Here is a quick writeup on basic Speaker and Crossover information. I'm looking for RHunter to fill in some of the gaps with the more complex stuff, as Crossovers, Imaging, and Sound Quality seem to be his neck of the woods.
Co-axial vs Components
What's the difference?
Co-axials are speakers that have the tweeter permanently mounted in the middle of the midwoofer. Co-axials typically do not have external passive crossovers.....only a capacitor in-line with the tweeter to highpass the tweeter. They are generally much cheaper than components, and will work well off of headunit power (but will decent off of external amplification as well).
Components have separate midwoofers and tweeters as well as an external passive crossover. The midwoofers and tweeters are separated for a number of reasons.....for example, to allow optimal speaker placement. The passive crossovers are usually quite complex (more advanced than what's used for co-axials) and are designed to optimize the performance of the speakers (by way of crossover points, crossover slopes, tweeter attenuation, tweeter protection, impedence compensation [zobel network], etc.). The speakers used in component sets are typically of much higher quality and better performance that those used in co-axials. Typically components are best used with external amplification only.
2-Way vs. 3-Way
In a perfect world, we'd have a single speaker that could reproduce all frequencies perfectly, 20hz to 20khz. Unfortunately for us, such speaker does not exist…..so, we need to break the frequency spectrum down and play it through multiple speakers (mids, tweeters, subs, etc.). This is where we get "2-ways, 3-ways, 5-ways, etc." from.
In co-axials, a 2-way speaker is a speaker that contains only a midwoofer and a tweeter…..the midwoofer playing the lower frequencies (down to around 80hz or so), the tweeter playing the higher frequencies (around 3khz or 4khz and up). 3-way co-axials typically have a midwoofer, tweeter and "supertweeter", with the supertweeter being designated to handle the very, very high frequencies only. Co-axials can go as high as 5-way (midwoofer, midrange, smaller midrange, tweeter and supertweeter). For all intents and purposes, anything more than 2-way in co-axials is a marketing gimmick. Going with 3-way co-axials or higher usually does not increase performance much, if at all.
For component speakers, a 3-way system includes a dedicated midbass (generally plays around 60hz-350hz), a dedicated midrange (generally plays around 350hz-6500hz or so), and a tweeter (generally 6500hz and up). Whereas a 2-way system is only a midwoofer (playing around 60hz-4000hz or so) and a tweeter (4000hz and up). Ideally, for a 3-way system, you'd want to put the midbass in your door, and have kicks built for the midrange & tweeter. For a 2-way component set, kickpanels or door mounting will suffice with generally good results.
General advantages of a 3-way component set:
1) There isn't a crossover point in the middle of the midrange frequencies (which are generally the most important to imaging and tonality), and they aren't being split up between drivers like they sometimes are in a 2-way setup. In a 3-way, they will be played by mainly one speaker, which is the dedicated midrange.
2) In a lot of cars, the mids will need to be flipped out of phase to help correct some midrange frequency phasing problems. In a 2-way system where one speaker plays midrange & midbass, running one of them out of phase will decrease the midbass impact. By running a 3-way, the midrange can be flipped out of phase and it has no effect on the midbass since it is being played by a separate driver.
3) The midrange and midbass frequencies in a 3-way may sound "cleaner" since each speaker has more of a limited bandwidth to play.
Disadvantages of a 3-way component set:
1) Tuning and aiming the speakers can be a much bigger pain the ass with 3-ways. Installation, tuning, phasing and aiming speakers will be much easier/quicker to perfect with 2-ways.
2) Room. It can be much more difficult find the room to fit all of the speakers. In some cars, kick panels are simply out of the question.
3) Money. 3-ways are normally considerably more expensive than 2-ways.
As you can see, 3-ways aren't necessarily better than 2-way. It's more of a personal preference. Some people would rather have a 3-way (for the advantages above), some people would rather have a 2-way (easier to tune, less room is occupied, etc.).
Active vs. Passive Crossovers
- This is a very very basic rundown of the differences in Active and Passive Crossovers.
Just some terms to know before reading:
Low pass filter
A low-pass filter is a filter that passes low frequencies well, but attenuates (or reduces) frequencies higher than the cutoff frequency.
High Pass filter
Exactly the same as a low pass filter but passes high frequencies.
Bandpass Filter
Is a combination of a low pass filter and high pass filter.
Octave
An octave is doubling the frequency. For example going from 50 Hz to 100 Hz is one octave. Going from 50 Hz to 200 Hz is two octaves, ect…
Crossover slope or roll off (reference
Basic Car Audio Electronics)
Crossover rolloff (or slope) describes the rate which the audio level increases/decreases per octave as the frequency increases/decreases. Usually a crossover slope is given as 6db/octave, 12db/octave, 18db/octave, 24db/octave, etc. If you want to see a visual of this here is a great picture:
Cyan = 6dB/octave
Red = 12dB/octave
Green = 18dB/octave
Violet = 24dB/octave
As you can see the different types of slopes and also notice that the crossover point is 1k.
Crossover Point
This is where frequency where the roll off or slopes starts to begin. As with the picture from above the crossover point is 1 kHz roll off begins at that frequency.
2 way crossovers
These crossover have two difference types of crossovers: Low pass filter and high pass filter.
3 way crossovers
These crossovers have three different sets of crossovers: Low pass filter, bandpass filter and high pass filter.
Active vs. Passive:
Passive Crossovers
Ok, passive crossover networks are unpowered crossovers (i.e. no external power source) that split the frequencies between the speakers in a component set. They send the higher frequencies to the tweeter and the lower frequencies to the mid(s). They accomplish this by using a combination of capacitors and coils to create certain crossover points and slopes. They are wired in line with the speakers, between the speakers and the amplifier. The amplifier's output is connected to the passive's input, then the mid(s) and tweeter are connected to the passive's output.
Now, when two speakers (a mid and a tweeter) are on a passive crossover, the mid and tweeter are not wired in series or parallel. Two 4ohm speakers (a mid and a tweet) do not make a 2ohm load or an 8ohm load. Two 4ohm speakers on a passive crossover network create a 4ohm load on the amplifier. Two 8ohm speakers on a passive xover create an 8ohm load. A 4ohm mid and 8ohm tweeter on a passive xover creates a 4ohm load for the mid's frequencies and an 8ohm load for the tweeter frequencies. Reason for this has to do with the fact that passive's are based on frequency distribution and not power distribution.
When you have components sets with passive crossovers, the power from the amp is not split between the speakers. If you have a 70 watt amp, then each speaker is going to receive 70 watts (assuming all speakers are the same impedance). If you are sending 70 watts @ 4ohm to the component set, and the mid is 4ohm and the tweeter is 8ohm, then the mid will receive 70 watts but the tweeter will only receive 35 watts.
This probably isn't a very technical explanation….but it gets the point across none-the-less Let's pretend theoretically that we are running a 70 watt @ 4ohm amp full range. That amp (theoretically) puts out 70 watts at all frequencies at 4ohms, correct?? Now, pretend that we are running that amp to a component set (with all 4ohm speakers) through a passive crossover with a crossover point of 3500hz. So, we are taking that full range signal from the amp and splitting up the frequencies between the mid and tweet at 3500hz. Now, since we are splitting the frequencies and nothing else, there is still going to be 70 watts worth of power at all frequencies below the crossover point and at all frequencies above the crossover point, just the same as there was before we split the signal (since it was putting out 70w at all frequencies).
Active crossovers
A key ingredient to an active crossover is that the filtering now occurs before amplification and now hence needs an external power source. This is a basic diagram of what it is:
Head Unit --> Crossover --> Amplifier --> Speakers
This is compared to a passive crossover in which the diagram is:
Head Unit --> Amplifier --> Passive Crossover --> Speakers.
Now basically what an active crossover gives you the ability to do is choose the crossover points and slopes for your speakers rather than a predetermined crossover slope and points determined by a passive crossover. This is a huge advantage because we all know that each car has different characteristics that can alter a speaker’s response. An active crossover can be used to make up for these discrepancies in a car. Here’s an example.
On my first set of components I bought the Rainbow SLCs that came with its own set of passive crossovers. According to their specification sheet the passive crossover is designed to have a crossover point of 4.5 kHz with a 12db/octave slope. I can’t change this at all to adapt to the car environment. But with my Eclipse 8455, which has a built in 3 way crossover I now can choose a crossover point of 4khz for the tweeters at 12db/oct and a bandpass filter for the mids at 3khz @ 12db/oct and 80khz @ 12db/oct. Not to mention I low passed my sub at 80 Hz @ 12db/oct.
I can change these points at any time I want. If I feel now that the mid performs better when low passed 2.5 kHz @ 6db/oct then I will change it to that slope and point. A huge advantage is that you can change these points and slopes to your liking instead of having some company telling the speakers where it sounds best.
Another thing about active crossovers is that each speaker will need its own independent channel so you can't go active by going off of a two channel amp. in order to run a two way active frontstage you must use a 4 channel amplifier or a combination of two 2 channel amps. Why? well if you have your mids and tweets running off a two channel and trying to go active then you can't cross the mids and tweets correctly. So its important to have a channel per speaker to run active.
One thing about going active is that it takes a ton of time to tune. If you are a type that likes to set it and forget it (using passive crossovers), going active isn’t for you. Going active takes a lot of time and effort because you are constantly changing crossover points and slopes to fit your needs and takes a lot of time to find that right combination. Not only that but it takes forever to get your staging and imaging exactly the way you want. Staging and imaging is a totally different animal as well.
Just a quick note on how to choose crossover points and slopes, just simply look at a speaker’s frequency response graph and it can give you a rough idea where to cross everything. Every manufacture has these graphs, so look at them and it can give you a rough idea on where to choose your points and slopes.
Source for Crossovers: Active vs. Passive: An attempt by me to explain - Car Audio Forum - CarAudio.com
Speaker/Crossover FAQ and Sound Quality Discussion
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