Re: Need help building a R-C fixed LPF for crossover

Chris Hornbeck <chrishornbeckremovethis@xxxxxxx> wrote in
news:o7kse2tak7bs8mo8959hsjiud6vuan8ojv@xxxxxxx:

On 24 Aug 2006 03:41:24 GMT, Jim Saurman <jsaurman@xxxxxxxxxxxxxxxxxx>
wrote:

Here is what I've got as a rough draft:

Crossover point 100hz
Slope 12db
R1=1000 ohms (does it matter what wattage these are? will 1/4 watt
work?)
C1=1.59 microfarads (maybe a 1 ufd and a .47 ufd wired in parallel?)
R2=10000 ohms
C2=.159 microfarads (I think they sell .150 ufd)

One thing to keep in mind is that the amp's 12K ohm input
is in parallel with the crossover's 10K resistor, moving
the second pole up almost an octave.


The article discusses this issue very well; just a
matter of choosing a resistor for R2 that totals to
10K when paralled with 12K. Piece of cake.

So I should change it to an 8K resistor and work backwards to update C1,
R1, and C2 to the appropriate values, or should I leave C1, R1, and C2 as
is?



FWIW, a second order Linkwitz-Riley high pass may or
may not be a good choice for your particular use. The
system's total transfer function includes the response
of the drivers, who are doing all kinds of whacky stuff
in this region.

Well this is for hotel A/V, and as much as I'd like to set up a better
system, I'm constrained by a budget of zero dollars. Anything would be
better than what we've got now. I'm not as worried as I would be if this
was for a nightclub or band.


Also note that an idealized LR2 crossover gives flat
magnitude (frequency response on axis) with the low and
high pass drivers in opposite "DC" polarity; that is
a battery across the terminals gives opposite cone travel,
(in vs. out).

So when these are feeding the sub amp, the phase needs to be reversed?
I'd totally forgotten that. Thanks for that info.
.