Interior speaker capacitors

Have any of you used inline capacitors to your interior speakers to run them straight off your head unit and filter the bass? A simple high-pass crossover. What value worked best for you?

Something like this 150uf:
http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=027-364

Use them all the time for that very purpose.

Here's a tip: buy some 100s and some 50s instead of 150s and just wire them in parallel. If you want to go lower just wire two 100s instead, if you want to cut out more bass just use a 100.

Check with your local hobby electronics shop, you might be able to save shipping. They should cost about a penny per uF.

Cool. Good tips. And thanks for reminding me that capacitors must go in parallel to add together. (Not in series like resistors).

If anyone's wondering why you would do this-
if you're on a limited budget this is a great way to save some money and still get good sound. Run the stock interior speakers straight off the head unit with the bass filtered through a capacitor(s). Most stock speakers only sound bad when they are driven to distortion because of too much bass. Then use a 2-channel amp bridged to a single 12" sub to handle all the bass. Or a 4-channel amp to power your tower speakers and your sub. Or if you have a really high-powered tower speaker system that overpowers the interiors anyway, you could save some battery power and just run the interiors filtered off the head unit. Some will have a use for it, some not.

A capacitor-only simple high-pass filter is called a 1st-order 6dB filter. On the following chart, pick the crossover frequency you want, and then look at the first C1 column to determine the capacitor value you (may) need to put inline before the positive speaker terminal. Remember a 6dB slope is pretty gradual so a higher crossover frequency may be needed to keep your particular speakers from distorting. I guess it's somewhat trial error and personal preference as Mikeski describes. Also, this chart is only for a 4ohm speaker load. There are other charts for other impedances.
http://www.the12volt.com/caraudio/cross4ohm.asp

Yep, that's my electronics dyslexia acting up again, mixing caps and coil formulas.

thanks for the correction

It was a long day...

Capacitors in series: Ct=C1+C2+C3+...

Capacitors in parallel: 1/Ct=1/C1+1/C2+1/C3+...

So if you want 150uF capacitance you just put a 100 and a 50 in series
with the speaker. You can actually put it anywhere on the plus or
minus terminal, the speaker doesn't know the difference. There is a
very slight interaction with the impedence of the speaker wire but it
doesn't matter for our purposes. Put them at the deck if it's easier.

Make sure to use non-polarized capacitors.