Tech Talk: Burned Speaker Voice Coil Diagnosis

Tech Talk | WRITTEN BY AARON TRIMBLE | May 2018

Ever been baking cookies, only to find out that the softened butter you need is still in the freezer?

We get a lot of emails here at the Tech Talk. People ask us, “what sort of box should I build?” Or “what woofers should I buy?” And of course, “why did my woofer blow?” Now we’ve addressed woofer failure, both mechanical and thermal, before on the Tech Talk. Today, though, we’re going in depth on the various forms in which thermal failure can manifest itself. Plus, I’m going to use some fancy butter analogies, and how often do you get to hear that?

The Rattle:

So, you’re making cookies, and you’ve got a butter popsicle. What’s a baker to do? Well, if you’re like me, you’ve had the brilliant idea to unwrap the stick of butter and pop it in the microwave for a minute. You’ll just watch for when it gets melty, pull it out and let it cool a bit. However, instead of the stick of butter becoming nice and soft like you wanted, you watch like a fool, as the butter paints the inside of the microwave like a Jackson Pollock painting in hot liquid fat. What causes this delicious, buttery murder? Why, water vapor of course. Microwaves have a funny way of heating up things from the inside out, and as a result, the inside of the frozen stick of butter melts and starts to evaporate before the outside has a chance to soften. As the butter heats it releases water vapor which expands and explodes out of the weakest wall of the stick. Voice coils work pretty much the same way… well, minus the radiation.

butter vs voice coil

Car audio users have an unwitting propensity to apply insane amounts of power to speakers that aren’t rated for it. Because of this, buttery murder occurs. Mind you, I’m not just talking about a standard, run-of-the-mill dead voice coil either. In this case, we’re referring to a far more annoying form of blowing a woofer: the Rattle. The Rattle is caused by too much power, too fast. Voice coils use various resins to hold their copper and aluminum windings on the former, and just like butter, those resins release gases as they are heated. Because the inside windings of the voice coil are covered on both sides by a former and other windings, the inside layers of the voice coil will heat faster than the outside winding layers. When this happens too quickly, the released gases have to expand somewhere. The gasses can either try to pass through the still hard resins and windings of the outside layers, or through the thin inside layer of the aluminum former. So the gases press against the voice coil former and they create a bubble. Because of the tight tolerances of the woofer’s motor geometry, this bubble is usually large enough to rub on the pole piece, which creates that lovely rattle that we often hear from a “blown,” but working subwoofer. Often times with the Rattle, the voice coil has so much power applied to it, so quickly, that the resins on the outside of the coil don’t even have a chance to discolor.

The Scrub:

The Rattle is easy to distinguish from its cousin, the Scrub. The Scrub is a result of mechanical failure, non-linearities and the woofer spider’s inability to keep the voice coil straight up-and-down in the magnetic gap. The Scrub leaves a wide arc of rub marks across the former, whereas the Rattle typically only affects the top of the gas bubble point.

voice coil failure

The Burn:

Now back to the butter, because we’re here for the cookies after all, right? After cleaning up my milk fat reenactment of my favorite Dexter scene, I was still short a softened stick of butter. So, grabbing the rest of the pound from the freezer and setting it on the counter, I took one more stick from the package and again put it in the microwave. This time the power was turned down. There was no explosion, but the inside of the stick was still liquefied. Alas, liquefied butter doesn’t work very well for my chocolate chip cookie recipe, and liquefied voice coil resins don’t work well for woofer longevity either.

power vs time

Voice coils come in two flavors of traditional burn, fast and slow. The Fast Burn is easily characterized by a gradient in the coil. The bottom of the voice coil is black while the top may still be nice a copper color. In the world of roasted coils the Fast Burn is the middle of the pack for too much power for too long. This coil also typically rattles, but this isn’t a former rubbing on the pole piece. Instead, the Fast Burn is when the windings rub and bang against each other. As the resins melt, they do so more evenly than the Rattle. Gases are allowed to escape from the inner layers of the voice coil, you may even notice small resin bubbles form on the gaps between the windings as the resin boils. When the power is decreased even more and played for even longer, we get the classic thermal failure. This is the Slow Burn or as it’s more popularly known, the Slinky.

