So using the calculator available at
http://www.carstereo.com/help/Articles.cfm?id=1

I have figured out that with a 300 uf cap I can get a cutout from 66Hz and down. What I'm wondering, what voltage of cap should I get? 16v 25v 50v? anyone with corssovers wanna peer in and see what voltage the caps are on there?

 

A cap only isn't really worthwhile. It will only filter @ 6db per octave, so you would have 6db less volume @ 33hz. Either move the xover point up higher or get a steeper slope on the passive or an active xover.

 

cap = economic tho, I'm broke and a cap will only cost me $1.50 ea. and I'm not pushin much volume, no amps (on the front speakers, only for my sub)

 

then don't bother. It's very little protection, robs power, save the $1.50

 

ok, what's the difference between a cap in a passive crossover and doing this?

 

i would say.... go with 16V that should be enough... the car battery itself is only 14V max.... 12 at the amp... the power coming out is amplified and measured in DB/watts... so not going to do much if you get a high Voltage cap....

 

yeah, I would put it on. It will save the front speakers and keep the sound good.

 

voltage coming out of your amplifier is much higher then voltage in. I can't site exact #s for the midrange/high freq set, but on the sub side, it's not uncommon to see 100v+ I remember us amps powering a dewalt drill off thier outputs w/a 60hz linear note.

I can make a call and find exact #s for output voltage, it's going to be closer to 50v then 16v though if i recall

 

16 volts is lots... car decks run usually 22 watts RMS (they way 50 watts, but that's a peak measurement, more of a guess really) watts = (volts)^2 / resistance

so we know our watts = 22 and our resistance is generally = 4 ohms

we get this

22 = (volts)^2 / 4
4 x 22 = volts^2
88 = volts^2
volts = 9.4

a 16 volt cap is fine.

 

you're on the right track, except that total resistance is variable depending on load. stick an ohmeter on a speaker while it's playing a long sweep, and watch it change.

the reason people don't worry too much about inducing noise into their system via speaker wire, is because it's at a higher voltage.

I've been too lazy to go take a look at an old pair of caps to see what voltage they are. I've got a box of em layin around here somewhere.

 

I know that the impedance is variable, since there is very little resistance to a speaker, it's mostly impedance, which is a reactive load, which does change depending on frequency, but the power supply of the amplifier doesn't change, it'll still run at 9.4 or 9.5 volts. as your impedance rises, your power drops. 9v output is standard on speaker leads for decks. higher power amplifiers obviously have a higher output voltage so that they can throw more power into the same load.

 

all the caps I have sitting around here are 100v....