Planning Your System

This part of the game can be fun or disappointing depending on what you can do. First I'm going to give you an example system that I believe includes everything you need to have a pretty good system. After that I will show you how to make compromises and leave out parts that may not be as important to you to keep your system within your budget. If you want to go beyond my basic system you probably already know more than what this site can tell you. Also, you do not have to get everything at once. I put my system together over a few years. With a little planning you can upgrade your system in steps and that way its like getting a new system every time you change something instead of getting everything at once!

Basic System: This is my opinion only but I think that a good system should start off with a good head unit that either has a CD player and/or is connected to a CD changer. A good system sounds best when playing CDs, tapes just do not cut it. Next I think component sets are made with fewer compromises than coaxial speakers so I suggest getting a good midrange/tweeter set for the front. Head units generally do not put out enough clean power so you will want an amp to drive the component set. In the rear where you only need some "fill" for ambiance you can get away with cheaper coaxials and set their level lower than the fronts to keep the sound stage in front. A modest (50x4) 4 channel amp is a good choice here for powering the component set up front and the rear speakers. You could use a good 2 channel amp and run the front and back in parallel on the amp but it would harder to adjust the level between them. Midranges sound best when they do not play bass so you will want a 2 way electronic crossover and use the high pass output to drive your 4 channel amp. I did not forget the bass! Most people are happy with a single 10" woofer or a pair of 12"s. Use an appropriate enclosure and a big amp (at least 75x2, preferably even more). Throw in installation and wiring accessories (like fuses and distribution blocks). Here's an approximate price break down of what this costs in my area. Your prices may be significantly different.

      head unit: $300-$500

      4 channel amp for highs: $250-$400

      2 channel amp for lows: $300-$700

      sub(s) (1-10" to 2-12"): $150-$450

      enclosure for sub(s): $0 (free air) - $250 (custom)

      component set: $200-$500

      coaxials for rear fill: $100-$400

      crossover/equalizer: $100-$500

      wiring and accessories: $50-$250

      installation: $0 (do it yourself) - $100 (basic)

This comes out to $1450-$3950! I realize that this is a lot of money and that most people do not spend nearly this much money on their car stereo. However, the things listed above are what I feel is necessary to have a system with only a few compromises. If you are less concerned about highs, get coaxials in front instead of the component set and power them off of the head unit and use some bass blockers on them. This will save you about $400. Getting a bargain head unit can save you some money as well. If you are really not into bass much you can forgo all the bass related equipment and run your component set full range. This will still give you clean sound but not much bass. However, you will save $550-$2300. I would start with what I have listed above and take out parts you do not care about as much. Only you know what kind of system you can be happy with.

Please do not email me asking for recommendations about specific brands. There is a lot of equipment out there that I have not used so I will not comment on them. I am happy with the components that I have but that is as far as I can go with recommendations. When buying equipment try to spend time listening to it before you buy, especially with speakers. Also try to use equipment that is similar to yours when listening in a store. As for amps, it costs money to build a good amp so if you see some awesome price on an amp you have never heard of, it is probably a piece of junk. Stick with good names with amps.

Finally, if you are on a budget (aren't we all?) it works better to upgrade in steps.  The most important thing is to have a car audio system that sounds good to you not someone else.  If you are happy with just changing the factory speakers and stopping there then just do that.  There is a level when that new amp or speaker is not going to make a difference so it is not necessary to always upgrade.  There are people who think my system is terrible but it works well enough for me and anything else I do to it would be a minor gain and not worth my trouble.  Do not let a salesperson talk you into something you do not need!  Good luck!

Typical Systems
Depending on your budget and personal tastes, there are many different system configurations to suit your needs.  Here's some examples:

System 1: Basic

A lot of times less is better.  Less components means lower system cost and the ability to spend a few extra bucks on the components that really count.

When it comes to sound quality, less speakers is definitely better.   The more speakers you have, the more harmful interactions and cancellation of sound waves will occur.
Start with a good set of components (two tweeters and mids) that can go down to 60 Hz with no problem in a properly designed enclosure (i.e. custom kick panel pods).  Rear speakers are not essential in most cases.

Get a good head unit with a clean signal. If most of your music is in CD format, it is better to spend your money in a good single CD player than a cheaper set of tape player/CD changer combo.

Unhappy with the front speakers sound level?  Not to worry, get a good quality amplifier.  100 watts per channel should be plenty.  Don't be too concerned about the power rating on your speakers, unless you drive speakers with ridiculously high power levels.  As long as you have good speakers and protected by a crossover with a steep slope (i.e. 24 dB/Octave) on the lower end, you should be fine.

The system should sound pretty darn good by now. If not, fix any system design/installation flaws.

Now for the last part: Bass.  You need two things: subwoofer(s) and an amplifier.  For audiophile quality sound two 10" subs will satisfy most people.  The trick is a properly designed enclosure and lots of power.  200 watts or more per sub should add plenty of punch for the bottom end of your system.

Subwoofers need more power than speakers because they are bigger and have to move more air.  If you have limited finances, go with a mid-end (i.e. Sony, Pioneer, Kenwood) amplifier for the front speakers and a better high-current amplifier for the subs.

If everything is installed properly and tweaked carefully, you will be very happy with the results.
 

System 2: Competition Level

Competition level systems require deeper pockets and more components.  System presentation also becomes a big issue.

The guidelines of the previous system apply, but you need more gear.

Head units and amplifiers need to have impeccable sound quality and no noise (background noise or alternator noise) whatsoever.  Most people prefer to take advantage of head units capable of high line level voltages (3 to 8 volts) for minimum background noise.

Equalizers become a necessity to fine tune system's response.   Most competitors prefer to use a mono 30 or 31 band equalizer per channel.   Many people have multiple sets of equalizers to quickly change the system's response from sound quality to high SPL or RTA judging.

If the audio system is to be played when the car is not running for extended periods of time, extra batteries should be added to the car.  You might need to add a high power alternator if the car's electrical system can't handle the extra loads.

All the components should be very neatly installed.  Every detail of the installation must be meticulously executed.  Wiring and connectors should be neat and clean.  The car should also be treated against rattles and road noise.
 

System 3: SPL

SPL systems are very different.  The idea here is to be as loud as possible, especially in the lower frequencies.  For a system to be loud, it needs three things:  Lots of power, a lot of speakers and a closed place where all that sound can be concentrated.  This costs, as you can imagine, plenty of money.

The first upgrade here is the vehicle's electrical system.   Alternators, capacitors and batteries become essential.

Most people into SPL competition don't consider staging and imaging as important.  Multiple speakers are placed up front, wired in series/parallel combinations to maximize amplifier power output.

A very important aspect of an SPL vehicle are the subwoofers.   Subs need to have a big cone area and high excursion (Xmax) to be able to move as much air as possible.  The amplifiers moving the subs must be able to handle high current demands and to have low impedance capability.

SPL vehicles should also be treated to be as stiff as possible to minimize loses.  Flexing body parts take a toll on output.  Serious SPL competitors replace glass with thick Plexiglas, and reinforce the whole inside of the vehicle with steel, concrete, etc.  To minimize air leaks many competitors use bolts to hold doors in place, keeping door seals tightly closed.

How Do Speakers Work?

Moving Speaker Speakers are air pistons that move back (on the negative cycle of the signal) and forth (on the positive cycle), creating different degrees of air pressure at different frequencies. The amplifier (either separate or built-in your radio), produces electrical impulses that alternate from positive and negative voltages (AC).  This current reaches the voice coil inside the speaker, creating an electro-magnet that will either be repelled, or attracted by the fixed magnet at the bottom of the speaker.  The voice coil is attached to the cone, moving it back and forth, creating sound.  The surround (rubbery circle that joins top of the cone and metal basket) and the spider (usually yellow corrugated circle joining bottom of cone to magnet) make the cone return to its original position.

Speaker Sensitivity, measured in dB, is how loud a speaker plays (usually 1 Watt, 1 meter).  A higher Sensitivity rating means that the speaker will play louder using the same power as a speaker with a lower rating.

The back and front parts of the speaker should be isolated from each other.  When the front of the cone is pushing air, the bottom is pulling air, creating a canceling effect.  Ideally every speaker should be in an enclosure.   If you are mounting a speaker in a big hole, make sure you build a panel to isolate the front and back of the speaker (baffle).
 

Imaging, Staging and Directivity

Imaging - is being able to pick certain sounds from different places.  The singer would normally be located towards the middle of the car, guitars, trumpets, and other instruments towards the sides of the car.  If you scatter speakers all around the car your imaging would be very poor, since you would be producing the same sound at different places.  If you have a system with good imaging, the sound should seem to come from different instruments and voices, not speakers.

Staging - is the ability of a system to "fool you" into thinking that everything (including bass) is in front of you.  The sound should be similar to a stage in a concert, where the singer would be in the front center, and the rest of the instruments and background vocalists would be located to the left and right (but always on the front).

Good staging and imaging are not so easy to implement. It takes a lot experimenting with speaker location and direction.

Directivity - of sound is related to frequency.   At higher frequencies it is easier to pinpoint where the sound is coming from than lower frequencies.  This can be used to our advantage in car stereo.  Tweeters are the most important part of getting good staging.  They should be aimed towards the middle of the car.  A way to "bring" the bass to the front of the car is to fool our ears by overlapping frequencies played by midbases and subs, so that your midbases actually "pull" the bass to the front, since lower bass in not too directional.  You should crossover your midbases as low as you can (without getting distortion).  Then cut your subs at a bit higher frequency (preferably 60 HZ or less).  This will mix the bass coming from the front and rear, making the bass seem to come from the front.  Adding a center channel also improves staging, if it is set up correctly.
 

Types of Speakers

Coaxials - Coaxial speakers (or three-ways) are two (or more) speakers built-in the same frame.  They are cheaper than separate woofer and tweeters and also easier to install.  There is no need to worry about crossovers, since they are already built-in (you might still need to add a crossover to block bass if you are using high-power amplifiers).  A disadvantage of coaxials is the lack of flexibility.  For example, if the coaxial is all the way in the kick panel, or door panel aiming at your feet, you will not have good staging or imaging.  Some manufacturers try to compensate for this by making adjustable tweeters.  You should usually consider coaxial speakers for the back of the car, and separates for the front, unless you only have one speaker hole and don't plan to cut any more holes in the car.

