22 replies to this topic

[DrBoom]

I have a pair of Kicker CompVR-12's and they are rated at 400RMS per speaker. They are currently in a sealed box made by Doran Pro audio and have no dividers between them. The internal enclosure is 2.7cu ft total for both drivers.

Looking at the speakers manual, I found out that different enclosures makes the power handling fluctuate, in a small sealed box of 0.5cu ft is rated at 400rms. large enclosures close to 2.0cu ft sees a power rating of 150rms.

So in conclusion, the speaker is not 400rms or is it?

Secondly, an installer friend of mine advised me that the subs will die later due to not getting adequate power as I am feeding them around 70rms per driver.

I don't see the point of my blowing them up since I know speakers only blow due to distortion and DC going though them since the amp runs out of power at high volumes.

I don't see why I will blow them up if I am happy with 70rms per speaker and compairing to home audio speakers which tend to last decades being fed with only low power most of their lifetime, I see no logic to my mates advice even though he is an installer.

As a matter of fact I have a 30 year old Pioneer 3 way speakers rated at 30watt RMS at home which still works being run of a 70 watt home amplifier. Sorry the back of the amp states 70watts so I am assuming it is peak power???? Could you audio gurus shed a light in this matter?

[>WAYCON<]

DrBoom said:

I have a pair of Kicker CompVR-12's and they are rated at 400RMS per speaker.  They are currently in a sealed box made by Doran Pro audio and have no dividers between them.  The internal enclosure is 2.7cu ft total for both drivers.

Looking at the speakers manual, I found out that different enclosures makes the power handling fluctuate, in a small sealed box of 0.5cu ft is rated at 400rms. large enclosures close to 2.0cu ft sees a power rating of 150rms.

So in conclusion, the speaker is not 400rms or is it?

Just read the manual online, and some of the "tech" speak (read: marketing) was amazing. In any event the volume of the the enclosure will of course affect the efficiency of your sub. However I think that you have forgotten to add your second Sub to the equation. You have roughly 1cuft for each sub (2cuft shared for 2 drivers) so if you look at the manual you will see that this is spot on for what Kicker reccomend for a 12".

Kicker Manual said:

CVR12 1.0 ft3 Power Handling = 400W RMS  
4.6 ft3 Power Handling = 300W RMS

So you should be getting the max power output from the current box.

DrBoom said:

Secondly, an installer friend of mine advised me that the subs will die later due to not getting adequate power as I am feeding them around 70rms per driver.

lol really? Tell us who he works for so that I can never take my car there....
Seriously - you will not kill a sub from underpowering of this nature. Think about it - unless you had your speakers on full bore all day every day then your speakers wouldn't be seeing 400wrms anyways. And as no one I know does that, and all of their speakers continue to work just fine, I think you will be right

DrBoom said:

I see no logic to my mates advice even though he is an installer.

Spot on

[audioquest]

DrBoom said:

Secondly, an installer friend of mine advised me that the subs will die later due to not getting adequate power as I am feeding them around 70rms per driver.

What! Never heard of this before in my life!!! Who is this installer? I am running 75rms for each coil in my subwoofer. Never die before.

[mack202]

DrBoom said:

Secondly, an installer friend of mine advised me that the subs will die later due to not getting adequate power as I am feeding them around 70rms per driver.
   
I don't see the point of my blowing them up since I know speakers only blow due to distortion and DC going though them since the amp runs out of power at high volumes.

Your friend probably didn't explain it to you well enough, or he doesn't know exactly what he's on about (neither do i really)

It is only a problem if YOU give the subs a clipped signal from trying to drive your amp too hard. Its the same thing as though if you were running splits. If you drive your amp beyond its abilities, it will start to clip, and give the speaker unhealthy power bursts.

