What You Need to Know Before You Buy PART II

Size and Style

Some people want to hide their amp; some people want to show it off. Lifestyle and space constraints often dictate amplifier size. If you leave your car parked on the street a lot, you might want to have a small amp hidden under your seat or in your trunk. If you want to show off your amp to your friends or display it in plain view, a designer look might suit your needs. If you don’t have much space, sometimes two or three small amps can be better than one big one. These days especially, amplifiers come in all sizes; some are the sizes of old pocket radios. They also come in lots of colors and styles. Whether you’re plain or artistic, you should have no problem finding an amp to fit your personality.

Fine-tuning the Sound

Many amps come with built-in bass equalizers, filters and crossovers, all designed to help your installer fine-tune your system. For example, you might be stuck with a pair of 4” speakers only capable of reproducing midrange and high frequencies. A properly adjusted filter or crossover will cut out the low frequencies and only allow midrange and high frequencies to those speakers. Sure, filters and crossovers improve the quality of sound, but they’ll also save your system from damage by allowing each speaker to focus on its core strengths or design intentions. For subwoofer applications, bass equalizers can be helpful in compensating for a car’s acoustics. Bass equalizers are certainly useful, as long as they’re not abused.

Digital or Analog?

Years ago, a 1,000-watt amplifier was about the size of small surfboard. However, with Class D technology it is not unheard of to get this kind of power out of an amplifier measuring 12” in length. However, Class D amps have been limited to mainly subwoofer-specific amplifiers due to their switching (digital) power supplies. These amplifiers are typically 25 to 30 percent more efficient than their Class AB counterparts, which is why their packaging is so small and one reason why they are a great match for subwoofers.

The old reliable Class AB amplifier is well known for its sound quality and makes up a good 80 percent of the car audio amplifier market. They are also available in virtually any size imaginable, from 25 watts to beyond 2,000. Class AB always makes for a good option to run your mids and highs.

Some multi-channel amps are now combining both digital and analog technologies. There are several available that combine analog (Class AB) channels for the mids and highs with a single digital (Class D) channel dedicated to subwoofer applications.

Pay for Quality

These days a good 2-channel amp starts around a couple hundred dollars, while a high-quality 4-channel amp starts around $300. If you need a 5-channel model, you’ll have to spend at least $400 to get something good. Don’t be enticed by no-name equipment with hard-to-believe prices. Cheap equipment may not always hold up well, especially in abusive situations.

Use a Professional Installer

Have your components installed by a reputable, certified installer. An inexperienced individual could easily connect something incorrectly, causing expensive vehicle damage. While quality audio components are a necessity in reproducing an artist’s music accurately, even the best equipment installed incorrectly will yield poor results. Happy amplifier shopping!

And finally, whether you listen to rap, classic rock, jazz or classical, there’s nothing like having plenty of power on tap when you really want to crank it up. However, one killer power amp coupled with average speakers and a stock CD player isn’t going to translate into an audiophile-quality experience. If you want more from your car stereo, a speaker upgrade will definitely result in the most noticeable improvement in sound quality. Since budget is often an issue, upgrade your system one step at a time—fullrange speakers first, amplifier second, subwoofer, etc. Each step of the way, simply purchase the best gear you can afford.


How can the average consumer go about choosing a high-quality amplifier?

First: Beware of the “bling.” It is there to hook you and costs money. Power meters, see-through panels, chrome and LEDs do nothing for the sound. Find a balance and don't get sucked in by stuff that has no use and is only meant to distract you. Money spent on “bling” for the outside is money not spent on quality for the inside.

Second: Ask to see the manuals. A company taking pride in its product will want you to understand how the product works and will provide a useful, informative manual. If you can't understand how the controls work from the manual, you should probably look elsewhere.

Third: Check out the car audio dealers. Specifically check out the sales guys and installers. See what they have in their cars. Yes, the manager will have his people using the products he wants to sell. But, by the same token, those guys want decent stuff in their cars, so if they're using it, that's (generally) a good sign.

These external things will help narrow your choices to the better performing products. Of course it's the internal elements that contribute most to reliability and performance. Multi-layer circuit boards, symmetrical design, heavy-gauge traces and appropriate power supplies are just a few. Unfortunately, these are hard to recognize and most sales people won't be much help.

So read those reviews. When magazines review a product they take a good, close look at how it's built. Read the whole text of the reviews. If you can't find the amp you're looking for, find another one from the same series. The build methods will be the same and you'll get a better feel for the real quality.

What You Need to Know Before You Buy PART I

How Much Power?

You want more power. That's the whole point of adding amps. But first you should define your power needs, so think about your system goals. If you're going to your local shop, expect your installer to pose a few questions: What kind of music do you listen to? Is it bass heavy? Are you planning to install a subwoofer? Do you listen to your music loud? Do you drive a convertible or a hot rod? How much money are you willing to spend?

