Crossover and bi-amping

[Camillo]

I've built some Otops and when bi-amping it is suggested to keep the LP-section crossover. I use a dbx active crossover, do i use the internal crossover along with the passive one? Or just fullrange signal for the low part and active crossover for the hf section with 20 uf cap?

Also.
A 20uf CAP for dc-protection when bi-amped, how crucial is the value?

Thanks

[RunTheOtherWay]

I don't know what the OmniTop 15 is like so I don't have enough info to quite address your question. Sounds like the "internal" (internal to the cab?) crossover *is* the passive one, so I don't understand what you're asking there. I also don't know if your dBx active crossover is three-way or two-way. Anyway, I'm pretty sure in no case would you want to send fullrange signal to "the low part," that much I know.

Were it me, if the OmniTop is a two-way and if I were to make it biamp-ready, I'd fix it where the high and low inputs bypass the internal passive crossover altogether and use an active crossover ahead of the power amp(s) with a cross frequency about where the internal crossover's is (my Crown XLS1000 amp will actually let you set up a crossover between the two channels, which is pretty darn sweet but of course that means one amp per cab). Pretty much all the decent power amps in operation today have DC protection built in, by which I mean DC gets detected and the speakers are cut out, so I wouldn't worry about a cap for DC protection but if you do use one, make sure it's an unpolarized (aka bipolar) cap.

[Camillo]

I don't know what the OmniTop 15 is like so I don't have enough info to quite address your question..

The OmniTop15 is a two-way. I'am currently bi-amping it, using a dbx as a crossover for both lf and hf. In The plans you can choose to build filters for it and that when bi-amping It's useful to still make the low pass filter for increased response in the mid area. I believe that then i shouldn't use an active crossover for the lf-part aswell and that is my question.
(i guess the dbx lets me increased the sensitivity in the mid-area with the eq but no idea if that is the same as the passive filter does when lowering the impedance in the mid-area to increase sensitivity there)

Since i will use the active crossover in the hf-section it is recommended to place a cap in series with the tweeters for dc protection. As a first order filter, that cap would also work as a crossover from about 450hz somewhere, which is lower than where the active filter will kick in, so i wonder if the value of that cap is crucial or within, say 10% of the recommended. Since i find a cap this is 2 uf larger i wonder what range to think of when using only for dc protection in general, without it interfering with the active crossover.

If I build both the low pass and high pass filter, i guess i want to disconnect them(or at least the hf) when bi amping (with active crossover in the hf - section and passive in the lf)

[Bruce Weldy]

You haven't said what kind of high frequency section you are using. Melded Array? CD Horn? Either way, there is NO 450hz crossover point for that box. You might be thinking of the crossover in you Omni 15TB, but not the Omnitop 15

[Camillo]

You haven't said what kind of high frequency section you are using. Melded Array? CD Horn? Either way, there is NO 450hz crossover point for that box. You might be thinking of the crossover in you Omni 15TB, but not the Omnitop 15

I use the cd-horns with active crossover (actually from your advice about the 1.2khz sound vs 2khz dispersion choice).

The cap I am taking about is for dc-protection only - but- if the value of that dc protection cap is considered a first order crossover it would be around 500hz. The cap that i am looking at is instead 2 uf higher (22uf), making it a first order with a crossover point at 450.
My question was then, how crucial is the value of the CAP that one would use for dc protection for the tweeters. That got me thinking, is there a frequency range from the crossover point that you want to stay away from?

Like for instance " dc protection cap should be as high as possible without interfering with the active crossover point, normally around two octaves below crossover point.." <-- as an example.

I asked an engineer and his advice was, try one, if you hear a difference, double the CAP value. If you still hear it, double again, if you stopped hearing a difference, double again.

The plan states 20uf, I found a good priced mkpa 250v at 22uf from a reseller i like, i guess that would be okay but for knowledge i wonder if there is a rule of thumb. A lowe 8 uf cap would be around the crossover area, a 40uf would cut from 250hz but would still protect from dc right?

I guess 20uf is better in the way that if someone connects a signal that is not active crossovered they might not blow the driver before they notice with some luck?

Hope this cleared what i mean.
Thank you