Car Computer Audio HOW-TO

By: Dmitry Borisov and Damien Stolarz

Introduction

This HOW-TO is a simple set of instructions for mounting your Car PC into your car with the sound quality you've come to expect. Audio integration is usually the first step in getting PC to work in a car, and it is one of the most important steps.

Many people are discouraged about their car pc installation because they can hear a big difference between computer and audio system they use right now. Despite the versatility of a car PC, if the sound quality is not good enough, it can't compete with an aftermarket stereo system.

This how-to focuses on basic to intermediate installations, but will also be informative to those installing premium auto sound systems and components.

Choices

In this article, we're going to assume you've already figured out what computer you're going to install in your car. The next step is to determine if you retain your existing head unit, replace it with the aftermarket one or even replace it with an LCD screen. Once you know what's right for you, you can jump to the appropriate section in this article. The final section on Sound Quality Issues applies to all installations.

Car stereo Installed (OEM or aftermarket)

The least dramatic way to install a car PC is to leave the car stereo intact and just use its well designed controls, display, FM tuner and amplifier. Depending on the solution you choose, you will get different levels of sound quality and control over your car PC. There are 4 options available right now, each with their own pros and cons.

AUX input ready car stereo

You can purchase an aftermarket stereo from almost any major brand which has AUX input option, either built in or available through a simple adapter. This provides is the easiest way to feed the audio from PC to the car speakers, just as you would connect a DVD player or video game system to a television. All you have to do is to plug the head phone output from PC into that input. Very simple!

Pros:

1. Simple and very cost effective

2. In most cases, no installation is required

3. No additional sound processing, feeds directly to amplifier

Cons:

1. No matching of audio levels, some PCs may sound very quiet even if using headphone output

2. Have to use external device to control the PC such as IR/RF remote, wireless keyboard

3. Some head units have AUX in as an option and require an adapter to be connected inconveniently to the back of the stereo

4. For stereos with wires on the front, unsightly wires run from front of the stereo to your car PC

Keywords for search engine: AUX input receiver

FM / Cassette adapter

Your head unit is almost certain to have an FM receiver and may have a cassette deck as well. In this connection category, you have 3 options:

Cassette adapter

This device takes an audio signal from computer and retransmits it into the cassette-like device which is inserted into the cassette slot of the car stereo.

If your car stereo has cassette it may be simplest and cheapest option.

Pros:

1. Simple and affordable solution

2. No need to pull out the car stereo or disassemble dashboard

3. Works for all cars having cassette player

Cons:

1. Sound goes through the magnetic heads, reducing quality. In some cases head alignment is needed to achieve decent quality

2. No matching of audio levels, may lead to weak audio output

3. Have to use external device to control your PC Such as IR/RF remote, wireless keyboard

Keywords for search engine: car cassette adapter

Wireless FM transmitter

FM transmitters are small devices that turn your car PC or other audio source into a mini-radio station broadcast. The audio signal is retransmitted to a selected FM frequency. If you tune your FM tuner to the same channel as the transmitter you will hear the audio.

This is the most universal solution, since there are almost no car stereos on the market without an FM tuner!

Pros:

1. No tangled wires are involved

2. No need to pull out the car stereo

Cons:

1. Sound quality is reduced, as FM is not as high quality as a direct connection,

2. May need to re-tune the adapter several times during the commute to find an empty spot in FM range, especially if when traveling over hills

3. Have to use external device to control the PC such as IR/RF remote, wireless keyboard.

Keywords for search engine: wireless car fm adapter

Wired FM transmitter

This device works exactly as Wireless FM Transmitter, the only difference is the method it feeds the FM signal to a car stereo. This allows it to deliver the FM modulation directly to the radio, like cable TV vs. antenna. This means that the quality of the signal will be much higher due to no interference with the outer world.

It is also a very universal solution due to the fact that it uses FM part of the car stereo.

