What is minimal power to drive subs?

[jhaymon]

I am pretty new to car audio. I have two 15" subs rated at 300 W RMS and 400W max at 4 Ohms. What is the lowest wattage necessary to drive those subs properly? I realize 300W is ideal. I have an amp that runs hot with them and cuts out because at 4 Ohms it only puts out 140W RMS. I assume this is the reason the amp cuts out. Is it ok to get an amp that would push 300W RMS but would max at higher than the 400W rating of the speakers? Would that blow the subs? If someone would help me out I would appreciate it.

[Mouser]

You can get an amp that is rated at a higher power than the max of your sub.....but you have to make sure that the gains on the new amp are set properly

[geolemon]

300w may not be "ideal".
300w is simply a limit - in other words, don't apply more than 300w to this sub, because it cannot thermally shed the resulting heat efficiently after that point.
That is why that spec is known as it's "thermal powerhandling" limit.
It's no measure of what is "ideal"... that number is a variable, not a constant. ;)

You cannot consider what "ideal" is without knowing several other factors, most of them related to your enclosure:

At the most fundamental, overly-simplified level... the larger the enclosure, the less power that you need to reach full excursion... and therefore, full output.
Applying any more power to the sub beyond the point where it's reaching full excursion is simply sub-suicide... you can bottom the sub out, causing mechanical damage to the sub.
Overexcursion damage is different than thermal damage... although both will result in "blown" subs.
Thermal damage occurs from exceeding that thermal powerhandling rating, the glue eventually heats to the point where it lets go of the windings inside the sub, and you end up with copper spaghetti.
Mechanical damage (overexcursion) occurs from exceeding the mechanical excursion limits of the sub, bottoming it out... damaging whatever collides first... whether that is the former on the backplate, the spider tearing, the tinsel leads pulling, etc.
It's caused from driving the sub beyond it's Xmax (technically, past its Xmech)... and the power it takes to do that is dependent on the enclosure that it is in.
It's very easy to bottom out a sub on a fraction of it's thermal powerhandling limit, given free reign over the enclosure design parameters.

The bigger you make the enclosure, the less power you need to reach full excursion...
...which means, the less power you need to reach full output.
You'll reach the same output with 300w on that sub in a small box, as you will with 100w on that sub in a bigger box, if both enclosures allow the subs to reach the same excursion levels on their respective amount of power. ;)

So, if you "only" have 140w, build a larger enclosure for your sub than the manufacturer recommends for it, and in doing so, you'll make it more efficient. It's that simple.
To better approximate how large of an enclosure you'll need to reach full output on 140w requires more than a "rule of thumb" type advice...
I'd suggest that you download software such as WinISD, and model up a sub on 140w, pull up the excursion plot, and monitor how excursion levels change (and by frequency!) as you manipulate enclosure variables.

The quicker answer to your question...
Yes, you absolutely can reach full output with your 300w sub on "only" 140w. Your enclosure dictates the behavior of the sub, and the output it produces, much more than the actual sub itself.

Good luck! :cool:

[ComfortablyNumb]

I am pretty new to car audio. I have two 15" subs rated at 300 W RMS and 400W max at 4 Ohms. What is the lowest wattage necessary to drive those subs properly? I realize 300W is ideal. I have an amp that runs hot with them and cuts out because at 4 Ohms it only puts out 140W RMS. I assume this is the reason the amp cuts out. Is it ok to get an amp that would push 300W RMS but would max at higher than the 400W rating of the speakers? Would that blow the subs? If someone would help me out I would appreciate it.

Geo knows all, listen to him.

Do you have these subs wired in series or parallel? If in Parallel the amp is seeing a 2 ohm load. Is the amp 2 ohm stable? If not that may be why it's overheating and cutting out.

[_gonz_]

Geo knows all, listen to him.

x2 :cool:

[johnybass]

Geo knows all, listen to him.

Do you have these subs wired in series or parallel? If in Parallel the amp is seeing a 2 ohm load. Is the amp 2 ohm stable? If not that may be why it's overheating and cutting out.


Ya if your subs are both 4ohm subs and there wired together in paralel and then bridging then the amp is seeing 2ohms while bridged and thats a no no for most 2 channel amps. Definitely could cause it to cut out and come back on once it cools down. If you have it wired any other way though with a 2 channel amp then your not even getting the full power out of the amp anyways. Hopefully you have a mono amp. Otherwise your subs dont really match your amp anyways and that means you need a new amp or sub. We could tell you where to buy one.