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How to Pick the Perfect Power Amp for Your Car Subwoofer

If you're looking to add big low-end sound to liven up your commute's playlist, then choosing the best car subwoofer for your automobile is only half of the equation   the second half is finding the correct power amp to power said subwoofer. Since low frequencies have such long wavelengths, car subwoofers have to move a lot of air. If you try to wire your sub to the car stereo, as you do with the car speakers, it won't have enough power to move the speakers. Without a power amp, your car subwoofer is just a bowl with a large magnet.

However, there are many different types of power amps, and each amp is designed to power different types of speakers and subwoofers. You can't simply pull a power amp off a shelf and assume it's going to work with your subwoofer. Some important specifications need to match up before you can add that epic bass to your playlist.


The best power amplifier for a car subwoofer is a single-channel amp. This means that the amp processes a single audio signal through one channel, which is wired to your subwoofer. You can wire multiple subwoofers to this single channel, but each sub receives the same mono frequency. Low-end frequencies aren't generally heard stereophonically like the midrange and high-range frequencies your car speakers produce, so one channel is all you need. The best power amps also have filters and tone controls that allow you to optimize the bass reproduction.

RMS Watts

Subwoofers have two power-handling specifications   RMS watts, also referred to as continuous power handling, and peak watts, or peak power handling. The RMS (root mean square) wattage of the subwoofer indicates the amount of power the subwoofer can handle on a continuous basis. The peak wattage indicates the maximum amount of power the subwoofer can handle for brief periods before experiencing damage.

You need to match the RMS watts of the subwoofer with the RMS watts of the power amp. Many power amps list an RMS watts range. This range indicates the minimum and maximum power range that the amplifier is capable of producing. If the power amp has a wattage range, you want to ensure the minimum power is 75 percent of your subwoofer's RMS watts and the maximum is 150 percent of the RMS watts. If you're ever in doubt, remember an overpowered subwoofer is better than an underpowered one.

For every additional subwoofer you install to your system, the power amp's wattage range needs to reflect the additional sub's RMS watts. For example, if you install two subwoofers with a 300 RMS watts rating, then you need a power amp with a power range of 450 to 900 watts. Otherwise, both subwoofers only receive half the power they need to operate effectively. If you decide to add a second or third subwoofer to your car audio repertoire, you need to upgrade your power amp as well.


Impedance measures electrical resistance. Matching the impedance with your power amp is like matching a water pipe to a faucet   the water won't flow effectively if you try to fit a small pipe on a large faucet, and vice versa. Impedance works much the same way. If you fail to match the impedance correctly, your power amp and your subwoofer could over heat, leading to damage and terrible audio.

Most car subwoofers give you the option to purchase a model with an impedance of either 2 ohms or 4 ohms. Matching impedance seems like a fairly simply concept on the surface, and most of the time it is simple if you're just installing one or two subwoofers. However, it can get complicated when you're dealing with multiple subs or dual-voice coil subwoofers, which have two input and output connections. For example, if you're installing two 4-ohm subwoofers, you need a power amp with 8-ohm impedance. If you're installing a dual-voice coil subwoofer with 2 ohms, you need a power amp with a 4-ohm impedance because each connection has 2 ohms.

Once you've found a power amp that matches the RMS watts and impedance of your subwoofer, all you have to do is connect the subwoofer to the power amp and connect the power amp to your car stereo. A properly powered subwoofer can be the difference between listening to a lifeless playlist on your commute and rocking out wherever you go.