should i?

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06-27-2007, 11:33 PM

should i?

my friend is in the air force and is in town for a little bit and offered me his system out of his truck for $350 including a 2500 watt max Rockford Fosgate Amp, two MA audio 12" sledgehammers, a under backseat truck box which obviously wont fit, the amp wiring to handle the high wattage, and a 2.0 farad capacitor

he also said i could just buy the amp alone for $150

i dont know the model of the amp but i know its never been used heavily or to the maximum and its about a year and a half old but in tip top shape

even if i dont install is that a good deal for the amp if i plan to resell, perhaps on ebay?
06-28-2007, 01:00 AM
aveosummit

Can you find out the model number of the amplifier that will give you a better idea of the resale value? Just FYI there are 421+ Rockford Fosgate amps selling on e-bay as of this post. I hope this helps.
06-28-2007, 04:16 PM

It's an alright price, but it depends on what you're going for. IMO, the average person doesn't need 2 12's in a hatchback/small sedan. A decent 10" with some power in a tuned box will bump plenty hard.
06-28-2007, 10:32 PM

Quote:

Originally Posted by Eugenio

It's an alright price, but it depends on what you're going for. IMO, the average person doesn't need 2 12's in a hatchback/small sedan. A decent 10" with some power in a tuned box will bump plenty hard.

i had a kicker 12" L7 solobaric and a kenwood 1000w amp and it was way too much but i could do the two 12's to win audio competions though hehe :twisted:
06-29-2007, 06:53 AM
o4aveohb

2500 watts :shock: you'll have to upgrade the battery, even then expect heavy dimming of the lights. If you want really loud bass that might possibly shake the car apart then that'll do it, I had 500 watts and it was plenty enough.
06-29-2007, 09:30 AM
aveosummit

To open your eyes about car power amplifiers

To actually produce 2500 watts you will need :
Watts = Volts * Amps

@12.5V you will need 200 amps
@13.8V you will need 181.16 amps
@14.4V you will need 173.61 amps

Our alternator is 85 amps peak, you add in DRL, AC, you are looking at maybe 40amps available, with the car just running maybe 60 amps available, and when on ACC you are looking at a 12-12.5V available oppose to a max of 14.4V (16.1V in some vehicles) and average of 13.8V.

To actually produce 1000 watts you will need:
@12.5V you will need 80 amps
@13.8V you will need 72.4 amps
@14.4V you will need 69.4 amps

To actually produce 500 watts you will need:
@12.5V you will need 40 amps
@13.8V you will need 36.2 amps
@14.4V you will need 34.7 amps

--------------------------------------------------------

Quick crash course on amplifier efficiency:
Class AB max of 78.5% and greater then 50% or an average of 64.2%
Class D average 80%+

----------------------------------------------
Example: JL Audio 1000/1 Class D

Rated at 1000W at 11-14.5V

@11.0V you will need 90 amps
@14.5V you will need 68.97 amps

that would be given that the amplifier is 100% efficient
FYI the amplifier is built to pull the equivalent amperage to produce 1000 Watts at the given voltage between (11.0V and 14.5V)

Fused at 100AMP(req'd to install as the amp will shut off if the input voltage drops below 10V) fuse you get the following:

100amps x 11V = 1100Watts
1100 x .8= 800 watts (80% efficient) this the average wattage produced the rest is lost to heat.

To draw the 800 Watts
@11.0 you will need 72.73 amps
@14.5 you will need 55.17 amps

In a sub-compact/compact vehicle where the subwoofers pull 800Watts RMS your lights will dim no matter what you do unless you have a high performance alternator capable of delivering 80 amps at 1500-2000rpm.

---------------------
Compact and Sub-Compact vehicles
Average Alternator rating 85amps (peak)
Available to power after market stereo 50-60amps given no A/c or Heater running with an average voltage of 13.8V.

At 50amps:
12.5V x 50 amp = 625 Watts

13.8V x 50 amp = 690 Watts (Average the system can handle)

14.4V x 50 amp = 720 Watts (Max the system can handle before dim lights and other electrical problems occur)

At 60 Amps:

12.5V x 60 amp = 750 Watts

13.8V x 60 amp = 828 Watts (Average the system can handle)

14.4V x 60 amp = 864 Watts (Max the system can handle before dim lights and other electrical problems occur)

----------------------------------

Morale of this story you are not really getting the power you think you are! You gotta love marketing.

"Honesty is still the best Policy"
06-29-2007, 04:35 PM
deniswhite1

sorry for hijacking, but i have a quick question, i was given a 12" dual voice sub that is rated a 1200Watts (600watts RMS), now im looking for a an amp to power that sub.

what would be a good amp? (not the brand but power wise) 1200Watts?
and can it be asumed that amps RMS is half of the rated watts just like the subs?
06-29-2007, 08:22 PM
aveosummit

Quote:

Originally Posted by deniswhite1

sorry for hijacking, but i have a quick question, i was given a 12" dual voice sub that is rated a 1200Watts (600watts RMS), now im looking for a an amp to power that sub.

what would be a good amp? (not the brand but power wise) 1200Watts?
and can it be asumed that amps RMS is half of the rated watts just like the subs?

Depending on the ohm rating the voice coils 2ohm DVC or 4ohm DVC

If it is 2ohm DVC you could present an amplifier with a 1 ohm or 4 ohm load.
If it is 4ohm DVC you could present an amplifier with an 8 ohm or 2 ohm load.

Any Class D amplifier that is rated at 1ohm stable would be fine as long as it was able to give you 600 watts rms (750rms is what is needed when you add in amp efficiency) or less at either 4,2,or 1 ohm.

Any Class A/B amplifier that is rated for 2 ohm stable given you have a 4 ohm DVC as long as it is able to produce 600 watts rms (970rms is what is needed when you add in amp efficiency) or less at either 4 or 2 ohm.

Remember distortion kills speakers and amplifiers. Also under-powering a sub will not kill the sub but it can create a surge in your electrical system if the amplifier can not produce the rms of the speaker.
------------------
It is not safe to assume that the amp RMS is half of the rated watts just like the subs because amplifiers are classified by efficiency.

Example

Amp 1 has a 600W rms @ 4 ohm and is a class D Amplifier.
Amp 2 has a 600W rms @ 4 ohm and is a class AB Amplifier.

Given they have the same fuse ratings

Amp 1 would give you 480w rms on average (heat consuming the rest)
Amp 2 would give you 372w rms on average (heat consuming the rest)

Read the above post for information on amplifier efficiency's.

Hope this helps
06-29-2007, 10:32 PM

thats good posting so it makes sense now that 2500 in a truck would be doable but not for us considering we cant push more than 600 or so rms with the stock alternator
06-30-2007, 01:29 AM
deniswhite1

Quote:

Originally Posted by aveosummit

Quote:

Originally Posted by deniswhite1

sorry for hijacking, but i have a quick question, i was given a 12" dual voice sub that is rated a 1200Watts (600watts RMS), now im looking for a an amp to power that sub.

what would be a good amp? (not the brand but power wise) 1200Watts?
and can it be asumed that amps RMS is half of the rated watts just like the subs?

Depending on the ohm rating the voice coils 2ohm DVC or 4ohm DVC

If it is 2ohm DVC you could present an amplifier with a 1 ohm or 4 ohm load.
If it is 4ohm DVC you could present an amplifier with an 8 ohm or 2 ohm load.

the sub is 4 ohms, so i need an amp that would be 8 ohms or 2 ohms? (sorry, im bad with car audio)

can't any sub be setup for difrent ohms?

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