Eli5 Why do speakers blow out? Shouldn’t they be ableto handle the volume that they are set up to receive?
In: 1
It depends on a lot of things.
There are three main ways speaker drivers “blow out”
1) thermal overload. This is where enough current passes through the voice coil that it starts to deform and ceases to function. Because the materials get hotter over time, there is a maximim amount they can take for broef periods and a significantly lower maximum thet can handle indefinitely. These are the “max” and “rms” ratings you would see if you looked up car speakers online, as an example. Those are thermal ratings, which are different than mechanical tolerances l’ll talk about below. A lot of lower end pre built systems will be basically immune to this until their materials start to degrade because they’ll use an amplifier rated for less than the continuous output rating of the speaker. Higher end systems may not, though. Amplifier “headroom” is the concept that an amp should be able to deliver more power than it needs to for most things, so that it has enough power to handle particularly intense passages briefly. This can result in having an amp that’s capable of burning out it’s driver if cracked too loud.
2) general mechanical failure of the suspension or cone. This is just…an over time wear and tear type failurebas can happen with any moving parts. Things age and degrade and they may be damage by their environment. For example In speakers you’re looking for things to be as light as possible, generally, there are cone dampening advantages in certain applications but even in those the cone and suspension are very light. Point is, things like Paper and poly cones are great materials for making a new speaker. But paper degrades over time, especially if exposed to moisture, and poly-based cones are susceptible to UV light. Over time and age, the material of the speaker cone and suspension may degrade to the point where it quite literally falls apart under the stress of moving, causing it to “blow”.
3) rapid mechanical failure from over-excursion. Speakers move back and forth, we all get that. The amount they move is a function of the power input, the electrical and physical resistance is the speaker’s voice coil and suspension and the environmental resistance acting on the cone. That last one is where it gets tricky. In a sealed enclosure, the cone needs to either pressurize the enclosure (to move into it) or pull a vacuum against the enclosure (to move outward). The force required to do so makes it harder to move the cone than if it was just sitting bare in a bench or mounted in car door with a wide open airspace to work on. So…an amount of power that would produce acceptable motion in one enclosure may allow the cone to exceed the mechanical limit of its suspension with no enclosure. When you get into the frequency-dependent resistance provided by ported enclosures or the both sides pressure of things like bandpass enclosures this gets even more complicated but the gist is that, depending on what signal you send it and what it’s mounted into its perfectly possible to force a speaker beyond it’s mechanical limits with a shockingly low amount of power, a few watts even. For a given speaker and scenario that limit could easily be an order of magnitude lower than the thermal tolerance of the driver I mentioned in #1.
That’s for the speaker, but there’s also failures in other parts of the system.
For example if the amplifier experiences shorts or clipping it can wind up basically delivery direct current to the speaker instead of alternating back and forth. So the speaker just pushes out constantly and can easily hit the mechanical limit I talked about in #3. Clipping can be caused by asking the amp to do more than it actually can, by cranking up the bass boost for example.
Similarly a failure/degradation in a crossover, a circuit designed to control what frequencies different drivers get, can cause a speaker to receive signals it was never meant to handle. Like a small, high frequency tweeter getting mid or low frequency, higher amplitude signal meant for larger woofers or subwoofers and hitting its mechanical limits.
This is…a complicated subject but hopefully that gives you an idea of the kinds of failures possible.
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