Too Little Power

Hey guys.

I'm having a debate at work on this topic.  I took a W7 in a sealed enclosure tonight and hooked it up to one of our small 250 watt Alpine amplifiers with the gain and bass boost all the way up and ran it for about half an hour.  It played just fine afterwards.  But for some reason they still don't believe me that too little power does not blow speakers.  I then showed them the information at bcae1.com.  I was hoping that someone here might have some good links to other reputable websites that also disprove this myth.  Thanks for any help!

ADDED BY MOD:  Link to great discussion on this topic from some respected industry experts, including people like Manville Smith of JL Audio, Mark Eldridge of JL Audio and multi IASCA world champion, and Andy Wehmeyer of Harman Kardon. :  http://www.audiogroupforum.com/csforum/showthread.php?t=4332&highlight=clipping+blown

boy, its late and i feel stupid.  after i thought about it then yeah, id have to agree with you that youd have to overpower the speaker in order for it to blow. put me down for myth busted.

This is a very tricky question. With the situation you stated with the small Alpine amplifier, your right. You would smoke that amplifier faaaaar before that subwoofer would ever blow.

On the other hand, I have personally heard a subwoofer DAMAGED by running too little power to it and blasting the volume. Of course this equation all depends on two things:

1) The volume at which you play the "under-powered" subwoofer.

2) How "little" of power your actually applying to the subwoofer.

I once did a little experiment with a friend based on this underpowering theory. We hooked up a nice JL sub (don't worry it was free) to an old 60 watt Hifonics amplifier. We played the subwoofer the whole time in free air resonance to try to keep the results from being flawed by different enclosure sizes. I am by no means a scientist, but we did try our best to keep experimental errors to a minimum. We cranked the amplifier gain just as you stated with your test. At low volumes it sounded all right, but certainly nothing special. Lets just say that at low volume, it played....

We then began to slowly turn up the volume. The louder we got the volume, the worse it sounded... until we got the volume past 80%.... we then heard a loud popping sound from the woofer and immediately shut it off. We thought we had blown the subwoofer, but to our surprise after examination the subwoofer appeared to be intact. We played that same subwoofer later on hooked up to a 500 watt JBL amp and it still thumped! I do know for a fact that we definitely did damage to the speaker though, because it just didn't sound the same. It had a little internal rattling on certain frequencies and couldn't hit the low ones like it could before. (kinda sounded like the voicecoil was in the early stages of blowing) By the way, it was originally hooked up to the JBL amp and it sounded great... until I asked the question about putting a lot less watts on it. That's when the experiment begain and the subs "sound quality" got decreased. lol.

My friend also told me that a week later, the subwoofer blew. He didn't unhook it from the JBL amplifier and he claims that it didn't even blow at a high volume. He said he was just listening to some reggae beats and then say goodbye to the JL sub! I'm not going to say for sure that the sub blowing was a direct cause of our "experiment". There could have been other factors that played a part in the course of the week that caused the failing sub.

Is it possible to BLOW a sub with too little power? maybe.  With continued use at very low wattage and very high volumes, I would say it could be possible. Typically, no. Almost all subwoofers blow with too much power and not too little. As far as concrete, scientifical evidence goes, I don't know a site that states this too little power theory to be true,sorry. I do know what I saw and heard. Hope that helps.

OK, One thing I did not see is any significant mention of heat.  This is the most prominent killer of subs that I know of.  Mechanical damage springing from the over stressing of the spider is another main source BUT...  I think the main point of BCAE explanation about clipping is that it prevents the speaker from cooling itself well enough. SO heres my take on this...

Driving a speaker with a clipped signal creates the opportunity to damage the speaker.  This depends on the speaker and how much power is used.  The first thing we need to establish is that a speaker(voice coil) makes heat.  I was going to go into great detail here but decided not to.  (it was getting to be quite the work of art though :)).  This is the enemy we face when we talk about underpowered amplifiers and clipping.

If we can agree that a voice coil makes heat then we should also agree that it needs to disapate this heat otherwise bad things are going to happen.  When a speaker moves, it moves air; not unlike a fan moves air.  When a speaker moves correctly it moves alot of air and so cools itself very well (hopefully if its designed well).  When a speaker moves with a clipped signal it is like only moving a fan in little burts (Swing left...Stop...swing right...Stop...etc.).  Beacuse of this the speaker is not cooling itself as the designers made it to.  All the while however, curent is still flowing through the voice coil (FULL power when its stalled at the top or bottom of a clipped signal) and this current is constantly making heat and leading to disaster (the cooling offsets this with equal magnitude normally).  So what ends up happening is you have a speaker not cooling itself and having lots of current flowing through it (the ratio of cooling to power gets worse as the clipping approaches a square wave). 

