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Underpowering can damage a speaker?

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Silver - Posts: 1,123
Silver spacespace
Joined: October 10, 2006
Location: United States
Posted: October 14, 2006 at 1:51 AM / IP Logged  

There is alot of debate on this topic. Many believe there is no way to "blow" a sub by underpowering. Others strongly believe by experience that underpowering is the main cause for blown subs as well as other type speakers. Well both are right.....and wrong? how can this be?

It mainly depends on how you view the "cause and effect" and certain technical aspects. Other considerations include the type of amp, quality of the speaker (this doesn't apply just to subs), and how hard [over driving] the listener operates the system.

Now those like myself that think "underpowering" causes problems are not trying to imply that this is the only way to damage a sub. There are thermal and mechanical limits with any speaker and that of course is always a consideration.

Some "blow by underpowering" theorists believe that clipping is the cause of the damage. Some "impossible to blow by underpowering" theorists believe that there is no reason an amp should clip regardless of power and/or that clipping won't damage a speaker. Some simply blame it on the user stating that they are playing the system too loud...which can be the case but "too loud" is another subjective issue, ie: maybe the listener is hard of hearing.

As for the technical aspects regarding clipping you can find a ton of info about that here, other sites or any textbook that deals with A/C- D/C and audio. A clean sine wave viewed on an o-scope or on paper will be curved at the tops and bottoms. This picture of a sine wave, or audio signal contains the following info: Amplitude (power, this is where you see the clipped signal although other properties are involved), Frequency (cycles per second expressed in hertz or hz), period (time) and wavelength (size of the sound wave).

If you are looking at the sinewave from an amp that is clipping the top and bottom curves will appear flat, or cut off. Basically the amp can't produce any more "clean" signal at this point - Some engineers state that the output at that point is DC, or that a portion of it is. All transducers (speakers) don't really take well to DC, not a big fan. When an amp is clipping even though its clean output hit a "ceiling" (won't play the speakers any louder no matter how much more you crank the volume control) the amp is putting out more then its "peak" rated power. Many engineers claim up to 50% higher, some believe even higher and some say "nonsense". Again, confusion so who do we believe? 

Heres my take on it (or opinion if you wish). If the amplifier had enough "clean" power to begin with no clipping would occur. Regardless, whichever theory you side with we are trying to prevent toasting a woofer. Been there, done that.

Many audio engineers tell us that a high powered, quality amplifier won't clip, or at least is very difficult to clip and that you can safely run more rms power to the speaker then it is rated for. I completely agree with this, but within reason.

For example say we have a 50watt RMS amp. If we replace it with a 100watt RMS amp we can expect an increase of 3db output from the speaker. (note that for every doubling of power, or # of speakers you can expect a 3db gain) We need a gain of 10db to be twice as loud. So just to make a 50watt rms speaker play twice as loud we would need to run over 400watts rms to it. Now that may be a bit [sarcasm] overkill in the headroom department but I would see no major crisis in doing this. The potential is there to blow speakers but it would sound so horrendous before they ruptured that even the most ignorant of the ignorant would want to turn it down, unless they are purposely trying to destroy equipment. Start getting greedy and apply 500w - 1000w to that same speaker and you can too easily exceeded it's thermo/mechanical ability. The speaker may not nessecarily blow from clipping in this fashion but can basically self destruct. Been there, done that as well. You will release the "voice coil smoke".

Think of it this way. The speed limit is 65 mph on the highways where I live. But I would not really buy a car that has a top speed of just 65 mph. I want a little "headroom". Now in comparing this to an amp would be why lowering the gain control (assuming it was set properly to begin with) will help, but is in a way it's just a band-aid. The same analogy applied to the car would be that I put an egg under the gas pedel so I can't speed or floor it. It will work, yes, but not always leave a very satisfied customer. (plus I would crack the egg and have a mess..I'd like more power... please)

In my day to day system installs, I find that most of my customers like it LOUD !!!! They trust me to deliver what they want. Afterall, they are paying good money (master installers don't come cheap). Now if a customer has 2 woofers that are rated @ 1000w rms each but want me to install an off-brand flea market amp that says 2000 watts on its casing they assume this will work for them. Well it will amplify and produce audio. The problem in this case is the specs are an outright lie, or at the very least peak @ high distortion levels. And by "distortion" I don't mean the good harmonic kind like with heavy metal guitar. I mean any unwanted audio, or "change in waveform" which is the literal definition of distortion when it occurs with electronics. Hmmm..change in waveform..can this mean clipping?

