How to Select a Car Amplifier

I’ve been selling car audio amplifiers online for over a decade now. Through the years, the single most often asked question is “how do I select an amplifier for my new speakers or subwoofer?”

Let’s try to de-mystify this selection process if we can. This information is presented to help the online-shopper make reasonable decisions. It is geared toward the published information that is generally available in most product descriptions on the web. Let’s face the facts, if you have been in the line of car audio for years and have completed several installs, you know what you are looking for. But many, if not most online shoppers are not that familiar with the finer points of car amplifier installations.

Many, who are new to car audio will first look for “US made” as a stamp of high quality. Although that might have been true when I first started out decades ago, it certainly isn’t a serious guideline anymore. Honestly speaking, even some of the most famous named amps, associated with good old American production are in reality developed and manufactured in the Far East today. You will be very hard pressed to find any car audio products made in the USA today. In addition if you do find that one out of fifty brands that might be assembled in the USA, you’ll choke at the price.

Most shoppers will purchase their speakers or subwoofers first and then go shopping for an amplifier. So you’ll have the recommended specifics in hand (for your speakers) as you start your amplifier search. This is definitely the suggested order if you desire to find a proper match.

Usually shoppers will immediately look at the power output of an amplifier first. When considering the power, you should also consider the maximum impedance specified by the amp. Most classic amplifiers by the likes of Nakamichi, Alpine, Linear Power, Orion, Precision Power, Eclipse, and US Amps will be capable of 2 ohm and even 1 ohm operation in the case of class D subwoofer amps. But in the real world, you should compare the amp’s output capability at 4 ohms. In the majority of installs, you will be building a 4 ohm setup. At one time, the names mentioned above and most other quality amps would only publish their specific output at RMS or continuous power ratings and never the maximum output. Unfortunately, due to the changing market place, almost all amplifier manufacturers publish the maximum output of their amps. Beware of this since it can be most misleading. Lets be honest, who cares what an amplifier can produce for a period of 1 millisecond? Published maximum output is really very misleading and near worthless to the installer. This is nothing but an advertising ploy to make the shopper think he is getting more power for his dollar spent. We want to compare the continuous output of an amp since it is a much better method of comparison and represents how your amp will be used.

The second subject to check is the “signal to noise ration” (SNR) of an amplifier. Obviously the higher this ratio, the better it is. Although this is not particularly important if searching for a subwoofer amp, it certainly should be a deciding factor in purchasing a good amp to drive your mids and tweeters.

The above two points will enable a shopper to match an amp to his new speakers but there are several other more general points to consider also. One such point is: does your car radio or source unit have a low-level output connection? This allows you to connect directly to the standard low-level inputs on your amp. If your head unit isn’t so equipped, you’ll need an amplifier with a high-level input. This high-level input enables you to connect your speaker wires from your head unit directly to the amp. There are adapters available if your selected amp doesn’t have this feature, so don’t let this point rule out an otherwise acceptable amplifier.

You should also consider your physical location for your install before shopping. Be sure you can secure your amp properly and that the location provides enough air circulation. Don’t forget to measure the installation area to ensure you purchase an amplifier that will fit. Don’t laugh, I’ve had more then a few customers over the years forget this basic requirement until it was too late.

If your amp will power two sets of speakers such as a component set in front and a coaxial or mids in the rear, I would recommend purchasing a four channel amp instead of a stereo amp. This will give you full fader control which will not be available if you split one stereo channel for two sets of speakers, front and rear. Sometimes your local installers will suggest going with multiple amps instead. Could the reason be that they desire to sell another amp and set of installation parts?

Another option to look for is built-in low-pass and high-pass crossovers. Finally, be sure your amp has a gain control. This is necessary to properly match your vehicle sound levels to your speakers when installed in your specific vehicle. This also allows you to purchase an amplifier that might be a bit larger or more powerful then your speakers with a view to expanding your system in the future. Going along with this thought, if purchasing a multi-channel amplifier, you should consider one capable of running at 2 ohms in case you ever decide to add a subwoofer at a later date. Spending a few dollars more up front can save you in the long run.

If you are looking for a subwoofer amplifier, look at the class-d amps on the market. These amps are specifically made to power the monster subwoofers available today. A good rule of thumb is to run an amp at 80% to 90% RMS of what your speakers or subwoofer is capable of. You’ll get great performance and a long life from your amplifier.

On one additional note, if you are a do-it-yourselfer? Most often the problems that customers have had over the years have always been related to a bad ground or insufficient sized ground on their system. Most often the amplifier has simply been installed improperly. This has also happened in installs performed by so-called professionals.

Take this simple step if installing your first amplifier. Cut out a piece of plywood slightly larger then your amp. Cover the plywood with a piece of carpeting. Connect the amplifier to the plywood. Then bolt the plywood to the location within your vehicle without allowing the bolts on the amp to contact ANY steel within the vehicle (you may place a piece of carpeting under the plywood as well). At this point, your new amp is completely isolated from any steel surfaces on your vehicle. Now you connect a ground wire of the same size as your power wire to a good ground on your vehicle’s frame. This simple and inexpensive step has saved many an installation.

Hopefully these few points will enable you to select an amplifier to properly power your new speakers or subwoofer.