Pros:

1. Much better sound quality than wireless transmitter

2. Fairly straightforward to install and use

Cons:

1. Sound quality is reduced, as FM is not as high quality as a direct connection

2. May need to re-tune the adapter several times during the commute to find an empty spot in FM range, especially if when traveling over hills

3. Have to use external device to control the PC such as IR/RF remote, wireless keyboard

4. May need to disassemble dashboard for installation

Keywords for search engine: wired fm adapter

AUX adapter

An auxiliary inputadapter is a small electronic device which makes a cd-changer capable car stereo into "think" that it has CD changer attached. The biggest challenge with these adapters is that every car manufacturer has it own set of protocols, CD changers and formats, so manufactures are constantly playing catch-up with new car makes and models, and thus you may not be able to use this solution for your specific car.

Pros:

1. Much better sound than any other options such as FM or cassette adapter

2. Best quality for digital sound inputs

Cons:

1. Not all car makes can have such adapter

2. Have to use external device to control the PC, such as.IR/RF remote, wireless keyboard, etc.

3. Removal and of the car stereo may be needed

4. Turning the PC on can produce a noticeable "thump" in speakers

5. Usually requires disassembly of dashboard to access rear of head unit

Keywords for search engine: <your car make> aux adapter or auxiliary adapter

Car2PC adapter

This device works exactly as AUX adapter providing a direct audio interface to a car stereo via the CD changer port. In addition, a Car2PC provides control commands to PC via a USB connection. So whenever you press button on the car stereo you can translate that press into a particular command on PC. The most common mappings are: 1-6 translates into changing the playlists, <,<<,>>,> into track navigation and so on. The track information can also be sent back to a car stereo display.

This solution also provides audio level matching. So the audio signal from PC will be at the same volume as FM or cassette.

Just as with the AUX input adapters, the biggest problem with the Car2PC adapter is that every car manufacturer has it own set of protocols, CD changers and formats, so you may not be able to use this solution for your car make and year.

Pros:

1. Much better sound than any other options such as FM or cassette adapter

2. Best quality for digital sound inputs

3. Direct control of the PC from car stereo

4. Shows track information and track time

5. May display additional information such as track title, artist etc

6. Anti "thump" protection

Cons:

1. Not all car makes can have such adapter

2. May requireunmounting the car stereo to access rear of head unit

Keywords for search engine: car2pc adapter

No stereo

Some people who use PC in a car prefer to use touch screen displays in order to control the PC and get even more information from it such as video, navigation, weather, Internet etc. In many cases in order to install the monitor, the dashboard needs to be changed. Often, car PC enthusiasts will have a custom mount for a touchscreen fabricated so that the installation looks seamless, like it came from the factory. This usually requires the relocation or complete removal of the existing head unit and stereo control knobs to make room for the touch screen.

When the head unit has been removed, the only way to produce sound for the speakers is to use a 3^rd party audio amplifier, usually installed in the trunk. While this is the most costly car PC integration solution, it also provides the most options such as an attractive graphical display, and the ability to use visual information like GPS navigation or the Internet.

Amplifier

The amplifier is the most important part in the stereo-replacement option. There are many choices for amplifiers on the market, but here are the things to look for if you are integrating it with a car PC:

Audio input level

Depending on the amplifier model the pre-amp input level (i.e. the voltage expected from the audio source) could vary from .2V-8V. The nominal input is somewhat that needs to be taken into account, so you better check the nominal sound output level of your PC first before deciding to buy the amplifier As a general guideline: notebooks and built-in soundcards produce from 0.5-0.8V nominal output on the headphone line, built-in sound cards produce around 1V. Most amplifiers on a market use 3V nominal input, so you should check if your amplifier can accept 1V nominal audio input. Usually it is mentioned in the manual as pre-amp input line. Trying it out first would be the best, which is true for any audio equipment.

Speakers / Channels

Most modern car have at least 6 speakers of which 2 are tweeters (high frequency). Usually, these are all driven by a 4-channel amplifier built into the head unit (Front left, front right, rear left, rear right.)Even though your input is only stereo (two channel), you'll need at least 4 channel amp for quality sound, and the ability to fade (change volume between front and rear).

