[tmd]

I asked this many moons ago and got a one line reply from someone which I didn't understand so here goes again.
Why shouldn't I actively cross all three drivers? At present I am splitting between bass and the other two, so the mid and tweet are still on the speakers passive XO. I know it is supposed to be a no no to use three amps and drive them directly but why?
Thanks, Neil.

[doug s.]

this should answer your question, direct from brian cheney:
================
"You can replace the bass lowpass filter with an active crossover and separate bass amp. Find a crossover with 6 or 24 dB slopes, avoid 12 and 18 dB.

It is easy to disable the lowpass filter: you move one wire (black Monster Cable) off the coil and onto toggle switch lug 5.
Remove the woofer and stuffing to access.

You cannot use the electronic crossover for the highpass to the mid and treble, since there is some trickery (staggered filter poles) built in to tame some FR irregularities. The highpass is executed at the high quality level (AXON polyprops plus our own custom polyprops) so you need not worry.

Of course you can use our electronic crossover but at $950, it's only for purists. You'd do better upgrading the speakers.

Brian"
=============
the thread it came from is here:
http://www.harmonicdiscord.com/forums/viewtopic.php?t=1895&highlight=active+xover

w/brians' latest new tweeter upgrade, which changes the x-over point, perhaps no "trickery" now needed?  it may be worth investigating, if you're gonna upgrade the tweet...

hth,

doug s.

[tmd]

Thanks Doug but I am an inquisitive soul so it only goes part way to explaining it. Can someone explain the "there is some trickery (staggered filter poles) built in to tame some FR irregularities. The highpass is executed at the high quality level (AXON polyprops plus our own custom polyprops) so you need not worry." part to me please?
I would really like to understand it. If I am stubborn and go ahead anyway, what will problems will I run into?
Thanks, Neil

[doug s.]

hi neil,

i' sure brian could explain it better than me, but i imagine it's not a simple straight crossover.  probably, differing slopes on the hi-pass & low pass, & different frequencies where they kick in...

for example, a crossovers' super-tweeter high pass may be a straight 24db/octave, cross, at, say 10khz.  the tweeters' low pass may be 6db/octave at, say, 8khz, then 24db/octave at 9.5khz.  

it's unlikely the vmps' crossovers are anything like the above examples, but it's something like that, not just a simple 24db/octavre cross, at, for example, 200hz, as brian suggests, forbas/midrange cross...

hth,

doug s.

[tmd]

Thanks again Doug for your reply. That helps.
Brian, any chance of you chiming in? What is FR?

[JohnR]

I'm not entirely sure if I'm answering the right question... but I do believe that VMPS uses a series crossover for the mid-tweet crossover which means that "passive biamping" there can't be done.

[JohnR]

Oh, and now I see that the title of the thread says "active crossovers"

Are you using an active crossover between the woofer and mid-tweet now? Or the inbuilt passive crossovers? Your questions seem to indicate the latter.

FR = frequency response.

[tmd]

John,
I am using the active crossover to feed two amps, one for the woofer and the other for the mid/tweet. I would've tried to split the mid and tweet up before but I was told it was a nono. I now want to know why as I am contemplating giving it a try. I will have to come up with another interconnect and go inside the speakers so if it is a disaster waiting to happen, I won't do it.
Thanks, Neil.

[tmd]

Brian,
Could you please help me out here? I am in the speakers at the moment anyway, doing the 'upgrade' to the ribbon mids so I could change the wiring to try out the active amping of all three if it isn't a complete disaster waiting to happen.
Please let me know what I would hear or why it shouldn't be done.
Thanks, Neil.