Theory
My car

Designing a setup

The best or most expensive components do not necessarily make the best audio system. It is always a combination of the right components and the correct way of installing them. Take the most expensive and powerful amplifier and give it insufficient current, the result will be most disappointing. Quality of components is 25%, correct installation makes up for the remaining 75% of the total result. As to subwoofers, AudioDIY has an excellent site on how to build subwoofers and enclosures. For brands, makes and models go to the equipment page.

More is not always better. More speakers make your car sound like a chicken farm, numerous speakers make a lot of noise but not one coherent sound. More speakers only make your system play louder because they can move more air. More components mean a longer way for signal to travel and more risk of distortion. Things like equalizers, DSPs or bass enhancers are patches for a bad setup. However, many people will disagree with me on this saying a car is a terrible environment for sound making a DSP essential.

Ideal setup The ideal system is based on a head unit with one or two amplifiers, one superb set of front speakers and a little subwoofer. The head unit should have at least one pre-out (=outlet to amplifier). Choose front speakers very carefully as they are the "face" of your system, the part responsible for 80% of the final result. Compare to this: what would a perfect VCR with the best movie on the best tape do on an old black and white television?
Rear fill Rear fill is something you don't want. If you really want speakers for people on the back seat, turn the off when you're alone in the car. The sound should be focused from one point and will be severely affected by rear fill if done the wrong way. In the few cases rear fill helps making a better sound the rear fill should not have tweeters and is preferably mono.
Cross overs Each speaker should only be playing those sounds it is made for. A tweeter should only get highs, the mid speaker should only receive mid and your bass speaker should only get low notes. Filters, also called "cross overs" are used to give each speaker the correct frequencies. The purposes of filtering are:
  • Improve sound. A subwoofer can handle high frequencies but it won't play them properly. If it does play them it will disturb the sound quality of the real tweeters. Therefore a sub shouldn't get highs and a tweeter shouldn't get lows.
  • Make sure the system can't destroy itself. For example: a tweeter isn't made to play bass. If it receives bass it may break down eventually.
  • Make best use of amplifier power. Low notes require a lot of power. If your amplifier drives a mid range speaker it is a waste of energy, and therefore power, by sending bass to a speaker that won't play it and may not be able to handle it.

Simple example:

Filtering example

The full signal is divided into lows and highs, generally 50 or 60 Hz is a good frequency to filter at. The example above gives you a safe system (no speaker will get sound it cannot handle) and a more efficient system (each amplifier uses its power for sound that will actually be played).

Basically filtering can be done in four ways:

  1. Head unit has built in filter. In this case the head unit sends the correct frequencies to the connected amplifers. No installation, no risk of problems. Just a few head units can do this.
  2. Separate cross over. A separate box with one input and two or three outputs, each giving a different frequency range for different amplifiers. Requires extra purchase, extra installation, extra current and therefore may give some problems if not installed properly.
  3. Amplifier has built in filter. Just like the head unit. No installation, no risk of problems.
  4. Harrison F-mods are plugs that go between your head unit and each amplifier. The plug only passes frequencies above or below (depending on the model) a certain frequency. An F-mod can only filter one frequency, if you decide to change you have to buy different F-mods. No serious installation, no risk of problems.
When you buy "separates" (one pair of speakers that consists of separate full range drives and tweeters) the filter that sorts out which signal goes to the tweeters and which goes to the full range is sold with the speakers. External filtering may still be required. If the speakers are to be used in combination with a subwoofer the subwoofer frequencies should not reach the full range speakers (as explained above). The example below shows an example of my very successful setup using an amplifier cross-over (the subbass amplifier) and Harrison F-mods to prevent subbass frequencies to reach the full range amplifier.
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Practice

System setup

Fuse and battery Top view Head unit
Harrison F-mod Cross over
Front speakers subwoofer
Stereo amplifier mono sub amplifier

Click on any photograph to download a larger version

Part 1: The power plant Remember: a chain is as strong as the weakest link. A battery and cables may not be spectaculair, without it the system won't perform. When setting up a system be sure to reserve sufficient fundings for proper cabling. Poor food means poor resuls, just like a sportsman needs good food to compete. The main fuse is visible in the upper right hand side of the engine room. The IASCA rules force to install the main fuse within 30 cm from the battery.
Part 2: Head unit The head unit is at the start of the audio chain. I choose a Becker Mexico PRO headunit because of the quality of the pre-amplifier and tuner. Also it had a simple two colour display, not a toybox like those modern Clarion and Panasonic units. This particular unit also has an AUX-in for connecting my mobile VCR
Part 3: Filters From the head unit to the amplifiers. Like explained above there's many ways to filter. I prefer Harrison F-mods. One of the head unit's signal cables has Harrison F-mods in it. This will cut of all sounds below 50 Hz. The amplifier won't waste energy amplifying these notes, the front speakers cannot be damage by such low notes and the amplifier doesn't get as hot as it would when amplifying low notes.
Part 4: Amplifiers The Audison LR-1140XR SUB MONO amplifier is my personal reference for subwoofer amplifiers. Based on listening (and not measuring) I rate it a perfect 10. The power is unbelievable, the sound a blessing to the ear, the size almost adorable and the price stiff but fair.
Full range is handled by an AudioSystem 11002 amplifier two channel stereo amplifier which has an excellent value for money. Although not my first choice, I've been using it for years now. Not a bad amplifier and recommendable if you're looking for high quality for little money.
Part 5: Full range speakers The MB Quart speakers come with separate cross overs (second picture on the right) that allow the owner to set the tweeters at 0 dB, -3 dB or -6 dB. I mounted the cross overs on both sides of the glove compartment to have them near the speakers. At the moment the tweeters play at -6 dB. Front speakers are the most important speakers (and preferably only speakers) of the audio system. Take extra special care on choosing and installing these. Front speakers are responsible for 75% of the characteristic of your audio system, every other component is just a help to the front speakers.
Part 6: Subwoofer A subwoofer can be used to finish the system. It will add some extra impact and make the sound complete. Don't make the mistake of buying very large subwoofers. In my case this single 8" does 130 dB and literally blows the car apart. Many people with bigger or even multiple subwoofers get a less impressive result because of improper setup and installation. One subwoofer is enough for hifi and normal every day use.
In my case the subwoofer changes a lot. I've had MTX, Rockford, Focal, Power Dynamics and many more. In this picture it's a Pioneer. The sound is very disco'ish, fluffy and not very dry. Not my style.


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