Now on to reality, perhaps this amp can deliver 100w rms of clean power. Everything I have ever been told about audio would lead me to think this will cause clipping. The amp will send too much "dirty" power to the woofer(s) and cause destruction as the user attempts to enjoy the "2000 watts" of power, which is what they are expecting since the amp is labled so and the woofers are rated to safely handle it.

So, from that example you can see "cause and effect". The fact that the amp is not powerful enough can send  it into clipping, which in turn will send too much "dirty" power (possibly DC) to the woofers. Sooner or later this will cause a problem. If the amplifier had sufficient rms power to begin with the woofers will..... and DO, last for years. Once again, been there, done that, over and over again...oh what a life.

CAUSE:  The amplifier didn't have enough clean power.

EFFECT: Blown woofer(s)

Another factor was the user, agreed. The user likes it really loud. This problem would not occur at moderate listening levels-

CAUSE: User cranked the wiz out of it because they like it loud

EFFECT: Blown woofer(s)

And we haven't even talked about transient response, damping, voltage issues and a host of other goodies. And we won't talk about that here to avoid information overload....we don't want to "clip" our brains :)

My feelings about this is to simply use an amp with at least  the rms power rating of the speakers (if you can find anything with an accurate or honest spec...good luck), or go higher, within reason. Of course if the end user is not a bass head you can certainly get away with less power. The key is you can't be general in this industry, there are too many factors to take into consideration, especially when dealing with car audio where 2 ohm loads are commonplace, and loads as low as 1ohm and less are sometimes utilized. (this is rarely the case with home audio so I don't pay alot of creed to home audio or musical instrument specialists when dealing with mobile electronics as too many variables exist and the same physics don't always apply, in what other industry do they have off the chart mega wattage and insane spl levels with 12 volts???).

With all this said I hope some clarity can come out of this topic without there being any fights or name calling.

Yes, I might be pathetic and have no life (well, this industry is my life) but the things I sometimes hear regarding this topic bug the crap out of me.

Note that some info here is just my opinion but it is based on books, schooling, seminars, experience and actual events I see all too often. Other info is from professional sources and engineers in the industry.

Replacing speakers until I upgrade the customer to the proper amp,,,, and only then the speakers blow no more. That in itself is enough proof for me and regardless of what anyone believes is causing the problem....I found a solution that WORKS!  MORE RMS POWER!!  My credentials should be apparent.

Thanks for listening everyone. Any feedback, positive or negative is welcome, just no name calling please.

Steven Kephart 
Platinum - Posts: 1,738
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Posted: October 14, 2006 at 2:15 AM / IP Logged  
Read my too little power sticky to get the details on this. But to make some points:
1.It is impossible to blow a speaker with too little power. If damage occurs it is because too much power was applied (ignoring direct damage from say a knife to a surround, etc.)
2.There is no DC in clipping. Put an amplifier on a scope and actually watch what happens when pushed to clipping and you will see what I mean.
3. I have never heard any engineer say it is impossible or even hard to send an amplifier into clipping. I used to do it all the time when I worked in the warranty department of Adire Audio. I have repaired quite a few speakers that were damaged from the user running their amplifier into clipping.
Here's a link to another great technical paper on this topic:
Silver - Posts: 1,123
Silver spacespace
Joined: October 10, 2006
Location: United States
Posted: October 14, 2006 at 3:19 AM / IP Logged  

I will check the technical paper you suggest but, I bet for every paper on this topic you could find 10 that contradict it.

In college my electronics professor actually was a student of einstein before he died.  A bit old (real old)school and arrogent but seemed to know his stuff.

