First I must apoligize as my knowledge of car stereo is lacking in spots, my knowledge lies in the tech/general engine.

The store I work at got a new car Stereo merchandise buyer who is, a, full of himself. He asked me the other day why I thought speakers blow. I told him it could be because factory speakers could dry rot, are made of thin material, get too much volume or bass. He of course said I was wrong and speakers blow because they are underpowered.
So I thought I would ask here as to why speakers blow.

 

He's a typical salesman that knows just enough to be dangerous, and not enough to actually be of any help.

He's sorta right, though I guarantee that he doesn't know why.

There are 2 basic things that can cause a speaker to fail:

1. Too much heat
2. Too much motion.


Too much heat can result from two things. You can grossly overpower the driver to the point where the voice coil melts, burns, or in some other way distorts. The other is when you drive a clipped signal into it. A clipped signal is one that results from overdriving an amplifier. The result is that although the peak waveform doesn't go any higher, the area under the curve (or the RMS) power does. The situation is a lot easier to understand if you see the voltage represented as a sine wave, but I guess you'll just have to trust me.

So... in a sense that guy is right. If you have too small of an amp, and if you grossly overdrive that amp so that it is severely clipping, you will destroy a driver with much less power than what it would take to destroy it with an undistorted signal.

The other source of failure, too much motion, is just over excursion. This can happen from too much power, an improper enclosure of many kinds, or it can happen with a clipped amplifier signal again, because once again, if you look at a clipped waveform, you'll see that essentially it's asking the driver to move, instantaneously transition to a fixed position, then instantaneously reverse direction. That can cause a lot of stress on a driver.

All in all, you'll only blow a speaker by underpowering it if you're too stupid not to turn it down once it starts to sound sh*tty. Unfortunately, most people are that stupid and blow up their speakers.

 

Yeah I hate salesman like that. But just to clarify, u'd want to see the wattage (not voltage) represented as a sine wave to see the area under the curve get bigger.

Voltage is like the "pressure" that forces electrons thru the circuit. Amperage (or "current") is the amount of electrons moving thru the circuit, and this what creates heat. Wattage is volts*amps -- but not all wattage is created equal -- so 100W could be 20V and 5A, or it could be 5V and 20A -- and 20A will generate a lot more heat than 5A. Resistance is the physical resistance to electrons moving thru a material. Inductance is the resistance to change in current flow. U might notice that some speaker specs will show the DC resistance of the speaker as 2.3ohm or something like that, even though it's a 4ohm speaker. It's becuz that 4ohm rating is the combination of the DC resistance and the inductance of the speaker.

The reason why the area gets bigger even though the voltage isn't increasing is becuz the speaker stops moving for the time the amp is clipped (the cone stops in position, much like when u hook up a battery to the speaker). When the speaker stops moving, its inductance drops becuz there aren't any changes in eletrical flow for as long as the amp is maintaining a constant voltage (ie, its maintaining its max voltage becuz it can't go any higher even though the input signal is telling it to)

So u've got the same voltage, but less resistance (becuz there's little or no inductance), so the amperage increases. Amperage is the amount of current flowing, and that's what generates the heat. So higher amperage = more heat = blown voice coils.

1 more thing: becuz the voice coil isn't moving while the amp is clipped, it's not cooling itself either. So not only is there more heat being generated, but it's also harder for the speaker to disipate that heat.

 

Very good explanation. Much better than mine.

 

print this page out, and hit that guy in the mouth.

 

 

post in here if you talk to that guy, see what he says....

he may just have been an arrogant ******* and didn't feel like explaining the whole thing to you.. when it seemed that you knew enough already...

cocky bastard.

 

Or he was one of the 99% of sales guys that doesn't know jack. There aren't too many guys who know this stuff in and out who haven't moved onto much more high paying careers.

 

this is true.... unless they are working at a high-end stereo shop, where they make some good money... they probably don't know crap from a butterfinger.

 

Not only do those kind of people not know anything, but they will never admit they are wrong, BS and excuse, and tell the same thing to every other person they talk to. Trust me, I know, I work for one of those people.

 

is murder illegal in Illinois?