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Too Little Power


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DYohn 
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Location: Arizona, United States
Posted: March 10, 2006 at 11:48 AM / IP Logged  

Alpine Guy wrote:
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?

No, this can't happen as long as the power rating of the voice coil is not exceeded.  What you are describing might happen if too high a voltage was presented to the coil.  The insulation on the coil windings are rated for a particular maximum voltage (as is the insulation of any wire) and if it is grossly exceeded you might be able to arc-over (or flash) the windings.

The way clipping can damage a loudspeaker is if the available amplifier power is already at or over the coil's thermal limits when the signal gets clipped.  A clipped signal presents an increase in power over an AC signal by as much as 100%- and sometimes more.  If an amplifier is producing say 100 watts of music signal, in full clip mode this will jump up to as much as 200 watts (or depending on the available rail voltage, even more.)  So if your speaker is only rated for a thermal load of 100 watts, the clipping amplifier will overload it and potentially fry it. 

This is the origin of the "under-power myth."  If your speakers are rated for 150 watts and you use a 100 watt amplifier then drive it into full clipping, it is actually delivering more like 200 watts of effective power to the speaker when the speaker blows.  "Oh," you say, "I used a smaller amplifier than the speaker rating and it blew.  Therefore under-powering must blow speakers."  No, what happened was idiotic amplifier setup blew the speaker.  If on the other hand you are using a speaker rated for 500 watts and run the same full-clipped signal from the 100 watt amp, it will hum along all day producing horribly distorted clipped sound, but it will not care since you are not exceeding it's power capacity.  Did that make sense?

Also, a clipped signal is in effect a momentary DC signal.   A DC signal will make the loudspeaker motor stop moving.  Movement of the voice coil is what cools it.  The heat generated by a DC signal may be enough to overheat the coil windings if you again are using an amplifier that can exceed the power capacity of the speaker, it is possible to overheat the speaker due to loss of cooling.  I believe this is what gbear was getting at.   But the amp must be operating over the power limits of the speaker and the clipping must be severe or the speaker will not care.

It's a complex problem, actually.  Many people will recommend that you always use larger amplifiers than a speaker's ratings in order to stay away from the clipping threshold (this is called amplifier headroom.)  This is good advise IF and only if you understand how to ensure you never overpower the speaker.  Fuses or gain adjustments can help in this, but ultimately it is all about monitoring the power levels and paying attention to not exceeding them.  Not commonly done in car audio.  The other recommendation is to always use speakers rated to handle at least 3X the power output of your amplifiers (speaker headroom.)  This way, even if you do clip the signal now and then, the speaker can handle it.  But again, in car audio most customers feel they are somehow being "cheated" if they cannot use "the full potential" of their system - whatever that is.  So, the compromise, and what I usually recommend, is to use amplifiers that do not exceed the average power handling capability of the speakers, and then carefully set the gain so the amplifier will not clip under normal usage.  Then be careful with the volume knob and don't "crank it."

If under any circumstances a user finds themselves "cranking it" too much, or wanting to turn up gains to try and squeeze more out of a system, then they need to purchase a new system, plain and simple, or they will fry what they have in short order.  Too Little Power - Page 2 -- posted image.

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Alpine Guy 
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Posted: March 10, 2006 at 12:08 PM / IP Logged  
This thread should be added to the long sticky list, its very informative.
2003 Chevy Avalanche,Eclipse CD7000,Morel Elate 5,Adire Extremis,Alpine PDX-4.150, 15" TC-3000, 2 Alpine PDX-1.1000, 470Amp HO Alt.
Steven Kephart 
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Posted: March 10, 2006 at 1:21 PM / IP Logged  
DYohn wrote:

Also, a clipped signal is in effect a momentary DC signal.   A DC signal will make the loudspeaker motor stop moving.  Movement of the voice coil is what cools it.  The heat generated by a DC signal may be enough to overheat the coil windings if you again are using an amplifier that can exceed the power capacity of the speaker, it is possible to overheat the speaker due to loss of cooling.  I believe this is what gbear was getting at.   But the amp must be operating over the power limits of the speaker and the clipping must be severe or the speaker will not care.

