Crossover (Newbie Inside)

[dirtyhanfri]

Hi

First of all sorry for the long and divagating post (newbie`s doubts).

I`m monitoring in the studio with a pair of Fostex Pm-1 and a Teac sub wich has no crossover (it comes from a home-cinema), so I`m using 3 outptus of the interface and filtering them via Software (APITA). So. I`d like to build a crossover (passive? active? dunno which is better for my purposes) with a Stereo In and L-R & Lfe Outs.

I think it could be really simple, I`ve been searching in the internet and I`ve found calculators wich gives cap and resistor values and the schematics, but I think It`s for speaker building, and I`m not sure if it works the same for my needs (really.. why not?).

The other issue is how to get 3 outs from 2 ins... what the calc tolds me is how to filter one signal, thats ok. So in first place I think I need to get a copy of one of the channels and filter all them, I think I could double wire one of the ins (L, for example) to 2 of the filters (a HPF for L, and a LPF for sub), but I don`t know how will this affect to impedances and level of the signal.

I`d be pleased if somebody helps me designing this. because I can solder some components in a PCB, I can understand basic things about a schematic, but I really have no idea on design it. In the other hand, I know the filters and freqs to work with, but, I know, is the easiest part...

Thanks.


This is a Great Comunity, by the way.

Greeetins From Madriz

 

[abechap024]

If you want to get really simple....

Buy one


on fleebay.

OR You could just filter out the highs before the sub. That will take one cap and some experimenting/calculating.
Take one end of the cap and attach it to the (+) and the other to ground and that willl shunt the highs to ground, thereby effectively removing them from your signal. The frequencies that get shunted depends on the value of the cap(...and the impedance of the circuit but don't worry about that)

 

[dirtyhanfri]

If you want to get really simple....

Buy one

If I`d wanted it really simple, I`d rather go and buy one after making a poll in Gearslutz  , but this is a pretext for learning a bit, and surely the first step to build a full monitor controller.

Ok, I understand that the cap value determines the frequency filtered. I`d really like to know how to get the copy of the signal for the sub, just something like this?

I just noted I did`t draw the sub filtering, but the issue is in the connection of the sub.


Thanks

 

[abechap024]

Ahh Yes it is a good way to learn ;D

Well if you are using balanced connections to feed your sub, you will probably need to cut the highs after it gets De-balanced Or maybe check and see if the sub is already low passed? It probably is if it doesn't sound too ridiculously bad. then it would just be a matter of changing parts to get the frequency you desire.

But if you want to build the reall deal type crossover....i dont know about those..

Good Luck!

 

[dirtyhanfri]

Well, some details;

All the connections are unbalanced. (interface outs and sub in)

The sub works with 4 or 8 ohms load.

And, yes, I`ve cheked it, it`s not filtered. 

I don`t know about the real deal crossover, i`d like to know if this is gonna work and then have a little fun soldering and casing everything up. (Time to invest...)

Thanks for the replys.

 

[abbey road d enfer]

I reckon you should use an active x-over. My favourite is Linkwitz-Riley 4th-order (24 dB/octave).
You can build one with 3 dual opamps and a bunch of resistors and caps; you'll need a PSU and input/output circuits, in particular if you want balanced ins and outs.

 

[PRR]

X-over at speaker-level for stereo signal with mono woofer is problematic.

It seems you must already have three amplifiers?

This is the ultra-basic concept for what you want. C-R filter takes boom off the mini-boxes. R-C filter takes the highs off the woofer. Since the mono is fed R-C, you can use two Rs to mix L+R into mono before low-passing.

This is "6db per octave". Not very stiff filtering.

If the mini-speakers "can take bass", then this mellow slope will give them a little more output without mudding-up. (Abbey's 24db/oct slope would take ALL the bass out of the minis, significant more power handling before slap, but is not dead-simple.)

The main "fault" is that a mere 6db/oct applied to a large cone will tend to pass significant middles including all the cone-paper resonances.

 

[dirtyhanfri]

Well, Thanks for the replys

Frist of all, the Fostex and the sub are active speakers, so they`re working with line level inputs, and unbalanced, (short cable lenghts, i don`t worry about keeping it unbalanced).

The Fostex have 5" woofers, so they handle the bass freqs, but with a clear fall below 100 Hz, then, maybe a 6dB per octave filter could be not enough (In fact, I`m filtering with a 12dB per octave in software). But I could build this circuit just for test.

I think I`m gonna google about x-over and see what do I find.

Thanks again

 

[abechap024]

Boom...haha!