Active crossovers - is it this simple? - diyAudio
Go Back   Home > Forums > Loudspeakers > Multi-Way

Multi-Way Conventional loudspeakers with crossovers

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 23rd September 2002, 11:03 PM   #1
diyAudio Member
 
annex666's Avatar
 
Join Date: Jul 2002
Location: England
Default Active crossovers - is it this simple?

I have a seemingly simple question to ask about going active.

If I can open my speakers and look at the crossover (and therefore find values for it's components) and I know the crossover points, can I not just make a miniature (low power) version of the same crossover and place it between my pre-amp and quad mono amps?

I'm guessing this would keep the same frequency dispersion and inherent phase shifts implemented by the original crossover the same?

Is this always a good thing?

Is this a "safe" way of doing things - i.e. not driving the speakers with signals they weren't originaly intended for, as would possibly be the case if I were to make my own crossover points.

Also to (slightly) complicate matters my speakers are 2.5 way B&W603-S3's which use a bass driver (I'm guessing in parallel) with the mid/bass for low frequencies.

Has anyone gone active with these speakers?

Any responce would be good, cheers.
__________________
...if it ain't broke don't fix it - make it BETTER!
  Reply With Quote
Old 23rd September 2002, 11:39 PM   #2
diyAudio Member
 
Join Date: Feb 2001
Location: Mars
The component values are based on the speaker impedance.
Using the same components values will not match
the input impedance of the amplifier.

Save yourself the headache and make something
like a linkwitz riley active crossover, 24db/octave.
Make it so you can replace the frequency modules
so you can experiment with or use ganged potentiometers
for variable adjustment. Use some sockets so
you can try various op-amps that meet your
taste in music.
  Reply With Quote
Old 23rd September 2002, 11:45 PM   #3
diyAudio Member
 
Holger Barske's Avatar
 
Join Date: Jan 2001
Location: Ruhrgebiet
I am afraid it is not that simple.
The passive crossover construction is a more or less complex circuit that is matched with the impedance curve of the drivers.
Your power amp input won't have that characteristic impedance - neither concerning ampltude, nor phase. It will most probably look like a simple resistor of a rather high value (compared to the drivers).
The electrical environment is completely different, so you can't directly do a tranfer from the passive filters.
---
Holger

p.s.: ok, mey reply was a little too slow...
  Reply With Quote
Old 24th September 2002, 11:11 AM   #4
diyAudio Member
 
annex666's Avatar
 
Join Date: Jul 2002
Location: England
There's me not thinking about the obvious!

I totaly forgot about impedance matching of the crossover - I was just thinking about it's act as a frequency filter!

I was indeed thinking about a Linkwitz type filter (an ESP variant) as the phase is unchanged through the filter inherantly due to it's design.

If I open my speakers tonight (
) and check out the crossover and maybe get a schematic on here could you guys advise me more on implementation?

I'm thinking it could be awkward due to the 2.5 way design - especially as this is seen more often in manufactured speakers rather than DIY.

Maybe the best option for me is to use the original crossover mid/high pass filter for the tweeter / kevlar midrange and isolate the bass to the aluminium "mushroom" bass driverthrough the active filter.

Cheers again for the responses guys

One last thing now I think of it - will the amp(s) (ESP P3A X2) be (for want of a better word) "upset" by the removal of the impedance-correction network (if there is one present)?
__________________
...if it ain't broke don't fix it - make it BETTER!
  Reply With Quote
Old 24th September 2002, 03:09 PM   #5
diyAudio Member
 
MRehorst's Avatar
 
Join Date: May 2002
One more consideration:
A passive, high-level crossover located in the speaker usually provides some protection to the relatively delicate tweeter and midrange drivers. When you go to an active crossover, your amplifier is usually connected directly to the drivers. A small malfunction, DC offset, or even just a turn-on thump from one of your amps can blow a tweeter to pieces. You will have to be careful to protect the drivers against such things.

MR
  Reply With Quote
Old 24th September 2002, 04:13 PM   #6
diyAudio Member
 
Join Date: Feb 2001
Location: Mars
I'm paranoid when using active systems, I like to insert
a fuse on the tweeter for sure, perhaps the midrange
too. I have to experiment to get the right value,
typically I start with 3/4 amp and do some tests,
either increase or decrease the value to get the fuse
to blow just beyond the sweet spot. The sweet spot is when you "feel" like the tweeter is just starting to "stress".

cheap fuse = piece of mind
  Reply With Quote
Old 24th September 2002, 08:43 PM   #7
diyAudio Member
 
annex666's Avatar
 
Join Date: Jul 2002
Location: England
Thanks again for the advice all, but unfortunately I can't get to my passive crossover anyway after having a look today

One of the reasons I was thinking of keeping the high-pass circuit was because of the series cap to protect the tweeter although I guess the whole plan has gone out the window now (due to the inability to "adapt" the crossover) so my dreams of perfectly (well relatively at least) phase coherent speakers goes up in smoke.

Thanks for all the posts guys - maybe when I get round to it (and I mean in quite a few years when I finish my degree and get some serious ) I'll build my own hybrid speakers and complete custom home brew setup, but until then...


..cheers again for the posts
__________________
...if it ain't broke don't fix it - make it BETTER!
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Active Crossovers zenmasterbrian Subwoofers 77 21st September 2006 06:14 PM
active crossovers, please help herbd2 Multi-Way 2 23rd February 2005 04:21 PM
How are active crossovers so simple/clean? tcpip Multi-Way 56 8th February 2004 09:54 AM
Active crossovers Ilianh Solid State 6 5th November 2002 04:13 AM


New To Site? Need Help?

All times are GMT. The time now is 07:55 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2