[[email protected]]

Hi.

Can someone answer these questions about using pre-built passive
crossover for basic speaker system. More specifically for a Subwoofer
application.

1) If I have an 8 Ohm sub and use a 120Hz 4 Ohm (2nd order) crossover
with it, what frequencies will go through to that sub (240 Hz, 60 Hz)?
2) If I have a 4 Ohm sub and use a 120Hz 8 Ohm (2nd order) crossover
with it, what frequencies will go through to that sub (250 Hz, 60 Hz)?

Thanks.

[Scott Dorsey]

wrote:

Can someone answer these questions about using pre-built passive
crossover for basic speaker system. More specifically for a Subwoofer
application.

1) If I have an 8 Ohm sub and use a 120Hz 4 Ohm (2nd order) crossover
with it, what frequencies will go through to that sub (240 Hz, 60 Hz)?

That depends on the crossover design. If it's a first-order filter,
it will indeed just move up an octave. Anything else, and it will be
different.

Remember that ALL frequencies will go through the filter, they will just
get attenuated at some point. But even with a third-order filter, there
will still be appreciable signal two octaves above the crossover point.
These are not brickwall filters.

2) If I have a 4 Ohm sub and use a 120Hz 8 Ohm (2nd order) crossover
with it, what frequencies will go through to that sub (250 Hz, 60 Hz)?

If it's a first order filter. If it's more complex, it will be different.

And, of course, a 4 ohm driver isn't really 4 ohms everywhere. AND, the
impedance curve is dependant on the box it's in. That's why passive
crossovers need to be specifically designed for the driver and cabinet
they are used with. And it's why active crossovers exist.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

[Eeyore]

wrote:

Hi.

Can someone answer these questions about using pre-built passive
crossover for basic speaker system. More specifically for a Subwoofer
application.

1) If I have an 8 Ohm sub and use a 120Hz 4 Ohm (2nd order) crossover
with it, what frequencies will go through to that sub (240 Hz, 60 Hz)?

You mean 60Hz here but that'll only happen with a 1st order design

Not entirely predictable but possibly it'll act as an underdamped filter and
you'll get 'about' a 120Hz crossover with a bit of a peak in the response.


2) If I have a 4 Ohm sub and use a 120Hz 8 Ohm (2nd order) crossover
with it, what frequencies will go through to that sub (250 Hz, 60 Hz)?

In this case you're likely to get a 'sloppy' cutoff.

I strongly suggest using active crossovers. All such problems will vanish.

Graham