Is 100W output on amp enough for 400W Sub


New member
Username: Illusionaryman

Post Number: 3
Registered: Nov-04
i have Alpine MRV-F357 Amp and connected pioneer TS-W252C 400W 4ohms Sub to output speaker Terminal that gives 100W at 4ohms.... will 100W output be enough for 400W Sub??? and is 1W on Amp Equivalent to 1W on Speakers??? and if the sub was 2ohms will the output on the amp be 50W (half) or will it increase???

any replys will be Appreciated?

Silver Member
Username: Chevy_for_life

Post Number: 223
Registered: Sep-04
is 400 watts the subs RMS or peak?

Bronze Member
Username: Ohiopilot

Post Number: 32
Registered: Nov-04
Not all amps are designed to accept varying resistance. I don't see that model amp on the Alpine website, so I don't know it's specs. Remember these simple rules of thumb...

1. An amp has 3 basic ratings: Power, Channels, Resistance(s) Some amps allow bridging for certain resistances, some auto-sense, some don't allow bridging at all.

Both subs and amps have RMS power ratings and Peak power ratings. Pay attention to RMS, this is the rating that the manufacturer says the amp/sub can handle CONSTANT power at best, whereas Max simply tells you the biggest short-term blast it is rated to handle.

As for changing ohms by wiring parallel instead of example will illustrate best.

Say I have a pair of Widget Imaginary brand Subs, each rated for 500W RMS at 4ohms resistance each.

If I'm shopping for an amp, I have a couple ways to skin this cat. One choice is to search for a 2-channel amp that is rated for 500W RMS at 4ohms on each channel. Simple enough.

Another option is to connect the subs in parallel, creating a virtual single load at 2ohms with a target of 1000W RMS. In this case, we can buy a single-channel (mono) amp rated for 1000W RMS at 2ohms.

A third option is to find a 2 or 4 channel amp that says it is Bridgeable to 1000W RMS at 2ohms. This particular example's stats are not that common, but it makes the point.

***IMPORTANT*** Not all mult-channel amps are designed to allow bridging. Not all amps are designed to work at different ohm resistances. Be very careful, contact an authorized Alpine dealer or call Alpine tech support directly, it will be worth the 15 minutes of your time to be sure you have everything kosher.

The simple rule of thumb for matching subs to amps: Pick your amp so that it is as close to the Sub's RMS power rating without exceeding it.

The first sub-rule is that all subs have a RANGE of safe operations on either side of the published RMS rating. I had a JL Audio engineer tell me that I could drive a little 6w0 "sub", originally rated for 70W RMS at 4ohms with an amp that would be pumping it 125W RMS on it's channel. Sure enough, looking at the documentation for the 6w0, there is a RANGE of power, from Minimum to Optimum to Danger Zone to OUT OF WARRANTY. I'm sure most other brands are the same.

The second sub-rule is that most subs actually operate at 75-85% of their RMS power rating. So, a sub rated at 100W RMS actually will likely operate at peak efficiency at 75 or 80W RMS.

Hope all that helps. Best of luck on your installs. Sorry I couldn't get into specifics for your setup, I just couldn't find a doc for the components to help guide you better.

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 5944
Registered: Dec-03
a 100 watt amp with 400 watt subs will work fine.
the only drawback is that they may not be as loud as you want.
in this case my only warning is that you shouold never turn up the amp gain to compensate for lack of power.
If the amp isn't enough to make the subs as loud as you want, get a bigger amp.
setting teh gain too high only causes clipping, distortion, and driver damage which can result in amplifier failure as well.

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 5945
Registered: Dec-03
"The simple rule of thumb for matching subs to amps: Pick your amp so that it is as close to the Sub's RMS power rating without exceeding it."
bad rule.
it'll work, but remember the "power handling" of a speaker is only a thermal rating to tell you the amount of heat the coils can handle without incurring damage.
It has nothing to do with the amount of power required to reach peak output for the speaker, which is usually considerably less than the rated power handling.
An example is the Adire Brahma, rated to accept 1600wRMS, but only needing ~500wRMS to reach peak output in a proper enclosure.
Any more power won't really gain you anything with the possible exception of a steeper power increase curve, meaning more bass at lower system volumes without need to turn up bass levels on an EQ or head unit.

Bronze Member
Username: Ohiopilot

Post Number: 33
Registered: Nov-04
As the saying goes, we agree to disagree. I approach advise on these boards from a position of understanding my audience rather than lauding my own credentials or experience with ultra-specialized exceptions.

In terms of advising newcomers, this rule works well for 98% of any application they will encounter on consumer-grade equipment, and I stand by it. Not too many folks hooking up exotic gear like Adire Brahma will be asking basic RMS power rating questions and how to match a sub to an amp. I also indicated that there is a range, so again, the rebuttal posted is somewhat brow-beating as opposed to useful. As Einstein would say, IT'S ALL RELATIVE.

I also believe there was something in there about consulting with their equipment's manufacturer...

Gold Member
Username: Glasswolf

NorthWest, Michigan USA

Post Number: 5949
Registered: Dec-03
If you read past thraeds throughout this forum, you'll prove yourself incorrect on several of your points above.
What I pointed out isn't ultra-specialized. It's almost universally true. No opinions. Simple objective data.
My experience and credentials weren't in question, but they speak for themselves to the accuracy of my data. For a 19 year old though, you have a good start to an understanding for audio basics.
Never stop learning.

Bronze Member
Username: Ohiopilot

Post Number: 35
Registered: Nov-04
Poor Glass, when he gets nailed, he has to resort to character assassination (and is grossly wrong even there). How sad is must be to be both condescending AND insecure enough to lash out like that. Now we understand why you spend so much time here to rack up that kind of post count...
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