Wires

Many preinstalled car speakers are 8 Ohms and specifically designed for a low output head units (30-60 Watts). To use the most out of the high powered amplifiers you should consider getting lower resistance speakers such as 4 Ohms or even 2 Ohms. Otherwise, you might easily blow your speakers (tearing them) from high powered amplifier. For that you may need to change the wiring to reflect higher current going through. 16 gauge(thicker), in some cases even 8 gauge (even thicker) is recommended.

"Anti thump"

All amplifiers have remote-on ability to prevent "thump" during the car power on. This remote on wire makes sure that the amplifier is the last thing to turn on, so it doesn't amplify the noise made by car PCs as they are first turning on. Make sure you enable that remote-on signal to prevent the hearing loss! Most of the Car PC power supplies provide the line to connect to the remote-on input of the amplifier.

Volume

Another issue with the no-stereo solution is the lack of tactile volume control. This can be a real problem in cases when your monitor is off or inactive of some reason, and you need to rapidly mute or lower the volume. There are 3 ways to control the volume in a safe fashion:

Analog

Simply putting a variable resistor between your PC and amplifier can do a trick. Make sure you select a low noise resistor and mount it properly. To have this solution you may need 2 parts: potentiometer (resistor) and volume knob. Resistor can be something like 10KOhm and can be purchased at any electronic store. Online or offline. Volume knobs are more hard to find. It should match your interior and be ergonomic. Many electronic stores also have standard volume knobs, just choose which is better for you.

Keywords for search engine: potentiometer 10K

Keywords for search engine: Volume control knob

Digital

Another way of controlling the volume is to connect some sort of encoder to a PC so it reads the position of the volume "knob" and changes the volume accordingly. It is most preferable way of doing volume control since it does not introduce any noise or signal quality problems. For that you may use many solutions on a market from USB to simple PS/2 devices.

Keywords for search engine: PC Volume knob

Amplifier's gain control

Most car amplifiers on a market have gain control knob which is usually used to match the incoming signal to a right level of volume at the speakers. It will work very similar to volume knob even though not exactly and you may not be able to have fully muted audio this way. The simplest way to use it is to set PC output level for master and PCM volume to 75% (do not use 100% as it may produce distortion). Then use gain control to get the sound volume you need. Make sure you have read topic about matching input levels of audio signal for the best sound possible. In order to use gain control instcanad of volume you may need a knob connected by a long wire that you can extend to the front of the vehicle and mount cleanly in the dash.

Sound quality issues

Audio signal level

The most common problem when using AUX inputs or FM/Cassette adapters is to match the input level for audio signal. As a general guideline: notebooks and built-in soundcards produce from 0.5-1V nominal output on headphones. Most of the AUX and FM/cassettes adapters and amplifiers require about 1-1.5V, so you better check if your audio signal will match the device you're feeding it to. It can be done by reading the technical spec or using the voltmeter.

In case if level is too low, you'll hear a very high level of background noise from the audio system since the amplification will be at maximum.

When the input signal level is too high you may experience another problem. You'll hear a lot of sounds from the PC itself. Such as hard drive spinning, power supply noises or even distorted sound due to overwhelmed audio inputs.

Car noise

Car inducted noises is the most common issue for all PC based installations. In many cases it is caused by the fact that power supply unit used in PC is pulse regulated which does not physically isolates PC power lines from the car power lines and many car noises can go through the PC on your car speakers even when PC is off. Like the regular audio signal they will be amplified and may get very loud. There is no simple way to get rid of engine "whine" completely but you can reduce it to a level you won't hear. Very simple steps are mentioned below will help to reduce the noise: proper grounding and ground loop isolator.

Proper grounding

Usually grounding the chassis of the PC is required in order to provide the equal ground level for all electronic equipment preventing the chaotic current flow within your system. In many cases grounding the chassis of your PC can help to get rid of most noises !

Ground loop isolator

Ground loop isolator prevents the DC current from flowing freely in the different parts of the system and making a loop which causes a constant noise.