Separates - Separates consist of a tweeter and woofer, and [most of the time] come with an external crossover.  The woofer is usually mounted in the factory hole in the door or kick panel.  The tweeters can be mounted in different places. The most common place to install tweeters is towards the top front corner of the door panel, aiming (if possible) between both front seat head rests.   Another popular location for tweeters is in the dash, either surface mounted, or in factory dash holes.  Yet another location where tweeters are commonly mounted is in the blank plastic piece on the top front side of the doors (where the mirror is on the outside).  You would have to experiment with angle and location to achieve the best possible imaging and staging.

Horns - Horns are very good at directing sound and have high efficiencies.  Horns are usually mounted under the dash.  By doing this, difference in distance from left and right speakers are greatly reduced over conventional mounting locations.  Since horns play mids and highs, tweeters are not needed.  Horns cost more than conventional speakers and require customization.  In many installations a good equalizer is required to compensate for their high sensitivity.
Horns are not for everyone though.  Many audiophiles complain of unnatural sound.   It is very hard to properly setup a set of horns.

Midbases - Midbases are usually 5, 6 or 8 inch speakers that are designed to go lower in frequency and are part of a three way system with a mid and tweeter. The problem is that 3-way arrangements require more complicated crossovers.  Midbases are most commonly mounted in the doors.

Subwoofers - Subwoofers add lower frequencies to the system.  They have to be enclosed in a box, with the exception of free air subwoofers, which use the trunk as an enclosure.  There are many different types of boxes and implementations discussed in the "subwoofers" section.
 

Mounting Locations

Front Speakers - The best place to mount speakers in the front, in custom kick panels.  By doing this, the path between the speakers and ears is minimized giving the best possible sound without having to add time delay circuitry.  If this is not possible, try to point the speakers towards the center of the car, and try to minimize the distance between the right and left speakers to your ears.  Custom kick panels are usually built from fiberglass or molded plastic, and are available from some manufacturers such as Ai Research.

Rear Speakers - Rear speakers should give a sense of space to the music, but not overpower the front speakers.  You should be able to barely hear the rear speakers.  If you are using rear speakers to add more bass/midbass to the system, at least use a crossover to cut off higher frequencies.  A lot of hi-end systems don't even have any rear speakers.  Tweeters are not necessary for the rear, a set of coaxials will work good for rear fill.

Center Channels - Center channels consist of a midrange speaker (3 or 4 inch) mounted in the middle of the dash (usually) on the top.   Center channels play a mono (Left + Right) signal between 350 - 500 and 3500 Hertz (voice range). The purpose of the center channel is to raise the sound stage, by creating the sensation of the singers "being" in the front of the car, and not in the door panels.  Center channels are hard to implement: First, a bandpass crossover is needed. Left and right channels have to be summed up.  There are various commercially available center-channel processors (many with built-in amplification).  The volume level of the center channel should be lower than the other speakers, since it is only supposed to make subtle changes to the total sound image.
 

Sizes and Shapes

There are many speaker sizes ranging from 1-inch tweeters to 18-inch (or bigger) subwoofers.  A smaller speaker will reproduce higher frequencies better than a bigger one.  The wavelength of a 20,000 Hz signal is very small, while the length of a lower (bass) note moving in the air could be as big as 40 feet.  That explains why a 4-inch speaker can't really put out bass (the lower the frequency, the more air mass that has to be moved by the speaker).  Tweeters are designed to play frequencies from 3500, 4500 or even 6000 Hz, all the way up to 20,000 Hertz.   Midranges (3, 4 or 5 inchers) play music from around 300, 500 Hz, to where the tweeters start in the upper level.  Midbases (5, 6, 8 inches) play from around 50 Hz to 500 (and even 1000) Hz.  Subs handle frequencies below 120-60 Hertz.

Do round speakers sound better than oval-shaped speakers (i.e. 6x9's)?  The answer is yes for most practical purposes. A round cone is more rigid than an oval-shaped one, so at higher levels, an oval-shaped speaker will distort more.   The reason why there are oval-shaped speakers is because of rear deck space considerations by manufacturers.  An advantage of a 6x9 speaker over a 6-inch speaker is that it has a bigger area, so it will move higher air volume, producing more bass.
 

Power Considerations

Most people think that if they use a 50 watt per channel amplifier on their factory speakers, the speakers will be damaged.  This may be true if the speakers do not have crossovers blocking off frequencies speakers were not designed to play.  What destroys speakers is distortion.  If you turn the volume all the way up on the radio, there will be distortion.  If you start hearing distortion, turn the volume down.  A high power amplifier allows the volume in the system to be higher, while the volume control on the radio is down in the range where no distortion is present.   It is better to have more power than what you need to get cleaner sound.

So how much power do you really need? As much as you can afford.   At a minimum, 30 to 50 Watts (each) would be OK for your front and rear speakers, while a little bit more (100-150 Watts) should be applied to each sub.  If you are powering up your tweeters independently, they require less power (20 - 40 Watts). Example: A four-channel set-up with separates in the front and coaxials in the rear with two subs will need about 40 Watts on each channel (Total=160W), and 100W going into each sub (Total=200W).  Notice that total power going to subs is more than total power going to the rest of the speakers.  This is because our ears are less sensitive to bass.