voice coil failure

Everybody has seen a slinkied coil. They come in all sorts of shapes and sizes, but no matter how they look, they all have a pile of raw wire that has come free from the former. These coils have cooked for so long that they have cooked off most of the resins that hold the coil together and the windings have started to fall off the former. Once this happens, all hell can break loose. The windings can impede the movement of the rest of the coil, and cause mechanical failures. The wires can also get bent and shear or break apart, causing the coil to short out against the motor. The Slinky is by far the most dangerous to amplifiers, not to mention the Tech who has to pull all that wire out of the magnetic gap if they don’t use gloves. The Slinky, in butter terms, is more like when I take one of the two remaining sticks of butter on the counter and leave it on the windowsill on a hot day for too long and the stick completely loses its form. While this is great for spreading on toast, it’s not very awesome for cookies.

At the end of the day, when you make cookies, the right temperature butter is just a matter of applying the right amount of power (heat). Woofers have the advantage of having that power written right on them. They have a listed RMS for a reason. Audio engineers figured out a long time ago, through countless baking experiments, how much power was the right power.

Check out our full line of Subwoofers!

Install Highlight: 2004 Saturn Vue

Install Highlight | WRITTEN BY LEWIS JACKSON | MAY 2018

This month’s install focuses on the 2004 Saturn Vue of Tony Tricoche, a military veteran and sales rep at Lawson’s Car Audio, a premier shop in the Augusta GA area. With their tight knit staff, owners Su and Morgan Lawson are able to offer fully custom car audio, video and lighting, as well as marine and motorcycle applications. Not one to miss an opportunity, Lawson’s plans to get into the truck accessory and wheel business in the near future as well. Sales staff include armed forces Veteran Thomas Iirley, and Tay Parker. Adding to their military family are Serge Corvington and Stephen “Rob” Roberts, between them and Daryl Hacker there is a 50 year pool of experience at their disposal.

This build was possible because of the contributions the fabrication and install staff were able to make, such as  the custom door panels by Rob. The original goal for the car was to not only create an impressively loud daily driver, but to showcase just what Lawson’s is really capable of. Tony has even been known to dabble on the competition scene when the mood hits him. The list of equipment featured in the vehicle is as  follows:

4 – DD REDLINE 815 
4 – DD-VO-B3

8 – DD-VO-M8
4 – DD-VO-B4
4 – DD-VO-M6.5
3 – DD-C3d
1 – DD-A5
2 – DD-M3c
1 – MTX LSB1- (rare, owned for about 16 years)
1 – Pioneer nex-4200

This equipment is fed by a high output alternator and a substantial battery bank, allowing Tony to enjoy his equipment to the fullest without skipping a beat! Being that Tony is a basshead like us who will only have this system in the vehicle until the mood strikes him to change it again, (this is the 3rd system in 18 months, guys!) you may want to keep an eye on the crew at Lawson’s Car Audio — or better yet, keep an ear out! To the military staff at Lawson’s, we thank you for your service.

This slideshow requires JavaScript.

Visit our FREE Audio Upgrade Guide to Upgrade YOUR Sound™.

DD Audio #SpeakerSeries Featuring Special Guest Jabee

Oklahoma City, OK, May 14, 2018 — DD Audio’s upcoming “Speaker Series” features special guest Jabee and is scheduled for Thursday, May 24th at the Project 3810 Event Center, 3810 N. Tulsa Ave., OKC, OK – 73112. This is the inaugural #SpeakerSeries presentation and will be free to attend with RSVP only (reserve your spot). Doors open at 5:30pm for networking. The program will start at 6:00pm. The Q & A will immediately follow at 6:45pm. The full event will last until 8:00pm.

In their continuing effort to support the creative community, DD Audio holds their “Speaker” Series twice a year. They invite individuals with diverse talents to speak with audiences about visionary marketing tactics, the use of technology and innovative approaches to starting or running a small business, personal brand or passion project.