The reason someone may say that it is dangerous to use this amp with those subs, is because the 70rms may not sound very loud to you (or not as loud as you want it to be on occasions) and pretending you had no idea about amps and speakers, you would just try to crank it up as loud as possible. Im sure a clipped signal from your amp wouldn't instantly destroy your sub, but if you fail to notice that you are giving your sub a clipped signal ( you should hear it i think, although i don't know what it sounds like personaly, just bad) over a period of time, then you might be able to say bye bye to your speakers.

[stazed]

Underpowering a speaker, AND pushing it to put out the same volume that it would put out with an ample amount of power, will definitely destroy a subwoofer!



I have a Hertz HX300D subwoofer. It's a 600w RMS speaker.

I've seen one of these at Marty's.... destroyed.
I ask, how did this happen, someone gave it way too much power?

The answer was that the speaker was given 50W RMS..and was at maximum volume because the owner was outside his car testing for rattles. As such he couldn't hear (well, he probably could hear, he just had no idea what it was) the absolutely awful distortion since the amp was clipping to buggery.

Long story short, the speaker cone was destroyed, coils melted, etc etc.

So it can happen.. and I think this is a good time to quote the fhrxstudios.com FAQ:

http://www.fastfoursforumscarclub.com/temp...ios/faq.asp#1.5

It explains exactly why an underpowered speaker simply burns itself to death!

[niteflyer]

http://www.bcae1.com/2ltlpwr.htm

amp clipping destroys speakers
you can underpower your subwoofer til the cows come home, just don't push your amp into clipping

but if you are underpowering your sub then you are "more likely" to drive your amp into clipping when you turn up the volume

[bob]

Assuming the clipped signal heats up the voice coil enough. You could run a clipped signal all day long from a 1watt amp into a sub that can handle 500wrms and theres no chance it would die anytime soon!

[stazed]

bob^ said:

Assuming the clipped signal heats up the voice coil enough. You could run a clipped signal all day long from a 1watt amp into a sub that can handle 500wrms and theres no chance it would die anytime soon!

lol...

That's like saying "if you connect your subwoofer up to the remote turn on wire, you won't have a problem"

We're talking about amplifiers here... not connecting a subwoofer to your iPod!

[mack202]

yeah but i have to say im suprised a clipping 50rms amp was able to destroy a sub capable of more than 600rms. I thought that you only really get 2-3 times larger bursts of power when its clipping.
Well at least i have learnt something.

[Cyberpunky]

there is no such thing as UNDERpowering period. This was pointed out in the second or third post and correctly pointed out. I listen to my system at less then full power all the time....doesnt do squat.

The issue with a sub blown off a 50w amp is what was he playing ? obviously was test tones or sweeps if he was rattle hunting, not music. Obviously he had gains set wrong too so it clipped these test signals.

If you have gains set correctly then 70 rms wont hurt your sub at all, it cant. Maybe running more power would be a good idea if you wanted more output as I imagine your subs arent super efficient and so more power will be required to go louder but only if you want more. If your happy then its all good as long as you are using music. *note test tones should be used with caution on any system regardless of power

as with any advice, check the source, as info is only as good as the source is.
peace
Cyberpunky

[bob]

Sorry Stazed but I still stand by my statement. OK my power examples might not have been the best, but its only if the clipped signal is producing more power than what the woofer can handle is where it will blow things.

[Blackrazor]

In answer to the first part of your question Dr Boom, the answer is 'depends'... there are two main types of power handling, thermal and mechanical...

Thermal power handling is the amount of power the subwoofer can take on a reasonably common basis before the voice coil melts, shorts, or delaminates... its usually pretty constant, in that the size of your box wont affect it...

