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

Too much power or distortion damages subwoofers

By

Buck Pomerantz

Buck Pomerantz was born and raised in Philadelphia. His parents bought their first television set when he was born. He figured out how to run it by the time he was two. Besides athletics, his formative interests included electronics, amateur radio, music, and stage crew work. He got his BA in writing from Brown University. Then he joined a rock 'n roll band as their soundman and moved to Charlottesville, Virginia. After that venture failed, he spent time in Boston, New Orleans, and Berkeley. He worked in a music store in Austin manufacturing, installing, repairing, and operating sound systems for recording studios, clubs, and bands. He moved back to Charlottesville, ran a little recording studio and finally joined Crutchfield as a copywriter. He has 2 grown children and 3 grandchildren, but after a good nap he can still rock out.

More from Buck Pomerantz

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.

Subs are made to withstand a lot more than their specified RMS ratings, so giving them a little more than their highest RMS rating is safe, as long as it's clean and distortion-free.


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 less than 75% and no more than 150% of 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
  • grasshopp from charleston wv

    Posted on 7/14/2015 1:49:53 AM

    WOW

  • johnny hall from Mansfield

    Posted on 7/19/2015 7:17:21 PM

    Why does my sb16 harman kardon subwoofer goes in and out the light will be blue play a while then stop can you reset it

  • Buck Pomerantz from Crutchfield

    Posted on 7/20/2015 9:36:29 AM

    Johnny, If you bought your home theater system from Crutchfield, you could call Tech Support for free help troubleshooting it. Their toll-free number is on your invoice. If you purchased your equipment elsewhere, you can still get expert Crutchfield Tech Support - 90 days-worth for only $30. Click on this link for details.

  • Cohen Moonsamy from durban

    Posted on 8/27/2015 11:34:20 AM

    I have a pioneer 150w 8 inch active sub in my car. If I turn i turn up the volume will I blow my woofer? It has a box and amp spec for the driver. For its size it really packs a huge punch with tight bass.

  • Buck Pomerantz from Crutchfield

    Posted on 8/27/2015 12:56:12 PM

    Cohen, An active subwoofer, one with a built-in amplifier, will have its amp and woofer matched for power, but I'm fairly confident it can still be blown from excessive input volume.

  • thomas

    Posted on 11/22/2015 11:03:23 AM

    i noticed my subwoofer isn't as strong as it was before. had it for about 9 months. could my sub be a little bit blown or have some kind of internal damage? the cone looks fine and i've never had a burnt smell coming from the trunk.

  • Buck Pomerantz from Crutchfield

    Posted on 11/23/2015 3:39:18 PM

    Thomas, Usually, a blown sub makes no sound, so yours is probably not blown, although something else may be wrong. If your sub has dual voice coils, you can test to see if they both are okay by "bumping" each coil's connections with a 9-volt battery. If they both make a click sound, then both coils are good. You may just be noticing the changes in the sub's performance due to break-in, the softening of a sub's suspension and tone over time with use. Try re-setting the amplifier gain to see if you can regain any of the power that you sense was lost.

  • David Drake from Palomar Mt.

    Posted on 1/6/2016 3:13:31 PM

    Would this happen with a rotary woofer?

  • Buck Pomerantz from Crutchfield

    Posted on 1/6/2016 4:20:36 PM

    David, I had never heard of a rotary subwoofer until now. After reading a bit about them, I can say that I really don't know for sure how they fail, when they do. I can only assume that as in any moving coil and magnet arrangement, too much power and attempts to reproduce large square waves can cause damage.

  • Martin from Joliet

    Posted on 2/15/2016 7:35:59 PM

    Wow Buck your on the ball!

  • Eric Pokorny from Juneau Alaska

    Posted on 3/23/2016 1:13:50 PM

    I have two JL audio 12" w7's in my car wired parallel (1.5ohm) I'm using a JL audio SlashV2 (1000/1) so I only have 500 watts going to each sub....I should also state the car has a fully upgraded charging system (HO alternator, XS power d6500 battery, 0 gauge Big 3, true 10 farad capacitor, and 0 gauge wiring all the way back to the amp...I also have a JL audio HD 600/4 running 2 sets of C5 components.....ok now for my question...as I'm sure your familiar with all the above mentioned equipment...I want to drop the slashV2 (love the amp it's physical size is just to demanding of space) and replace it with the JL audio HD 1200/1. Aside from the obvious major physical size difference in the amps, do you think that extra 100 watts to each sub will make them noticeably louder? Also have them in a shared chamber custom ported enclosure tuned to 33.5hz.

