i havnt had the subs in since january.. and even then i though they were messed so i took em out.. my buddie said it may have just been the amp lol. so of course i bought a new amp and they still sound the same.

 

subs can still make noise even though they are blown, some people fry the voice coil so much they dont move after they cool, i would check the wires make sure the + and _ are correct

 

That would be how to calculate it IF the amp were putting out a true 850watts. In todays amp world...Highly unlikely.
What you want to do is look at the fuses on your amplifier. I doubt there is 80A of fusing on there??? It's prob more like 40A.
I'd say the 60A would have been plenty unless your amp has a higher fuse rating than that??
To find a REAL close measurement of how many watts your amp is putting out, you take the AMP fuse rating and multiply that by 12v. So a 40A fused amp will put out close to 500watts PEAK.
For a true 850watts, you would need 72A for 850 Peak wattage and 100A for 850rms watts.

Not trying to knock anyone's stuff, just trying to create reality here is all so you have a better understanding of what truley is needed.

 

find somebody who has a multi meter and run a test on the speaker, while its in the box this can be done as long as its not wired to the amp or other speaker....test the ohms of itr if its a 4 ohm speaker it will test over 4ohms if it tests under its going or gone....

 

Not necessarily. Most speakers meter out slightly below their rated spec. An auto 4ohm speaker may meter anywhere between 3.1-4ohms.
If there is no reading at all or the reading is very high (27, 99..etc) there is a problem with the voice coil of the woofer.

 

Well we can just agree to disagree. You should ALWAYS choose your fuse size based on the rated power of the device. What you are suggesting is that he simply guess at what size fuse is needed. What would be the advantage to the OP of cheaping out and guessing on the fuse size?

 

I never said anything about guessing, you have by saying an 80A should be good and that is based on the assumption the marketed/labeled wattage is correct... No need for an 80A fuse if he's only got a 40A fuse in his amp was all i said.
Most amps in todays market are way overrated and I gave a simple suggestion on how he could calculate approx he is actually putting to the speaks. 12volts X's his amp fuse total will generate that absolute most wattage possible.
I simply said that the power line fuse does not and should not be significantly more than your amp fuse.
Looking at the amp, if there is a 25A fuse, then why would you possibly need a 60, 80 or 100A fuse for the supply line?
Most companies CLAIM huge wattage supply yet they only have tiny fuses. No way around Ohms law.
You said Volts X Amps =watts ......so, take this randonly picked amp

Sony claims 1000w max ...so, 12v X 60A worth of fuses = 720w max, NOT 1,000w. Even at an overrated 14.4v X 60A =864w.
Using the overrated wattage to find the fuse rating would get you 1000/12 = 83Amps rather than the correct 720/12=60A
Also, no mention of power wire size here? Telling the guy to use am 80A fuse on a 10ga is asking for trouble. Even 8ga is pushing it.

Also, the above calculations are estimates as they dont include the efficiency calculations either which would result in 20-30% lower output #'s.