The engagement will be hosted by Kyle Golding, CEO of the Golding Group and award-winning creative professional with 30+ years of business experience, and will feature the multi-talented Emmy award-winning OKC rap artist and DD Audio ambassador, Jabee, who will speak on topics such as artist/business partnerships, product endorsement and the power of collaboration.

Join DD Audio and others for a casual but informative conversation about inspired ideas and practical execution from Jabee and Kyle. Food and craft beer (over 21 with ID) from local partners will be served. Free with RSVP only (reserve your spot). Door prize drawings will be held for DD Audio products. Time will be provided before the program for networking and Q/A. Guests will be welcomed to tour the Project 3810 facility and meet everyone involved in this new office, co-working and start-up space for entrepreneurs and small business.

The #SpeakerSeries will be an ongoing program with presentations sponsored by DD Audio with support sponsors The Golding Group and Project 3810. New guest speakers will be featured at each engagement with the goal of providing information and inspiration to attendees.

DD Audio 2nd Annual Invitational – Cinco DD Mayo Party

PRESS RELEASE

Oklahoma City, OK, May 11, 2018 — DD Audio held its second annual DD Invitational on May 5th, 2018 – dubbing it Cinco DD Mayo. Attendees were welcomed to DD Audio’s Oklahoma based factory and warehouse where fine weather permitted a fun outdoor celebration. Dealers, partners, employees and their families enjoyed catered tacos, local brew, games, raffles, product training, warehouse sale and after party.

The event was very well attended, with dealers traveling from as far away as Georgia to join in on the festivities.

Product training provided by DD’s Aaron Trimble included a detailed first-look at the recently revised Redline Series along with several other exciting new products slated for release later this summer. Kevin Doyle, the master of ceremony, presided over the games which featured a frozen t-shirt contest, subwoofer toss, and subwoofer mounting relay race with prizes going to the winners of each game. DD Audio also held a Propper Droppers style SPL competition which pinned daily drivers against professionally crafted demo vehicles.

When asked about the DD Invitational, Kevin Doyle said, “This event is a great chance to show appreciation to all of the people who allow DD Audio to continue growing as a company. It’s really fun to see the dealers interacting with the people who build the products they love.”

DD Audio Announces REDLINE Series Subwoofer Upgrades and Redesign

PRESS RELEASE

Oklahoma City, OK, May 8 2018 — DD Audio announces the immediate release of the revised REDLINE Series Subwoofers featuring both performance and aesthetic upgrades. The REDLINE Series is DD Audio’s value oriented product line, but as with all DD Audio products, the REDLINE Series is constantly evolving with changes being made specifically to meet the performance demands of today’s listeners and installers. The 612d-D4 is the first of these new offerings to become available with the remaining models to follow soon.

Performance Improvements Include:

  • Redesigned Frames and Suspension Geometries Allowing for Optimal Compliance, Lower FS and Greater Excursion Potential
  • Completely Revised Voice Coils Utilizing American Adhesives for Increased Thermal Handling and Double Slit Formers for Reduced Inductance and Increased Efficiency.

Aesthetic Improvements Include:

  • Black Matte Finish Cone and Dustcap
  • Reflective Foil Dustcap Logo
  • Thermoformed Multilayer Surround with Signature DD REDLINE Accent
  • Embossed Redline Logo On Inner Diameter of Surround
  • DD Branded Cast and Stamped Frames

REDLINE Series 612 Subwoofer

Specs:

200 Series

  • 300 Watts
  • 10” to 12”
  • 2” Dual 4 ohm Voice Coil

500 Series

  • 400 Watts
  • 6.5” to 12”
  • 2” Dual 2 ohm or Dual 4 ohm Voice Coil

600 Series

  • 600 Watts
  • 8” to 15”
  • 2.5” Dual 2 ohm or Dual 4 ohm Voice Coil

700 Series

  • 1200 Watts
  • 12” to 15”
  • 3” Dual 2 ohm or Dual 4 ohm Voice Coil

Click here to see the full lineup of DD Audio Subwoofers.