GhosT
05-27-2007, 01:38 PM
Posted by
Phase_One
Active Crossovers vs Passive Crossovers
Below will explain active setups vs passive setups.
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 www.bcae1.com)
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
http://i14.tinypic.com/4ue9l4y.gif
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.
PASSIVE CROSSOVERS
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
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.
Phase_One
Active Crossovers vs Passive Crossovers
Below will explain active setups vs passive setups.
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 www.bcae1.com)
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
http://i14.tinypic.com/4ue9l4y.gif
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.
PASSIVE CROSSOVERS
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
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.