4 Signs of a Blown Subwoofer
By Robert Jones · 2020-11-05
Hear strange noises or absolutely no bass from your subwoofer? I'll walk you through the four main signs your sub might be blown and what to do about it, based on my twenty years in the workshop here in Bristol.
It's a right kick in the teeth, isn't it? One minute you're soaking up every rumble and thud, the bass perfectly integrated, and the next… well, either nothing at all, or a sound that makes you wince like you've just trod on a Lego brick in the dark. I've seen it hundreds of times in my twenty-odd years getting my hands dirty with speakers and subs, and honestly, it rarely spells good news. That gut-wrenching feeling when your carefully tuned system suddenly goes belly-up? The low-end just vanishes, or worse, starts making noises that'd make a cat with its tail stood on sound harmonious. I've been there, pulling what's left of my hair out in the workshop here in Bristol, wondering what fresh nightmare has befallen my cherished gear. Sometimes, it's a quick fix – a loose cable, maybe a dodgy connection somewhere. But more often than not, it's something lurking deep inside the box, a sign that your subwoofer is well and truly knackered. That's when the dreaded words start to echo: "blown subwoofer." When your subwoofer starts acting up, playing silly beggars with your sound, it's a clear signal that something needs proper attention. It might not be "blown" in the Hollywood sense – no smoke, no gaping holes, no apocalyptic destruction. But it certainly isn't happy. And trust me, ignoring those early warning signs, those subtle changes in the sound, the odd little noises, can quickly escalate a minor, potentially fixable problem into a full-blown replacement job. Getting on top of it early, diagnosing the issue before it gets out of hand, is far cheaper than splashing out on a new driver or even a whole new sub. I've watched countless customers stubbornly push a dying sub past the point of no return, all because they didn't want to face the music. Don't be one of them. Your ears, and your wallet, will thank you. **Quick Verdict: Don't ignore the warning signs; a knackered sub will spoil your sound and could damage other kit.** ### Who it's for: * Anyone hearing unexpected noises or a distinct lack of deep bass from their subwoofer. * Folks wanting to understand *why* their sub has stopped pulling its weight. * DIY types keen to figure out sub problems themselves before calling in the cavalry or shelling out for new gear. * Anyone looking to protect their investment and stop future subwoofer damage. * If you love a good, clean bottom end and want your system to always sound its best. ### Who should skip it: * People who honestly couldn't care less about their home audio quality (if you're on SpeakersMag, I'm guessing that's not you). * Those who'd rather just buy new kit at the first hint of trouble than bother with understanding or fixing things. * If you're hoping for a magic cure for a truly annihilated sub; some things are just beyond saving, unfortunately.  *4 Signs of a Blown Subwoofer – tested in the SpeakersMag workshop. Sometimes it's obvious, sometimes it's not so clear-cut.* ## 1. The Dreaded Scratching: Voice Coil Rub – A Subwoofer's Squeal of Pain Right, let's kick off with the most common offender, the one that makes your stomach do a flip faster than a dropped needle on a prized bit of vinyl. You're chilling, listening to your favourite bass-heavy track – maybe some old-school jungle, a bit of dubstep, or a film score that relies on a weighty low-end – and then you hear it. A nasty, gritty, scraping or buzzing noise. It's not part of the music; it's your subwoofer crying out in agony. This, my friend, is almost certainly voice coil rub. What's happening here is that the voice coil – that tightly wound wire that sits inside the magnet structure and makes the cone move – has become misaligned. It's literally rubbing against the magnet pole piece or the former it's wrapped around. Think of it like a brake pad grinding against a disc, but far more delicate and expensive to put right. This usually happens for a few reasons. One is simply pushing the sub too hard, over-excursion, where the cone tries to move further than its design allows. This can warp the voice coil or deform the spider (the corrugated suspension that keeps the coil centred). Another common cause is mechanical damage – perhaps the sub was dropped, or something hit the cone, shifting the whole assembly slightly. Heat can also play a part; if the voice coil overheats from too much power, the glue can soften, or the coil can distort. ### How to spot it: * **The tell-tale sound:** It's usually a distinct buzzing, grinding, or scraping sound, particularly on bass notes with a bit of oomph. It might not be constant; it often happens during peak excursions of the cone. Try playing a bass sweep tone (you can find these on YouTube) and listen for where the rubbing starts. * **Gentle press test:** This is a classic workshop trick, but be careful. With the sub disconnected from the amp, gently and evenly press down on the cone near the dust cap with both hands. It should move freely, without any grating or resistance. If it feels rough, uneven, or you hear a scratch, that's voice coil rub. Don't push too hard, you can make things worse! This isn't a death sentence for every sub, mind you. Sometimes, if caught early and it's minor, you might get away with replacing the voice coil and re-shimming it – if