What do capacitors do?

[Evman]

I know that capacitors store electricity, but never knew why they were used in stereo's. Is it because you get better bass because you've got that extra power there waiting to use? Do they really make much difference?

[dephilile]

What size capacitors are you talking about?

You usually put huge capacitors (1 or 2 F) to stop voltage drops in your system. A capacitor is able to expel all it’s energy/electrical charge in a split second. A double A battery can actually hold more energy than a 1 F capacitor but is useless for stopping voltage drops because it can’t release all that stored energy when it’s needed. They have what’s know as a Thevenin resistance.

You can also put capacitors either in series or parallel to filter out the low and high frequencies respectively. I think a 220 micro F cap in series with a speaker filters out low frequency.

[Evman]

Awesome, thanks for ya help

[michaelw]

Think of a capacitor as a spring (infact their energy equations are the same). If a cap sees a drop in voltage it tries to compensate by delivering current. So the practical aspect of this is a big bass note needs a heap of current, drops the voltage on the power cable due to resistance in the wires, capacitor does not like this so it supplies current to boost the voltage. If you are asking about the 1F caps, mount them as close as possible to your amp.

ps. Don't waste your money on gold contacts.

Mike

[Phreddy]

Exactly right dephilile. Interesting explanation there too Michael! (never heard that "spring" thing before, but very logical!)

Capacitors impede the flow of low frequency energy, by virtue of what is called "capacitive reactance". As the frequency increases, the reactance decreases. Inductors (coils) do the same sort of thing, but in reverse - frequency up, reactance up. For that reason, the most basic type of speaker crossover is simply a capacitor in series circuit with the tweeter - thereby only allowing the higher frequencies through. (higher end crossovers will use inductors as well)

However, 220uF (micro-Farad) is far too large to use - you'd destroy your tweeters in seconds if you were to use a cap of this value. Generally for 4 ohm speakers, the series cap for the tweeter should be somewhere between 4.7 and 10uF, depending on where in the frequency range you want the tweeter to become active. (smaller capacitor, higher crossover frequency) For a 220uF capacitor the crossover frequency would be about 180Hz - I don't know of a tweeter in this galaxy that will enjoy a frequency that low, unless it happens to be a "piezo" type tweeter. Piezo's appear (to the amp driving them) as a capacitor, and in fact can be used without a crossover network at all, the device simply won't even try to produce low frequency energy. (but I'd never use a piezo except in PA type scenarios. They're tough, but the sound is a bit harsh and "tizzy")

Anyway - I'm doin' it again - writing a bloody book!!

Cheerz!

[Tasmaniak]

Also, another use for capacitors that I stumbled across. In main power supplies cables for amps, dropping a capacitor can quite often remove alternator whine It won't remove an earth loop, but engine noise can easily disappear. I didn't believe it until I thought about the way a Cap works then it made perfect sense!!!

[Phreddy]

Great trick Trunk!

Does make perfect sense.

[Phreddy]

OOPS! My apologies Dephilile....

Read your reply to another thread Trunk, you described using a 220uF cap for high-pass on front speakers - exactly what Deph is talking about.

My reference to the 220uF was specifically when used with TWEETERS. Not having a sub in my system sometimes I forget the little things :b: - yes, a 220uF is perfect for the HPF to 4 ohm door speakers, rolling off the response below about 125-150 Hz. The LPF on the sub amp is set to about the same, and the drive adjusted to balance the system.

I stand humbly corrected.

[dephilile]

No problem

Yeah, I used to have a 220micro F cap on my 6x9’s in the back because I have a 12” sub. I removed it after I realized my head unit could remove those low frequencies for me. Why did I get 6x9’s if I was only gonna filter out the bass? They were in my old car in which I didn’t have a sub.

[Tasmaniak]

Why did I get 6x9’s if I was only gonna filter out the bass?

You know, I asked myself the same question as I put four 10" subs into my old wagon...

[d_neo_b]

hey question would a 220 uf cap be alright to filter out some bass to my four way coaxels in the front? or would this be bad?

[t2te50]

Interesting? Thanks for the tuition Phreddy it's always handy to be good with electrical circuits especially in this day and age.

[Patrio7]

so long story short we all know a stero display will dim a little when it does doof so the cap sees that and powers up the line to take the strain off the system making the bass / doof kick sound normal but minus the dimming from the juice draw?

[Tasmaniak]

Patriot....sort of.
Basically what happens is the capacitor stores a little extra power in reserve. So, when you hit a bass note and ask for massive power from the battery..and it's not there. The amp wlil drain the capacitor of it's power then the capacitor will recharge itself waiting for the next discharge.

Heh...I still remember back when I first started. I didn't see the problem with just hooking the capacitor straighth upto the power supply....no-one told me I had to charge the bastard first...imagine the look on my face eh?

d_neo_b. The capacitor will be fine for filtering out the bass to your fronts. Put it in series with one of the speaker wires. Preferably the positive...but in reality. It makes no difference.

[Phreddy]

G'Day All.

Neo - just make sure it's a bipolar cap. It shouldn't have any polarity (+ or -) markings on it - a standard (polarised) cap will work, but will soon fail.

t2te50 - pleasure! I'm glad you got something from it.

Cheerz!

[spacattack]

best way to recharge a cap ( i thought this was total bullshit until i saw it bein done and it worked !!!! lol ) is to have a old car head light handy hook it up to a battery turn the light on stick the cap termanials in front on the light for about 2hrs and whaalaaa you got yaself a recharged cap lol pretty wierd ay lol

[Shivaga]

Hey guys, thanks for all of this, i've learned alot!!!!

[Phreddy]

Heh - a recharged cap, and a flat battery!

Seriously though Spac - what's the theory behind how that works? I can't figger it myself, but....

Cheerz!

[Tasmaniak]

I'm clueless too......

I've always used a resistor or a testlight personally....on the cap.

[Phreddy]

Absolutely - a headlight lamp in series with the cap - that's how I'd do it.

Although the average headlight filament is pretty low impedance, would be better to use a lower wattage globe, like a parker or something. (wouldn't take 2 hours to charge either!!)

[Tasmaniak]

Thats why I use the test light...or a 10watt 10ohm resistor...couldn't find either once so I used a 1watt resistor....bloody hell it got hot!

[Cameron]

you guys are way too smart!!!!

[Tasmaniak]

Sometimes....we outsmart ourselves!

[garfa]

with the light and the cap trick i gather thats because of the photons being emitted, they are transfering their energy (about 1-2eV per photon) to the car terminals. it would make sence. it sounds like it is (sorta) the reverse of the photoelectric effect. eg: instead of releasing voltage from a piece of metal using a light (i think it needs to be uv? or around that wavelength) using light to charge it.
i hope thats clear. doesnt seem to me but then again its pretty early (10am!)

[dephilile]

Huh, I thought you would use the light to tell you when it’s charged because when a capacitor is fully charged it can be thought of as an open circuit. No charge flows meaning the light wouldn’t light up. I don’t think it has anything to do with photons being emitted.

Plus, I’m not really 100% sure about this but I would have thought that the theory of electrons getting pushed up into a higher orbit about the nucleus and then dropping back and releasing a photon was only applicable for fluros and neons. I’m not sure about a normal light bulb. I thought it just glowed really bright because of it’s resistance. Maybe the same thing is happening, just within the wire. I dunno. Photons are getting created somehow.