07/03 - Larry Mundy - http://www.colomar.com/Shavano/reconing.html
Let me say right up front, this is not a do-it-yourself project. Rather, its a discussion of whether, and when, to take your tired or blown speaker to the speaker doctor to be tuned up, or brought back to life. Ive tried this at home, and believe me when I tell you, dont try this at home!
Types of speaker damage.
Since speaker drivers are mechanical things with moving parts, they are subject to wear and fatigue. And since pro-audio speakers are subject to extreme abuse, even the heavy-duty models can fail under stress. Damage to a speaker can take many forms:
Fatigue. While this is uncommon in heavy performance speakers, which are after all only used during performances (or at lowered levels, during practices and recording), it is fairly common in house speakers which play bass-heavy prerecorded music for hours on end, every day or night, or sound-company rentals which are in constant use under varying circumstances. I recently bought a pair of heavy subwoofers that had been installed in a disco for two years, pumping out bass seven nights a week. They worked, but didnt sound nearly as crisp as a matching pair of the same model Id bought new. There are three components of a speaker that are designed to flex as the cone moves in and out: the surround at the edge of the cone, the spider that covers the front of the magnet/voice coil assembly, and the braided wires that carry the signal to the voice coil. As the largest in area, and usually the most exposed to the elements, the cone surround usually suffers the most wear and can become floppy, changing the sound characteristics of the speaker. The cone itself flexes a bit in use, and environmental conditions (primarily humidity, including such extreme forms as spilling a beer into the cone) can accelerate its structural breakdown. After protracted use and exposure to the elements, a speakers moving parts can become - and sound - tired. Many pro sound companies and large clubs rotate and replace or recone their drivers on a regular basis to keep them fresh and functional.
Physical damage to cone or surround. A fatigued speaker can develop splits and cracks in the cone or surround, and once this happens, it can no longer move air as designed. Continued use will only place more stress on this weak point and enlarge the split or crack. Even worse, without adequate protection of the face of the speaker, some projectile (beer bottle, cue ball, Pete Townsends guitar) can pierce the cone more dramatically, rendering the speaker useless. The only exception to this is the dustcap, the little round bump in the middle of your woofer that covers the voice coil and magnet pole assembly; its principal purpose is simply to keep dirt and junk out of the voice coil gap, and if it is slightly dented but not actually pierced, thats only a cosmetic problem and the speakers sound will be unaffected.
Voice coil burnout or rubbing. This is what is typically meant when we say a speaker is blown. A blown speaker commonly exhibits no external indications of damage, because the voice coil is not visible without disassembly, but this is by far the most common sort of speaker malfunction. It results from a buildup of heat in the voice coil, from excessive amplifier power or clipping distortion, which overcomes the ability of the speaker design to dissipate. When the overheating is sufficient, the relatively thin wire in the voice coil can actually melt at some point and develop an open circuit; when this happens the speaker stops making sound of any sort, and an ohmmeter placed across the speaker terminals will indicate no resistance whatsoever, because of the open circuit. Or the voice coil can deform from the cylindrical shape it must have to move back and forth in the magnetic gap. The speaker may still make sound, but it will be distorted, and when you push the cone in and out by hand there will be a scraping noise, felt as much as heard, which indicates that the voice coil is rubbing in the magnet gap. Other physical indications of a blown speaker can be an inability to move the cone in and out manually, indicating that the voice coil is stuck in the gap (from overheating, deformation, maybe even melting of the insulation or adhesives used to assemble it). I have seen speakers where a combination of voice coil damage and overexcursion has resulted in a cone which can be pushed in and will stay there, can be pushed out and will stay there, but will not center to its normal resting position.
Damage to nonmoving parts. This rarely (okay, never) happens from simply overpowering a speaker, because the magnet assembly and speaker frame or basket are pretty tough. However, if a speaker is dropped onto a hard surface it is possible to bend the frame (particularly if the speaker lands on the frames edge) or even break the magnet. This is the only type of speaker damage that is completely and totally unfixable. A bent speaker frame can never be straightened with sufficient precision to restore the close tolerances necessary for the voice coil to move unimpeded, and a broken magnet is simply that. A speaker so damaged must simply be discarded, although its a free opportunity to tear it apart first and see all the internal pieces and parts youre reading about here, and then throw it away.
What is "reconing?"
All types of damage or fatigue other than magnet or frame damage are fixable through a process called reconing. Basically, all the moving parts of the speaker (cone and surround, voice coil, lead wires, spider) are removed and replaced.
First, of course, the old components are removed, along with anything that holds them in place (such as the front sealing gasket, which is cemented over the edge of the cone), resulting in an empty frame/magnet assembly, then the various adhesives that held them in place are removed by scraping or solvents and the voice coil gap cleaned of crud dirt, dust, bits of burned voice coil. Then a replacement cone/voice coil assembly is fitted very precisely and secured in place with strong adhesives, a new front gasket is fitted, new lead wires are hooked to the terminals, and the result is a like-new speaker.
Far left: new cone/spider/voice coil assembly. Near left and above: empty frame/magnet assemblies for reconing.
Sometimes the magnet is even recharged on a giant machine that makes the lights dim for blocks around. All of this requires precise tools and jigs, powerful glues and solvents, etc. and is a job for a professional reconing service. The only thing you can probably accomplish at home is a process called refoaming, which is replacement of deteriorated foam surrounds, usually on older hi-fi speakers. No speaker intended for live musical performance should ever have a foam surround. You can read about refoaming somewhere else, because if you are using any sort of foam-surround speaker for any instrument amplifier, public-address system or similar application, it is the wrong sort of speaker and is ill-suited for your use. Replace it with an actual pro-audio speaker, which will almost certainly have a pleated-type or accordion surround.
