Basic Mobile Electronics

Basic Mobile Electronics
These articles, listed below, written by Rayfes Mondal, are done on a more basic level than the ones linked above and would be a good starting point for those that are newer to mobile electronics installations.

Head Units Car Systems

Ideally, your head unit would be used to provide a signal to your amplifiers that is line level and you would not use its internal amplifiers (if any). They usually do not have the power and strength to drive speakers both loudly and cleanly. The line level signal is cleaner than the speaker level outputs on the head unit because it is does not go through the internal amplifiers in the head unit. That being said there are occasions where you would use the head unit's internal power. One situation is when you are on a budget and are building your system over time. The head unit can be used to drive speakers (but not subwoofers) until you can get an amp. The other situation is when you are building a system where the benefits of an amp are not important to you. Read my planning page for more details about what is right for you.

No head unit typically has more than about 60watts of total output power because more would require a real DC-DC power supply (which does not fit in a head unit easily). Using the head unit power can be a temporary solution until a separate amplifier can be purchased, just make sure you do not try to power any subwoofers or insensitive component sets with the head unit's built in power. According to Car Audio and Electronics magazine, most head units use the same chips for the internal amplifiers so they all produce about the same low power. The best they have measured is about 14watts into 4 channels at 1% distortion. Their power level at a better lower distortion figure (like 0.1%) is significantly lower.

Note about using factory head units: Many people ask me about using the factory head unit that came with their car with external aftermarket amps. Typically you cannot get a clean signal from the head unit because factory heads do not have line level (RCA) pre-amp outputs to drive an amp. You can use a speaker level to line level converter but the sound is still going through the factory head's internal amps. Some people are willing to sacrifice some sound quality in order to keep their factory head. Also, if your factory system uses an external amp you may be able to find an adapter so you can use an aftermarket amp instead.

Things to look for:

Usability: Your head unit is the part of the car stereo that you interact with most so it is important to get one that "feels" good to you. Always look at a head unit in a store display and use it for awhile. Try to flip through radio stations and tracks on a CD to see if it is quick and easy. If you have problems with small buttons, imagine what it will be like when you are driving! Since many models in the same price range are similar in features and sound quality, usability is often the deciding factor between models.

Power: Even though I just said not to use the built-in power of a head unit I know sometimes it is necessary. Bear in mind that the power specifications given by most manufacturers for head units are not accurate. They often use terms like "music power" or "peak power" which have little real meaning because there is no standard definition of those terms. If the power is quoted in "RMS" terms then it is usually accurate. However, there is still one other place of misconception. Often manufacturers will quote power as "30watts x 4 RMS". The "RMS" seems to mean it is a true indication of power but they are implying that all 4 channels can produce 30watts rms AT THE SAME TIME. With a head unit, this is almost always not true. Because of the small power supplies in head units they can rarely output more than 15-60 watts TOTAL. This means that the power to each channel at maximum loading would only be 1/4 of that total. Some manufacturers are better than others about giving accurate specifications and a few models are available with sophisticated power supplies which have higher power output but they are VERY expensive. If you're paying less than $800 for a head unit (and most of us are!) then your head unit will not put out much power. I have written a more comprehensive explanation of power amplifier specs as well. Speakers which are not producing bass do not draw nearly as much power so you can get away with using the head unit to power them but use passive high pass crossovers (bass blockers) and they will play even louder and cleaner. Bear in mind that the distortion may be higher from the head unit than an external amp however.

Cassette vs. CD: This choice is mostly a matter of preference. If you do not have many cassettes then an in-dash CD player is probably right for you. If you need the capability to listen to cassettes and CDs then a cassette head unit with changer controls should be adequate. Be aware that many in-dash CD head units can control a CD changer as well so you can use both. An in-dash CD is convenient for changing discs quickly while on the road. Because of size of most CD changers they are usually mounted in the trunk or under the seats although there are some newer models which are small enough to fit in glove compartments. Under the seats or in the trunk are not easy places to get to while you're driving!