I'm wondering what are the pros and cons for choosing a 4th order active crossover? i've been recommended a using 3 way crossover with tweeter having a 3rd order hp (4.7khz), mid using a 1st order lp (4.7khz) and 1st order hp (250 hz), and finally for bass a 2nd order lp(250 hz) when i first wanted to design a passive crossover. I guess this would be possible to do as an active crossover would i end up with a better result with this than with the 4th order 3-way?
As I understand it active crossovers have many benefits, including:
- significant increased damping factor which is particularly noticable in the bass range by eliminating the inductor in series with the woofer
- ability to align phase
Here's some threads that go into this concept in detail
soundandvisionmag.com/idealbb/view.asp?topicID=37235&forumID=40&catID=1&search=1&searchstring=
soundandvisionmag.com/idealbb/view.asp?topicID=27324&forumID=40&catID=1&search=1&searchstring=
- significant increased damping factor which is particularly noticable in the bass range by eliminating the inductor in series with the woofer
- ability to align phase
Here's some threads that go into this concept in detail
soundandvisionmag.com/idealbb/view.asp?topicID=37235&forumID=40&catID=1&search=1&searchstring=
soundandvisionmag.com/idealbb/view.asp?topicID=27324&forumID=40&catID=1&search=1&searchstring=
Perhaps i'm not clear in my question:
Is it better to go with the 3 way all 4th order crossover, than to build a 3 way crossover which has the same slopes as what the passive crossover has (would have)?
is the reason for not building 4th order passive x-overs only the fact that you would get very complex, expensive and high-losses (i guess) in the filter?
Is it better to go with the 3 way all 4th order crossover, than to build a 3 way crossover which has the same slopes as what the passive crossover has (would have)?
is the reason for not building 4th order passive x-overs only the fact that you would get very complex, expensive and high-losses (i guess) in the filter?
Thats probably the biggest reason you don't see high order passive crossovers, the second being that with active XO you would then amplify each driver directly, instead of having one channel of an amp looking at a very complicated load covering the entire audible freq range.
Also, the flexibility of active XO's can't be ignored either. When you can change crossover points with plug and play modules, adjust the damping at the XO point, and even have a little EQ in there to help balance out a driver that needs a help, the prospect of designing your own speakers becomes so much more attractive. ie: you don't need to be joe d'appolitto himself to make sure you get the XO right, you can just tweak it afterwards.
IMHO, active XO's are the only real solution to the XO issue.
Pro: easier to amplify each driver individually
easier load on the amps/don't have to use as much power
more flexible than passives
makes speaker design options virtually limitless
Con: Cost of active components and amps.
some argue for having the least active components as possible in the signal chain.
Also, the flexibility of active XO's can't be ignored either. When you can change crossover points with plug and play modules, adjust the damping at the XO point, and even have a little EQ in there to help balance out a driver that needs a help, the prospect of designing your own speakers becomes so much more attractive. ie: you don't need to be joe d'appolitto himself to make sure you get the XO right, you can just tweak it afterwards.
IMHO, active XO's are the only real solution to the XO issue.
Pro: easier to amplify each driver individually
easier load on the amps/don't have to use as much power
more flexible than passives
makes speaker design options virtually limitless
Con: Cost of active components and amps.
some argue for having the least active components as possible in the signal chain.
It depends on the drivers and what you are aiming for really with the filters you will use.
Take a standard tweeter, all of them are sealed back which means their final roll off is 12dB per octave. This means that depending on what xover frequency you are after you can get a 24dB roll off using 2nd or 3rd order slopes so a 4th order electrical is not required.
There are very few situations where you actually require a full on 4th order electrical xover to achieve a 4th order acoustic slope. These would be when you are using wideband drivers. For instance using a scan speak d2905/97 tweeter, these reach down flat to roughly 500hz this means that if you want to xover at 4000hz its 3 octaves above the cut off, here you might need a 4th order electrical to achieve 4th order acoustic.
