[wgscott]

If I want to bi-amp, and use an active crossover, such that everything below 150 Hz goes to the bottom of the speaker (the woofer) and everything above goes to the midrange and tweeter.

Why, then, do I have to disconnect the passive crossover, if the upper and lower parts have no bridge between their sets of binding posts?  In other words, if the signal going to the bottom (for example) only has information below 150 Hz, wouldn't the passive crossover simply pass that through unaltered?

I think I am missing something conceptually.

[JohnR]

The passive crossovers will still be having an effect. You would have to provide more information for a more meaningful answer i.e. what speakers and current crossover point.
 

[wgscott]

Sorry. 

The speakers are Bowers and Wilkins CM7.  The passive crossover between the bass and the mid/treble currently in these speakers is 150 Hz, and if I get an active crossover, I assume I should get one with the same crossover frequency. I haven't gotten that far.  Currently, I have a passive bi-amp system (two Class D audio 254 amps).

I'm sure I am being too simple-minded, but if the active crossover has the job of sending everything above 150 Hz to the higher-frequency midrange and treble, and everything at or below 150 Hz to the bass, what would the passive crossover do to each of these signals, since they have already been split?  In other words, if there is nothing left for them to process, why wouldn't they simply pass the signal, relatively unscathed?

[Pez]

First i want to say good on you for considering going active. Think of it this way, passive components are lossy. They damage the signal just by being in the signal path. They cause phase smear, power loss, and other nastiness by virtue of their design. It is because they are passive that this is the case. It is the physical removal of these components that is beneficial. Simply adding an active crossover in line with the passive parts would be bad because both the active crossover AND the passive crossover would be in the signal path and god only knows what they are doing together. My guess is double attenuation which would probably sound really awful.

Any way, yes you MUST get rid of the passive parts. That is the point of active. Taking those lossy components out of the post amplification signal path.

[wgscott]

A phase shift I guess is something I hadn't considered...

I guess my inhibition is not wanting to damage my speakers (or even knowing how to go about doing the surgery).  I assume I have to take the speaker cones off somehow, and then go in and wire the posts directly to the speaker cones, in the case of the bass (and what of the mid-range and treble)?

[Pez]

That is exactly what needs to be done. It's relatively minor surgery and usually takes a screwdriver or alan wrench (depending on which one the manufacturer used to attach the drivers) some wire cutters, maybe some wire of your choosing and a soldering iron. There is just one other thing I would suggest and that is to put a DC blocking capacitor inline with the tweeter so there is never any risk of blowing it when your amp is turned on and off. I would suggest using something like a 5µF / 600VDC sonicap from here http://www.soniccraft.com/sonicaps.htm . Then once you are assembled you should be good to go with the speakers. Then you'll obviously just need to active xover. Did you have one in mind?

[jtwrace]

I think it's great that you're thinking about doing this.  You do realize that this is a huge undertaking that will require many hours of testing and measurements.  Right?

Not to discourage you but it does take time and a lot of patience. 

[chester_audio]

Then there is the question of what slope to use. IIRC, B&W uses rather simple crossovers, 1st or 2nd order with the drivers they use. Maybe send a note to their tech support and get their recommendations.

edit: You're going to need a test mic and RTA software to help dial things in.

[Pez]

Agreed, these are very important steps to getting active done right. Most folks are using either a DCX, DEQX, or the newest craze the MiniDSPs. Do some research here and figure out which one is right for you. I personally use a modded DCX and it does wonderful things for me.

Just to throw it out there an even bigger improvement would be to Tri-amp those CM7s! 

[PRELUDE]

1.It is nice that you want to go active and I wish I could see posts like this every day.
2.Are you patient? No patience no active and if you think I am discouraging you, you are wrong but you should know this stuff before take the next step.
3.Do you have any crossover in mind that you are going to use?
Any way, you are not doing any thing to your speakers and you do not have to take the passive crossover out the box.Just disconnect an run the wires out from drivers and don't forget that B&W CM7 is three-way and to go active you will need another power amp with same output gain like the other two that you are using right now.Think about a mic and a software for test and measurements.
I would say go for it and if are not sure about any thing just post it here and everybody would help you.
Good luck.

