Crossover Points-Crosover Slopes-Active vs. Passive
Octave-Before getting into any of this, an octave needs to be explained. An octave is ANY doubling or halving of a frequency. This means one octave from 20hz is 40hz....then 80hz....then 160hz. An octave above and below 1,000hz (or 1khz) is 2khz and 500hz respectively.
Cut-off frequency-This is the point where one driver is selected to have the frequency response "stop".
Crossover point (or xo point)-This is where two drivers cut-off frequencies meet, overlap, or underlap. It is basically where one driver stops playing and another starts. The most commonly set crossover point in any system (passive or active) is sub to midbass. Ex.--setting the high pass (or hp) crossover on the midbass to be 80hz and the low pass (or lp) crossover on the sub to be 80hz. mid 80hz sub 100hz is overlap-and-mid 80hz sub 65hz is underlap.
Crossover slope-This is how quickly information (sound) is reduced one octave away from the selected crossover point. If a sub has a cut-off frequency of 80hz and has a 12db slope, information played at 160hz will be down 12db from information played at 80hz. A reduction of 3db is generally consider a halving of sound (and a increase of 3db is generally considered a doubling of sound), so you can see that the sound should be drastically lower at 160hz. Most amps allow you to select between 12db and 24db, if you were to flip that switch, the sound would now be down 24db at 160hz.
The purpose of different slopes is to set up options for blending sound better between drivers and to protect the drivers themselves. Most drivers can only play a certain frequency range before they begin to distort, and having options on crossover slopes allows you to select where you want the cut-off frequency. Say you have a 5.25" driver and it can play CLEANLY down to 160hz at high volume. If you wanted to get closer to that 160hz as your cut-off frequency, you should select a steeper slope. Ex.-160hz@36db, 180hz@24db, 200hz@12db, and 240hz@6db might be something you would see for that driver to keep it from distorting. Now depending on driver location, processing power, and the speaker that is on the other side of that crossover point, any of those options may be best.
Passive network-When a shopper goes into best-buy and buys a standard 2-way component system, the box contains a midbass, a tweeter, and a crossover network for each side. The passive network basically does what was mentioned above for you. It has a point and a slope set for the midbass and for the tweeter. This is a very simple solution for most consumers, hook it up and it is done. Some crossovers are much more advanced than others as well allowing some additional control, but the overall result is the same.
Active network-This is where the user has control over the crossover points and slopes. This is performed using a active capable head unit (or hu), an external crossover with bandpass capabilities (setting a low pass and high pass point for a single driver--ex. midbass set at 80hz@12db highpass and 2khz@24db low pass), an amp with bandpass capabilities, or a sound processor. "Going active" leaves the user with the ability to select crossover points and slopes for every driver as well as the ability to time align (or t/a) or control the eq and gain settings with some processors. This gives the user much more ability to set the drivers up for their install. Since a tweeter down in the bottom of a door panel, in the kick panel, or in the a-pillar will all react differently having this control allows custom tailoring to your install. The downside to going active is that while more control is allowed for potential better sound, there is also more varibles available to totally screw up the install.
Parametric EQ, Graphic EQ
A Graphic EQ (or GEQ) has fixed point that frequency response (or FR) can be adjusted. Generally it has 3,7,13,31...etc bands and can be adjusted both + or - so many decibles. The higher end units that have a GEQ generally have more bands since YOU cannot pick which to adjust, they give you more options. 13-band Ex. 50, 100, 160, 250, 500, 1k, 1.6k, 2.2k, 3k, 4.5k, 6.7k, 10k, 16k hz are the ONLY places you can adjust frequencies.
A Parametric EQ (or PEQ), allows the user to either pick the Q (width) of the bands or pick both the frequency and the Q. PEQ's typically have fewer bands (3 or 5 is common), but you can pick the frequencies you want to adjust. Say you have a problem at 2.6k-2.8khz, well the above 13 band eq doesn't cover that area. With a PEQ, you can actually select 2.7khz for the frequency, adjust the Q so it covers 2.6-2.8k and you have no fixed your problem and only used one EQ band.