Take a standard tweeter, all of them are sealed back which means their final roll off is 12dB per octave. This means that depending on what xover frequency you are after you can get a 24dB roll off using 2nd or 3rd order slopes so a 4th order electrical is not required.
There are very few situations where you actually require a full on 4th order electrical xover to achieve a 4th order acoustic slope. These would be when you are using wideband drivers. For instance using a scan speak d2905/97 tweeter, these reach down flat to roughly 500hz this means that if you want to xover at 4000hz its 3 octaves above the cut off, here you might need a 4th order electrical to achieve 4th order acoustic.
description of actives
Marchand XO kits, take note of XM-9
theres plenty of info on the net about kits, etc.
Marchand XO kits, take note of XM-9
theres plenty of info on the net about kits, etc.
I see the point on the amps - that it of course becomes much more expensive, but at the same time a lower output is necessary for a given soundpressure when comparing with a passive x-over since there are practically no losses from power amp to speaker - and this with addition of less complex load - a much lower powered amp would do (at least for mid & tweeter, perhaps some simple lowpower class a - i think i've read a PASSage 
about such an amp on this very website) an thus perhaps cheaper...?
I'm in fact going to use the scanspeak 9700 tweeter and an audiotechnology flexunit 4". For bass i'm going to use a scanspeak 21-8555-01. The crossover i mention in the first post is upon recommendation from skaaning himself (the x-over points and slopes for mid/tweeter). its quite high x-over freq for the 9700 but i'm willing to try it...
about such an amp on this very website) an thus perhaps cheaper...?I'm in fact going to use the scanspeak 9700 tweeter and an audiotechnology flexunit 4". For bass i'm going to use a scanspeak 21-8555-01. The crossover i mention in the first post is upon recommendation from skaaning himself (the x-over points and slopes for mid/tweeter). its quite high x-over freq for the 9700 but i'm willing to try it...
You may not need as much power to reach the same sound pressure between active and passive xovers, but remember watts = sound pressure.
You still need the same number of watts to reach a certain lvl.
A 30 watt amp will only give you 15dB more output from your speaker it cannot give any more. Which if you take the scan driver you end up with about 104dB max soundpressure.
You still need the same number of watts to reach a certain lvl.
A 30 watt amp will only give you 15dB more output from your speaker it cannot give any more. Which if you take the scan driver you end up with about 104dB max soundpressure.
Yeah true but i don't think i need that kind of levels. But more importantly the quality must be better without a passive x-over - at least when considering how much of the amp's "quality" goes into the unit and how much is (or isn't) lost in x-over components. Then theres the quality of the active x-over...
But isn't it true that without a passive x-over you can use the full power of you amp, whereas with the passive x-over some power will be lost in the components, and how about compression? wont there always be less compression with an active x-over compared to a passive? And still some amps will sound less convincing playing into complex/difficult loads?
The only thing i'm still not sure off is whether or not a 4th order/3-way x-over is better than lower/mixed order/3-way x-over (both active)....
By the way thank you all for answering my questions...
But isn't it true that without a passive x-over you can use the full power of you amp, whereas with the passive x-over some power will be lost in the components, and how about compression? wont there always be less compression with an active x-over compared to a passive? And still some amps will sound less convincing playing into complex/difficult loads?
The only thing i'm still not sure off is whether or not a 4th order/3-way x-over is better than lower/mixed order/3-way x-over (both active)....
By the way thank you all for answering my questions...
The only thing i'm still not sure off is whether or not a 4th order/3-way x-over is better than lower/mixed order/3-way x-over (both active)....
.. depends on drivers you use. If you have drivers which are both flat in amplitude +/- 2 octaves around the crossover freq., there is no reason to use different slopes. But this is not so obvious. Irregularities in drivers responses are reason for using different slopes. Some phase originated problems also can occur.
According to Septimus wrote take also note of XM-1 which is 1st-4th Butterworth state variable filter. Misfortunatelly the PCB is very simple and do not offer even attenuation on board. Also baffle step compensation, attenuation of possible resonant modes of drivers or shelving filters etc. would be desirable and must be made out board.