  • Buck Pomerantz from Crutchfield

    Posted on 3/23/2016 3:04:06 PM

    Eric, As counter-intuitive as this may sound, increasing the power to your subs from 1,000 watts to 1,200 watts, 200 watts total, will increase their output power by about 0.79 dB, which is considered inaudible. It takes about a 1 dB increase for our hearing to notice a difference. A 1,500 watt amplifier, for example, would increase the sound level by 1.76 dB, which you would definitely notice.

  • Eric

    Posted on 4/7/2016 12:59:05 AM

    Follow up question....i was told by by adding a rather expensive new piece of equipment I would get a DB increase of 4.5DB...how much louder is this really? I am obviously into quality and Being as loud as possible, to a serious bass head is 4.5DB worth 600 more dollars in your opinion

  • Buck Pomerantz from Crutchfield

    Posted on 4/7/2016 10:50:38 AM

    Eric, Loudness is a subjective perception and can't exactly be measured - it's different for each individual person, although most agree that a 10 dB increase in SPL sounds like a doubling of the loudness. An amplifier that produces 4.5 dB more power than your 1,000 watts RMS amplifier would be a 2,800 watts RMS amplifier. If 1,000 watts isn't loud enough for you, maybe 2.8 times as much power will do - only you can tell. And $600 for a 2800 watts RMS amplifier sounds like a bargain to me.

  • Ameer from Trinidad and Tobago

    Posted on 4/15/2016 3:50:07 PM

    I have one 10jl audio w6 v3 subwoofer with a sound magus 800.1vs amplifier. When playing at medium volume it works fine but when I raise more volume the subwoofer starts to knock, stick and shuts off (not all at once). I taught it was the subwoofer but when I tried another one it did the same. Is it current?

  • Buck Pomerantz from Crutchfield

    Posted on 4/19/2016 1:04:20 PM

    Ameer, I'm not familiar with that amplifier, but it sounds like you're just plain overpowering your subwoofer. The knocking is the voice coil hitting against the back plate - you're lucky the sub hasn't died altogether, unless it has by now. To get more bass, you'll need to add another subwoofer.

  • erik from greenville

    Posted on 4/26/2016 9:19:59 AM

    i hav 2 american bass xfl dual 2 ohm 15 subs on a soundstream t1.6000 3000.1 at .5 oh i have 250 amp high alternator and a deep cycle 100 amp hours in the back sounds good at moderate volume when i turn it up the speakers pop ive tried everything can you please help me the subs 1000 rms and can take 1500 rms a piece all day

  • Buck Pomerantz from Crutchfield

    Posted on 4/26/2016 12:28:47 PM

    Erik, When an amplifier sends a clipped signal to a sub, it also sends it twice its top RMS power - so your subs may be trying to play with 6000 total watts, 3000 each. The popping sounds you hear are the voice coils bottoming out against the back plates and the cones trying to reproduce a square wave. To me, it sounds like you're over-driving your receiver or amplifier or both. Set the receiver's output and amplifier's gain so no distorted signals will ever play. If that result isn't loud enough for you, you'll have to add another amp or sub to your system.

  • Clairice Dale from Knightdale, NC

    Posted on 4/27/2016 12:22:41 AM

    Buck, first I'd like to say great content. I have a question for you. My fiance installed a brand new rockford power sub (I forget which model but it doesn't matter to my question) about a month ago and came home looking like a sad panda today because it blew. He was screwing around with his head unit and he says he dropped the hertz to the lowest rockford says that sub can handle. Is there such a thing as blowing a speaker because you're trying to get it to play too low of a frequency or was it more likely too much power? Thanks!

  • Buck Pomerantz from Crutchfield

    Posted on 4/27/2016 10:53:11 AM

    Clairice, There's always a chance someone can damage audio gear by fiddling with controls, especially when they're not sure what those controls do. "Dropping the hertz" could mean a few different things, from lowering a low-pass setting to adding bass boost. A common reason for subwoofer failure is a mis-set gain control, allowing over-driven, distorted signals to burn-out the sub. Knowing exactly what receiver and powered sub your fiancé has (yes, make and model number do matter to the discussion), might make it possible to access the owner's manuals and find out what each control does and how to use it safely to get the best bass possible.