This is something I have been curious about.  When I've set gains on amplifiers in the past using an Osciloscope; at the point when I meet and then exceed the point of clipping, the wave form doesn't just cut off the top flat like you would expect.  What instead happens is the peak inverses on itself.  This seems to show that the signal doesn't hold the cone in place, but in fact still keeps it moving.  This makes sense based on how Dan has always described a subwoofer as being a constant acceleration device.  So whether it is accelerating or decelerating, it is constantly in motion as long as there is some form of signal on the driver.  And that is why I believe the "loss of cooling" is rather insignificant.  Or am I understanding this wrong?  I will admit that this is something I haven't fully studied.

Steven Kephart 
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Posted: March 10, 2006 at 1:25 PM / IP Logged  
DYohn wrote:

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.

Thanks!  I actually tried to do a google search on this, and was rather shocked at how many topics I came upon that perpetuate this myth.  But I figured some of you guys may have ran into something in the past that might help.

DYohn 
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Posted: March 10, 2006 at 1:45 PM / IP Logged  

Steven Kephart wrote:
This is something I have been curious about.  When I've set gains on amplifiers in the past using an Osciloscope; at the point when I meet and then exceed the point of clipping, the wave form doesn't just cut off the top flat like you would expect.  What instead happens is the peak inverses on itself.  This seems to show that the signal doesn't hold the cone in place, but in fact still keeps it moving.  This makes sense based on how Dan has always described a subwoofer as being a constant acceleration device.  So whether it is accelerating or decelerating, it is constantly in motion as long as there is some form of signal on the driver.  And that is why I believe the "loss of cooling" is rather insignificant.  Or am I understanding this wrong?  I will admit that this is something I haven't fully studied.

No, actually you are right on.  Many other effects such as inductive or capacitive discharges will impact the signal as soon as it approaches DC and cause the waveform to continue changing.  The only time the loss of cooling effect becomes significant is in a hard clipped square-wave at a very low frequency, and even then the signal would try to instantaneously accelerate the voice coil from full positive to full negative deflection, which of course cannot happen.  There is also the effects of power compression which will blow a speaker and are often masked by clipping.  The reason I mention it as a contributing factor is because of cumulative effects over time (meaning the longer the signal is in clipping condition the more heat can build up inside the motor assembly.)  A clipped signal can and does cause the woofer motion to "stop," even if it is only a micro-stop.

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gbear14275 
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Posted: March 10, 2006 at 11:56 PM / IP Logged  

Steven Kephart wrote:

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."

Ok if this is what you mean then your argument and answers are trivial.  It's like you claim all car accidents are the result of excessive speed and then when someone disagrees you reply.  If the car crashes rolling around at 1 MPH and runs into a garbage can that 1MPH is what caused it to run into the garbage can and so the 1MPH was excessive speed.  Technically your right because without the movement the there would be no accident but you see there really is no value in arguing in this technical manner.

You obviously understand the technicalities of speakers and power but for those who do not have the knowledge or don't think in that manner you are probably conveying to them that under rated power cannot blow speakers.  Which is obviously untrue.

So yeah we were both right and both wrong depending on our definitions of the problem.  I think what the best course of action would be though is for both of us to explain the matter as if we were talking about whether or not an amp rated as putting out less power than a speaker is rated for can cause damage.  Of which the answer is yes.

I understand what your saying and therefore know that you are in fact 100% correct but we should help the less educated...and argue about problems that are less easily solved.  That should be way more fun :)

But good debate even if we were arguing the same point at one another! (I hate when that happens lol) :) :)

willdkartunes 
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Posted: March 11, 2006 at 12:22 AM / IP Logged  

Steven Kephart,

Were you saying that the speaker damage was due to the subwoofer not being in an enclosure? Wouldn't I have to drastically change the enclosure size when going from 500 watts down to 60 watts?

By the way, I ran the same experiment with the same amplifier and same type of subwoofer. I obviously couldn't use the exact same subwoofer since  I mentioned earlier it is already dead. So I just used the same exact model and brand - JL 10w7. With the same 60 watt amplifier I didn't turn the amplifier gain to full, but instead left it half-way. I got an identical result of what I described in the first experiment. It just took a little longer for the "damage" to occur.