When to recone, and when to replace.
This is the eternal question should I have my blown or damaged speaker reconed, or simply replace it with a new one? The answer to this depends on several variables, but the principal one is the quality and replacement cost of the speaker in the first place. Reconing is not cheap, starting at probably $40-50 for a smaller speaker and running to well over $100 for a large one. So just as theres little economic sense in spending $100 on repairs to fix a $50 VCR, theres little point in reconing a cheap speaker, which is cheaper to replace than repair. Generally, smaller speakers (up to 8 or so) are cheaper to replace, unless you really really need to fix that particular speaker (as when restoring a vintage amp). A thin, stamped-steel basket (as opposed to a thick, cast frame) is a hallmark of a cheaper speaker which may not be worth the reconing cost, regardless of its size. A no-name speaker (i.e. one thats not a name brand, and likely produced cheaply in the Orient) is probably not worth reconing. One good indication is the availability of factory reconing parts in the first place; name-brand manufacturers who know their speakers are worth reconing, and aftermarket suppliers who know the same things about certain brands or models, sell reconing kits complying with the original materials and specifications, and sometimes even exceeding them. A manufacturer of cheap, disposable speakers wont offer reconing kits for them, and aftermarket suppliers wont either. If in doubt, place a call to (or email) two or three speaker reconing services and ask about your particular model. If it will take weeks to get parts, or if the new cone or voice coil will have to be custom-fabricated (a very expensive proposition), thats a good indication that your speaker is probably not worth reconing.
Another consideration is, do you know why and how your speaker was damaged in the first place? If it is a fairly light-duty speaker which burned up in normal use, after reconing you will have a like-new, light-duty speaker which just might do the same thing in the same circumstances. In that case, you might consider spending the extra money for a heavier-duty speaker which will better resist your sonic enthusiasm. If, however, your speaker was destroyed in unusual circumstances (an amplifier malfunction sending excessive current through the voice coil, a surface-to-air missile fired through the cone), or if your speaker is already a very heavy-duty model that is dead or dying from fatigue, by all means consider reconing.
Finally, if you have a speaker thats a good candidate for reconing, consider whether there is a competent reconing service near you, because otherwise in addition to the cost of reconing, you will probably have to bear shipment costs and risk in both directions. Speakers appropriate for reconing are likely very heavy and difficult to pack for shipment. I live in a large metropolitan area that has three reconing shops within an hours drive of my house, and most sizeable cities probably have at least one. But if you have to pay two shipment charges in addition to the cost of reconing, you may find you can buy a new example of the same speaker for not much more.
How to find a reconing service, and what to expect.
Dont expect overnight service from a reconing shop. The process takes time and a lot of personal attention, and proper curing of the adhesives used can take time as well. Speaker reconing is a specialty, and there arent a lot of reconing shops because its not a get-rich-quick specialty, either. If the shop recons a lot of speakers of your brand and type, they may have a freshly-reconed spare lying around they can send you in lieu of the time it will take to work on yours, but this is rare.
How do you find someone to do this work? Some of the larger shops place ads in audiophile or pro sound magazines, and in larger cities might be listed in the yellow pages. The best source, however, is probably a web search engine, entering a phrase like speaker reconing Philadelphia or speaker repair Fort Worth. Many speaker manufacturers list authorized repair services on their websites; depending on the manufacturer, authorized can mean anything from they buy parts from us now and then to weve checked out their work and reputation. Call the reconing service and describe your speaker my manufacturer, model, and impedance; they should be able to quote you an approximate (or sometimes even exact) reconing price over the phone and give you a time estimate for the work. Based on that, you can further consider the options of repair vs. replace.
A properly reconed speaker is the functional equivalent of a new one, and should have the same characteristics and sound as a new one of the same model. For some discontinued speakers which nevertheless enjoy a good reputation, reconing is the only option. You can even, in some instances, change the characteristics of a speaker in the reconing process; for example, the venerable JBL 130 and 140 series, now discontinued, varied primarily in the cone and voice coil design with similar or identical magnet/frame structures, so now and then you will see JBL E130 reconed as E140 or something like that. You reconer will know what is possible if you ask. And if you have that favorite speaker reconed, not only do you save a little money, but you can feel environmentally responsible that a perfectly good frame and magnet arent sitting in a landfill somewhere!
There are two exceptions to my dont try this at home advice. One is the rare type of speaker with a bolt-on magnet and field replaceable cone assembly that includes the new cone pre-mounted in a new basket assembly. The best known of these is probably the Peavey series of Black Widow and Scorpion drivers. A careful amateur can probably effect this replacement, although there is still the risk of deforming the voice coil or leaving crud in the magnetic gap, and replacing the basket and cone assembly can be more expensive than replacing the cone assembly alone. I dont happen to use these speakers much in the first place, but I have to hand it to Peavey for pioneering a field-replaceable approach. It is also possible for a careful and painstaking amateur to replace the diaphragm of a high-frequency compression driver, since the radiating surface is usually contained within the circumference of the voice coil and there is no adhesive-covered cone-frame interface to worry about. But it is certainly possible for the kitchen-table engineer to botch this job too, and it is a job a professional reconer wont charge much for (in fact, he can probably buy the replacement diaphragm assembly cheaper than you can). If you have a large number of pro-audio speakers and subject them to constant abuse, get to know your local speaker doctor and over time you could save a considerable amount of money.
NOTE: We do not work on Home or Car Audio. We work only with Pro-Audio applications. We cannot help you with Home or Car Audio questions.
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