When I was training coordinator at a tech school the man I replaced and who wrote the original curriculum was an army engineer. The instructor under me was a fresh audio engineering school graduate so these is some pretty good credentials and I learned alot from them but I guess anyone can be wrong or misunderstand, it happens to me enough.

I had to read the loudspeaker cookbook and memorize alot of info to pass the mecp master (I scored a 98% in electronics so I must be somewhat on the right track.) Unless all these kids that are killing subs and then when I finally get them to replace the amp to a much more powerful one and the woofs don't take a dump again..whats with that? Are the higher power amps rating too conservativly or the lower power amps way exagerating. are they all lying?

I will keep an open mind to anything but I also have to stick with what works for me.

Much appreciate the feedback, thanks

Silver - Posts: 1,123
Silver spacespace
Joined: October 10, 2006
Location: United States
Posted: October 14, 2006 at 3:33 AM / IP Logged  

Oh I was told by an engineer that  high powered amplifiers won't clip, that it only occurs at with low power amps being driven into saturation.. If I find any info on that to verify I will post a link, this was told to me at a seminar. But you can probably find it on a search. Thats why I stated "high power, quality amps don't clip" but not to say it's impossible thats wrong, just what I was told by a source I trust.

You also state you easily clipped amps and  repaired quite a few speakers damaged by clipping. Do you think an amp with more RMS clean power would have prevented the clipping, hence no damage?  Or is it that high RMS powered amps clip easier? If thats the case everything I was ever taught is backwards and hence I have been teaching wrong. Hope thats not the case.

Let me know what you think. Thanks again

Silver - Posts: 1,123
Silver spacespace
Joined: October 10, 2006
Location: United States
Posted: October 14, 2006 at 3:59 AM / IP Logged  

Ok I read the article. It seems like he is saying the same thing I am for the most part but using different concepts and verbage, such as Bul$&^t. ,lol, well you get the point. for the most part I agree with him, on other issues my personal real world experience contradicts him somewhat. 

He states that you can not underpower a woofer since thats like if you turned the volume down all woofers would blow. That is ridiculous and I don't think anyone thinks that and the anaolgy holds no wieght against what I have been saying.  But then he consistantly states thoughout the writing that supplying clean power is good for the speaker and using an amp with not enough power for the speakers rating will cause clipping and damage the speaker.

I don't know this persons credentials or where he attended school but regardless I understand everything technical in the writing and have been through most of it back in the day and think we more or less agree, but view certain aspects differently.

If you read through my entire post I think you will see what I mean. my anaolgies and experience make more sense then some of these "tech heads" trying to make a point, basing everything on charts and graphs but have never installed as much as an air freshner into a car.

Thanks again.

Platinum - Posts: 2,762
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Posted: October 14, 2006 at 6:31 AM / IP Logged  
Any amplifier can be driven into clipping if it's fed too strong a signal.
My ex once told me I have a perfect face for radio.
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Posted: October 14, 2006 at 7:32 AM / IP Logged  

This subject "underpowering causes speaker damage" is debated only because of a general disagreement in the interpretation of the meaning of that phrase.

"Underpowering" should be understood to mean that the speaker in question is receiving less power than it is thermally rated for.  With this basic understanding of the use of the word, anyone with a little bit of knowledge in the matter will understand that this is entirely untrue.

The matter only becomes debatable when the term "underpowering" is referring to the mismatch of audio gear to the end user's expectations.  If the user is expecting his system to get louder than it actually can get, his system is not meeting up with his expectations.  If he is a fool with a volume knob, he is likely to abuse the system and cause damage.

In the audio profession, dealers and installers see this occurrence.  The consumer wants "loud but cheap", buys below his expectations, and ends up damaging speakers and consequently complaining about it.  In order to head off this well-known possibility, the dealer wants to set the user up with a system that will meet his expectations to begin with.  While it is impossible to educate the user in all the details of "how and why", it becomes the most reasonable course of action to just inform him that "too little power will blow his investment".  It is not actually a lie, but a truth based on the reality of the end result but not in the reality of how that end result occurred.

Those who have an education in audio electronics know that a 10 watt amplifier will not damage a speaker rated at 200 watts unless it is used incorrectly.  A 100 watt amplifier will not damage a speaker rated at 1000 watts.  It is the usage of such systems that cause problems, and ultimately begins with the initial buy and setup.  When a dealer has 5 out of 10 users coming back with complaints that their speaker blew, it is understandably justified to try to head off this known problem by declaring, from the onset, that "underpowering causes speaker damage."  It is a reality-based "known" based on the interpretation of the concept of "underpowering".

Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.
Platinum - Posts: 5,052
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Location: Michigan, Bouvet Island
Posted: October 14, 2006 at 10:20 AM / IP Logged  
master5, you seem like a smart guy... really.
What about "underpowering a speaker can never thermally damage a speaker" don't you understand?
If you had read those articles, (as you claim) and you REALLY understood them, (as you claim) you would (or should) realize that IF you take a 1000 watt woofer, and play ABSOLUTE square waves (i.e. perfectly clipped, and 100% distortion) from a 100 watt amplifier into it, it CAN'T EVER thermally overload that woofer, the margin is too great. With the voltage rails in a 100 watt amplifer, there is NO WAY to ever produce enough thermal energy to destroy a 1000 watt voice coil. At BEST it could produce 200 watts - an extremely far cry from 1000 watts, I believe a 5:1 ratio, or a 500% safety margin. Now, if you do nothing but replace the 100 watt amplifier with a 250 watt amplifer, and re-setup the test. Will it blow? No, for the same reasons (but this time with a 2:1 margin). Now use a 500 watt amplifier, and do the same thing. Will it blow? Hmmm, possibly, but I think the margin will still be in the favor of the woofer (for a shorter period of time, possibly) as a decent 1000 watt woofer will actually take 1000 watts (and possibly more) on a very continuous basis. Here we are looking square on a 1:1 ratio. Rated input power to the woofer.
Repeat this experiment one more time, but this time with a 750 watt amplifier, and yeah, I guarantee you're gonna blow that woofer in short order, thus "proving" your "low power blows woofers" theory. Why? Because a 750 watt amplifier could probably easily produce over 1000 watts, in a severly clipped, over-driven, saturated (whatever the word you want to choose) situation.
I am NOT even touching on the physical mismatches in a mis-aligned vented enclosure, where it is certainly possible to destroy a woofer with what one might describe as a "drastically underpowered" amplifier, but this is NOT thermal damage as described above. It is mechanical damage in this case.
It all reminds me of something that Molière once said to Guy de Maupassant at a café in Vienna: "That's nice. You should write it down."
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Posted: October 14, 2006 at 10:26 AM / IP Logged  

Again, where's the "head against the wall" icon?

IMO the only people who preach the "underpower" myth are those trying to sell high-power amplifiers to unsuspecting car audio buyers.

It is ALL ABOUT APPLICATION.  You may use ANY amplifier with ANY loudspeaker as long as you understand how to set it up and how to use it.  Period.

And master5, your points are similar to many made by folks over at places like Rane or Harmon, but you have missed the point that it is never "distortion" that blows loudspeakers, it is always thermal energy, or "power."  The source of the power and how the user controls it is the key.  Power hidden inside a clipped or distorted signal is simply harder to control.  And please, you keep harping on your "credentials" as some sort of justification for your posts.  No need for this, as many of the posters here are not only experts in their fields but have "credentials" as well.  Check profiles sometime.  People who post accurate information become self-evident.  posted_image

kicker guy 
Copper - Posts: 87
Copper spacespace
Joined: August 25, 2006
Location: United States
Posted: October 14, 2006 at 10:37 AM / IP Logged  
I will say that it is impossible.... I have 2 L7s in my car right now... and well my amp took a crap cuz well its old and I beat the crap out of it... now because I was lacking bank for the time I had to put a 200 watt amp on them cus its what i had laying around.... and they haven't blown yet and I really really don't see how a 200 watt amp is gonna kill those subs EVER...
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