High pass filter does not work

Hi.

I have read your information about passive crossovers and this is the situation:

What i want is to create a filter so that my car's front speakers don't receive lower frequencies then 100hz. If they receive too much bass, the door starts to vibrate and the speakers will distort.

What i did was i bought a capacitor with 100v and 470uf (following the instructions i saw on this site) and connected it in series.

What happened was that there was no difference at all. Everything stayed as it was before.

The speakers are JBL with 135 watts peak, 50 watts nominal power and 4 ohm impedance.

Please let me know what i am doing wrong and how i can solve this annoyance.

Thanks in advance.

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Nuno Gomes

A 470 uf cap will (assuming a 4-ohm speaker) provide a 6db / octave high pass at approximately 80Hz.  Assuming it is a non-polar cap, you should be able to connect it in series with the positive leg of the woofer and it will cross at that frequency.  If it is a polarized cap, you will indeed get no effect since it will only function on half the sine wave.  Perhaps the X-over frequency is too low to have a noticable effect in your application.  I suggest changing it with one rated at 398uf (+/- 10%) if you want to cross at 100Hz (into 4 ohms.)

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470uf cap with a 4 ohm load will give a 6db slope of about 90hz. So this is still pretty low and will help some but not tons. Consider raising the point to about 400hz with a 100uf cap instead and see how it sounds.

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Top Secret, I can tell you but then my wife will kill me.

Basically what i want is to keep almost all the bass from reaching the front speakers.

I asked for a non-polarized capacitor at the store, but (sorry for the ignorance) it has the (-) sign on it. Does it mean it's polarized? the guy at the store told me about other types of capacitors with 3 pins (i don't know if it's the right name for it). This one has 2 pins, it says "REC" (brand) and has the minus sign on it.

Can you please tell me the values for a capacitor that allows no bass at all to reach the speakers? (they would work almost as  tweeters).

Thank u very much

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Nuno Gomes

If the cap has + or - on it, it is most likely not non-polar. This page has a good general reference chart for you.  If you want to "block all bass," you will need to cross over at about 400 to 600Hz like Rob suggested. HERE is a good on-line source for audio crossover capacitors.

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I will try your solution and of course give you a feedback.

Let me just say that i've been using the internet and a few forums for about 8 years and i could never get help like the one u gave me.

Thank you.

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Nuno Gomes

Hello once again

I´ve searched this little city where i live that is Coimbra-Portugal, and i couldn't find a capacitor of 100uf. I was asked if i was sure of that value that is not commonly asked for. I found a 22 uf capacitor maximum. I guess i'll eventually  connect 5 of them.

Thank you once again for your precious informations.

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Nuno Gomes

I got 4x 22uf, 100v capacitors and connected them in parallel on my car's front speakers and it works just as i wanted. I know that the  final value is not the one i was aiming for (the crossover point must be around 1000hz), but it sounds as i wanted it to.

Thanks

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Nuno Gomes