Info on active/passive sticky?

[LX2 10+ year member]

Quote:

Originally Posted by squeak9798

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).

Im still new here and I find a lot of this info informative.

There is a lot of info above pertaining to impendances and components I

was not aware of.

But there is still something I dont get and it has to do with the

power distribution and how its handled by the passive.

My understanding is that if you are sending 70 w @ 4ohm into a passive

then TOTAL power produced cannot exceed 70W rms.

In the explanation by squeak9798 he states that if all speakers are the

same impendance then EACH speaker will recieve 70 w which means

the amp is now producing 140W or the passive is amplifying the power itself.

This doesnt make sense.

Im not arguing that its possible. But up untill anyone includes other variables that

explain this I cant except this info. Or is there something I am missing?

If the impendance or the amp is 4 ohm (rate 70 w @ 4 ohms)and both speakers are 4 ohms from the passive how can each speaker recieve 70watts - total 140w?

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[BigProof 10+ year member]

read it again!

 

[T3mpest 10+ year member]

Quote:Originally Posted by squeak9798

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).

Im still new here and I find a lot of this info informative.

There is a lot of info above pertaining to impendances and components I

was not aware of.

But there is still something I dont get and it has to do with the

power distribution and how its handled by the passive.

My understanding is that if you are sending 70 w @ 4ohm into a passive

then TOTAL power produced cannot exceed 70W rms.

In the explanation by squeak9798 he states that if all speakers are the

same impendance then EACH speaker will recieve 70 w which means

the amp is now producing 140W or the passive is amplifying the power itself.

This doesnt make sense.

Im not arguing that its possible. But up untill anyone includes other variables that

explain this I cant except this info. Or is there something I am missing?

If the impendance or the amp is 4 ohm (rate 70 w @ 4 ohms)and both speakers are 4 ohms from the passive how can each speaker recieve 70watts - total 140w?

Dont' believe ^, this is somewhat confusing I'll do my best. First things first, the power will NOT be 70 watts to each speaker. Let's look at it this way, we have a amp that can put out 100 watts at all frequencies 20-20k. Let's say the tweet is 20% effecient and the mid is 10%. How much power would we lose to heat using what I believe squeek is saying? Hmm, 90% of 100 is 90, 80% is 80. So 170 watts of power... How can we start with a 100 watt signal and lose 170 watts to heat? To get the same SPL across a wider bandwidth does require more power than getting it out of a smaller range. This is part of why we crossover speakers, while it wont' actually improve the thermal power handling, they'll get louder off of less power.

It's a very fine line. A speaker can put out 60 watts of power at all frequencies at the same time. However, this is within 1 channel, once you split the frequenices you split power as well. it put out 60 watts with total components being 20-20k. Once you ask it to split frequencies across the drivers, your losing power the power within each band. The power within each band depends on how big of a band you ask the speaker to play. At 1 frequency the power in that one freuqency is 60 watts. If you ask it to go fullrange, sure it's still 60 watts, divided within all the frequencies. That' will be no different, until you ask it to split off by frequency. Essentially the more frequencies within a waveform, the less power that can be contained within each individual frequency that makes it up. So when you split them up, the power splits accordingly. This is part of why mids are more "power hungry" than tweeters. To get an even spread in terms of crossover power, you'd need to a crossover to be set a 350hz, meaning the energy to produce 85 decibels of 20-350=351-20,000. Since most crossovers are closer to 2-3k, a very large portion of the engery is going to the woofer.

I can't explain it much better than that, but I think my last paragraph makes sense if you think about it. if anyone else has question I may be able to elaborate, if you can let me know what's holding you up.

 

[dleccord 5,000+ posts]

tempest, that's very interesting man. never thought of it like that.

 

[LX2 10+ year member]

Dont' believe ^, this is somewhat confusing I'll do my best. First things first, the power will NOT be 70 watts to each speaker. Let's look at it this way, we have a amp that can put out 100 watts at all frequencies 20-20k. Let's say the tweet is 20% effecient and the mid is 10%. How much power would we lose to heat using what I believe squeek is saying? Hmm, 90% of 100 is 90, 80% is 80. So 170 watts of power... How can we start with a 100 watt signal and lose 170 watts to heat? To get the same SPL across a wider bandwidth does require more power than getting it out of a smaller range. This is part of why we crossover speakers, while it wont' actually improve the thermal power handling, they'll get louder off of less power.
It's a very fine line. A speaker can put out 60 watts of power at all frequencies at the same time. However, this is within 1 channel, once you split the frequenices you split power as well. it put out 60 watts with total components being 20-20k. Once you ask it to split frequencies across the drivers, your losing power the power within each band. The power within each band depends on how big of a band you ask the speaker to play. At 1 frequency the power in that one freuqency is 60 watts. If you ask it to go fullrange, sure it's still 60 watts, divided within all the frequencies. That' will be no different, until you ask it to split off by frequency. Essentially the more frequencies within a waveform, the less power that can be contained within each individual frequency that makes it up. So when you split them up, the power splits accordingly. This is part of why mids are more "power hungry" than tweeters. To get an even spread in terms of crossover power, you'd need to a crossover to be set a 350hz, meaning the energy to produce 85 decibels of 20-350=351-20,000. Since most crossovers are closer to 2-3k, a very large portion of the engery is going to the woofer.

I can't explain it much better than that, but I think my last paragraph makes sense if you think about it. if anyone else has question I may be able to elaborate, if you can let me know what's holding you up.

Thank you for taking time to answer my question.

I kinda get impatient with this forum coz replies always take forever.

But then I remembered it must be the different time zones.

Im in South Africa

 

[T3mpest 10+ year member]

I answered this 2 days ago //content.invisioncic.com/y282845/emoticons/fyi.gif.9f1f679348da7204ce960cfc74bca8e0.gif