If you like your music loud and bass heavy, and you’re planning to install a subwoofer, you will definitely need big power. The same holds true for people with cars that inherently have lots of road noise, such as convertibles. For most basic applications though, a quality 50-watt x 2 or 50-watt x 4 amplifier will work wonders to amplify your factory, component or coax speakers. For example, a basic system might consist of two 6 1/2” coaxes in the front doors and two 6” x 9”s in the rear. Using a 50 x 4 amplifier you end up with one dedicated amp channel per speaker. If it is not in your budget to purchase a 4-channel, a 2-channel amp could be substituted to either run the front speakers or both front and rear (with resistors to attenuate the rear). To be assured of good, “clean” power, always buy the proper amount of power for the given speakers you plan to amplify. If you underpower your speakers, you may risk pushing your amp to the limit, which could diminish sound quality by generating distortion and cause speaker and/or amplifier damage. Extra power means your amp will run cooler and more efficiently, translating into better quality sound.

How many channels?

If possible, you’ll want to dedicate one amp channel per speaker. But no worries, there are also perfectly acceptable ways to have your installer wire a 4-speaker system with a 2-channel amp. A 50 x 2 or 50 x 4 amplifier will be fine for basic 2- or 4-speaker systems. If you’re planning to power a subwoofer, a 5-channel amp is a godsend, with the fifth channel dedicated to your sub. Since bass demands more power, the fifth channel usually delivers more wattage. A 5-channel amp might spec out like this: 50 watts x 4 plus 100 watts x 1.

Most amps today are capable of being bridged. With bridging, multiple amp channels are combined to get more power from a single amp channel, allowing for excellent installation flexibility. A 50 x 4 amp could be morphed from a 4-channel into a 3- or 2-channel amp. Here’s how it might spec out: 50 x 2 plus 200 x 1 or 200 x 2. Bridging is great for sub applications.

Note: some amps include a remote level control allowing you to manage the bass level from the driver’s seat. Since bass varies greatly from one musical genre to the next, a remote sub control is a super convenient feature.

Compare Power Ratings and Specs

When it comes to power ratings, manufacturers have many different ways of saying the same thing, making it confusing for consumers. You’ll need to know what to look for when you’re shopping around. One thing you should know is that your car battery and alternator are responsible for generating the voltage and current that power your amp. But voltage is not regulated equally from car to car and may vary from engine idle to that of a higher RPM. More voltage typically equals more amp power (with the exception of amplifiers using tightly regulated power supplies). This is very important since most manufacturers rate their product at 14.4, 13.8 or 12.5 volts. Respectively, an amplifier (those using unregulated or loosely regulated power supplies) rated 50 watts x 2 at 14.4 volts may see a decrease in power output by as much as 15 percent when powered with 12.5 volts. In retrospect, a 50-watt x 2 amplifier rated at 12.5 volts may see up to a 15 percent increase in power at 14.4 volts. That, my friends, could be the difference of up to 30 watts between two 50-watt x 2 amps. It is important to know that you are comparing apples to apples since there is no governing body verifying the product specifications in car audio. While this may be problematic with certain brands, there is a way to confirm some products’ specifications. The CEA (Consumer Electronics Association) developed the CEA-2006 specification guidelines that confirm specifications. Mobile electronics carrying the label must remain true to the published specifications taken at 14.4 volts (just look for the CEA-2006 label). More information on participating manufacturers can be had at www.ce.org. However, when in doubt, ask your installer.

Some amps state “RMS” power while others utilize “continuous average” power. These monikers can be construed as the same, leaving amplifiers using this verbiage open for comparison. An amp that’s 50 watts RMS x 2 into 4 ohms (we’ll discuss ohms in a second) can effectively deliver 50 watts x 2 at the onset of or below a clipped output level (clipping is when a sine wave turns into a square wave otherwise noted as distortion). In contrast, “maximum” or “peak” power ratings are marketing terms that typically use figures relating to at least double the RMS power and are generally not practical for comparing amps (and in some cases should be followed by the clause “when lightning strikes”). An amp rated at 50 watts x 2 maximum into 4 ohms more times than not is equivalent to an amp that’s 25 watts RMS x 2 into 4 ohms.

Other amps offer “total” power ratings, such as 100 watts total RMS power. This is another tactical marketing maneuver manufacturers use that essentially is the sum of all the channels of the amplifier. In the case of my example, this could relate to an amp that is 50 watts x 2 or 25 watts x 4 into 4 ohms.

Now, back to the issue of “ohms.” Amp ratings are typically given at 4 ohms. Ohms refer to impedance or electrical resistance. Every speaker has an internal resistance due to the wire on the voice coil and additional components such as those of a crossover. Heck, even speaker wire has resistance—but let’s not get sidetracked. The majority of car speakers are 4 ohms, so that’s why amplifier manufacturers generally rate them as such. Often there will be other impedance ratings such as 2 ohm and sometimes 1 or 0.5 ohm depending on the amplifier. Again, power ratings and specs come in many different and often misleading forms, so don’t be fooled. Make sure you’re comparing apples to apples.


12" Differential Drive® Design Subwoofer.

Features of the JBL W12 GTI include:

  • Cast aluminum heat-sink cooled magnet system - for an extreme power handling
  • Differential Drive System - consisting of dual-edgewound voice-coil and dual-gap technology for a doubling of Power Handling, Sensitivity and an "electrical brake" to control cone motion at extreme excursions
  • more than +/- 20mm linear cone excursion - provides extremely high sound pressure levels
  • Symmetrical-Field-Geometry (SFG) - reduces distortions to minimum at any level
  • Aquaplas coated cone - for exceptionally stable performance even at extreme levels
  • Butyl rubber surround - for better sound quality and long durability
  • Two separate gold plated screw/plug terminals - provide long lasting electrical connections