I have very limited experience with EQ work myself, and plan to use an RTA to help me before I begin to tune by ear. I think that either form of EQ can do more harm than good unless you have plenty of experience or some form of measuring equipment to help.
2-way, 3-way, rear fill
I will point out that technically a sub is part of the system so 3-way can be sub, midbass, tweeter. On this site however, when people speak of running 3-way they are generally referring to midbass, midrange, and tweeter up front and a sub in the rear is assumed. To clear things up, the only hu that can currently run a 3-way active setup (with a sub) that is available in the US is the Clarion DRZ9255. The Pioneer P9 combo, the Sony XDP-4000, the Audison Bitone, and the Alpine H900 are all hu/processor combos or standalone processors that can also control a 3-way active setup.
2-way-This is a midbass and tweeter combo. The pro's to this setup is there are fewer drivers, which is usually easier to install in a car, and easier to set up if running active. The con to this setup is that your midbass (or MB) and tweeter (or TW) is asked to cover what is generally the midrange (or MR) frequency which MIGHT now produce as clean of a sound. Ex.-MB 80-2khz TW 2.4khz-20khz
3-way-This is the same setup mentioned above except a midrange driver is added. The pro to this is that the midrange is there to basically give the midbass and the tweeter the ability to a smaller range which can lead to clearer sound. The con is that adding one more driver makes tuning more difficult and is usually harder in implement properly in the car. Ex. MB-80-500hz, MR 500-4khz, TW 4khz-20khz.
Rear fill-There are people that will tell you there is nothing good about rear fill. It messes up your soundstage no matter what you do. There is a such thing as proper rear fill that many think is a positive addition to a system. It is achieved by removing any common information, delaying the signal, and bandpassing the frequency. I have not run "proper" rear fill, but did want to try it very much as it can supposedly widen and deepen your soundstage. If you are interested in the learning more, try searhcing the words "hey werewolf" and read the thread started by Geo. It will explain how it can be done if you are interested.
I probably should have put this first, as many will say it is the most important part of any system. Generally you can make low quality components sound "good" in a well set up system for less money than buying super expensive components and just slapping them in your car.
Constraining Layer Deadener (or CLD)-This is what most people thing of when they refer to deadening. It is also what most people call dynamat (like Kleenex though, there are other, equal or better brands to be found for less money). This basic principle is pretty simple, it is a component that when placed on a panel that resonates, stops the resonance. This means if you have long flat areas of metal (or plastic) in your car, you can place a piece of CLD on that area and it will help kill some of the resonance. It does not do very well at actually stopping sound from entering the car, which is why other items need to be used. I suggest looking for something the uses butyl instead of tar for adherance, and search for which brand fits your needs the most.
Closed Cell Foam (or CCF) and Mass Loaded Vinyl (or MLV)-By itself, CCF does not serve much purpose, but when used with MLV (or any other object that weighs around 1lb. per sq/ft like sheets of lead) it helps act as a sound barrier. This can be purchased as two items and put togetheror can be purchased as a one piece product. If you want to do more research for the "why" it works, by all means do, if you want to just trust me that it works, you can do that too.
Others-There are also paintable options that can be used in place of CLD, there are pads that help deflect sound that can be placed behind speakers, there are different open cell foams (OCF) that can be used to absorb sound. I have covered the two main parts of sound deadening IN MY OPINION, if you would like to learn more, feel free to seach, the info is out there on this site.
Subwoofers: Ported vs. Sealed, Smaller vs. Larger
Many people have the view that a ported box is sloppy and a sealed box is tight. This generally comes from people buying pre-made, universal boxes or from ported boxes being tuned high for SPL and is not a true statement. A sealed box is easier to not screw up and GENERALLY is less efficient and has a harder time playing low notes. So why not always run ported?? Well because it is much easier to screw up and GENERALLY can't play as high cleanly to match up with smaller drivers as well (but this doesn't mean it is sloppy). Until this last year, I always had sealed boxes. I built a ported box that was big and tuned low and IN MY BUILD sounds better than the sealed setup it replaces. There are many threads about the pros and cons, you can read them and find the tradeoffs but I wanted to dispell the big myths here.
