Find the Perfect Head Unit

The Most Vital Specs and Features

Some people can't settle for a dinky little head unit.
Everyone has their own opinion on exactly what constitutes the perfect car stereo system. Image courtesy of Les Chatfield, via Flickr (Creative Commons 2.0)

There are four primary factors that can affect the suitability of a head unit for use in any given car sound system. Depending on the specific situation, some of these factors will be more important than others. In no particular order, they are:

  • budget
  • power
  • features
  • aesthetics

Anyone who is working on a budget will want to find a head unit that meets or exceeds his or her needs in the other categories without breaking the bank. However, someone who is trying to build the perfect sound system one piece at a time will have different priorities. Let’s take a more in-depth look at the different qualities that you should look for in a great head unit.

Form Factor

Before the process of selecting a head unit can even begin, it’s important to check out the dash of the vehicle that it will be used in. Most head units fit into two size categories that are referred to as single DIN and double DIN, and most vehicles have either a single or double DIN dash receptacle.

If the existing head unit is about 2 inches (50mm) tall, the replacement needs to conform to the single DIN standard. If the existing unit is 4 inches (100mm) tall, then either a single or a double DIN head unit can be used. However, a spacer is needed in order to install a single-DIN head unit into a double DIN receptacle.

OEM Vs. Aftermarket

Leaving the OEM head unit in place typically isn’t the best idea, but there are some exceptions. If an OEM head unit already has all of the desired features, pairing it with an amplifier and premium speakers can save some money. However, that typically won’t provide the best possible sound. Unless the OEM head unit has preamp outputs, that type of setup will typically result in some sound distortion. If the original equipment head unit does have preamp outputs, or if the vehicle has a factory amp, leaving it in place can work out just fine.

Audio Sources

The right head unit audio sources will depend on personal preference since everyone has a media library made up of differing amounts of cassettes, CDs, MP3s, and other digital music files. Depending on what you have in your own collection, you may want to look for a head unit that can play:

  • Cassette tapes
  • Compact discs
  • DVDs
  • Blu-ray discs

Some double DIN head units can play both cassettes and CDs, and there are also head units that include CD changer controls. Other units are capable of playing digital music files, including MP3, AAC, WMA, and others, that have been burned to CDs, and there are also in-dash CD changers that fit into the double-DIN form factor.

If your entire media library is digitized, then you might want to look for a mechless head unit. The term “mechless” indicates that there are no moving parts inside these head units. Since they are incapable of playing CDs or cassettes, you can play music from USB sticks, SD cards, or internal hard drives.

In addition to those options, head units typically include some type of radio tuner. Aside from the basic AM/FM radio that most head units offer, you might want to look for:


A head unit that has great features and looks slick won’t necessarily be easy to use. Since the head unit is the command center that you’ll use to control your entire sound system on a daily basis, ease of use is vital. This factor is easy to gloss over, but it’s also a leading cause of buyer’s remorse. Even if you’re buying a head unit online, it’s a good idea to look for a display model at a local store to try out the controls.


For audiophiles, power is one of the most important factors that get considered in the process of constructing a car audio system. However, it’s typically the power of the amplifier that gets people excited. Good sound systems bypass the built-in head unit amp with RCA line outputs.

There are two reasons to consider head unit power. If you’re building a car audio system on a budget, and getting the best possible sound isn’t that important to you, then it’s important to find a head unit that has sufficient power output. It’s also possible to build a car audio system piecemeal, in which case you’ll want to find a head unit that has a good built-in amp and RCA line outputs. That will allow you to enjoy good sound right off the bat, and you’ll still be able to drop a good amplifier into the mix later on.

The way to determine the power of a built-in amp is to look at the RMS value. RMS refers to root-mean-square, and this number is actually meaningful in a way that advertising terms like “peak power” and “music power” aren’t. However, head units typically aren’t capable of outputting the full RMS value across all four speaker channels at once. It also takes more power to produce bass than other frequencies, so you can typically expect some distortion unless you use a high pass crossover.

Additional Features

Depending on the audio system that you’re trying to build, there are a number of other features to look for. Some of these are vital to the future expansion of the system, like preamp outputs, and others will be immediately useful.