Computer noise

Along with the noises coming from the car and outside world, there are many other sources of noise inside the computer itself. Just to name a few: Hard Disk, Optical drive, Fans and many others. In general: the less devices you use, the less noise you'll get. Below - simple summary how to get rid of very common noises.

Hard / Optical drive

Hard drives can be hard to avoid, since all latest are very "fat" and require a lot of storage space. If you use the hard drive, keep in mind that the smaller drive the less noise it produces. It is related to the power consumption of it's electronics and motor. So whenever possible use 2.5" or even 1.8" hard drives.

Optical drives shares the same idea, the smaller, slimmer the drive, the less power it consumes and less noise it adds to the system. Be sure to use modern slim DVD-ROM instead of bulky and power "hungry" 3.5" "standard" drive.

Fan

As in case with the hard drives: the smaller fan and slower it spins, the lower noise added. Of course if your system is Pentium 4 - 3.4Ghz, you will be forced to use those high speed and high power fans, but if you use any modern processors which produces very small heat, it is possible to run the systems without any fan at all. And this is the best solution of course.

In case if you can't avoid fan, try to reduce it's speed so it spins slower but still cools your system. Some motherboards can regulate the fan speed programmatically which is a very good way to reduce fan noise.

Power supply

Power supply can also be a source of noise even if it does not contain fans. As mentioned before the power supply transforms power in very small chunks at a time, in so called "impulses". So whenever the impulse is generated it produces EMI spread around. The more powerful PSU, the stronger that impulse gets and stronger EMI, affecting your computer parts. So the rule still applies, the lower power consumption, the lower PSU wattage should be, the lower noise it generates. In case if your power supply is high powered (100+ Watts) it should be shielded and properly mounted to not to introduce any EMI to the motherboard itself.

Conclusion

Let's summarize the pros and cons for every option discussed above.

OEM car stereo

Pros:

1. You car's factory look and feel is maintained

2. You keep familiar controls and well designed features

3. Wheel buttons, central gauge display, phone and other equipment will function properly

4. There is no need to remove your car PC installation before selling the car

5. There is no need to rewire your speakers as they aligned with the stereo already

6. Can install in-dash VGA display for GPS or video

Cons:

1. OEM sound system may not sound as good as aftermarket ones

2. OEM system may lack output power

3. OEM system may lack support for text or other information that PC can handle

4. Most OEM systems lacks AUX input

Aftermarket car stereo

Pros:

1. Well designed and functional car stereo

2. May have AUX input

3. May sound better than OEM car stereo

4. Many aftermarket units have support for text and other media data to display

5. Can install in-dash VGA display for GPS or video

Cons:

1. The interior may suffer in terms of design. Very true for all modern cars, which do not have standard inputs for aftermarket stereos

2. May need to change OEM installed speakers

3. Most of functions in a car such as wheel control, central gauge display or phone may stop working (although there are adapters on a market to address that)

4. In all modern cars the installation is not simple. Have to buy additional bezels or faceplates

5. Harder to sell even if the sound system is good

No stereo ( LCD molded or in-dash LCD )

Pros:

1. Hi-tech looking display may bring a new look into the car's interior if done right with professional fiberglass fabrication

2. Graphical information such as GPS, Internet and video can be displayed

3. Audio may sound very good with the right set of amplifier, speakers and wires

Cons:

1. No way to use controls blindly. Additional devices needed to address volume, car PC navigation issue.

2. Current car PC VGA monitors lack anti-glare coating. Will be hard to operate in direct sunlight. Also difficult in darkness due to lack of automatic brightness control

3. Have to use external amplifier

4. May need to change OEM installed speakers

5. May need to rewire audio cables

6. Most of functions such as wheel control, central gauge display or phone may stop working (there are adapters on a market to address that)

7. The installation is not simple in all modern cars. Have to buy or build additional bezels or faceplates

8. Harder to sell even if the sound system is good

9. No decent FM tuner available for PC