.. depends on drivers you use. If you have drivers which are both flat in amplitude +/- 2 octaves around the crossover freq., there is no reason to use different slopes. But this is not so obvious. Irregularities in drivers responses are reason for using different slopes. Some phase originated problems also can occur.
According to Septimus wrote take also note of XM-1 which is 1st-4th Butterworth state variable filter. Misfortunatelly the PCB is very simple and do not offer even attenuation on board. Also baffle step compensation, attenuation of possible resonant modes of drivers or shelving filters etc. would be desirable and must be made out board.
It is a little more complicated. First of all SPL is not proportional to power (i.e. Watts) but to voltage. Therefore 6dB more voltage = double voltage = double power = quadruple power.
If you now spread a wideband audio signal over several amps you can in fact achieve higher SPLs with a specific amount of total audio power than you would achieve with passive crossover and a single amp.
Regards
Charles
Why? Can you explain?
I've read this before in some thread which I can't find now. There was written something like: the system actively crossed into 3 bands with 200+100+50 watt amps give you capability as the passively crossed 500 watt single amp system, say. Is there any other reason than resistance loss in passive xo?
My experience so far with active Xo
I'm in the process of replacing the passive crossovers in my Energy speakers with active Marchands. I started out with a pair of Marchand XM1's, and then I bought an XM44. This is an experiment in process, so I don't have conclusive answers yet.
My speakers originally were 2-way, with a second-order slope for the woofer and third-order for the tweeter, crossing at 1.5kHz. I tried L-R 4th-order at 1.5, 2.0 and 2.4kHz. Of these, the 2.0 sounded least compromised, but none sounded right. I suspect this is due to the following:
- the original passive crossovers included BSC and probably some driver resonance traps.
- the slopes on my drivers are not flat in these crossover ranges, which resulted in slopes greater than 4th-order.
- there is a lot of processing going on with a 24dB L-R. Less aggressive slopes may be better, even with a flat driver response.
I just bought some new modules from Marchand, which should mimic the slopes on the original Xo (second-order slope for the woofer and third-order for the tweeter, crossing at 1.5kHz). I'll compare the new modules with the original Xo and see what I need to do next (BSC etc).
Originally I thought I could just throw an active Xo into the circuit and I'd be done with it. That's what I was led to believe by various sources on the internet. The fact is, you still need to do a design with an active Xo, to accomodate your particular drivers, your cabinets and your tastes. The nice thing about a good active Xo is that changing the design is simple, it just takes a little more money.
Dan
I'm in the process of replacing the passive crossovers in my Energy speakers with active Marchands. I started out with a pair of Marchand XM1's, and then I bought an XM44. This is an experiment in process, so I don't have conclusive answers yet.
My speakers originally were 2-way, with a second-order slope for the woofer and third-order for the tweeter, crossing at 1.5kHz. I tried L-R 4th-order at 1.5, 2.0 and 2.4kHz. Of these, the 2.0 sounded least compromised, but none sounded right. I suspect this is due to the following:
- the original passive crossovers included BSC and probably some driver resonance traps.
- the slopes on my drivers are not flat in these crossover ranges, which resulted in slopes greater than 4th-order.
- there is a lot of processing going on with a 24dB L-R. Less aggressive slopes may be better, even with a flat driver response.
I just bought some new modules from Marchand, which should mimic the slopes on the original Xo (second-order slope for the woofer and third-order for the tweeter, crossing at 1.5kHz). I'll compare the new modules with the original Xo and see what I need to do next (BSC etc).
Originally I thought I could just throw an active Xo into the circuit and I'd be done with it. That's what I was led to believe by various sources on the internet. The fact is, you still need to do a design with an active Xo, to accomodate your particular drivers, your cabinets and your tastes. The nice thing about a good active Xo is that changing the design is simple, it just takes a little more money.
Dan
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