In order to define your needs, you have to set the results you want to obtain from your system. Just answer the questions a Car Stereo Specialty Store would ask you: What kind of music do you listen to? Do you need great amounts of low frequency bass output? Do you plan to install a subwoofer? Do you listen to music at loud volume? Do you own a convertible or an old car with a loud powerful engine?
If you like listening to music at loud volume and plan to install a subwoofer with lots of bass output, or if you own a car which is very noisy on the road, like open air convertibles are, you will need a powerful amplifier. For a basic installation, a 50 W x 2 or a 50 W x 4 quality amplifier will work wonderfully to amplify a factory speaker system or entry level aftermarket coaxial or component speaker system.
For instance a basic audio system could be made up of two 165 mm (6 ½'') coaxials in the front doors, and two 6” x 9” coaxials installed in the back doors or on the rear deck. In this case one 4-channel amplifier would be a perfect choice; one amplifier channel for each speaker. If your budget doesn't allow you to purchase a 4-channel amplifier, then a 2-channel could be a good alternative to power the front speakers by themselves, using the head unit to power the rear speakers. You could also choose to have both the front and the rear speakers powered by the amplifier, although in this configuration you would lose front to back “fader” control.
In order to make sure you generate the “clean” volume or output levels you desire, always choose speakers that are rated to handle the power of your amplifier. In regards to achievable output levels, it is a big benefit to choose speakers with high efficiency: otherwise you may risk pushing your amplifier to its limit to achieve the desired volume level. This will result in reduced sound quality and even distortion that could eventually lead to damaged speakers and/or amplifiers. It is always wiser to choose an amplifier with slightly higher power rating than your speakers are rated at. In this situation, your amplifier will perform with better sound quality, run cooler and thus be a lot more reliable. The amplifier will then have the headroom and dynamics to bring music to life!
The best solution would be to assign one channel of the amplifier to each speaker. This is not a big concern, as there are proper methods that a qualified installer can use to have a 2-channel amplifier driving a 4-speaker system. For instance, a 50 W x 2 or 50 W x 4 amplifier could be good configured to drive a 2 or 4-speaker systems.
If you plan to install a subwoofer as well, a 5-channel amplifier, with a 5th channel dedicated to the subwoofer, is surely the quickest and easiest solution. Since the subwoofer section of the system generally requires higher power than the high frequency ranges, the fifth channel usually delivers more power (watts) than the front and rear channels. For instance, a 5-channel amplifier could have the following power configuration: 50 W x 4 + 100 W x 1 channel (at 4 Ω).
Most amplifiers today can have two channels “bridged” together. When “bridged”, a pair of amplifier channels is combined to create one single channel with higher power, thus making the installation more flexible. With this set-up, a 50 W x 4 amplifier could be configured as a 3 or 2 channel amplifier with the following power output: 50 W x 2 + 200 W x 1 or 200 W x 2. Because of the higher power, the “bridged” output is ideal to drive the subwoofer.
REMARK: Some amplifiers feature a remote level control which lets you comfortably control the volume of the subwoofer from the driver's position. Since the intensity of the bass output can vary drastically from one musical genre to another, the remote subwoofer volume control feature is very useful.
When stating the amplifier output power of their amplifiers, manufacturers rate their amplifiers in using completely different testing methods, often causing confusion to consumers.
You need clear information when purchasing an amplifier.
Something you should know is that your car battery and alternator provide both the voltage and the current that your amplifier requires to make its power. Voltage can vary from one vehicle to another. Voltage can also vary in relationship to the engine revolutions (RPM).
Usually, a higher voltage output from the vehicle equals to a higher power output from the amplifier (except for those amplifiers which use strongly regulated power supplies which then have drawbacks from other point of views). The supply tension used to state power output of an amplifier is very important since most of the manufacturers measure power at 14.4 V, 13.8 V or 12.5 V.
A 50 W x 2 amplifier supplied with 14.4 V (those with non-regulated or loosely regulated power supplies) could show a decrease in output power up to a 15% when supplied with 12.5V. While, in the opposite case, a 50 W x 2 amplifier tested at 12.5 V could show an increase in power up to a 15% when supplied with 14.4 V! This means a 15 W difference between two amplifiers both with rated power output of 50 W x 2.
It is important to know that we are comparing two or more amplifiers with power rates tested using the same method, since in the car audio industry there isn't any authority which checks and certifies the product specifications. Some manufacturers state power in “RMS” Watts, while other use the “Continuous Average” power method, two measurement methods which yield almost the same power output rating. A 50 W RMS x 2 on 4 Ω amplifier (we will discuss ohms later on) can actually deliver 50 W x 2 with an output of the amplifier “clipped”. “Clipping” occurs when the sound coming from the amplifier is distorted. Clipping particularly occurs when the sinusoidal wave (music) presented at the amplifier input from the head unit, is output from the amplifier as a square wave (distortion). Some manufacturers state power using the “Maximum” or “Peak” ratings. This is a marketing “ploy” that generates numbers that are double that of an amplifier rated using the RMS method. Generally speaking “Maximum” or “Peak” ratings are not the right measures to use to compare amplifiers power output. A 50 W x 2 “Maximum” power at 4 Ω is equivalent to a 25 W RMS x 2 at 4 Ω.
Now let us get back to the “ohm” matter. Amplifier power output is usually stated at 4 Ω. “Ohms” express the speaker voice coil nominal impedance or “load” presented to the amplifier. Each speaker has nominal impedance according to the voice coil design. Most car audio speakers have a 4 Ω nominal impedance. This is why speaker manufacturer's usually state the nominal power at 4 Ω.
