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Flyin11 13th December 2007 02:25 PM

Amplifier output question
Probably a stupid question but I was trying to figure this out...I have a Alpine MRP-M450 which is rated at 400w into a 2ohm load. I have 2 4ohm 12's paralleled to make a 2ohm load. That beaing said, do you calculate the wattage to be 200w into each speaker or do you say it is really dishing out 400w into 1? :cannotbe:

glen65 13th December 2007 03:43 PM

Re: Amplifier output question

Originally posted by Flyin11
or do you say it is really dishing out 400w into 1? :cannotbe:

Total output power will be divided among all of the speakers
connected to it.

Flyin11 13th December 2007 04:20 PM

Thanks...Of course my first order of business is getting my HU situation straight and get what I want and all but after that, maybe if the price is right, I'm thinking of getting a capacitor (Or maybe a amp change from Class D to just stereo for 2 channels or a higher wattage Class D in March after tax returns) for my amp as my headlights seem to dim with the bass hits and I just got a new battery so it's not the battery. I saw that they say a general rule of them is 1 farad per every 500w. I tried a capacitor a long time ago on a Hyundai Excel and that was on a 280w MTX Thunder amp that was only running like 78w X 2 into 3 10" subs but that didn't help at all as my lights still dimmed on that car and I got the audio place to take it out and I got my money back.
I think that was a 2 farad cap but not sure.

I just don't want to waste my money :smash: so what might someone suggest? Would a 2 fard cap be enough or I'm looking at a good price on a 5 farad cap, would that be overkill? I don't want too much but then again I don't want to get something like a 1 farad cap and it not work and I'm stuck...Any suggestions (Also any good cap brand suggestions)?

richie00boy 13th December 2007 04:41 PM

Caps are a waste of time all they do is drag the system down to the dimmed level. You need to upgrade the wiring, particularly the three main earths from the battery to the car and engine.

jpruden 13th December 2007 05:19 PM

We should nip this in the bud right now...

Caps are, at best, a band-aid.

Your system is *really* powered by your alternator. Upgrade the alternator and you'll see the problem go away.

Without going into the BigBucks™ department, you might want to take a look at a Class D amp for your sub. I used to dim my headlamps often with my McIntosh MC440 (all class AB) because my poor 8 year old car's alternator couldn't keep up (it did sound great, though).

I swapped out for my current setup (JL Audio 300/2 and 500/1) and I can get MUCH louder with it and never get any dimming of the headlights... even when I'm sitting with the engine off. No capacitor required as the bass amp is now more than 70% efficient and can get better use out of the output from the alternator.

Electrical systems are similar to plumbing systems. Your alternator is like the line into the house. Low pressure or low flow here causes problems for everything.

Your battery is like the lines in the house. They hold some capacity to deliver water, but they only last so long...

A capacitor is like the reservoir on your toilet. Good for short shots, but they don't last long at all (<.5 seconds) and once they're empty, they have to pull energy from somewhere to refill. If the pressure and capacity of the rest of the system are bad, it won't refill.

Hope this helps.

jol50 13th December 2007 05:51 PM

I have a kicker with 420wrms at 2 ohm running 4 infinity 12s, so 105wrms each. Of course that would only be at 14.4v (in someone's dreams) and right at max output.

Going class D is about the only thing you can do to reduce power draw (or a smaller amp). Adding a battery will help more, or getting a large capacity battery. Larger wiring is needed to carry more current without voltage drop to keep output up, but not sure if that affects light dimming that much or not. From what I read a cap helps your alternator survive longer more than anything. It can help dimming only if very short duration. Adding a battery is more help than anything IMO, if you don't want to put in a larger alternator. Alternator runs at ~13.8v also, so you get more out of your amps than at a battery voltage of over a volt less. An alternator still can't always react fast enough to the sudden draws of an amp, depending on amp draw you might still need more battery at some point to hold voltage up until the alternator gets going.

If you had well water at your house, the battery would be the water tank that only has so much pressure and water in it. The pump would be the alternator, the pipe size to your faucet the wire size to your amp. You can imagine what happens if you change each component's size/capacity.

I bought a 1f cap for $15 and I'm going to use it with my stock alternator, but I will not be running huge wattage either. I also have a small sealed jumper battery I was thinking of mounting near the amps and I bet it would do much more than the will start a car and caps will not.

Flyin11 13th December 2007 06:13 PM

The Alpine is a Class D ;)

Also, I'm know there have been some capacitor threads in the past but...All in all, I wonder if they don't do anything then why do I see so many reviews from people saying that they solved their headlight dimming issues?

jol50 13th December 2007 07:47 PM

I think they help smooth things out a little, but are not a battery. Plus it might matter what you listen to, something with a drum beat might be fine but they are not going to help on a bass test CD with continuous bass tones. It seems like people just have way too high of expectations for what they can do, and too much marketing on them.

I was thinking that alpine was a D. I have a little mrd M to try next, it even shows the voltage on the amp, temp, etc.; pretty cool. I'm not used to all that new kind of Heck it was only $30 and I hope enough power for two cheap efficient IB 15s is the plan. These infinity will take more power IB but the efficiency is 89 or something, it gets about loud enough for me this way so why not reduce and take 100lb out of my trunk...they weigh a lot. Found some 15s that are 99db.

I would also recommend you check the grounds on your headlights, usually a little bolt near and behind them. I have had them not work that well and make it easy for other things to affect them. Also check the ground wire frame to battery, as all this stuff has to go through that wire together. It is easy to add another one of those to test, remember all that stuff can add up if you have a restricted path for the power. You can run the lights for a while and feel if the wire/connection gets hot, that is a real basic way to check the headlight grounds....and be careful if you have a bad one it will get real hot.

17DoubleE 13th December 2007 11:58 PM

A capacitor's esr (equivelent series resistance) X the ripple current it's being subjected to equates to power dissipation and thus heat. I believe the primary current in an amp's power supply can easily reach or exceed the ripple current rating of the relatively small capacitors built into the amp itself. How many times have you found bulged capacitors on an amp's input? If for no other reason, I believe an external capacitor will off load some the work being done from these internal caps and therefore reduce their temperature rise, extending their life. To minimize the total esr (the capacitor itself and the wiring) you'd want short wires between the external capacitor and the amp.

Music of course doesn't put the continuous strain on the power supply like sine waves do. During continuous output testing with sine tones my Punch 200's internal input caps will exhibit much temperature rise. I have not collected definate temp data but my fingers tell me they run cooler when I connect an external capacitor during this type of testing.

Any thoughts along this line of thinking?

Flyin11 14th December 2007 02:38 AM

No disrespect but...ummmm...LOL What? :confused: You just confused me with a lot of tech talk :smash: :o

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