Subwoofer Boxes
A box ranges in complexity from the "plain vanilla box" (sealed) to bandpass and even more exotic enclosures.  Each enclosure has advantages and disadvantages and should be designed accordingly to the individual speaker parameters (the "one size fits all" rule DOES NOT apply to subwoofers and boxes).

Subwoofers need more amplifier power than everything else in the system.  This is because human ears are less sensitive at lower frequencies, so a higher bass level is needed for everything to sound even.  A low-pass crossover is required to block off high frequencies.

What type of subwoofer is better?  A bigger subwoofer gives more bass, but needs a bigger box.  Since most people like to have a trunk, 10 and 12-inch woofers are most common.  When buying a subwoofer always keep in mind that bigger size is not necessarily better.  A good quality 8-inch sub will outperform a cheap 12-incher.  Big subs (12", 15") have slower responses, yielding to boomier bass.  Small subs (8", 10") have a tight and more controlled sound.
 

Types of boxes
Free Air - subwoofers are either mounted under the rear deck or behind the rear seat of a car. This configuration will not work very well for hatchbacks. Holes have to be cut where the woofers are to be mounted. Since the woofers use the whole trunk as a box, the trunk has to be as sealed as possible from the cabin. Trunk can be isolated usually by putting particle board under the deck and behind the seat.
The drawback of free air subwoofers is that bass will not be very accurate (especially at lower frequencies), and more amplifier power will be required than with a regular box, but then again, you still have a full trunk.
 
Sealed - is the most common box and easiest to build. These boxes will give the flattest frequency response, and best overall sound quality (especially at lower frequencies). The box internal volume should be as close as possible to the recommended by the manufacturer. If a box is smaller than what it is supposed to be, the sound will be tighter, but more amplifier power will be required. If the box is too big, then the sound will be muddy.
 
Ported - boxes are usually bigger in size than sealed and have a "tube" (port) that lets some air out of the box. The idea of a ported box is that the speaker port pushes (or pulls) air at the same time as the woofer, reinforcing bass. The box itself acts as an amplifier, yielding to more bass than a sealed enclosure (3 to 4 dB). Ported boxes do not have a linear frequency response.  If the box is not built according to specifications, it will not sound good. The box design acts as a filter, cutting off lower frequencies.
 
Isobaric - configuration is a good way to get bass in a smaller box. This is done by building a box about half the volume of a sealed box, and placing two woofers facing each other. Note that everything must be sealed, including space between woofers. A spacer between both woofers must be used in most cases to avoid subs hitting each other. When wiring, make sure that woofers are out of phase: Wire one of them backwards (negative to positive, and positive to negative), so that both pull or push at the same time. An isobaric configuration will NOT put out much more power than a box using a single woofer.  Its main purpose is to reduce box size.  Another drawback is that since one of the subs is exposed, it is more prone to damage.
 
Band Pass -  enclosures consist of a woofer between a sealed and ported box.  Bandpass boxes  will yield more bass than sealed and ported boxes (especially at lower frequencies), but over a narrower frequency range. Since the box acts as a filter, mechanically blocking lower and upper frequencies, a crossover is not needed in most cases.  These enclosures are usually big, and very unforgiving when precise volumes and port sizes are not followed.  Bandpass boxes also tend to mask distortion.  If you can't hear distortion and turn your stereo down in time, you could damage your subs.
 
Aperiodic - Very small boxes that "breathe" through a moving membrane.  Both the membrane and cone can not be in the same exterior space.  Either the membrane part has to be isolated by cutting a hole in the car so that it is outside, or the subwoofer has to be isolated from the rest of the trunk in a similar fashion to free air woofers.  The "box" has to be as small as possible (ideally the membrane should be right up against the sub), since it is used only for coupling the sub and membrane.  Aperiodic membrane configurations are very hard to design and tune, but give good frequency response and respond faster to transients, giving accurate and tight bass as opposed to boomy sound.  They are not ruled by Thiele-Small parameters like other designs, so any woofer would work with the membrane.

Amplified Bass Boxes
A good choice for small cars and (ideal) for hatchbacks and pickup trucks.  They usually take up very little room, putting out to fairly good bass. The most known manufacturer is Bazooka® for it's Bass Tubes®.  Their design is a ported box. The woofer has to be close to a wall or, better yet, to a corner.   To fine-tune, the bass tube is moved either closer, or farther form the wall or corner.

It is convenient to get an amplified tube, since amplifier, crossover and subwoofer are all integrated in a small package. If you buy the components separately, you will end up spending more money. Another good feature of tubes is the fact that they can be easily and quickly installed and removed.

If you decide to get one, keep in mind that even though they all look the same, cheaper brands will not sound good. A decent tube will run in the $300's (amplified), and in the $100's for a non-amplified.

Custom Bass Boxes
Many manufacturers such as JL and MTX are making custom boxes (with subs included) to fit in center consoles, under seats, or in other small spaces.  Although these boxes do cost a lot of money, most give superb performance and integrate easily in a car without taking up too much room.

What is a Crossover?