you're handy with a soldering iron and have a steady hand. But often, it signals that the driver is on its last legs. I had an old REL Strata III in for repair once with classic voice coil rub. The owner had been thrashing it for years in a tiny flat. We managed to fix it, but it was a close call, and it wasn't cheap. Cost him about £150 for parts and my time. A new driver would have been £400+. So, early diagnosis, as I keep banging on about, is key. ## 2. No Bass Output: The Silent Killer This one's perhaps the most frustrating, because there's no dramatic noise, no warning. One minute you've got bass, the next… nothing. Just dead silence from your subwoofer. The other speakers are chugging along, the amp's fine, but the sub has just packed it in. This can be down to a few things, some less serious than a blown driver, but often it points to a complete voice coil failure. If the voice coil has completely snapped, or if the tinsel leads (those thin braided wires connecting the voice coil to the speaker terminals) have broken, then no electrical signal gets to the coil. No signal, no movement, no bass. A complete open circuit. Sometimes, the thermal fuse on the voice coil (yes, some have them to prevent overheating damage) can blow, acting like a miniature circuit breaker. Or, it could be a fault in the amplifier section if it's an active subwoofer. ### How to spot it: * **Total silence:** No bass whatsoever, even when you crank the volume. The other speakers are working fine. * **Check connections:** First things first, always check your cables. Is it plugged in? Is the RCA lead firmly seated? Is the power light on the sub amplifier glowing? Silly I know, but you'd be amazed how often it's something simple like this. I once spent an hour trying to diagnose a "dead" sub for a mate, only to find his toddler had unplugged it at the wall. Felt a right fool. * **Amplifier checks (for active subs):** Is the fuse blown on the sub's plate amp? Are there any obvious burn marks or smells coming from the amplifier panel? If it's a passive sub, try connecting it to a different amplifier or use a multimeter. * **Multimeter test:** This is the definitive test for a completely open circuit. Disconnect the subwoofer from your amplifier. Set your multimeter to measure resistance (Ohms, usually denoted by Ω). Touch the probes to the subwoofer's positive and negative terminals. You should get a reading, typically between 2 and 8 ohms for most subs. If the reading is "OL" (Open Line/Loop) or infinitely high, then your voice coil has completely failed. It's snapped. Game over for that voice coil. A complete voice coil failure usually means a new driver, or a very specialist repair job if you can source the parts and find someone skilled enough. It's usually not cost-effective unless it's a high-end, expensive driver. I had a Velodyne DD-12 come in with this symptom once. The voice coil had completely melted and severed. Luckily, Velodyne offered a recone kit, but it still set the owner back about £300, plus my labour. Much cheaper than a new DD-12 though! ## 3. Distorted or Weak Bass: A Lingering Illness This one is more insidious, often creeping up on you gradually. The bass is still there, but it's just not right. It sounds fuzzy, muddy, weak, or distorted, especially when the volume goes up. It's lost its punch, its clarity. It's like your sub has caught a nasty cold and can't quite perform as it used to. This can be one of the trickiest to diagnose because it's not a complete failure, just a degraded performance. This kind of behaviour often points to partial voice coil damage, perhaps the windings have started to unravel, or the coil is rubbing intermittently at higher excursions. It could also be a problem with the surround (the flexible ring around the cone's edge) or the spider starting to tear, which affects the cone's movement and linearity. Sometimes, it can be a symptom of a failing amplifier in an active subwoofer, where the amp simply can't supply clean power anymore, leading to clipping and distortion at lower volumes than it should. ### How to spot it: * **Lack of definition:** The bass just sounds "woolly" or indistinct. Notes blur together, and you lose that satisfying impact. * **Distortion at moderate volumes:** What used to sound clean at a certain volume now sounds rough and distorted. * **Uneven sound:** Some bass notes might sound okay, while others are noticeably distorted or weak. * **Visual inspection:** With the power off, carefully inspect the cone, surround, and dust cap for any visible tears, cracks, or sagging. The surround should be pliable and intact. Check the spider through the vent holes (if visible) for tears or detachment. I once had a cheap Q Acoustics sub in the workshop where the surround had completely perished, turning the bass into a flabby mess. A new surround kit (about £30) sorted it right out. * **Amp troubleshooting (active subs):** If you suspect the amplifier, try connecting the sub to a different source or even another sub (if you have one handy and it's safe to do so) to see if the problem persists. Check if the plate amplifier is getting unusually hot. This scenario gives you a bit more leeway. If it's the surround or spider, these can often be repaired with a recone kit or a specific replacement part. If it's partial voice coil damage, it's usually a new driver. If it's the amp, that's a separate repair job for the electronics. I always advise people to run through a few specific bass tracks