Of course if the reasons for the speaker damage were due to having the subwoofer in no enclosure then the experiment is indeed flawed...

I know your original thread had stated for another website to provide more information on this topic. I'm really sorry about not being able to produce a website so you could read someone elses findings. I figured that maybe my experience with this topic could possibly be of some help. Or maybe I was wrong....

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stevdart 
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Posted: March 11, 2006 at 12:23 AM / IP Logged  

gbear wrote:
you are probably conveying to them that under rated power cannot blow speakers.

That's an odd inference.  I didn't understand him to say that at all.  Even we uneducated and technically illiterate  understand that power is power, regardless of a manufacturer's rating.

Too Little Power - Page 2 -- posted image.

Sometimes subjects like this need to be beat around a bit.  There's always a few more of us who "get it" each time.

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Steven Kephart 
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Posted: March 11, 2006 at 1:19 AM / IP Logged  
gbear14275 wrote:

Ok if this is what you mean then your argument and answers are trivial.  It's like you claim all car accidents are the result of excessive speed and then when someone disagrees you reply.  If the car crashes rolling around at 1 MPH and runs into a garbage can that 1MPH is what caused it to run into the garbage can and so the 1MPH was excessive speed.  Technically your right because without the movement the there would be no accident but you see there really is no value in arguing in this technical manner.

Not at all.  In your example, there are possibilities of outside sources that could cause the results (turning of the wheel, etc.).However in a subwoofer system as I describe, there isn't any extrenal source causing the damage.  It is the excess power causing the voice coil to thermally open, or drive the cone beyond it's mechanical limits.  And if the power available is lower than what it takes to cause those situations, then there won't be any damage, no matter how distorted, clipped, or low the power levels are.  Claiming that "underpowering" causes the damage would suggest otherwise, and is propogating a myth.  Instead of lying to someone, wouldn't it be better to explain the truth, or at least say be careful or they could cause damage?

Also, in your example it wasn't the speed that caused the damage to the vehicle, but excessive force (Force=Mass*Acceleration).  So to keep the analogy going, would you claim that too little force is what caused the damage to the vehicle?  Too Little Power - Page 2 -- posted image.

gbear14275 
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Posted: March 11, 2006 at 3:08 AM / IP Logged  

*sigh* OK...So your arguing if dmage happens to the speaker then there is too much power otherwise nothing will happen?  Your argument seems circular.  The fact of the matter is you have to redefine your terms.  The myth is propogated using an amps rated output and a speakers rated power handling.  By redefining your definition of power your not keeping the myth from propogating, instead your just trying to prove a truth: 

*If a speaker is damaged because its (pick one: thermal, mechanical, etc. ) power limits were exceeded, there was too much power.

This really is basically what your saying.  And I think you know your being difficult. 

If you define your terms according to the myth then your argument is not longer true. 

If you want to get technical geek style *pushes glasses up* then here is a techincal example of an underpowered speaker being damaged.

Speaker A is powered by Amplifier B whos power ratings in no way exceed the capabilities of the sub.  The amplifier recieves a signal and energizes the voicecoil (some steps may be skipped).  Magnetic field is created, forces begin to cause the speaker assemply to move.  and the underpowered amp causes the speaker to travel into a screwdriver tip which has been positioned within the comes limits of travel. OR The gap has been contaminated by grains of sand which preceed to eat away at the former and voicecoil until it causes failure. OR current starts to flow through the speaker terminals which happen to be wired in parrallel to a current detecting detonaiton device which explodes thereby rendering the speaker useless.

You never said that the speaker had to be in a suitable envronment. 

Or heres a more realistic one:  The speaker has a manufacture defect that makes the former detach from the cone and spider.  Underpowering strikes again.

Basically what I am saying is play fair.  You know the common understandings of the myth and your insistence on redefining ratings, power, and limits is not helping the situation.  A good sticky would be an explanation of how "underpowering" as it is commonly referred to can actually be "too much" power in a clipped signal situation to cause speaker failure.  That way something constructive actually comes from this thread.

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