Crossovers are an essential part of an audio system, often ignored.   A crossover splits frequencies so that each speaker receives a certain range of frequencies.  This is done for two reasons:

   1. Avoid speaker damage: Speakers are designed to play only a certain range of frequencies. If other frequencies are played, then the speaker will produce distortion, which eventually will destroy it.
   2. Overall balance: If a system with subwoofers, and full range speakers doesn't have a crossover, then the subs will be playing, for example, from 20 to 1000 Hz, while the full-range speakers will be playing from 60 Hz, all the way up to 20,000 Hz. As it can easily be seen, there is an "overlap" of frequencies between 50 and 1000 Hz. In this overlap region, the levels are higher than levels below 50 and above 1000Hz, yielding to a non-balanced system.

There are 3 types of crossovers:  High-pass, low-pass and band-pass.  As it can be deducted from the names, a high-pass crossover will block low frequencies, a low-pass will block high frequencies, and band-pass will block low and high frequencies below and above crossover points.

From the description above, crossover operation sounds very simple, but it is a bit more complicated.  Crossovers do not block undesired frequencies completely (unless you are using digital crossovers).  Crossovers cut frequencies progressively.  A crossover "slope" describes how effective a crossover is in blocking frequencies.  The minimum slope is 6dB/octave.  For example, a high pass crossover at 1000 Hz, will let anything above 1000Hz pass.  The farther lower frequencies are from 1000Hz the lower levels will be.  At 500 Hz (1 octave), the level at the speaker would be 6dB less.  A steeper slope (i.e. 24dB/octave) will block undesired frequencies more effectively, but will cost more than a lower slope crossover.

If a speaker will be played near it's frequency range limit, then you need a high slope.  For example, a midbass rated at 50Hz on the lower range could be crossed over at 55 or 60HZ with a 24dB/Oct crossover.  If you want to use a lower slope crossover, then the frequency would need to be higher (i.e. 100 Hz at 6dB/Oct).

So what are good crossover frequencies? It largely depends on the car, speakers, and speaker location. Typical crossover frequencies are 100Hz (bass), 350Hz (midbass), 3500 - 5000Hz (highs). For more details of what frequencies to choose, see the speakers section.
 

Active Crossovers

Active crossovers (and equalizers) need external power to operate and work at low signal voltage levels (RCAs). Signal from the head unit's RCA's is split it into low-frequencies (bass), mid-frequencies (mids), and high frequencies (tweeters), to go to different amplifiers.

What are the advantages of active crossovers? Signal is not affected as much as with passive crossovers, since everything is done at low voltages. There is much more flexibility, since all that is needed to adjust crossover frequencies is to turn a knob, while on passive crossovers, the components have to be replaced. The problem is that more amplifier channels are needed to go to all the speakers.
  

Passive Crossovers

Passive crossovers work after the amplifiers, receiving high signal levels. Since all the frequency splitting is done after the amplifiers, more speakers can run off an amplifier channel, obtaining maximum power by playing with the resistances "seen" by the amplifiers.

Passive Crossovers are capacitors and inductors either in parallel or series, or combinations that are added to cut off highs and/or lows. A capacitor stores voltage, acting as an open circuit (blocks off signal) at lower frequencies, and acts as a short at higher frequencies (lets signal pass). An inductor, on the other hand, stores current, acting in exactly the opposite way of a capacitor. Inductors act as shorts at lower frequencies, and open circuits at high frequencies.

If a capacitor is hooked up in series with a speaker, it will be a high-pass crossover (signals at lower frequencies will be blocked, and higher frequency components of the signal will be allowed to pass). An inductor in series with a speaker will be a low-pass filter. Subwoofers need inductors in series (low-pass), while midranges will need both a high-pass (cut bass off) and a low-pass (cut higher frequencies that tweeters will be taking care of). Tweeters need also high-pass filters, to block lower frequencies.

An octave is double the frequency: i.e: 20Hz --> 40Hz --> 80Hz --> 160Hz, etc. The more components are added, the more effectively the filter will be, so if both an inductor and capacitor are used, the cutoff slope will be 12 dB-per-octave, then 18 dB-per-octave, then 24 and so on.  There are many types of passive crossovers that can be implemented, starting with the capacitor or inductor in series, and getting complex as more capacitors and inductors are added.

Capacitors and inductors also dissipate power, wasting energy that speakers could be using. Low order passive crossovers are not very expensive: Capacitors run $1 - $5, inductors run $10 - $20. Higher order (i.e. 24dB/Oct) crossovers can get really expensive, especially at low frequencies/high power applications.  Passive crossovers have another drawback, that is ignored most of the time for practical purposes: They introduce phase shifts, which put voltage and current out of phase with respect to each other, affecting delivered power to the speakers and affecting overall speaker "timing".  A 6dB/Oct crossover has a phase shift of 90 degrees, 12dB/Oct = 180, 18dB/Oct = 270, 24dB/Oct = 0.  Try to stay with even-order crossovers.  If you have a 180 degree shift (2nd order crossover = 12dB/Oct, hook up the speakers out of phase (+ to - and - to +).  On 4th order crossovers (24dB/Oct), there is no phase shift.

