Car Speaker Basics: What Car Speaker Ratings Mean

This guide will prepare you to choose speakers to match your head unit. It covers the principles of peak and RMS power ratings, as well as channels and ohms.

Selecting speakers to fit your car's stereo can be a daunting process. Not only do you have to find a speaker that is the right size, but it is important to match the power of the speaker to the power of the amplifier or head unit. To further complicate matters, there are many different kinds of ratings for each speaker. Don't worry; with this guide you should be able to decode the numbers.

The first power rating a speaker manufacturer will probably display is the max, or peak wattage rating. They do this because the peak rating is the absolute maximum amount of power that a speaker can handle for a very short duration of time. This power would only ever be reached at max volume during the peak of a song, and even then it would only last for milliseconds.

Max power can be very misleading; if you actually pushed this much power through the speaker for even a second it would blow. Hence, when you are selecting a speaker, you should try and match the peak power of the speaker to the peak power of the amplifier or head unit you are running. It's OK if your speaker can handle more peak power than the amp can put out. In fact, this will ensure that you will not blow the speaker.

The other wattage rating of speakers is the RMS wattage. In the interest of simplicity we will say that the RMS is the average power that the speaker can handle over a sustained amount of time. At the loudest volume, your stereo would theoretically be putting out its RMS power for most of the song.

RMS power is the best measurement of power handling capabilities for a speaker. Make sure to match the RMS of your speakers to the RMS of your head unit or amplifier. Again, it's perfectly fine if your speaker can handle more power than your head unit can produce, but not the other way around.

Now that you have a basic understanding of the lingo used to talk about speaker power ratings, it is important that you also understand how to determine the actual power coming from your head unit or amplifier.

When the manufacturer writes the wattage of an amplifier, they will usually write something like 80w peak x4. This means that 80 watts are pumped, at peak power, into four channels. A channel is a line to a speaker, commonly labeled as left front, right front, left rear, and right rear. The problem is that the 80 peak watts coming out of the head unit get split into 20 peak watts per channel. This means that each speaker only receives 20 peak watts. So when you select a speaker, you must select one that can handle at least 20 peak watts. If you have a two channel amplifier, the power only gets split two ways.

To further complicate the matter, most power ratings will also include a number followed by a horseshoe shaped omega symbol. This represents ohms, which is a measurement of resistance. The rating for your amp or head unit will probably read something like this: 80w peak x4 @ 4Ù (ohm symbol). This means that at a resistance load of 4 ohms, the amp will be produce 80 peak watts (20 per channel). The resistance of 4 ohms will be coming from your speaker. Hence, the best speaker choice will be one that has 4 ohms of resistance, and can handle 20 peak watts per channel.

It is generally not recommended to use a speaker with a different resistance rating than the amp that will be supplying it. However, if you do, keep in mind that if the resistance doubles (as with an 8 ohm speaker rather than 4), the wattage will be cut in half. Conversely, if the resistance is halved (a 2 ohm speaker instead of 4), the wattage will double.

If you keep all of this in mind as you are selecting a speaker, you should be able to make a good choice. Ideally, you will find a speaker that perfectly matches your head unit. If not, remember to always err on the side of too much power handling as far as your speakers are concerned.

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