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Receiver Power vs. Amp Power

A Difference You Can Hear

Heads up!

Welcome to this article from the Crutchfield archives. Have fun reading it, but be aware that the information may be outdated and links may be broken.

Imagine truly dynamic sound. The detail in soft passages is clear and crisp, and the loud notes hit home with solid impact. How do you make this happen in your car? Add more power.

Car audio manufacturers are packing more power than ever into aftermarket receivers. That's good news if you're looking to improve your sound — compared to low-powered factory systems, a new receiver will make a big improvement in your car's sound.

Yet, if your goal is to get the best possible sound, it's a good idea to go the extra step and install an external amplifier to power your speakers. Why does an external amp have an advantage over an in-dash head unit?

The power difference
A lot of aftermarket receivers claim high power output. Go to any store and you'll see "50 watts x 4," or more, printed on the face of most models. That's plenty, right? After all, you'll find there are a lot of amps that list 50 watts x 4 as their output. Just be careful that you're not comparing apples to oranges, though.

The 50 x 4 wattage rating on your head unit is a "peak power" rating. The problem is peak power ratings aren't a realistic way to measure performance. They are only a reflection of wattage output for very short "bursts" of music — like a single loud note. RMS wattage ratings — a measure of the continuous power output of your equipment — are a much more realistic way to evaluate performance.

A head unit with a 50 watt x 4 peak power rating probably produces about 20-25 watts of continuous, or RMS power. If you compare that to an amp with an RMS wattage rating of 50 x 4, you're looking at double the power. That's enough power to make a real difference in performance.

Why higher power output is good
You may wonder exactly why the higher power output of an amp makes a difference. There are some very good reasons why it does.
  • Clipping
    If you need (or like) to turn it up loud, an amp is essential. You may turn up the volume to compensate for road noise, to power a subwoofer, or maybe you just like it loud. If you ask the receiver's amp to go beyond its limits you'll end up with "clipping."

    A normal sound wave looks like Fig. 1 (below). Clipping occurs when the tops and bottoms of the sound wave are "clipped" off by the amp's lack of power, and the sound is distorted, like in Fig. 2. Clipping not only sounds bad, it can damage your speakers.

    Fig 1 - Normal sound wave

    Fig 2 - "Clipped" sound wave

  • Speaker efficiency
    You also need the extra power if your speakers aren't efficient. A speaker with a low efficiency rating requires extra power to produce the same volume of sound as a more efficient model. If you try to run an inefficient speaker at high volume without adequate amplification, you'll get distortion caused by clipping. For a more in-depth discussion of speaker efficiency check out Matching Speakers to Your Mobile A/V System.

  • Improved clarity and detail
    External amps offer lower THD (Total Harmonic Distortion) ratings — a measure of how clean the sound is.

    The larger chassis of an amp allows engineers to locate sources of noise, like the amp's power supply, far from the other amplifier circuits. Plus, engineers can use upgraded components, like bigger power supplies, capacitors, and heat sinks — all elements that combine for better performance. This gives you cleaner sound, a good idea no matter how loud you like to play it.
Summing up
An amplifier is an essential component for getting the best sound from your system. While a new head unit is a big step up from a factory system, there's just no substitute for the power, clarity, and detail that an amp can add to your system. You'll hear your music in more detail, and reach higher volume levels without clipping and distortion.

The choice is as clear as the sound you want. To get the most out of your system, put in an amp!