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Two Common Car Amplifier Power Mistakes

MTX MUD100 Car Amplifier

The science behind car audio is often misunderstood. 

Have you ever heard someone talk about their 4,000 watt amplifier? What about when they ask which amp is best for their two 12” subwoofers? These are simple comments on the surface, right? However, there is more information needed if you are really going to answer this question or really understand what this “4,000 watt amplifier” can really do.

Here are two facts you must understand to help you make an informed decision when shopping for a car audio system.

1. Don’t mistake PEAK power with RMS power

Some car audio manufacturers have confused the public by misleading them into believing their amps are more powerful than they really are. They advertise exaggerated power output specifications on their amplifiers to make customers believe they are buying 4,000 watts of power for $49.99. In the industry, ratings like this are known as “W.L.S.” ratings, or “When Lightning Strikes”, because getting struck by lightning is the only way some amps will ever see the kind of power these manufacturers advertise.

Peak power ratings are a marketing angle for some companies to claim their amplifiers are more powerful than they really are. The amplifier may occasionally produce the peak power rating for a second or so, if the car battery is fully charged and adequate signal voltage is coming from the head unit, but it will never produce that amount of power for an extended period of time.

Reputable amplifier manufacturers use “RMS” (root mean square) ratings for power. RMS power ratings express the amount of power the amplifier will produce continuously, assuming it is getting adequate voltage from your battery. This is the power you will hear, both in volume and in dynamic response such as a cymbal crash or a heavy hit on the drum. This is the rating you want to compare when selecting an amplifier and is the realistic rating of power your amplifier is capable of producing.

So if an amplifier has a peak power rating of 2,000 watts and an RMS power rating of 750 watts, it really should be called a 750 watt amplifier...

2. Don’t choose an amplifier based on a power rating at an impedance your subwoofers cannot provide

Just because your amplifier will do 1,000 watts RMS doesn’t mean it’s the right amp to power two subwoofers that have a power handling of 500 watts each. You need to consider the impedance (ohms) that your subwoofers are wired to provide and match the power output of an amplifier at that same impedance.

If an amplifier produces 1,000 watts x 1 channel @ 2Ω, but your subwoofers are wired to 8 ohms in combination, you wouldn’t be providing them with 1,000 watts .  Most of the 1000 watts of current will be restricted by the additional resistance of 8 ohms and the amplifier would more likely be delivering 250-watts to the subwoofers when wired in this fashion.

Wiring subwoofers to the wrong, or unmatched, amplifier impedance is a VERY common cause of blowing amplifiers and burning voice coils in subwoofers. 

Even if you don’t understand the science behind circuit impedance, MTX makes it easy for you to wire your subwoofers correctly with our Subwoofer Wiring Diagrams tool on our website.

MTX Car Subwoofer Wiring Calculator

MTX Car Subwoofer Wiring Calculator

MTX Car Subwoofer Wiring example

In this example using two subwoofers with dual 4 ohm voice coils,
you could wire them to a final impedance of 1ohm or 4ohms at the amplifier.

Simply enter the number of woofers you are wiring,  their impedance and the number of voice coils on each (single voice coil or dual voice coils ).  The tool will then show you  options for wiring them to the amp with different resulting total circuit impedances. The wiring you should use is the circuit that provides the total impedance you need for your amplifier, or the one you should use when selecting a new amplifier.

(For more information about single vs. dual voice coil subwoofers, CLICK HERE)

If you choose an amplifier that will output the 1,000 watts @ 1ohm and even though your subwoofers are rated at 500 watts each, if you wire the subwoofers to a final impedance of 4 ohms, your amplifier is probably only putting out around 250 watts or less at that impedance and your subwoofers will be under powered. But since the 4 ohm subs can be wired differently resulting in an effective total impedance of 1 ohm, you get the full 1000 watt power from your amp and match the rated power of your subs for full performance.

For example, our XTHUNDER1200.1 amplifier is rated for 1200 watts RMS @ 1 ohm. If the subwoofers are wired to a total impedance of 4 ohms, this amp will only produce 400 watts @ 4 ohms.  800 watts of its potential output power are lost due to the added resistance.

So, as you can see, an amplifier might be capable of providing your subwoofers the correct amount of power, but you must wire your subwoofers with the proper impedance circuit to ensure you are getting the power you expected. Otherwise, you may be paying for unused performance and your money may be going up in smoke (literally).

Under-powering subwoofers due to wiring them at a higher impedance than needed causes your amplifier to work harder. When amplifiers work hard, they heat up. When heat builds up in electronics, it can cause amplifiers to go into thermal protection or even cause failure. When heat builds up in subwoofer voice coils, the coils can burn and the subwoofers no longer work.

When choosing an amplifier for your car audio system, first determine what impedance circuit you are going to use to wire your subwoofers. Then determine the amount of power your subwoofers can handle. RMS power handling of a 55 series 12” dual 2 ohm voice coil subwoofer is 400 watts. Two of these subwoofers would mean you need 800 watts of power at to the total circuit impedance. In this case, let’s say we are going to wire them to a total, effective impedance of 2ohms.

MTX 55 Series 5512-22 12 inch 400w rms dual 2 ohm Voice Coil Car Subwoofer
MTX Car Subwoofer Wiring Example 2

Then find an amplifier that has an RMS output rating of 800 watts at 2ohms. The XTHUNDER1200.1 amplifier that we talked about earlier produces 750 watts @ 2 ohms which would be a good match for these two subwoofers when wired to a 2 ohm impedance as seen in the first wiring diagram.

So, when shopping for your next car audio system, don’t get fooled by Peak power ratings on amplifiers and be sure to match your subwoofers with an amplifier that will do the right amount of power at the impedance you plan to wire your subwoofers to.

If you do this, you are much less likely to have any product failure and you can be confident that your car audio system is giving you all the performance you paid for.

If you would like help matching up your subwoofer(s) with an amplifier that would be appropriate, we are here to help. You can Chat with our Customer Service Techs online at  You can contact us through Facebook or Twitter at MTX Audio USA Facebook or MTX Audio Twitter.  You can email us at or you can call us at 1-800-CALL-MTX (1-800-225-5689).


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