they know inside out when they suspect this. A familiar track highlights the subtle degradation much better than just random listening. One of my go-to's is "Limit to Your Love" by James Blake – that deep, sustained bass note will reveal any wobbles straight away. ## 4. Burning Smell or Smoke: The Catastrophic Failure Right, if you're getting a burning smell, or worse, actually seeing smoke wafting from your subwoofer, then you can pretty much guarantee it's blown. This isn't a subtle hint; this is your subwoofer screaming "MAYDAY!" It means extreme overheating, usually of the voice coil, leading to the insulation burning, the glue melting, and potentially even the coil wires themselves fusing together or snapping. This is generally caused by supplying far too much power, or sustained clipping (where the amplifier is pushed beyond its limits and sends a distorted, squared-off waveform to the speaker, which is incredibly damaging). When the voice coil gets this hot, it's effectively destroyed. The copper wire can literally melt, the former it's wound on can char, and the surrounding adhesives turn to goo. The magic smoke that makes electronics work has escaped. There's no coming back from this one, usually. ### How to spot it: * **Distinct burning smell:** It's usually a sweet, acrid smell, like burning varnish or electrical components. You won't miss it. * **Visible smoke:** If you see smoke, power down immediately. No questions asked. Unplug it from the mains. * **Heat:** The driver or the amplifier plate will be incredibly hot to the touch (again, be careful). * **No sound, or terrible distortion:** Before the smoke, you might have heard horrible distortion or the sub might have just gone silent. If you get this, then I'm afraid you're almost certainly looking at a completely new driver, or if it's an active sub, potentially a new plate amplifier and driver if the amp took the driver with it. For a passive sub, the driver is almost certainly fried. This is often the result of prolonged abuse, pushing the volume too high for too long, or mismatching your amplifier to the sub. I once had a client who had "accidentally" connected a huge PA amplifier to his home cinema subwoofer. The results, as you can imagine, were spectacular, but not in a good way. The voice coil had literally turned to charcoal. New sub for him, no question. ## What to Do When Your Subwoofer Shows Signs of Trouble Okay, so you've identified one or more of these grim symptoms. What's your next move? Panic? No, not yet. Let's go through a sensible course of action. 1. **Power Down Immediately:** As soon as you suspect a problem, especially a burning smell or nasty noises, turn off your amplifier and unplug the subwoofer from the mains. Don't risk further damage to the sub or potentially to your other equipment. 2. **Basic Checks:** I know I mentioned it before, but seriously, rule out the simple stuff. Are all cables (RCA/speaker wire, power) securely connected? Is the phase switch set correctly? Is the volume knob on the sub turned up (if it's an active sub)? Is the sub's internal fuse intact (for active subs)? Sometimes a loose connection can mimic a serious problem. 3. **Listen Carefully:** Try to pinpoint *when* the problem occurs. Is it only on certain frequencies? Only at high volumes? This helps narrow down the diagnosis. 4. **Gentle Inspection:** With the power off, gently press the cone as described in the voice coil rub section. Look for visual damage to the cone, surround, dust cap, or spider. 5. **Multimeter Test (for voice coil issues):** If you have one, test the resistance across the speaker terminals. If it's an open circuit ("OL"), the voice coil is definitely gone. 6. **Contact a Professional or the Manufacturer:** If you're not comfortable with DIY repairs or the damage seems significant, get in touch with a specialist audio repair shop or the subwoofer's manufacturer. Provide them with as much detail as possible about the symptoms and any tests you've performed. For premium brands like JL Audio, SVS, or Velodyne, they often have excellent customer support and might offer replacement parts or repair services. 7. **Consider Cost-Effectiveness:** Be realistic. For cheaper subs (under, say, £200-£300), the cost of repair might outweigh the cost of a new unit. For higher-end subs, repair is often the more sensible and sustainable option. ## Preventing a Blown Subwoofer: Look After Your Kit! Prevention is always better, and usually cheaper, than cure. Here's how to give your subwoofer the best chance of a long, healthy life. * **Match Your Amplifier:** If you're using a passive subwoofer, make absolutely certain your amplifier is appropriately matched in terms of power output and impedance. Too much power or sustained clipping is a killer. Too little power can also make you push the amp too hard, leading to clipping. Consult the manufacturer's recommendations. * **Don't Overdrive:** Listen to your sub. If it's starting to sound strained, distorted, or you hear mechanical noises, back off the volume. Don't push it past its limits. That's when voice coil rub and eventual failure happen. * **Proper Gain Setting:** For active subwoofers, set the gain (volume) correctly. Don't just crank it to maximum. Start with it low, then slowly increase it until it blends well with your main speakers. There are plenty of guides online for proper sub integration. It's not about making the bass loudest, it's about making it *right*. * **Crossover Settings:** Use