June 23, 2016
A blown speaker is arguably one of the worst things that can happen to your pro audio rig, whether you are a sound pro, bassist, guitarist, or DJ. It may be a freak feedback, clipping amplifiers, or poor AC power, but it can happen to the best of us. Knowing the basic steps of what to do next after blowing a speaker will help you get your rig up and running as soon as possible. Here we are only looking at “abuse” causes of failures and not factory defective speakers. A defective failure is diagnosed by looking at the speaker internally and is caused by misalignment, poor gluing or fragments in the coil gap. These failures are very rare and look much different than a blown speaker.
How Speakers Blow: Over Excursion & Overheating
What happens when a speaker blows can generally be attributed to two things: mechanical or thermal failure. Mechanical failure occurs through over excursion of the cone, which is when the cone moves too far beyond its limits to the point of damage due to excessive power or low frequencies beyond the cabinet’s or speaker’s ability. Mechanical failure can show in the voice coil tearing away from the cone, the voice coil moving so far it hits the rear plate bottoming out (sometimes you can even hear a click when it hits) or the surround getting over worked and breaking down. Thermal failure is the result of excessive power heating up the voice coil, causing the varnish on the coil wire to turn black and expose the wire to shorting and eventually even melting away the wires themselves! Either will result in a speaker that just won’t make any sound or perform very poorly.
How to know if it is blown or not: What is the smell?
Now you have a cabinet not working, but is it blown? With a thermal failure, especially with larger woofers, you can usually smell the damage. The burnt varnish has a very distinct burnt smell. You can usually follow your nose on this one. You can also remove the grill and lightly push the cone in and release it. Don’t force the cone, if it does not move freely with what feels like a spring tension from the surround then it may be fried. If it is a mid frequency driver or a form of paper tweeter, it may not have much movement to begin with and this method of moving the cone is not going to tell much. Also while pushing, you may hear or even feel scraping or scratching. Besides preventing winding to winding shorts, the varnish on the coil wire also holds the wires coil form. If it has melted away the coil it can start to become loose and rub the walls of the magnet gap. Be sure to push in two points on symmetrical sides of the cone evenly. If you push uneven or not symmetrically on the cone, it will tilt the cone and the voice coil can rub the walls of the gap. This would not be showing damage, but it would just be you pushing the cone sideways. You may also find your speaker works sometimes cutting in and out. This could be the melted coil wires shorting to the gap or a broken wire that makes contact when the coil is moved enough by the music.
Mechanical damage does not usually completely stop the speaker unless it goes a longer time unnoticed. Bottoming out the speaker with large power low frequency peaks could damage the speaker and cause it to totally stop, but most mechanical damage has a loss of performance that is noticeable before no sound is heard. Of course the more speakers in the system the less you may notice one that is getting abused.
Remember there are the crossover, jacks, speaker cable, internal wires and sometimes several connections between your power amp and the actual speaker. These items will need to be examined if you don’t have the obvious smell or visual wear and tear symptoms. Test your cables with known working cabinets. If you are savvy with some level of digging in, you can check the connections, and if you have two of the same cabinets, you can test further, by swapping crossovers. You may even look over the crossover for broken solder, burnt or missing parts, or loose connections. Finally don’t void the warranty! Free warranty repairs should be checked first. Don’t be afraid to call and talk to a customer service guy. They can walk you through some checks and make the fix happen faster.
Replace or Recone: That is the Question
If your speaker is dead in the water, your two main options are to replace or recone it. Reconing is a process in which all the moving parts, including the voice coil, surround, and cone, are replaced. It’s a very tricky process that is usually best left to an experienced professional, but some manufacturers do offer recone kits for those inclined to do it themselves. If a recone is done correctly, it is as good as new. For vintage or rare speakers, reconing is often the only option as the required speaker is no longer available for purchase or it is beyond a reasonable cost.
If you opt to replace the speaker, here are a few things to know. If this is a standard guitar cabinet without a passive crossover you can usually change the speaker to another guitar speaker without an issue. This is often done just for tone changes and finding your sound. Do keep in mind the guitar head was probably designed using the original speaker, so it may not sound as good with a speaker that is popular with other amplifiers. For bass guitar cabinets and PA cabinets, your new speaker should ideally be replaced with the original specified ones or a recommended alternate that is very close in its specifications. Unlike with guitar cabinet there are multi drivers and more low frequency involved. Here the speaker is the essential part of the cabinet and crossover design. Choosing an off spec model will not only change the sound of the cabinet, but it may not perform as well leading to a future mechanical failure. Even a higher power speaker not designed for the cabinet’s tuning can fail at lower power. Finally, if you enjoyed how the cabinet originally sounded, the results may be undesirable. So if you’re going to have a local repair shop replace it or you will do it yourself, make sure you have access to a recommended replacement speaker!
Lastly, it goes without saying that you should choose the option that is more financially viable as well. With higher end and rare speakers, it’s often cheaper to have them reconed than to purchase brand new ones. While less important, you should also be aware that keeping the original speakers in the cabinet helps maintain its resale value, if you should eventually choose to go that route. If you blow a speaker, it’s not the end of the world, but do look at what may have happened, so you don’t blow the replacement.
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