Why did I blow my speaker?

I thought I'd post this up for the Moomba crowd. It's a post I put up answering a question about a guys 6x9 that has crunchy tweeters on another forum. The question was, which is a good brand of 6x9, but the real thing worth looking at is why did it poof in the first place....

This is good general info stuff for people if they are interested in knowing more about how things work in stereo land. It applies to all and not brand specific.

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Out there in the real world people tend to increase overall volume as the day goes onward and a few beers have been tossed back. And there's nothing wrong with any of that except at some point the volume goes up to a point where the amplifier exceeds its ability to reproduce its audio waveform (music) accurately. This inaccurate music usually takes the form of what we call clipped (compressed) and distorted output. Now everyone has heard before a stereo that is really loud but at the same time sounds really horrible. Chances are it has one of things I mentioned above going on.

Now on the surface someone might just say, "hey, who cares, the sound is the sound, let it rip," but in reality whats happening behind the scene is this compressed output of your amplifier actually sees electrical changes in its AC (alternating current) wave form. The ugly part is DC (direct current) shows up too. And I'm not talking ACDC the band. Muahaha! Without getting to complicated, what I'm saying is that our speakers that are attached to the output of the amplifier now start being fed this DC signal and it in turn begins to attack the voice coils of the speaker (think heat). We have to remember a typical speaker has a tweeter and midbass driver and each has a voice coil. Under this harsh operating condition, its usually the tweeter voice coil that gives up the ghost first and POOOOOF!!! it's gone. and gone forever. So the point of all this is, we cant always blame the speaker because rule number 1 is "garbage in garbage out"--- for a while at least until it smokes!

What can be learned from all of this? It's vitally important that the whole stereo system be able to operate in a range that it can handle. Gaining up an amplifier to the max, stacking on top of that some bass boost, flip up the volume to max, blend in some head unit EQ and we have a recipe for trouble. This is why you see many of the guru's on the forums providing install suggestions that bring things down a bit so the end result of blown gear can be avoided.

I often get asked, "how do i get more out of my system?" and that answer obviously varies depending on the unique attributes of the given stereo set up. It might be going from a 4x50W amp up to a 4x125amp so your system has more headroom. Or someone might have speakers rated for 300W and only driving them with 150W. or 150 speakers driven by 300 watts. You see how this goes. It might be adding nothing and just tuning the current setup so everything sync's well together. But one things is for sure, when your system gets fatigued things go pop! So be careful and look for the first signs of trouble.

Hope this insight helps!

-Brian @Exile

Thats some good info Brian. Sure, a few beverages can have the effect of a sedative. Also, the human auditory system has a built in self-protecting function that compresses the dynamic range of sound in anticipation of or in reaction to trauma (very loud). So what begins as a loud perception doesn't stay as loud for long. This is why the volume of a car radio that seemed normal when it was turned off at night can be startling upon powering up the radio the following morning.

Actually you can't have DC current on an AC waveform plus a series tweeter capacitor won't pass DC. In reality when you clip an amplifier and square off the waveform you're introducing an endless number of mathematical components that are AC and can be ultra high frequency in nature. Compressing the amplifier's output simply generates an inordinate amount of continuous power. Even a relatively small amplifier can produce enough continous power to damage a small and fragile tweeter. That would otherwise withstand many times the peak power (such as the transient nature of music under normal playing conditions). When the continuous or average power exceeds the speakers thermal capacity (ability to dissipate heat quickly enough) then the speaker is burned so to speak. The voice coil wire enamel insulating coat usually melts or burns first which is rapidly followed by a total voice coil failure. Distortion in itself doesn't necessarily damage speakers. Its the compression byproduct of overdriving an amplifier that will create excessive continuous power which toasts the speaker.

The other frequent cause of speaker failure is mechanical stress which results in broken tinsel leads, fatigued spiders, adhesive failure or torn materials. This is more prevelant in low frequency drivers.

As Brian mentioned, the audible signs of trouble may be apparent early in the day but not so much as the day wears on or when in motion with lots of competing noise.

David
Earmark Marine

Wow, good stuff from to expert resources. I think the secret to the whole thing is that speakers, like all electronics are very simple. They work off smoke. If you keep the smoke in they work. If you let the smoke get out they don't. Ever try to put the smoke back into something? Not easy.

David and Brian, I do appriciate your contributions to the board you guys are a wealth of knowledge.

good posts guys...

thanks..

yes, I should have said DC like. Meaning sustained clipped voltage = ouch on speakers.

Although I do think someone should do a youtube video on the smoke version Robert spoke about haha! Somehow that conjures up such a good laugh! Great description man.