[Tyson]

Agreed with everyone here - active has the potential to sound much, much better than passive, but you do need a good mic and mic-preamp and measurement software.  I like the Earthworks m23 mic, the M-Audio MobilePre, and HOLM Impulse software, which is free. 

[wgscott]

I just thought it was a matter of putting in the active and (now) taking out the passive.  So I guess I am being a wee bit naive.

Tom, the Class D audio guy, suggested I have a look at these:
http://www.marchandelec.com/

I also came across this:
http://www.audio-kits.com/catalog/item/4071180/3884480.htm

Finally, a few of you guys had recommended miniDSP modules, but I wondered about the idea of going from (DAC-generated) analog input, back to digital, and then back to analog again, in terms of degrading the sound quality.

[jtwrace]

I just thought it was a matter of putting in the active and (now) taking out the passive. 

So I guess I am being a wee bit naive.

In a HUGE way.

[wgscott]

So what do you adjust?  The relative gain for each amp?  The crossover frequency (it sounds like you have to specify before you buy), slope? 

[Pez]

I wouldn't get the Marchand, it doesn't do $hit other than attenuate. Get something that will also help you notch out bass peaks and speaker anomalies.

As the other Jason crudely put it ( ) , yes you need to be educated a bit it looks like in order to make this a reality. But once you are this is a journey well worth it.

-The other Jason

[Pez]

So what do you adjust?  The relative gain for each amp?  The crossover frequency (it sounds like you have to specify before you buy), slope?

Yes yes and yes.

And no you don't have to specify anything, just have a rough idea of what xover point you need and dial it in (depending on your x-over)

Seriously though you need to do some serious reading.

[YoungDave]

Actually, I do not agree that you need to be an expert to go active.  I started out by discarding the 3-way passive crossovers in my VMPS speakers for a simple 3-way active crossover from one of Dr David White's kits (White Noise Audio, now defunct).  Same crossover points, slightly steeper slope, very straightforward.  Immediate, massive improvement.

Being an audiophle & unable to quit fooling around, I went onwards to to DEQX and achieved even better results, but the original changeover to active triamp with a "dumb" active crossover was the single biggest improvement I have ever made to my system.  You can use the same parameters as now and triampng will still be an improvement, and you could quite easily quit right there without going the next step of measurement mics, etc etc.

[JDUBS]

How does (did) this setup compensate for differences in amplifier gain?

In all honesty, I think the DEQX, while not cheap, offers the easiest way of triamping.  Its way more powerful that the DCX and makes the process of measuring, crossover management, and curve adjustment pretty dang straightforward...relatively speaking. 

-Jim

Actually, I do not agree that you need to be an expert to go active.  I started out by discarding the 3-way passive crossovers in my VMPS speakers for a simple 3-way active crossover from one of Dr David White's kits (White Noise Audio, now defunct).  Same crossover points, slightly steeper slope, very straightforward.  Immediate, massive improvement.

Being an audiophle & unable to quit fooling around, I went onwards to to DEQX and achieved even better results, but the original changeover to active triamp with a "dumb" active crossover was the single biggest improvement I have ever made to my system.  You can use the same parameters as now and triampng will still be an improvement, and you could quite easily quit right there without going the next step of measurement mics, etc etc.

[wgscott]

Seriously though you need to do some serious reading.

Any suggested starting points?  My random internet googling, etc., only tipped me off to the idea that to realize any significant improvement from bi-amping, I would need to do this, but there is very little I was able to find on how...

This isn't something I am likely to rush into, but wouldn't mind doing at some point.

I do want to clarify one thing, though.  Both amps are identical (Class D audio 254) and are vertical (i.e., one amp board for the left speaker, the other for the right). I was under the impression that this was the "safest" way to do bi-amping in terms of matching gain, phase, etc.

[jtwrace]

Actually, I do not agree that you need to be an expert to go active.

I haven't seen anyone say this.