active cross over

[Kongen]

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?

[conscious]

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=

[MethMan]

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=

It does not work

[dooper]

Originally posted by MethMan
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=

It does not work

The links work fine if you stick http:// in front of them. That's using firefox 1.0.

dooper

[MethMan]

Oop, sorry.

[Kongen]

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?

[Septimus]

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.

[5th element]

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.

[Septimus]

description of actives

Marchand XO kits, take note of XM-9

theres plenty of info on the net about kits, etc.

[Kongen]

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...