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Re: Bi-amp crossover question/Rane AC-22 with 3.6's

Posted by andyr (M) on March 9, 2007 at 18:54:25

In Reply to: Bi-amp crossover question/Rane AC-22 with 3.6's posted by bfrank53 on March 9, 2007 at 13:46:11:

Several points:

* The 3.6 is such a wonderful speaker that it's a shame to drive it with second-class electronics. I have no idea what the Rane sounds like but - as a piece of pro gear - it may not deliver as good a sound as, say, a Marchand active XO. You can buy Marchands in either kit form or fully made up ... and either 2-way or 3-way.

* Secondly, having to make use of cable adapters *will* degrade the sound ... but possibly only a little (depending on their construction and materials).

* Re. what slopes to use - the 3.6 passive external XO (bass lowpass/mid highpass) is:
- 24dB bass LP
- 6dB mid HP.

However, IIIas and 3.3s/3.5s have an 18dB bass LP slope, so with an active XO replacing the passive, I suggest an 18dB slope would work just as well. If Al Sekela is to be believed, the reason the 3.6 has a 24dB LP slope is because this puts a cap across the driver, which damps out-of-band resonances (which makes a lotta sense! :-)) ). This is a good enhancement (on the 3.5) for a passive setup but in an active setup, the amp itself damps out-of-band resonances, so the "advantage" of going to 24dB is moot.

The frequency which the LP & HP slopes cross at (ie. the "crossover frequency") is almost exactly 200Hz. However, modelling this in lspCAD shows a pronounced hump at this frequency - which I suggest could be improved upon, with an active XO.

Does the Rane allow you to have asymmetric slopes ... eg. 18dB on the bass and 6 or 12dB on the treble?

If you are limited to 24dB slopes then choose 200Hz. In this case, you need to reverse the mid/treble connections, as the bass and mid drivers need to be in phase.

If you can have asymmetric slopes then I would suggest you try:
* 18dB LP/6dB HP or 18dB LP/12dB HP (and keep the drivers connected the way they are with the passive XO).
* I would experiment with setting the -3dB points of the bass LP and mid HP filters apart slightly, to tame the hump at 200Hz. First try 18dB @ 200Hz for the bass & 6 dB @ 250Hz for the treble - and go on from there! :-))

Regards,

Andy

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