Equalizers

Equalizers are used to fine tune a system, not to fix design flaws.  If you have to use a lot of equalization, there is a problem with the system that should be solved first by relocating speakers, changing crossover frequencies, amplifier gains, etc.  Equalizers are valuable instruments to flatten a system's frequency response (making the levels the same at all frequencies).  In competition, a measurement is taken on how flat the response of a system is.  More points are given to a competitor with a flatter response.  In a real system, a flat frequency response is a starting point, but does not ultimately mean perfect sound since human ears are not sensitive at the same level to all frequencies.

Many people believe that an equalizer is to boost power by raising signal levels.  95% of the time an equalizer should be used to cut levels rather than boost them.  In a well designed system the settings on an equalizer should not be too far from the zero dB line.

Frequency

Frequency Chart (4.7kb)
Click to View
Frequency is how many times per second a signal (AC) switches from positive to negative and back, measured in Hertz (see page on "Electrical Concepts" for a more extensive explanation).  The frequency range in which we are interested for audio is from 20 Hertz to 20,000 (20k) Hz.  The lower the frequency, the slower the signal oscillates.

The frequency spectrum is read using a logarithmic scale, and is divided in octaves (doubling of the frequency).   Octaves are for example, 20, 40, 80, 160, 315, 630 Hz and so on.  Equalizers are divided in octaves, 1/2 octaves or 1/3 octaves.  A 1 octave equalizer can only control 7-9 bands (frequencies), while a 1/2 octave equalizer can control 15 bands. A 1/3 octave equalizer would give you the most control over the system, by being able to adjust 30 -31 bands.

Q

Equalizer Diagram (8.6k bytes)Q is a measurement of how much the equalizer band affects a range of frequencies.  A high Q means that the EQ can control a lower "envelope" of frequencies, while a low Q is a larger envelope.  Looking at the image on the right, Q is the thickness of the affected frequencies.  A smaller Q means a wider range of frequencies boosted or cut, while a larger Q is a narrower shape.  Typical Q values are 1, 2 and 3.

Parametric vs. Graphic Equalizers

A graphic equalizer has usually fixed frequency and Q value.   The layout of a graphic equalizer is the typical sliding controls arranged by frequency.  The advantage of a graphic equalizer is that in the way it is laid out, it is easy to see what frequency is being boosted or cut and any person without much experience can adjust it.  Since a graphic EQ has fixed frequencies and Q, it has limitations on what it can control.

A parametric equalizer consists of knobs that are turned to desired levels, have adjustable frequencies and (usually) Q.  The advantage of parametric equalizers is a much greater control, since frequencies and Q values can be adjusted.  On the other hand, a parametric equalizer is much harder to adjust than a graphic EQ, requiring an experienced person and measuring equipment.

Mono and Stereo Equalizers

The main difference between mono and stereo EQs is that a mono EQ has only one input and one output, and a stereo has two inputs and two outputs.  They both have their advantages and disadvantages:   A stereo EQ controls your whole system (both left and right channels) and it is easy to adjust: Just turn the knob or slider and both left and right channels are taken care of.  If you want to adjust left and right channels independently, you can't!

A mono EQ controls only one channel, so you need two of them for the whole system.  Since you have now two EQs it takes a lot more time to setup the system.  Many people use mono EQs for the greater control they give over the system.  Since left and right speakers are not exactly at the same distance to our ears, two mono EQs can help compensate for time delays and problems caused by speaker placement.  Buying two mono equalizers is more expensive than buying one stereo EQ.

Low Level and High Level Output

A high level output equalizer takes either high level (speaker) or low level (RCA) inputs and has a built in amplifier.  The output goes directly to the speakers and can not be hooked up to another amplifier.  These equalizers are cheap and cause more damage than good to the sound system.  They do "boost" signals, but all this does is add distortion to the overall sound.

A low level input EQ takes RCA signals from the radio and has RCA outputs that get hooked up to amplifiers. Since these equalizers work at low signal levels, they introduce very little distortion, if any to the system.  They do cost more and require more wiring than a high level EQ.

A third kind of equalizer gets hooked up directly to the head unit via a special cable and is controlled by the head unit.  These EQs use low level signals and are usually of good quality.  The drawback is that if you want to upgrade the head unit or change brands, the EQ will not be compatible with other brands or even with different models from the same manufacturer.

The Head Unit is the most important part of the audio system.   You will always be staring at the head unit and touching it to control your sound system.  It is a good idea to look for something that is aesthetically pleasing, integrates to your car, has a logical button layout and has features that best suit your needs.

Head Units Features

CD Changer Controls - Whether you get a CD, cassette or MD head unit get a model that has CD changer controls, they only cost a bit more, but give you the opportunity of simply plugging in a changer in the future.

Power - Probably the most overrated feature in head units.  The power on head units is seldom given in RMS watts (see amplifiers section for definition).  Typically a head unit has an output of about 5-7 watts RMS per channel, while a high-powered head unit goes up to 13-15 watts RMS per channel (even if they claim 35 or 40 watts).

