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Why subwoofers blow: slam, bang, pop, and sizzle

Too much power or distortion damages subwoofers

A blown up subwoofer

An exploded view of the parts of a speaker. This particular example is the woofer from a set of Focal component speakers. (click the image to enlarge)

In a perfect world: the music sounds great

The sine wave below represents a signal that an amplifier sends to a subwoofer as a variation in voltage over time. The vertical axis represents voltage, the horizontal axis represents time. In AC (alternating current) signals, like music, the voltage swings between positive and negative values. Point A represents the point in time when the amplifier is telling the sub's voice coil and cone to be as far forward, toward the front, as that particular voltage (+V1) tells them to be. Point B is where –V1 voltage positions them toward the rear. Traveling back and forth rapidly, the cone pushes air and makes sound — and it's musical.

Clean sine wave

Overpowering your subwoofer – Slam and Bang

First we'll cover what happens when you give your subwoofer too much power. It's great to turn it up, but that extra volume starts to distort the music. Not only does it sound bad, but it can damage your speakers and subs, especially if you do this all the time.

Slam: The incoming signal tells the cone to move too far forward

Let's say that points A and B (and +V1 and –V1) are the maximum ratings of our subwoofer. If we increase the volume of the signal, the higher voltage (+V2) now tries to move the cone even further toward the front (C). The signal is still a clean signal, but now it is trying to move the cone and voice coil much further than they were designed to go, tearing the cone, spider, and surround apart, destroying the subwoofer.

Clean loud and louder sine wave

Bang: The signal tells the coil to move too far backward

On the other side of things, when the signal (-V2) tells the voice coil to move too far toward the rear (D), the voice coil crashes into the back plate of the magnet assembly, cracking the coil and its former (the tube it coils around), and probably jamming it in the voice coil gap.

Underpowering your subwoofer — Pop and Sizzle

Underpowering a subwoofer isn’t inherently bad for the sub. Not giving it enough power just means that the music will sound weak and lack detail.

The danger is when that power is coming from an amplifier that's being overworked and sending out a clipped signal. The clipped signal tries to make the sub do things it's not designed to do, which leads to it tearing itself apart or overheating and burning out.

First, what’s a clipped signal?
Clipping a signal, or squaring its waveform, occurs when the volume of a source signal exceeds the electronic capability of a circuit. Let's say our amplifier can't play a signal more powerful than what voltage V1 can produce. If we tried to increase the volume at the source, the amplifier wouldn't produce more voltage, it would distort the signal, eventually into the form of a square wave.

Square wave distortion

Pop: A clipped signal tries to move the cone too quickly

You will notice that the sides of the clipped signal are vertical. That means that the signal will try to move the sub's cone from all the way forward (point E) to all the way to the rear (F) in zero amount of time, travelling at the speed of infinity. Nothing travels that fast, and the sub either tears itself apart trying, or the flapping cone wobbles just enough to jam the coil in the magnet's voice coil gap, killing the sub.

Sizzle: A clipped signal also tells the voice coil to hold still and heat up

The other parts of a square wave, the top and bottom, are horizontal lines that represent the times the signal is telling the cone to stay all the way forward or all the way back. Current flowing through a stationary coil only heats up the coil, which doesn't even benefit from a cooling breeze due to movement. The coil usually burns through one or more of its windings, or heats up enough to deform its shape so that it jams in the magnet's voice coil gap.

There's another, more complex reason voice coils burn when subjected to over-driven, clipped signals. A square wave carries twice the RMS power of a sine wave of the same amplitude (height). So not only is the signal telling the voice coil to pop into a position and sizzle, it's doing it with almost twice the power of the sub's maximum capacity. Usually, it's the glue holding the coil wire to the former that first melts under all the heat, and the coil crashes in its gap.

Distortion is the sub killer

Low power and low volume will not hurt a sub – but distortion will. A clipped signal is a sub's worst enemy. It isn't loudness that destroys an under-powered sub, it's trying to get bass volume by turning up a distorting signal that does it.

How to not blow your subwoofer — match the RMS power ratings

Ignore all "peak" and "maximum" wattage ratings, and use only RMS ratings. They may be harder to find, but RMS ratings are the only power ratings you should use. To safely drive a subwoofer, use an amplifier that can give it no more than its highest RMS power rating.

It's also crucial you set the amplifier's gain correctly. If you don't know how, you can check out Tuning Your Subs or Using Test Tones to Set Amplifier Gain for some helpful tips. And remember, if you want to run two or more subs, you've got to supply enough power for each and every one of them.

JL Audio W3v3 exploded view
  • Maurice from TUAKAU

    Posted on 12/6/2021

    Hi hope you can help as I cannot find any answer to this on the net! I'm using mains L - R out on my mixer to send line out signal to a PA 15 active sub woofer which ha own level control ! We Question if I use my mains out level control it raises and lowers volume through the PA to the active speakers! Can I damage the sub woofer by using the mains out level control as this raises the line out gain!

