Amplifier output question

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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:
 
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)?
 
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.
 
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 caps....it will start a car and caps will not.
 
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 stuff....lol. 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.
 
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?
 
The way I was told is that a car battery releases it's power at a steady state and doesn't deal with power surge demands from a power hungry amp very well.A 1 farad cap mounted close to the amp after the fuse releases the needed short bursts of power that the amp wants during hard play.The power cap is said to improve the dynamic headroom of the amp by supplying very fast power bursts.

Another take on this is where I work...we use very large capacitor banks to compliment the power supply to all of the d.c. motor drives in the plant.:)
 
17DoubleE said:
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.

Sorry but that is incorrect. The caps inside an amps are in the secondary side and smooth the rectified current from the switch mode converter. So putting caps on the primary side which is where they will be if they are outside the amp, is not going to add to the secondary capacitance.

The reason caps stop dimming is because they average the current, i.e. drag the system down so that the lights don't get back up to full brightness so it appears they don't fluctuate as much.

As I said before, "the big three" wiring upgrade is the way to go.
 
richie00boy said:


Sorry but that is incorrect. The caps inside an amps are in the secondary side and smooth the rectified current from the switch mode converter. So putting caps on the primary side which is where they will be if they are outside the amp, is not going to add to the secondary capacitance.

richie00boy,

I'm refering to the caps on the primary side of the power supply, not those on the secondary....... Perhaps those amps you're familar with didn't have primary side aluminum electrolytics?
 
Well, I'm not sure what I'm going to do yet. First thing first is to look into a new headunit and get that straight as the higher voltage on the preamps completely rocks my system. I was just looking into my RMS wattage on my subs (which is why I was asking about the output on my amp cause I was thinking about getting another amp of the same kind, 1 for each sub, cause some reviewrs said that the amp hits harder on 1 sub than 2 so they would not recommend it on 2 subs) and I thought they were 300w max but they are only 150w. So, 2 subs=300w max power and I have a Alpine putting out 400w. So that's 50w over per sub. I'm not hurting anything because the gain is still down a bit but I was beginning to look into a higher wattage amp to get me more power but that doesn't make any sense now being as I'm already have a bit too much power. Might look into another brand amp to get me the power I want and need cause this one might not be cutting it, or by tax return time, get the next level up JL Audio subs that handle more power and upgrade that way. I know they say to match your RMS range of your subs with your amp and I thought I had done that but it's just not hard enough so I'm thinking the reviewrs might have been right about this amp with 2 subs. First though, I'm waiting to decide on what to do about a new headunit first. A lower wattage amp, maybe 2 channel instead of mono, would work a whole lot better sound wise and efficient wise than what I have.

What works better? A mono class D or a stereo 2 channel amp? I always thought the 2 channel mode was the best way to go and am believing that now...
 
Flyin11 said:
Well, I'm not sure what I'm going to do yet. First thing first is to look into a new headunit and get that straight as the higher voltage on the preamps completely rocks my system. I was just looking into my RMS wattage on my subs (which is why I was asking about the output on my amp cause I was thinking about getting another amp of the same kind, 1 for each sub, cause some reviewrs said that the amp hits harder on 1 sub than 2 so they would not recommend it on 2 subs) and I thought they were 300w max but they are only 150w. So, 2 subs=300w max power and I have a Alpine putting out 400w. So that's 50w over per sub. I'm not hurting anything because the gain is still down a bit but I was beginning to look into a higher wattage amp to get me more power but that doesn't make any sense now being as I'm already have a bit too much power. Might look into another brand amp to get me the power I want and need cause this one might not be cutting it, or by tax return time, get the next level up JL Audio subs that handle more power and upgrade that way. I know they say to match your RMS range of your subs with your amp and I thought I had done that but it's just not hard enough so I'm thinking the reviewrs might have been right about this amp with 2 subs. First though, I'm waiting to decide on what to do about a new headunit first. A lower wattage amp, maybe 2 channel instead of mono, would work a whole lot better sound wise and efficient wise than what I have.

What works better? A mono class D or a stereo 2 channel amp? I always thought the 2 channel mode was the best way to go and am believing that now...


it all depend on your power requirments and the subs you are trying to push. sound quality wise, I tend to prefer a standard class A/B amp with bipolar outputs over a class D amp or even a class A/B with mosfet outputs. there are exceptions of coarse. shop around and listen to a few different systems first. make sure the output gain from your head unit is compatible with the amp you choose and that you have the correct crossover options available as well. your sub enclosure and positioning will have a big influence on sound as well. are your subs in the recommended enclosure size?
 
Sub type, enclosure, sub size are all no problems...I love my subs...Just trying to get everything else straight. Made adjustments to the inside of the box a few weeks ago and knocked the internal cubic footage down from 1.37 to 1.27 per chamber...JL recommends 1.25 cu ft. so I'm about right on with no worries...
 
I just find it pretty hard to believe that the amp is really hitting that hard you know? I mean, if I'm sitting there with +50 watts more that the peak of the sub and my gain is 1 notch from max...It's not really mving me that much...It's just doesn't sound like it's doing it's job. I mean, if it was really hitting it hard then the gain would be say halfway...not almost full. So, maybe I need to try another amp. Or, heck...maybe I need to go to 15" speakers for my rock music...I mean, I thought 12's were suppose to be very loud :xeye: These are the answers I'm trying to find out about my system...If Alpines are such good amps, why isn't it driving it hard enough?
 
If it has some kind of problem, I guess you would need to describe what you have like wire sizes, box size/wood thickness/porting, how it is in what type of vehicle, HU and output voltage, any processors, using RCA input?, all that stuff. You should feel 400wrms no problem, I sure do and mine are less efficient IB that like to hit 30Hz not 50 as much. So they are not as 'loud', but they have the thunder and I can feel the thunder and the punch when they are cranked up. In fact my high side just gets blown away by the subs its ridiculous....and why I am dumping the big kicker because it does not have any power at 4 ohms as 4ch. Unless you mistakenly have it wired at 8 ohms or something, that will chop the power down.
 
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