RCA Outputs - If you are planning to run the speakers from the head unit's built-in amplifier, you don't have to worry about RCAs, but if you plan to add amplifiers in the future, get one with a set of RCAs (left and right), three sets preferably (left and right for front, rear and subwoofer).  An important feature to look for is high-voltage RCA outputs.  Typically RCA signals are less than 1 volt.  High-voltage RCA signals are 2, 3 or even 4 volts.  This allows for better noise immunity and gives you a higher headroom for amplifier gain settings.  Most high-end manufacturers are selling units with high-voltage RCA outputs which are frequently used in competition.

Security - There are many security options for head units nowadays.  None of them is 100% effective in deterring theft.  Detachable faces are the most common option.  The front part of the radio comes off, rendering the rest of the unit useless.  The problem is that after a while people forget to take the face off, or simply tuck it under the seat or in the glove box.

Another option is codes, key CDs (i.e. Blaupunkt, Eclipse).  If power is cut off, the unit asks for a code or a predetermined CD used as a key.  If the incorrect code is entered, it locks the radio up, requiring service from the manufacturer.  This has proven to be an inconvenience when the owner loses their code or forget which CD they used to program the radio.  Some radios, such as Blaupunkt are using a smart card, that when removed, renders the unit useless, but again, people forget to take it out or lose it causing aggravation to the consumer.

Yet another security protection pioneered by Kenwood is a flat panel that covers the radio when the ignition key is turned off.  While this will fool some people into thinking there is no radio in, it won't fool most thieves.
 

RF modulated CD Changers

FM modulated changers can be hooked up to any radio that has an FM tuner, whether factory or aftermarket.  They use the radio's antenna to introduce the signal.  They are usually simple to hook up and consist on the changer itself which is mounted in the trunk or under seats, the control box and the display/remote control.  The drawback is that the sound of the CD changer will not be "CD quality", it will be as good as the FM tuner is.  The signal coming from the CD player has a wide frequency range but the FM tuner limits the signal, cutting the lower and upper ends of the spectrum.

Basic System Design

Before you purchase any component, plan your system very carefully.   You need to consider if you are going to buy the whole system all at once or piece by piece, how much you want to spend and what quality and quantity of sound you want.  Are you doing a flashy or stealth installation?  Are you keeping your factory panels or are willing to cut your car to achieve better sound?   Are you doing the installation yourself, or leave it to a professional?

Sources

The most important part of the system.  Get a good head unit from a name brand.  If you skimp here, your whole system will suffer.  For people that are on a budget:  Get good quality head unit without all the bells and whistles.   A flip down face with a colorful display looks great, but it won't necessarily sound better that a regular plain head unit.  If you are planning to get amplifiers in the future, get a head unit with RCA outputs.
 

Speakers

The second most important part of the system.  If you are on a budget, just get a nice set of speakers up front and don't even worry about the rear speakers, amplifiers, etc until you have some more money later on.

Speaker installation is definitely the most important aspect that determines how your whole system sounds.  No equalizer or processor can compensate for poorly installed speakers.

Factory locations are usually not acceptable for audiophile quality sound. Speakers should ideally be pointing straight at you.   Speakers on each side should be as close to each other as possible with no obstructions. Speakers should be mounted on a good baffle (preferably an enclosure).   Difference between left and right speaker distances to your ears should be as small as possible.

The front speakers should also play as low as possible in frequency (ideally 60Hz or less), being able to handle full power.  This is where crossovers with high slopes come in to protect the speakers.
 

Amplifiers

Amplifiers do not only make a system sound louder, they make it sound BETTER.  The more power you get, the cleaner the signal going into the speakers.   A common misconception is that if a 100 watt amplifier is used on 50 watt speakers, the speakers will burn.  This is not true, as long as there is no distortion and the speakers are properly protected with crossovers.  More power is always better.

For systems with a lot of power, you might also have to upgrade the car's electrical system, by getting a high output alternator, capacitors, etc.
 

Subwoofers

Subwoofers cover low frequencies in the audio spectrum.  Subwoofers need to be installed in a box designed specifically for them.  Put a subwoofer in the wrong type or size box and it will not perform as it should and could be destroyed.

Subwoofers need a lot of power to play at acceptable levels without distortion.
 

Matching subs (and speakers) to amplifiers

This is a very important aspect of system planning that is often overlooked.  Amplifiers are designed to provide maximum power at a certain impedance.  An amplifier at this maximum level will be under more stress and produce more heat, so mounting location also becomes important.  Professional installers wire subs (and speakers) in parallel and/or series combinations to obtain a load that will make the amplifier perform at full power.
 

Processors

Many people believe that they need to have an equalizer, center channels, rear speakers, etc for better sound and compromise by buying cheaper components.  A properly designed system will sound great without the need for all this other components.

If you have the money and are an audiophile or into competition, then this "extra" components can become important.
 

Upgrading

Always keep in mind future upgrades when buying audio gear.  For example, let's say you are low on funds and want to add two subwoofers and an amplifier.   Since powerful amplifiers are expensive, you can get a 2-channel amplifier to drive the subwoofers at acceptable levels.  Later on, when you have more money, you can buy an identical amplifier and power each sub with an amplifier in bridged mode for more bass.   If you planned carefully, the impedance's of your subwoofers will match the amplifiers for maximum output in the bridged configuration.
 

