Capacitor as a filter?
Printed From: the12volt.com
Forum Name: Car Audio
Forum Discription: Car Stereos, Amplifiers, Crossovers, Processors, Speakers, Subwoofers, etc.
URL: https://www.the12volt.com/installbay/forum_posts.asp?tid=50880
Printed Date: May 15, 2024 at 10:50 AM
Topic: Capacitor as a filter?
Posted By: Envoyman
Subject: Capacitor as a filter?
Date Posted: February 26, 2005 at 12:25 AM
Once again thank you all for the help with my stereo and my friends tahoe...I am beginning to have a better understanding of car stereos ( Nowhere near you guys but decently) I have been reading quite a few posts and I havent found one of these...My friend with the tahoe just had me install an amp and sub....The guy he bought the equipment from was trying to sell him a cap telling him it was needed for a noise filter (OR SOMETHING LIKE THAT) and that it would help with current draw... From reading in here I found that an electronic upgrade was more efficient and advised my friend otherwise. But I would still like to know what the guy meant by the capacitor being a filter??? Thank you for furthering my learning... EM
Replies:
Posted By: shoelesscraig
Date Posted: February 26, 2005 at 1:52 AM
A capacitor sort of levels out the power, regulating it and making it smoother, much like a power conditioner does for your home equipment. The batter in your car is constantly changing (wipers, blinkers, brake lights, etc.). The capacitor is like a battery in that it stores energy. When the amp hits a loud note and draws power, it will draw it from the cap and not directly from your car's battery, thus keeping the lights from dimming as much and making life easier for your alternator.
Posted By: Master Asylum
Date Posted: February 26, 2005 at 1:53 AM
Capacitors can filter out frequencies from the speakers. I don't remember the EXACT details if it blocks out high or low frequencies, but I'm pretty sure it blocks highs. www.bcae1.com Read that section stuff in there on it, will explain it well. ------------- 1998 Monte Carlo w/
Eclipse CD8454
2xRockford 5.25" Power 2-way T152C
2xRockford 6"x9" Punch 3-way FRC4369
1xMemphis 16-MCH1300 5-channel
2xKicker 12" L5 Solobaric-2 Ohm
Posted By: Asmodeus
Date Posted: February 26, 2005 at 2:00 AM
I have never saw a complete use for them other than it adds a little bling into the install.. As far as a filter...I have seen it take some alternator noise out of the power wire... Only on like 2 installs by our shop...I dont sell them unless someone just wants one -------------  Making the World A Louder Place
Posted By: tronmonster
Date Posted: February 26, 2005 at 8:40 AM
Capacitors are said to "oppose a change in voltage" (as opposed to coils or inductors, which are said to oppose a change in current).
Another general statement about caps is that they pass high frequencies and block low frequencies. Used as a noise filter, a cap is passing the "highs" (noise) to ground. The lows pass right on by.
DC power can be thought of as the ultimate Low Frequency. After all, it is ZERO Hz. You can't go any lower than that!
The effective resistance of a capacitor in a circuit is called capacitive reactance. The formula for capacitive reactance is 1 divided by 2 X pi X frequency X capacitance. When a cap is connected from a point in a circuit to ground, it acts as a path to ground which acts differently at various frequencies. By the formula for capacitive reactance, it would be a very high (infinite) resistance to DC voltages, but a low resistance to high frequencies. The higher the frequency, the lower the resistance is.
An example: a ONE FARAD cap is used in a circuit. To DC power, it appears as a very high, or infinite resistance. It has no effect on the DC power. But, to a 60 Hz signal, it presents a load of 1 divided by 2 X pi X 60 X 1. That calculates out to be .0027 ohms, which is practcally a dead short! Of course, most caps are of values waaaaaay less than one farad---most are nominally in the range of just a few millionths of one farad (1 microfarad is one millionth of one farad).
Ultimately, a cap passes noise (a relatively high frequency when compared to 12 volts DC) to ground when used as a filter cap.
Hope that explains it!
-tm-
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Don't wanna hear your "boom-boom," just wanna hear my "weeee-yaaah-deedle-dee."
Posted By: kfr01
Date Posted: February 26, 2005 at 10:47 AM
Don't buy one. You don't need one and the seller is probably just trying to rip you off.
I've never seen any real evidence that Capacitors work as intended. In my mind they're a gimmick and an easy way for retailers to sell you a high profit margin item. (Kinda like radio shack making a killing on batteries).
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New Project: 2003 Pathfinder
Posted By: haemphyst
Date Posted: February 27, 2005 at 11:32 PM
Except that batteries DO do what they are supposed to, and DO work as intended...
just jabbin', man...
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It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
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