power cable
Once the amplifier is chosen, you must be able to power it correctly.
The cable gauge depends notably on:
- The amplifier's power consumption.
- The length of the cable.
- The material used.
- The vehicle's electrical installation.
For high-power installations, we recommend using a properly sized OFC copper cable. It offers excellent conductivity and helps limit voltage drops.
Two amplifiers rated at the same power
can have different power consumption.
Consult the manufacturer's recommendations
regarding the cable gauge
and electrical protection.
Installing the fuse correctly
The positive cable connecting the battery to the amplifier must be protected by a properly sized fuse.
In the event of a short circuit of the positive cable
against the bodywork,
the battery is capable of delivering
an extremely high current.
Without suitable protection,
the cable can get very hot
and pose a serious risk.
Install the fuse holder as close as possible to the battery, generally within the first few dozen centimeters when the installation allows.
Ground is just as important as +12 V
A poor ground is one of the most frequent mistakes when installing an amplifier.
The ground must be made at a suitable point on the vehicle, with a clean electrical contact.
- Use a suitable cable gauge.
- Keep the connection as short as reasonably possible.
- Remove paint or treatment preventing good electrical contact.
- Secure the terminal correctly.
- Then protect the area against corrosion if necessary.
voltage drop, protection mode, unstable operation, interference or overheating of the connections.
2000 W RMS and above: think about the vehicle's power supply
The higher the power, the greater the electrical demand.
On a high-power installation, the original battery and alternator may no longer be sufficient depending on the vehicle, the amplifier, and the conditions of use.
It may then be necessary to consider:
- A battery suited for Car Audio.
- An auxiliary battery.
- AGM or Lithium technology suited to the installation.
- A reinforced alternator.
- Reinforcing the vehicle's main cables.
- Voltage monitoring.
Monitor the voltage of your system
A car amplifier depends directly on the vehicle's electrical system.
The voltage varies depending on the vehicle, the type of alternator, electronic management, the condition of the battery, and the requested load.
On a high-power installation, monitoring the voltage at the amplifier allows you to more easily detect significant voltage drops.
However, avoid considering a single value as mandatory: modern vehicles can manage their charging voltage differently.
In what order should the amplifier be connected?
A clean and secure installation is just as important as the choice of amplifier.
- Disconnect the negative battery terminal before working when the vehicle procedure allows.
- Install the positive cable with its suitable protection near the battery.
- Route the cable to the amplifier, protecting it from rubbing and sharp metal edges.
- Install a properly sized ground.
- Connect the remote if the installation requires one.
- Connect the RCA inputs or high-level signal.
- Connect the speakers or subwoofer, ensuring correct polarity and impedance.
- Check all connections before switching on the power.
What About Gain, LPF, Subsonic, and Clipping?
Once you have correctly chosen and installed your amplifier, you still need to set it up.
But this part deserves a complete guide on its own.
We have therefore deliberately separated choosing and installing the amplifier from setting the Gain, LPF, Subsonic, and clipping to make each step easier to understand.
Common Mistakes When Choosing an Amplifier
Mainly compare RMS power at the impedances actually used.
1000 W at 1 Ω and 1000 W at 4 Ω do not meet the same needs.
A powerful amplifier requires a properly sized power supply.
A poor ground can cause many malfunctions.
Always respect the minimum impedance stated by the manufacturer.
A very powerful installation may require an upgrade to the battery or alternator.
How to Choose Your Amplifier in 6 Steps?
Check the RMS power of your speakers or subwoofer.
Determine the final impedance of your installation.
Check the RMS power the amplifier provides at this impedance.
Choose the number of channels corresponding to your installation.
Properly size cables, fuses, and ground.
Check that the battery and alternator can meet the needs of the installation.
Frequently Asked Questions About Car Audio Amplifiers
Which amplifier should I choose for a 1000 W RMS subwoofer?
Look for an amplifier capable of providing RMS power consistent with the 1000 W of the subwoofer at the final impedance actually used. Also check the manufacturer's recommendations.
Can an amplifier be more powerful than my subwoofer?
Yes, a certain power reserve can be used, provided that the whole system is properly sized and used. An amplifier that is slightly more powerful does not automatically damage a subwoofer.
Which amplifier should I choose for 4 speakers?
A 4-channel amplifier is generally the simplest solution: one channel can power each speaker, provided you respect their impedance and their allowable power.
What is the difference between a mono amplifier and a 4-channel one?
A monoblock is mainly intended to power a load such as a subwoofer. A 4-channel amplifier allows you to power several speakers independently.
What does "stable at 1 ohm" mean?
This means that the amplifier is designed to operate up to a load of 1 Ω under the conditions specified by the manufacturer. This does not mean that it can automatically operate at 0.5 Ω.
Why use OFC cable?
OFC copper offers very good conductivity and is an excellent choice for Car Audio power supplies, especially when the currents become significant.
A poor installation can damage an amplifier
An amplifier failure is not necessarily related to a manufacturing defect.
Incorrect impedance, a short circuit, unsuitable wiring, an incorrect power supply or use outside of specifications can damage the equipment.
During an after-sales technical assessment, the cause of a failure may be investigated. If the damage results from an installation or use that does not comply with the specifications, warranty coverage may be refused according to the applicable terms and conditions.
Any doubts before connecting your amplifier?
RMS power, impedance, number of channels,
cable gauge, or power supply:
choosing the right equipment before installation
helps avoid many mistakes.
Sound Auto Concept
can help you choose
an amplifier suited to your subwoofer
or your speakers.
1 Rue de la Manufacture Semely, 34120 Pézenas
09.85.13.66.35
fabrication@soundautoconcept.com