Cheap Components

Buying better quality components will definitely increase system performance.  Although name brands are more expensive, they are more reliable (read: will last longer).

For people on tight budgets, it is better to save for a better component and take longer building a better system one component at a time.
 

Installation

Even though you will save money and learn something new by doing the installation yourself, sometimes it is better to pay a professional to do things that might be a bit over your head.  An experienced installer has many years of experience that will definitely make a difference in your system's performance and reliability.  If something goes wrong, you can always go back and have them fix the problem.  Many manufacturers offer and extended warranty period if the equipment is installed by an authorized professional.

Planning Your System

Planning Your System
This part of the game can be fun or disappointing depending on what you can do. First I'm going to give you an example system that I believe includes everything you need to have a pretty good system. After that I will show you how to make compromises and leave out parts that may not be as important to you to keep your system within your budget. If you want to go beyond my basic system you probably already know more than what this site can tell you. Also, you do not have to get everything at once. I put my system together over a few years. With a little planning you can upgrade your system in steps and that way its like getting a new system every time you change something instead of getting everything at once!

Basic System: This is my opinion only but I think that a good system should start off with a good head unit that either has a CD player and/or is connected to a CD changer. A good system sounds best when playing CDs, tapes just do not cut it. Next I think component sets are made with fewer compromises than coaxial speakers so I suggest getting a good midrange/tweeter set for the front. Head units generally do not put out enough clean power so you will want an amp to drive the component set. In the rear where you only need some "fill" for ambiance you can get away with cheaper coaxials and set their level lower than the fronts to keep the sound stage in front. A modest (50x4) 4 channel amp is a good choice here for powering the component set up front and the rear speakers. You could use a good 2 channel amp and run the front and back in parallel on the amp but it would harder to adjust the level between them. Midranges sound best when they do not play bass so you will want a 2 way electronic crossover and use the high pass output to drive your 4 channel amp. I did not forget the bass! Most people are happy with a single 10" woofer or a pair of 12"s. Use an appropriate enclosure and a big amp (at least 75x2, preferably even more). Throw in installation and wiring accessories (like fuses and distribution blocks). Here's an approximate price break down of what this costs in my area. Your prices may be significantly different.

    * head unit: $300-$500
    * 4 channel amp for highs: $250-$400
    * 2 channel amp for lows: $300-$700
    * sub(s) (1-10" to 2-12"): $150-$450
    * enclosure for sub(s): $0 (free air) - $250 (custom)
    * component set: $200-$500
    * coaxials for rear fill: $100-$400
    * crossover/equalizer: $100-$500
    * wiring and accessories: $50-$250
    * installation: $0 (do it yourself) - $100 (basic)

This comes out to $1450-$3950! I realize that this is a lot of money and that most people do not spend nearly this much money on their car stereo. However, the things listed above are what I feel is necessary to have a system with only a few compromises. If you are less concerned about highs, get coaxials in front instead of the component set and power them off of the head unit and use some bass blockers on them. This will save you about $400. Getting a bargain head unit can save you some money as well. If you are really not into bass much you can forgo all the bass related equipment and run your component set full range. This will still give you clean sound but not much bass. However, you will save $550-$2300. I would start with what I have listed above and take out parts you do not care about as much. Only you know what kind of system you can be happy with.

When buying equipment try to spend time listening to it before you buy, especially with speakers. Also try to use equipment that is similar to yours when listening in a store. As for amps, it costs money to build a good amp so if you see some awesome price on an amp you have never heard of, it is probably a piece of junk. Stick with good names with amps.

Finally, if you are on a budget (aren't we all?) it works better to upgrade in steps.  The most important thing is to have a car audio system that sounds good to you not someone else.  If you are happy with just changing the factory speakers and stopping there then just do that.  There is a level when that new amp or speaker is not going to make a difference so it is not necessary to always upgrade.  There are people who think my system is terrible but it works well enough for me and anything else I do to it would be a minor gain and not worth my trouble.  Do not let a salesperson talk you into something you do not need!  Good luck!

Speaker Power Ratings and Amplifier Power Ratings

This page is intended to help people understand the relationships between speaker power ratings and amplifier power ratings.  A question that comes up in designing a system is "how much power do I need for my subs?" and "how much power do I need to run my other speakers?" I have a BS in Electrical Engineering so I do not know how much of this the average Joe is going to understand. I am also human so there may be mistakes below.

When most people consider how they are going to match their speakers and amps together they usually only consider matching the power levels.  There are many more factors that come into play.  A big factor is the sensitivity rating of the speaker.  The sensitivity (efficiency) rating of a speaker gives you a rough idea of how loud the speaker will play given a certain amount of power.  Let's consider a speaker with this sensitivity rating:

87 dB / 1 watt / 1 meter

What this spec means is that the speaker will produce sound at 87 dB 1 meter away from the speaker when it is given input power of 1 watt.  Typically the input sound's frequency is 1 kHz.  Depending on the type of enclosure and other factors the speaker may not produce 87 dB but it's still a useful spec for comparison with other speakers.

It takes a doubling of input power to produce TDB more sound (assuming the speaker is not reaching its limits).  Therefore we can make a table for how loud the speaker will play given a certain amount of power like this:

Source: http://www.carstereo.com/