There are some speakers with 2 Ω nominal impedance, some with 1 Ω, some with even a 0.5 Ω nominal impedance, but if the amplifier is stated as “stable” on such impedances, you can wire the speakers all together to produce, most of the times, more power than with 4 Ω speakers connected to amplifiers stable only at 4 Ω. Besides, you can find power data and power measurement specifications expressed in many different ways, which can sometimes be deceitful. So protect your investment: make sure you compare the stated power of two or more amplifiers using the same unit of measurement.
Some people like hiding their amplifier for a “stealth” type installation. Other like “highlighting” it off, like a fine piece of art! The physical constraints of your vehicle can affect your choice in amplifiers.
If you leave your car parked on the street for long you may prefer a compact sized amplifier, hidden under the seat or in the trunk. If you want to show your amplifiers to your friends or “highlight” them, you will surely find amplifiers with perfect cosmetics in the market. In some cases, if you don’t have much room, two or three small amplifiers can be more convenient than one big amp.
You can find amplifiers in many different sizes, styles and colors. If you like it simple and essential or if you’re a creative, extroverted type of person instead, in any case it won’t be difficult for you to find the amplifier which best suits your personality.
Many amplifiers feature built-in crossover filters, bass equalizers among other functions designed to help your installer tune your system to your vehicle acoustics. For instance, if you have 10 cm (4”) speakers installed in your system, which can only reproduce mid and high frequencies, a properly set crossover filter can eliminate the need for them to reproduce low frequencies and will send those speakers only the mid and the high frequencies, vastly improving the proper working of the system while preventing it from damages and from sound distortion. For the subwoofers, crossover filters and bass equalizers are useful tools to balance the low frequency to the rest of the system. Bass equalizers are useful, but remember.... don’t overdo it!
A few years ago, a 1000 W amplifier was the size as a small surf board! With the advent of D-Class (Digital) technology you can achieve that same power from an amplifier which is around 30 cm (12”) long. In most of the cases, the D-Class amplifiers are designed to amplify the subwoofers as their building technology doesn’t allow their use for mid and high frequencies.
D-Class amplifiers are usually 25% - 30% more efficient than the AB-Class amps. Also, D-Class designs produce much less heat, which is why their size can be much smaller. Besides, they are perfect to power the subwoofer sections of a system. On the other hand, we have the traditional AB-Class (Analog) technology. This amplifier class is well known for its sound quality and represents approximately 80% of all car audio amplifiers available. You can find them in different sizes and power a 25 W - over 2000 W power range. The AB-Class amplifiers are one of the best choices to amplify the speakers reproducing mid-low frequencies as well as mid and high frequencies.
Besides, some current multi-channel amplifiers combine D-Class technology together with an AB-Class section merged into the same heat sink. Basically, the subwoofer channel utilizes the high efficiency, high power benefits of D Class, while the mid-low, mid and high frequency channels are in AB Class. This combination reduces the size of the amplifier and provides each frequency range with the technology which most suits it.
In today's market you can find an average quality, average power 2-channel amplifier for 150-200 Euro, while you can find a 4-channel design for 250-300 Euro. If your needs dictate a 5-channel model, instead, you can expect to spend between 400-450 Euro. Do not let yourself get attracted to amplifiers from “no-name” brands or from an unknown brand at that “hard to believe” price. Amplifiers with that “great deal” stigma often prove to have poor reliability, poor performances and, most of all, poor sound quality.
In order to have your system installed properly, contact a Car Stereo Specialty Store or an Authorized Dealer; an inexperienced person could wire your system improperly, causing costly damage to your vehicle and/or to the audio devices. The car environment is completely different from the home environment, where in order to complete a hi-fi system installation you only need to place the components and wire sound sources (CD player, DVD player, Tuner, etc.), amplifier and the speakers. High quality audio components are fundamental to truthfully reproduce your music. However, even the best components can provide poor results if they are not properly installed and tuned.
- Do not focus only on the cosmetic details. Sometimes cosmetic enhancements are added to the amplifier to attract attention and hide the potential poor quality and reliability; fancy colors, translucent panels, chromed parts and flashing LED’s do not improve sound. Find a balance between performance and cosmetics. Don’t let these things, which are of no use and can be a distraction, attract you.
- Ask the store if you can look at the product owner’s and installation manual. A reliable brand wants the ability for anyone to understand how the product works, and will provide a useful, clear and complete manual. When reading the manual, if you can’t understand how the controls work, you’d better look at a different product!
- Observe the professionalism of the management and staff of the store you are visiting. Also, ask if you can listen to the audio system they have installed in a demonstration vehicles or their personal vehicle. This will give you an idea on their personal choice of product and on the results you can achieve for your system.
These final suggestions will help you make a sure, correct choice of the products according to their overall performances. The product engineering and the electronic components used in the amplifiers are directly responsible for the reliability and performance of the product. Multi-layered, thick printed circuit boards; symmetrical and optimized layout of the internal components; oversized traces to handle the high currents requirements of the amplifier; these are only some key aspects of a reliable, top quality product.
Unfortunately these aspects are hard to detect and recognize in a product. Big-box, mass- merchant retailers are not qualified to offer their customers this kind of information.
Read product reviews in the specialty magazines. When a magazine reviews a product, it examines it thoroughly, especially from an engineering standpoint. Read the whole review. If you can’t find on the exact amplifier you are interested in, look for a report on an amplifier within the same range. The way it was built will certainly be the same.
With a little bit of attention and some educational researches, you are sure to purchase the amplifier you paid for.