the crossover effectively. Don't ask your sub to play frequencies that your main speakers should handle. Setting the crossover too high can make the sub work harder than necessary on frequencies it's not optimised for, increasing the risk of damage. Conversely, setting it too low leaves a gap in the sound. Aim for the recommended crossover point, usually between 60Hz and 100Hz depending on your main speakers. * **Port Noise vs. Damage:** Learn to distinguish between healthy port noise (chuffing sounds from the port on ported subs at high volume) and actual driver distress. Port noise is usually just airflow; driver distress is mechanical grinding or distortion. * **Ventilation:** Ensure your active subwoofer's amplifier plate has adequate ventilation. Don't block the vents, and don't place it in an enclosed cabinet without airflow. Overheating can damage the amplifier and shorten component life. * **Handle with Care:** When moving your subwoofer, be careful. A drop or a hard knock can easily misalign the voice coil or damage the cone assembly. ## Comparison: Common Subwoofer Issues Here's a quick rundown of what we've talked about, to help you figure out what's what. | Symptom | Primary Cause(s) | Likelihood of Repair | Typical Repair Cost (approx.) | Prevention | | :-------------------- | :------------------------------------------------------------------------------------- | :------------------- | :---------------------------- | :--------------------------------------------------------------------------------------------- | | **Scratching/Rubbing**| Over-excursion, mechanical damage, overheating, spider/surround failure. | Moderate | £80 - £250 (voice coil/recone) | Don't overdrive, proper gain setting, careful handling. | | **No Bass Output** | Completely severed voice coil, broken tinsel leads, amplifier failure (active subs). | Low | £150 - £400+ (new driver/amp) | Proper power matching, avoid clipping, check cables. | | **Distorted/Weak Bass**| Partial voice coil damage, failing surround/spider, amplifier clipping (active subs). | Moderate | £30 - £200 (surround/amp repair) | Don't overdrive, proper gain/crossover settings, regular visual checks. | | **Burning Smell/Smoke**| Severe overheating, extreme over-powering, prolonged clipping. | Very Low | £250 - £500+ (new driver/amp) | Match amp power correctly, never overdrive, ensure ventilation, listen for distress signals. | ## FAQ: Your Subwoofer Worries Answered ### Q: Can a blown subwoofer damage my amplifier? A: Yes, it absolutely can. If the voice coil completely shorts out (becomes a very low resistance load), it can draw excessive current from your amplifier, leading to overheating, tripping protection circuits, or even outright damage to the amp's output stage. Always disconnect a faulty sub straight away. ### Q: Is it worth repairing a blown subwoofer? A: It really depends on the subwoofer and the extent of the damage. For cheap, entry-level subs, it's often more cost-effective to replace the whole unit. For higher-end, more expensive models from reputable brands like SVS, B&W, or REL, repair is often a good option, especially if it's just a voice coil or surround issue, as a new driver can be very costly. Get a quote before deciding. ### Q: How can I test my subwoofer to see if it's working? A: Start by checking all connections. Then, try playing some bass-heavy music. If you suspect an issue, disconnect it from your main amp and use a multimeter to check the resistance across the terminals. For an active sub, ensure the power light is on and try adjusting the gain and crossover. Many AV receivers also have a test tone generator that can send a signal specifically to the sub. ### Q: My sub makes a popping noise when I turn it on/off. Is it blown? A: A single "thump" or "pop" when turning an active subwoofer on or off isn't necessarily a sign of it being blown. Many active subs do this as their internal amplifier powers up or down. However, if it's a very loud, repeated, or harsh popping, or if it happens during playback, that could indicate an amplifier fault or a DC offset issue, which should be investigated. ### Q: Can my speaker wires cause my subwoofer to blow? A: Unlikely directly, but poor quality or damaged speaker wires could potentially cause problems. If wires are frayed and short-circuit, they can cause issues for your amplifier, which in turn could affect the signal sent to a passive sub. For active subs, it's more about the RCA or LFE cable, but again, a faulty cable usually just leads to no sound or hum, not a blown driver. ## Final Word There you have it then, the four main signs that your subwoofer is on the way out, or perhaps already there. It's never nice when kit fails, especially something that brings so much enjoyment to your films and music. But by knowing what to look and listen for, you can often catch these problems early, potentially saving yourself a fair bit of cash and grief. Remember, your subwoofer isn't some invincible beast; it's a finely tuned piece of engineering that needs a bit of care and respect. Listen to it, understand its limits, and address any odd behaviour promptly. Your deep, resonant bass will thank you for it, and you'll keep that crucial foundation of your sound solid and true for years to come. Don't be shy about getting a professional opinion if you're unsure – it's always better to be safe than sorry with your beloved audio gear. Happy listening, and here's hoping your subs rumble on healthy for a long time yet!