Newsgroups: sci.electronics.design,rec.audio.misc,rec.audio.tech
Subject: Re: Simple Crossover question..
References: <[email protected]>
From: Tomi Holger Engdahl 
Date: 01 Jun 2000 11:33:58 +0300
Message-ID: 
Organization: Helsinki University of Technology, Finland
Lines: 84
X-Newsreader: Gnus v5.6.45/Emacs 19.34
SkrewBall  writes:

> Hello..
> 
>  I was wondering if it is possible to use a simple passive crossover
> between my preamp-and my subwoofer amplifier..

It is possible to use passive crossover for this application.
The following circuit is one example what you can use:

 Sis��n o----+
             |
            | |
         P1 | |<-+
            |_|  |
             |   |
             +---+                +----+---o To subwoofer amplifier
             |                P2  |    |
            | |                  | |   |
         R1 | |               +->| |   |
            |_|     R3        |  |_|   |
             |     ____       |   |    |
             +----|____|------+---+    |
             |                         |
            | |                       ---
         R2 | |                    C1 ---
            |_|                        |
             |                         |
Ground o-----+-------------------------+---o Ground

Components         

P1   10k
P2   2.2k
R1   1k
R2   180 ohm
R3   820 ohm
C1   1 uF

P1 controls the signal attenuation in rnage of about 6-25 dB.
P2 controls the scrossover frequency in range of around 50-150 Hz.

This filter is a 6 dB/octave filter. You might propably want something
with steeper cutoff, preferablyh somethign in range of 12-24 dB/octave
for very good subwoofer performance.

> It would be a low-level
> signal,and there is really no need for somethng fancy like an active
> crossover with an Op-amp..

Operational ampliifer are especilay suited for handling this lind
of low level (line level) signals and for building active filters
with steeper cutoff than the passive one shown above.
 
> I was thinking maybe a Pi-Filter?  maybe a capacitor and a resistor?
> 
> In   100mfd     out
> o----| |---|---o
>                |  10K resistor?
>              --- Gnd
> 
>  something like that maybe?  (sorry for the icky Ascii drawing..)  
> Just something simple,to roll off the high frequency stuff.. 

This is a high-pass filter, not a low pass filter.
It does jut the opposite you want to do !

Swap the places of the capacitor and resistor, then you get
the right circuit topology and cna start thinking of right component
values for it.

-- 
Tomi Engdahl (http://www.iki.fi/then/)
Take a look at my electronics web links and documents at 
http://www.epanorama.net/