How are subs power ratings calculated?

[microhaxo 10+ year member]

I know that people go by the general rule of thumb W = v^2 / ohm

But that is not true W != v^2/ohm

The last few days have changed my views of car audio installation for ever.

True rms is

Watts = Amperage x AC voltage

and

Ohm = AC Voltage / Amps

So my question is how do companies determine the RMS rating of their subs?

Currently im running a hifonics amp that is giving my sub 40v at 1 ohm, thats 1600w rms to a lot of you guys but in reality its only 510w RMS...

My sub is rated to take 600w RMS but i believe that this is not quite true..

If i give my sub 600w TRUE rms it would go beyond its excursion limits by a great deal.

No bass boost all flat.

Sorry for the confusing jargon, i just want to be more educated.

Click to read more...

 

[stillfly45 10+ year member]

i dont think they really use a formula to determine the its RMS... it based on the subs magnet size, suspension, surround, etc.

U can look at a sub and get a estimate of what power it can take

 

[bones22 5,000+ posts]

How long they survive a wall socket.
6 seconds=600wrms

if it were only that easy

most subs wont last 6 seconds on a socket

 

[stillfly45 10+ year member]

How long they survive a wall socket.
6 seconds=600wrms

i am not 100% on the subject, but i kno for a fact thats definitely not true at all

 

[microhaxo 10+ year member]

lol..

All im saying is THERE IS NO WAY you can give 600 TRUE rms to a 600w rms sub and expect it to survive very long.

 

[Gavriley2007 10+ year member]

lol..All im saying is THERE IS NO WAY you can give 600 TRUE rms to a 600w rms sub and expect it to survive very long.

ever heard of 4" coils they love power and just because a couple crappy company's rate shit stupid doesn't mean all do

 

[htownplaya456 10+ year member]

With out reading anything and going by the title... Start at wall socket and go down or up from there so you know how much it'll handle.

 

[microhaxo 10+ year member]

Im not saying crap companies at all, im not running some sony or pyle crap.

Ive tested this on Phoenix gold RSDC's 12" and Fi Q 12"

The fi q had NO chance of taking 1000 True watts rms.

I wish a dealer or manufacture would chime in on how the Root mean square is determined for the sub..

I was always under the impression subs should be ran at RMS.. Questions that come up are, do the companies check to see how many watts can constantly be held by the coil before causing damage with no regards to quality of the bass that comes out at those watts?

 

[IDSkoT 5,000+ posts]

They use the T/S Parameters and the Electromagnetic parameters / etc.

They find these with a variety of tests / sensors.

And WTF is True-RMS?

RMS = RMS.

 

[microhaxo 10+ year member]

So which method of calculating RMS is accurate to run the subs at?

w = v^2 / ohm (which this cant be if you assume that the factory rms rating is actually a root mean square)

or

w = a * v * efficiency of amp (more could go here) ( this seems untrue as well because in an attempt to attain an actual RMS power to the subs i found that they couldnt handle them)

So since i am running my Sub at 40v off of the amp at a 1 ohm load that must mean that i am running at 1600w rms according to 85% of the car audio enthusiasts on this forum. (which is unlikely since the PEAK rating on my sub is 1200w. Not to mention box rise but we wont get into that..)

 

[scarolinablazin 10+ year member]

i may be wrong but not all amps put out the same power at 40 volts??? what amp??

 

[pjhabit 10+ year member]

i may be wrong but not all amps put out the same power at 40 volts??? what amp??

it depends on residence as well

Voltage = Sq. Root of (Watts x Ohms)

 

[microhaxo 10+ year member]

Ahh, i said assuming a 1 ohm load..

40v at 1 ohm on any amp is "1600w" provided it can do it..

I know for a fact that there are a few of you who know EXACTLY what i am talking about..

 

[n2audio 5,000+ posts]

in your OP where do you get "in reality it's only 510w"?

I have no idea how mfg's arrive at their speaker ratings, but would bet a lot that it varies pretty widely.

I think most speaker ratings are intended to identify the size of the amp that should be used, not necessarily the actual thermal power handling capability of the speaker.

The average speaker rated for 100w rms is intended to be driven with a 100w amp.

The 100w amp, in turn, will deliver roughly 20w (actual, average) to the speaker due to the crest factor of music.

Setting your gains with a DMM at the amp's rated power using a 0dB tone only assures the amp will never clip, and almost assures it will never reach full rated ouput, even dynamically, because of the way music is recorded.

 

[microhaxo 10+ year member]

in your OP where do you get "in reality it's only 510w"?

My amp is giving out 40v AC that is 1600w if you go by the equation to set gains by.

However that equation is wrong.

Wattage is Volts x Amperage NOT Voltage ^2 (not including resistance of course)

I am pulling 18 amps at 40v ac.. If you do the math that equates to 720 watts in a perfect world.

We know that class d is not 100% efficient so we take 720w and multiply it by its efficiency so we get 720 * .707 which gives me ~510w True RMS power to the sub.

Hope that explains it better for you.

Also i do not believe that my Phoenix Gold RSDC 12" 2 ohm subwoofer with an rms rating of 600w was designed to run off of a 600w peak amp.

It would be nice if a subwoofer engineer / designer would step in and clear things up.