Many people believe that larger subs are also sloppier than smaller subs. This is again not true. A larger sub can generally play lower notes easier and a smaller sub generally can play higher notes cleaner. Depending on the frequency range (or fr) you are asking the sub to play, determines which suits your needs. In my current build, I went from two 10's sealed, to one 12 ported and it sounds cleaner, responds faster, plays lower, and gets louder all on less power. Again, it depends on the application.
If you want to learn more about how to properly set up a ported sub, seach for unibox or winisd in google and download the free modeling software.
What speaker is best, what sub is best, what amp is best
I think Gyros are delicious but I am not a very big fan of Sushi. I am sure people agree with me, like both, hate both, and like the opposite of what I do. So much is life is about personal taste, speakers are the same way. There is no "best". This can also change based on install (including proper door sealing and deadening), vehicle used in, and music listened to. If you are down to a few different options, instead of starting a thread, I would try searching each model you like. GENERALLY, you will find a review, and GENERALLY, the review will tell you what gear is being run, what vehicle it went into, and what type of music was listened to for the opinion.
There is nothing wrong with asking others their opinions, but I generally find it better to look for a review and read it. If someone disagrees, you will typically find their opinion in the thread as well. Also, many established members HATE "which is better" threads, and will avoid them. Meaning that a new(er) member is telling another new(er) member what should be purchased and you could end up the victim of "the blind leading the blind."
If you want a great starting point to practice searching for both for getting tons of opinions on a speaker system and a good 2-way system to look at purchasing...search pioneer ts-c720prs.
I hope this information helps somebody. If it does, know that I only touched the tip of the iceberg here. There is so much more to learn. If reading this has left you wanting to know more before making a decision or asking for a hand out, I also enjoyed reading about: cone vs. dome midranges, how to fiberglass, kickpanel pros and cons, how to make your own rca cables, how to make your own phase inverter switch, effects of polyfill and the point of dimenishing returns, group delay, speaker impedence, speaker sensitivity, how to read response graphs, how to tune with an RTA.
I am sure there are more, but most of the topics I covered are in the tutorials section and those that aren't can be found on this site by searching. That is how I learned about them.
Polarity and Phase
Polarity-This is the + and – connection from amp to speaker. Something that was helpful for me to learn is that getting the polarity backwards WILL NOT hurt a speaker. In fact, it can sometimes help (see below). All that happens when power is placed to a speaker, is the cone moves back and forth. If you flip the polarity, it now moves forth and back (aka-the opposite direction).
Phase-Phase changes all the time as music is played across the frequency range and can change because distance of drivers from each other, crossover slope used, t/a implemented, etc . The times phase is most important, is at the crossover points. This is because if the two speakers are out of phase, the music will not sound focused in reference to each other. For example, if all other sources of phase change are discarded, when a 12db crossover point is used on both a mid and a tweeter, the phase should not change. When a 24db crossover point is used on a mid and a tweeter, the phase for the tweeter is 180 degrees out. This means the woofers is going back and forth and the tweeter forth and back. Remember polarity above? If you flip the polarity on your tweeters, you would be back in phase in this example. Now, a 18db crossover point changes the phase by 90 degrees, so polarity won’t fix that, but one way could sound better than the other, so you try both and pick the one that is best.
Sometimes, when speakers are in phase and facing each other, the soundwaves meet and cancel each other out (think mids in the doors). So sometimes it is better to be slightly out of phase from each other. That is why when you read tutorials, they say listen to the left side only, get it in phase. Listen to the right side only, get it in phase. Now play both sides. Now flip the phase on the every driver on one side and listen to both sides again. If it sounds better, leave it, it is sounds worse, change the phase back on that side. Pick the combination that sounds best to YOU.
What you may end up with is everything at +/- polarity, but you might end up Rt. Mid +/- ,Rt. TW -/+, Lt. Mid -/+, Lt. TW +/-. Who knows, but hopefully this quells the fear of hooking a speaker up backwards and blowing it.
One note, hooking power and ground on an amp up backwards IS NOT ok! It may seem like common sense to some, but I don’t want people thinking everything is interchangeable, damaging equipment, and blaming me.