crossover / summer for "2.1" active or passive

[Ensoniq]

i wanna take a 2 channel L/R stereo source and have it feed 3 amps:
Left, Right and Subwoofer.
Im thinking of crossing over at around 100hz.
which would be easier (minimal components) passive or active?
and how do i take the Left ant Right and summ them up to feed the sub amp?

 

[Zero D]

Hi, passive & easy is like this in my screenie.

Active requires an OpAmp/Components/Supply/Case

I'm presuming the SubAmp has a 100Hz etc filter in it ? If not, then more is needed for either solutions.

 

[Ensoniq]

No i don't have crossover yet.

Btw, active means before amp and passive means after amp correct ?

 

[sreten]

Hi,

Reducing input caps on the L+R stereo amplifier an idea.

rgds, sreten.

 

[Zero D]

Do you have the Sub Amp yet ? If not try & get one with a Xover built in. Also look for one which has L & R inputs which are merged internally. That way problem solved !

Active means any powered circuit, which in this case would be the OpAmp solution. Passive means unpowered, which could be before and/or after the Amp.

EDIT

Of course you would need a high pass filter for the L & R too, which matches the 100Hz etc low pass !

 

[abraxalito]

Passive is fewest components and normally sounds best. However a passive XO at 100Hz is going to call for some fairly huge inductors (in the range of 10H) to operate at line level. Probably you'll have to wind them yourself (on gapped ferrite cores) which will take a couple of hours for each.

You could employ the design resource here - Passive Crossover Design Equations Formulas Calculator - Two Way Second Order Network Chebychev Bessel Butterworth Linkwitz-Riley

 

[Zero D]

@ abraxalito

When you say "Line Level" i expect you actually mean output from the Sub Amp, not PreAmp output Line Level. We don't want to confuse the OP

For eg only, a single 10k resistor & a 0.159uf capacitor before the Sub Amp = 100Hz cutoff.

 

[abraxalito]

No, I was really meaning line-level - or I'd have written 'speaker level'

Yes you can do a first order LP without inductors but I was assuming the OP would want a bit more than a first order.

 

[AndrewT]

post6 link to a passive crossover calculator.

It shows a 2pole crossover consisting of only one capacitor and one inductor in each filter.

How can the roll-off characteristic be changed through the continuum of Linkwitz, Bessel, Butterworth, Chebychev?

 

[abraxalito]

By choosing the component values listed under those particular headings. Each of them is a different trade-off between passband flatness, steepness of roll-off, and phase response.

 

[AndrewT]

A 2pole LC filter is just a filter.
How does the different characteristic of Bessel come about by changing the C & L values from the very similar C & L values of the Butterworth?

 

[abraxalito]

A two pole LC filter has both real and imaginary components for its two poles, thus giving an extra degree of freedom - damping (or its inverse, Q). The damping is provided by the losses (ESRs of caps and inductors) plus any explicit resistance in the circuit (for example - the load). Chebyshev filters have the lowest damping (or highest Q), then Butterworth; Bessel has the highest (lowest Q).

 

[AndrewT]

Do I have to learn how to model this in a sim package?