hi,

i know that there are some car stereo / electronics geniuses here, so i thought that this would be a good place to post a couple questions about amplifier power...


I'm trying to figure out how much power I need to comfortably drive my component speakers and a new sub-woofer in my S2k.

Right now, I have a rockford fosgate 250.2 amp powering rockford fosgate components. (that's 62.5W / channel at 4ohm, for each of the 2 channels, right?)

Whatever the power, the system sounds really good, but I'd still like to add a sub-woofer.

component speakers (or any mid - high range car speakers) generally have 4 ohms of impedance whereas a sub would have 2 ohms, right? that means that 50 watts / channel of low-impedance (2ohm) power is actually 25 watts per channel to a non-sub woofer speaker, right?

If the above is true, a 600.4 amplifier with 2 channels bridged would put 75w @ 4ohm to each of the separate and 300w @ 2ohm to the sub, right??

If an amp is bridged, that means that 2 channels of power are piped into a single channel, right?

please, someone tell me if i'm a total moron. (i might be completely wrong on my assumptions) i didn;t pay enough attention in high school physics.

thanks for any insight!

 

Most car subs are 4 ohms, but you can buy two Ohm subs. Some subs have dual 4 Ohm voice coils that you wire in parallel for 2 Ohms. Usually when you bridge anamp you get 4 times the power of a single channel (you actually get twice the voltage output, and power is related to the square of the voltage). When running in bridged mode, you should not drive less than 4 Ohms. Check your owners manual, but that is the case for your Rockford.

So, a 600.4 would give you two 75 Watt channels, and one 300 Watt bridged channel, all driving 4 Ohm speakers.

When running in non bridged mode, a good amplifier (not all of them by any means) will give you twice the power into 2 Ohms as compared to 4 Ohms. This demonstrates the amp is acting more like a perfect voltage source, which is a good sign of quality.

 

[QUOTE]Originally posted by NSXS
[B]Most car subs are 4 ohms, but you can buy two Ohm subs.

 

[QUOTE]Originally posted by MacGyver
[B]

Oops, no.....

P=IV....if you double the voltage, you couble the power, not quadruple it.

 

If you double the voltage into a constant resistance you quadruple the power. Power=Vsquared/R . Power = IsquaredR. Look it up if you don't believe me.

If you wire two 4 Ohm voice coils in parallel you get 2 Ohms. I would not recomend using two 2 Ohm woofers, or even one 2 Ohm woofer on a bridged channel.

 

[QUOTE]Originally posted by NSXS
[B]If you double the voltage into a constant resistance you quadruple the power.

 

[QUOTE]Originally posted by Pinky
[B]

OK im not touching the quotations of specs for electronic values I know you know them better than I........though I know I know amplifier power outputs better than you.

You take an amp half the ohms resistance you get approximatly double the power.

 

As a dorky side note: I have two amps in my closet (Hifonics Series VII or VIII not sure Platinum series Ulyssis + Isis) that are 1/2 ohm stable in stereo and 1 ohm stable bridged mono... I had purchased them as competition amps to beable to compete in "low" wattage clases...

The ISIS is rated 50 x 2 into 4ohms but will put out 700 watss into (1) 1ohm channel... rather neat but not very practical... I paid $1100 for that amp... now all it sees is the closet...

 

Those amps would useful for running multiple driver arrays wired in parallel. Not really practical for everyday use, but during a car stereo competition they measure the max SPL of te system, and the way to get the best numbers, once you max out the power rating of the speaker, is to add more speakers.

 

[QUOTE]Originally posted by NSXS
[B]If you double the voltage into a constant resistance you quadruple the power.