    Commenter image

    Buck Pomerantz from Crutchfield

    on 12/7/2021

    Maurice, As with any piece of gear, your subwoofer can get damaged due to abuse. You need to set the sub's volume so that when the PA is playing at its loudest, the sub is not distorting.
  • Gustavo Herrera from Mexicali

    Posted on 12/2/2021

    My subwoofer starts making a strange sound when I turn it up [thump/crack], the amp levels/gain are at minimum and it still happens. It should be noted that this problem did not happen before. my components are as follows: -Stereo without filters or effects, EQ Flat. -Amplifier. KW XR901-5 -Box: Dbox 1X10XPC -Sub-bass: JL Audio 10w3v3-4

    Commenter image

    Buck Pomerantz from Crutchfield

    on 12/2/2021

    Gustavo, Your sub may already be damaged. Playing distorted music, even with the amp gain turned down, can still burn-out a subwoofer.
  • Michael from Bellport NY

    Posted on 10/2/2021

    is a 600w RMS amp with 600w RMS subwoofer safe?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 10/11/2021

    Michael, Yes. That's what those ratings are for: safety.
  • Carlos Almeida Jr. from Old Bridge NJ

    Posted on 7/2/2021

    Hello I have a jd1000/1 powering a jlwo12 in a box with a bass knob. I find that if I play it hard for about a half hour the sub gets warm is this normal. The gains are set correctly and it's really warm when I have the bass knob all the way up.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 7/5/2021

    Carlos, One of the products of work is heat. If your amp is working hard, it'll get warm. If it gets too hot, its internal sensors will either shut off or reduce the amp's power output until it cools down.
  • Liam. N from Regina

    Posted on 6/2/2021

    Hi Buck, I've recently had troubles with my 12 inch pionner 4 ohms 1400w max sub, 400 watt rms matched with a JBL 300w mono-amplifer, which I'm guessing means that I'm underpowered my sub (checked all connections) but my subwoofer cuts in and out, is the 100 watt deficit a problem and what would u recommend I do and how do I set my gain and lpf etc? The power on indicator stays solid blue on the amp, and the sub works well when it's working. What do u think the issue is?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 6/2/2021

    Liam, Under-powering a sub is only a problem if it is being sent distorted, clipped signals. Otherwise, it's just like turning the volume down - it won't hurt anything. What you're describing is an intermittent connection - something, somewhere in the wiring is a bad connection. It may even be inside the subwoofer itself.
  • Alex from Woodlake

    Posted on 5/14/2021

    If I give a sub 2500 watts rms but it handles 3000 rms will i clip it?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 5/14/2021

    Alex, A signal can clip at any power level, regardless of the devices' ratings. The original source can be clipped, overloaded receiver circuits can clip the signal, and incorrectly set amplifier gains can result in clipped signals.
  • colton from aurora

    Posted on 4/9/2021

    is powering a 12" SVC 4 OHM sub that is rated at 300 RMS with a 200 RMS amp okay?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 4/12/2021

    Colton, As long as the amp puts out less than the sub's rating, it'll be safe.
  • Rory Vogt from Lexington, SC

    Posted on 3/30/2021

    My Alpine truck subwoofer keeps tearing all along the edges of the subwoofer surround. Right in the crack where the surround meets the outside edge of the woofer; you can hardly see it unless you shine a light and press into the surround to reveal the crack that runs all along the edge. It's the 2nd sub (same sub) this has happened to. It's rated for 350w rms and I'm running a 600w alpine mono amp that is tuned properly using a multimeter. Is it just ooor quality material? Or is this user error?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 3/31/2021

    Rory, Without knowing precisely what amp and subs you're referring to, we can't know for sure, but it sounds like running a 350W sub with a 600W amp is the issue.
  • Shawn Decker from Pierz

    Posted on 3/10/2021

    When I turn my subwoofer up, there is an extremely annoying and loud popping sound, and it matches the hz. It goes away when I turn it down. What is it?

    Commenter image

    Bruce Southall from Crutchfield

    on 3/30/2021

    Shawn, Your amp's gain may be set too high, allowing the sub's coil assembly to bottom-out, hitting the back plate. Or the sub is already damaged and it shows up when played loudly.
  • John

    Posted on 1/15/2021

    My gain knob causes a crackle noise when I adjust it while playing music. Right after I touched the gain and caused a bad crackle my sub started making a rattle. When I push on the cone it has a scratchy sound. Did the amp send a clipped signal and blow the amp?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 1/18/2021

    John, You should never adjust an amp's gain control while playing music. The gain should get set when the amp is installed and then left alone. It sounds like your amp gain's controlling potentiometer is dirty which is why it makes crackling noises when adjusted. And it also sounds like your subwoofer is blown because of it.

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