SO depending on the heat tolerances of the speaker and how it was designed a underpowered amplifier could very easily cause speaker damage.  This will usually be by melting the insulating substance that keeps the coils from shorting out...thereby letting them short out...which only makes a huge drop in the resistance of the speaker...which means more current and more heat only now extremely localized...and eventually all this usually leads to the voice coil itself breaking because its now been turned into a fuse. 

But many speakers these days use quality materials in the construction of these key areas and speaker manufacturers are over building their subs.  What this means is that even with less than optimal cooling the speakers voice coils and insulating substance have heat tolerances that the conductive and radiating cooling is enough to keep any problems from arising for most amps rated under the speakers ratings.

Now you are completely right that a larger amplifier will manifest this problem much more quickly and putting more power through a speaker than it was designed for will obviously overload the designed cooling capacity.  But if your doing that your probably over loading your spider as well and other problems such as the former coming off the pole or destroying its voice coil through hard bottoms.

So still confident that its not going to happen?  I'll show you!  Set up the same speaker and amp but now instead of turning the gains up to produce clipping, I will just give you a clipped audio signal.  (why?  because many amplifiers these days have circutry in them that most likely limits clipping and so most amplifiers will not go into extreme clipping.  BUT...hehe... We are looking to prove your point that no amplifier putting out less power than a speaker is rated for can blow the speaker.)

So if your man enough to back your talk up with aciton...burn this to a CD (its just an audio file like any other song only extremely repetative) and put that speaker amp combo back on for another hour..If you can :).

6.25Hz Clipped Signal (MP3 Format): http://h1.ripway.com/gbear14275/6.25Hz_Clipped.mp3 (songs under 13 min, if you can play it for that long...)

(The W7 model has some advanced cooling technologies incoporated into it and so it might be fine...But if you do this I would be prepared to buy the speaker...and possibly the amp for some reason if its protection circuts fail.  Also this is an extremely low frequency mp3 file, make sure the amp you use does not have a subsonic filter on it.)

Hey guys, I think you misunderstood the purpose of this thread.  I wasn't trying to learn whether it is possible or not because I know for a fact that it isn't possible.  In every way, shape and form if a subwoofer was blown, it was due to too much power.  Even in your above example, you damaged that sub by too much power.  You pushed the sub past it's mechanical power handling which caused damage.  Keep in mind that mechanical power handling is a function of the enclosure, or in your case the lack of it.

The point of this thread was to gather some more reputable web links which I could use.  So, does anyone have any?

I think you would be surprised at how insignificant this is.  For one thing, the reduced cone motion you describe isn't as significant as you would expect.  But here's a great white paper about dual voice coil drivers that will show you how insignificant it is: http://www.adireaudio.com/Files/TechPapers/DualVoiceCoilDrivers.pdf

So how is that "underpowered"?  There is obviously too much heat causing the melting you describe, which means too much power.

And that's exceeding the mechanical power handling of the driver.  But you are still causing damage from too much power.

When did I say anything about "rated" power?  I am saying that damage to speakers is caused by too much power every time, independant of the rating the manufacturers marketing department decided to slap on the sub.  If you heard what the subwoofer at work was producing, it would be very obvious to you that the amplifier was clipped as the music was highly distorted.  But as Dyohn said in the link I provided above,

"I can drive speakers with a 100% clipped square wave signal all day long with no problems as long as the thermal and mechanical limits of the speaker are not exceeded.  I can feed a speaker 100% distortion all day long with no damage as long as the thermal and mechanical limits of the speaker are not exceeded.  I can exceed the thermal and/or mechanical limits of a speaker and watch it fail in short order.  These are electrical and  physical truths and anything else is a myth."

Steven: tell your colleagues who doubt you to go back to school and study some physics.  Maybe some basic electricity would help too.  :)

And gbear, please read Steven's responses carefully.  He is 100% correct.

As far as other web sites, that should be unnecessary for anyone who understands the basics of how a loudspeaker works.  But I'll see if any manufacturers have posted information about this pervasive myth.

I didn't really read the above posts, but i was thinking. Even if you were feeding a speaker less power than its rated for at a fully clipped signal, could it be possible for the power to jump across the windings and eventually just weld them so much that the VC windings actually melt and separate leaving a gap?

I can honestly say i don't know as much about the electrical aspect of the speakers as i should, i have 4 years of Electrical engineering in school ahead of me tho  ..and i can't wait!