Mechanical power handling on the other hand, is the amount of power you can feed a sub before it reaches its mechanical excursion limits and starts slapping itself on the backplate or various other peices of the sub structure... this is VERY box dependant, in that a larger box will usually require less power for the sub to reach full excursion A driver than may be able to take 1500w in a 0.5cf enclosure before it reaches its mechanical limit, may only take 500w to do so in 3cf

In the end, the actual power handling of the sub SHOULD be whichever is the lowest of the two above in the enclosure you're using... for instance, say your sub is rated to handle 400wRMS, and it reaches its mechanical limit with 400wRMS in a 1cf enclosure... that would mean that with a box smaller than 1cf, you would be limited by the thermal handling of the coil to 400wRMS imput. In a box LARGER than 1cf, you'll be limited by the mechanical handling of the driver, which can be 100w, 200w, or whatever the box size dictates

Hope thats not too complicated an explanation

[stazed]

bob^ said:

Sorry Stazed but I still stand by my statement. OK my power examples might not have been the best, but its only if the clipped signal is producing more power than what the woofer can handle is where it will blow things.

No need to apologise.
I made me judgement based on things I've read and seen with my own two eyes.

Obviously we can disagree, it just means you're dumber than me!

[bob]

hahaha. Most of us are grown men around here

[Bassaholic]

In regards to clipping, dc and thermal power handling.

Clipping does not cause DC. The clipped part at the top (and bottom) of an alternating wave is not DC. The part at the top of the wave actually contains odd order harmonics (ie, higher frequency sound).

That is why clipping sounds distorted. The speaker doesn't magically stop moving therefore there won't even be any reduction in cooling due to less coil movement.


(Actually, I don't believe the additional cooling due to movement of the coil is quite as significant as some people make it out to be, but that is another topic altogether...)

Secondly, in regards to thermal power handling, speakers don't care what signal you give them. If you have a speaker that can handle a 100w RMS sine wave continuously, then it will be able to handle a 100w RMS square wave continuously, or a 100w RMS clipped wave or whatever.
Mechanical power handling is different as explained by Blackrazor - in that case, it depends on the enclosure as well as power vs frequency. (low frequencies require more excursion)

On to the speaker power ratings though.

RMS speaker ratings are not continuous sinewave ratings. A speaker rated at 400w RMS will NOT be able to handle a 400w RMS sinewave for a long continuous period of time. The signal used to rate speakers (for thermal power ratings) is usually filtered pink noise (pink noise is equal RMS power per octave) with a crest factor of 6dB. That means that the difference between the peaks and the average RMS volume is 6dB. The rating is the maximum (usually rounded off) amount of power (of the peaks) that the speaker can handle for a very long period of time. A 6dB difference is four times the amount of power (twice the voltage). That means that a speaker that is rated at 400w RMS can only handle a 100w RMS continuous sine wave.

But fortunately for us, we don't listen to sine waves, we listen to music. Music also has a significant crest factor and even though the peaks may be at 400w RMS, the average power for a particular imaginary song may be only 50w RMS (or perhaps less depending on genre etc).

Where does clipping come into all of this?

Ok, in theory the RMS power of a square wave with the same peak voltage as a particular sine wave will result in twice the RMS power of that sine wave. This means that if you clip an amplifier playing a sinewave, you will get significantly more power out of it than you would without clipping it. In the real world, amplifiers won't output quite twice the power, but it will still be significantly more.

Secondly, going back to the power ratings and the crest factor - well if we use that same song (with the 400w peaks and 50w average) and clip it by 3dB the average power output will double. The peaks will be twice the RMS (and completely squared off, we are assuming a theoretical perfect amplifier), and the average power will be 100w. If you clipped it by another 3dB, the average power wouldn't quite be double (since the power of the peaks won't increase) but it will be close. (it will also sound extremely distorted). Since the average power is now over 100w RMS, chances are you would blow that 400w RMS speaker.

So what is the point of all this?

It is not the shape of the signal that overheats speakers, it is the amount of power that the speaker recieves.

Quote

Underpowering *(by using a smaller amplifier and clipping it)* a speaker, AND pushing it to put out the same volume that it would put out with an ample *(unclipped and close to the power rating)* amount of power, will definitely destroy a subwoofer!

(*I clarified what I think stazed meant)

So according to the facts, stazed's comment is mostly false. If the speaker can handle that amount of RMS power when it is unclipped, then it will handle the same amount of RMS power when clipped.

(anyone notice how I keep saying RMS?........)