Hello all,
Just a quick question, I went into Jaycar the other day and asked for a Non-Polarised Electrolytic Capacitor to HP my speakers @ around 150Hz. He said they didn't have them but ones that will do around 100-120Hz and so I was given 200uF 100V caps.

I tried wiring them on the positive side of my speakers ( cut the wire so it has to pass through the cap ) and having the negative wire left as it is. Now nothing has changed the speakers still play all the way to 30Hz just as loud as before. What is doing? :confused:

Beats me...
I have never used Caps before.. Never needed to as all of my gear have had Frequencies cut off at the Amps...

I dont know much about speakers with caps, but maybe 100v cap is just way to big.

caps store alot of volts, supercaps store millions of volts easily.

there probably was a difference but you couldn't hear it because your roll off was too low

Hello all,
Just a quick question, I went into Jaycar the other day and asked for a Non-Polarised Electrolytic Capacitor to HP my speakers @ around 150Hz. He said they didn't have them but ones that will do around 100-120Hz and so I was given 200uF 100V caps.

I tried wiring them on the positive side of my speakers ( cut the wire so it has to pass through the cap ) and having the negative wire left as it is. Now nothing has changed the speakers still play all the way to 30Hz just as loud as before. What is doing? :confused:


Did you tell the sales dude that it was for your car? A 200uF cap would high-pass at around 100Hz for an 8-ohm load only. For 4-ohm speakers (like in your car), the cross over frequency would be double that (ie; 200Hz), so you definatly should notice a difference.

You might be better off making a 12db octave cross over (using a capacitor and an inductor). Keep the 200uF cap as you've wired it in, but wire in a Inductor of about 8-9mH in between the positive and negative speaker terminals. That should give you a cross-over frequecy somewhere around 120-150Hz.

Yeah I told him it was for the car and he said yeah they will work without a problem. I tried the HPF on the Head unit and it is only like 6db/ octave and @ 125Hz there is like no lower Hz going through but the problem is it does it to the fronts as well ( HP @ 60-70Hz 12db / octave off an amp ). I only want the rear HP at a higher Hz.

Am I doing it right? I thought that if you cut the +ive wire and put the cap on either end it would work... apparently not thou :doubt:

Yep ur doing it right, they are non polarised (dont use polarised caps for this stuff) so the direction you wire them is irrelevent. A capacitor rated to 100v is fine for most car audio stuff... (short of 3kw of power from ur amps)

Your cutoff point will be at the right spot, but the roll off is only 6db per octave. This means that the cap wont be filtering enough out to notice a BIG difference.
To confirm: wire up the caps in series this will create a 100 microfarad capacitor This should give you a 6db slope from around 500 hz down. Even at this level you will still hear low frequencies all the way down to 30hz, but the cut point is higher so shouldn't be as noticeable.

Thats the problem with 6db slopes. Preferably you want a much higher slope. (i can get up to 24 db active other guys use even higher slopes) To do this passive you need to make up a much more complex config using caps and coils(inductors) just to make a 12 db slope

Try the two in series and see how that sounds. If it sounds good go back to jaycar and grab another two for the other speaker...

Good luck

I use this web page to do all the hard thinking for me!!!

http://www.the12volt.com/caraudio/crosscalc.asp

(refering to the web page) for the 6 Db crossover, that's an inductor OR a capacitor of that value (they make it look like you need both on the web page) :nuts:

inductors for low pass, caps for high pass.

yeah... that's the best rule of thumb (to keep costing down on freqs around/above 100Hz).

The web page shows you different diagrams on how to either use caps in series for a high pass or in parrallel for a low pass, and coils in parrallel for a high pass and in series for a low pass.

{EDIT:}

OOPS!!! Yeah, like Tim said, its best to use caps for high pass and coils for low pass, as it puts less stress on the amps... (eg, a cap placed in parrallel with no resistor network would short the high freqs across the spkr output terminals).

Ummm.... I think I'll just shut up... :redface:

Haha I have nfi what ur talking about... And then I look at ur signature and it all makes sense. :P

Tee HEE !!!

But I guess what I was trying to get at was that you shouldn't put stuff in parrallel before you put it in series...

If you put a coil in parrallel with the speaker, all the low freqs show as a short across the "+" terminal to the "-" on the amp (so you put a cap in series first).

If you put a cap in parrallel with the speaker, all the high freqs show as a short across the "+" terminal to the "-" on the amp (so you put a coil in series first).

I guess I was going off on a tangent with 12Db filters. :blah: