Reworking a Subwoofer Crossover?

[vinyldavid]

I just found a spare subwoofer crossover in a friend's parts box.

Specs are 20-250hz, at something like 400wrms.

Is there a way I can make the top end roloff adjustable? it's not at the moment.

 

[Zilch]

Yes, very likely.

Document what you have and post it.

 

[vinyldavid]

There's a piece of paper taped to the board that says:

Sequence, 8Ω

Model SAS-18, 350wrms, 1400w peak

Two inductors and a 188ufcap are on the board.

 

[Zilch]

Uhmmm, we need the circuit; there's a spare inductor in there....

 

[vinyldavid]

OK.

In order:

Cap
Inductor
inductor
output.

Thing is, I dunno which side is in the input...I would think before the cap..

 

[Zilch]

Still doesn't make sense.

Trace it out and sketch it.

Post the sketch, or a pic of it.... :yes:

 

[vinyldavid]

The almost-3am-sketch...

...was full of fail...keep scrolling.

 

[Sir.Byrd]

Looks to me like the two inductors are in series...

Not to me

 

[vinyldavid]

Not to me

They are...

 

[Sir.Byrd]

They are...

That's not how your text schematic was laid out!

 

[vinyldavid]

That's not how your text schematic was laid out!

Ak did not like to show spaces....so I added dots...whatever, fixed.

 

[vinyldavid]

Bumpin

 

[Zilch]

It's a second-order lowpass filter; the capacitor is across the output; the inductor end is the input.

Inductors in series add, like resistors.

See the Crossover Component Selection Guide in the PE catalog.

To really know where it is, we'd have to know the values of the inductors, but you can see the frequencies in the chart, and what's required to get lower, i.e., add more big inductors in series....

 

[vinyldavid]

So how can I vary it?

I know there's a way to measure crossovers, but I don't know it.

This is probably going to sound stupid, but, I know that there's a control on many consumer subs and plate amps that allow you to vary the crossover frequency....I want to add that to this, if that's possible.

 

[Zilch]

Those are active filters to vary the frequency. If you want to play that, it requires a separate amp running the sub; just buy an inexpensive active crossover like Behringer CX2310 and start leaning about this. You want the sub frequencies NOT to go to your mains, as well. $80 at Parts Express, cheaper at Guitar Center or equal.

Your closest approximation to that passively is to hook up a selector switch to bring more or fewer inductors in series. In theory, the cap value should change, also, as you see in the chart, but the difference is not huge....