jimrockford

Last night I was pushing my system a little harder than I normally do and thought I burned up the voice coil in my sub (Image Dynamics IDQ12 D4 v.2 driven by a Memphis 500D). It started making a buzzing noise and sounded like it was completely destroyed.

I pushed on the cone and it wouldn't hardly move. When it did it was really scratchy feeling. I disconnected the sub amp and listened without the sub for the rest of the night.

Today, I went out to take a look at it again, and after pressing the cone in a couple of times it kind of gave a little and the scratchiness went away. I hooked the sub amp back up and played some tunes. The buzzing was gone and it sounded perfect. What gives? I know it's damaged but seems to be working fine now. Does anyone know what physically happens when you burn up a voice coil and how it could go from bad to good like that?

midiwall

Sounds like you may have popped the voice coil core out of the channel (the problem was mechanical, not electrical). Don't do that. You're pretty lucky it still works. If the core came out that far, it could have easily gotten dented or ripped the speaker as it tried to get pulled back in.

Pictures can help:
http://electronics.howstuffworks.com/speaker5.htm


When you burn a voice coil, the speaker will usually go dead. It comes from too much current in the wire, the wire getting hot and breaking. Sustained heat can also melt the insulation off of the wire, which will short out the layers of the coil, which will decrease resistance, which will increase current, which will create more heat which will... cause a lot of smoke, and sometimes flames.

A neighbor at an apartment complex torched the whole back end of his Explorer by a sub catching on fire.

jimrockford

That makes sense. I hadn't thought about it that way. I figured it had overheated and melted through the wire insulation and fused with the magnet assembly. If that happened, breaking the voice coil away from the magnet wouldn't make it work again, right?

A mechanical "malfunction" makes more sense. The voice coil was driven beyond its physical limits and got stuck or hung up. I guess manually pushing on the cone popped it back into place. I wonder if I did any lasting damage. I know it sounds exactly the same as it did before.

midiwall

Right - you'd be VERY VERY lucky to get them to mate again. This is where a "reconing" would come into play - tearing the cone off, reattaching the voice coil, then replacing the cone. The sonic end result of a recone is a coin toss.


Yeup, exactly.


Ummm... if it sounds okay to your ears then it's "okay". Ya' know? I would suspect that you shortened the life of the speaker, but it's hard to say by how much, or if you'd ever see the failure (i.e., you'd swap the speaker or sell the rig before it failed).

I think the real issue here is how to stop it from happening again.

Ideally, you're gonna wanna limit the power to the sub so that it won't extrude so far - but finding that limit is gonna be hard without damaging the sub in the process.

I gotta say that I'm kinda' surprised that the sub didn't have some sort of mechanical stop pin on it to keep this from happening. I know that big-rig concert drivers do - the power that gets put to those things is incredible, and having something like this happen at a show would be disaster.

jimrockford

I was thinking the same thing. You'd think the design would incorporate something to preclude idiots like me from pushing it too far.

I really love that sub too. It's the best sub I've heard in terms of sound quality. I guess it just lacks a little in the SPL department and I was trying to squeeze a little more out of it that I should have. Oh well, it works for now. If it finally dies, I guess I'll have to look at upgrading to the iDMAX.

jimrockford

Well, last night everything was working great while listening to CDs. I switched over to Sirius and wound up in the middle of a farting contest on the Howard Stern channel. That channel is pretty bass heavy and almost immediately the sub cut out.

It turns out the fuse in my distribution block feeding the sub amp blew. Do you think the voice coil is shorted out causing the fuse to blow?

midiwall

Hmm... it does sound like you have a new upper-limit for the sub level. bummer. With the fuse blowing, then yeah, something sucking too much current - and this is a fuse to the _amp_ (not the speaker) right? It wouldn't make a lot of difference in my answer either way, the question's more about "what" detected the load first.

Ya' know... if you're figuring on running this way for a while, you may want to look into using a circuit breaker between the amp & the speaker. It'll save a large current draw through the amp, and since it's a breaker, you won't have to replace fuses every day.

mdh

This is where a "reconing" would come into play - tearing the cone off, reattaching the voice coil, then replacing the cone. The sonic end result of a recone is a coin toss.

Hey midi, are you saying that if ID reconed the sub it might not soung right? I thought a factory recone would sounf like a brand new sub.

-Worries about his brahma-

midiwall

Well, unfortunately, yeah.

Things may have changed over time, but in my experience with pro audio (recording studio style) and large PA systems, reconing is a real crap shoot. In the recording studio side, you would NEVER recone a speaker - toss it and get a direct replacement from the manufacturer. PA systems can be a bit more forgiving, 'specially things like mids, but I've seen good recones and bad. The bad's sound HORRIBLE.

The issue comes a difference in what the reconer is using for materials, shape, glue, wiring and even the frame (if applicable). There's a lot of research behind these materials in a high end driver, and a reconer will rarely have access to the exact stuff from the factory.

For example, look at a sub - see those ridges along the face of the speaker towards the edge? Those are there by design - they help keep standing waves from forming along the edge of the frame. Their height and distance from one-another are based on a lot of math that takes into account the frame, the size of the box that the speaker is in, the material, the glue, a LOAD of stuff.

If a reconer doesn't hit that _exactly_ then the speaker will sound "different". It could be "good", or "okay", or "OMG! WHAT HAPPENED???".

This isn't to say that things won't be okay - I'm just saying that there's a lot that goes into the design of a driver, and it all has to be taken into account when being repaired.

mdh

I am guessing that we are talking about a completely different thing in the world of car audio sub drivers. I can not recall hearing a complaint about a factory sub recone gone bad on any of the car audio boards I frequent.

Anyone else?

midiwall

Well, physics are physics, the science doesn't change from one industry to another.

I didn't notice that you had said _factory_ recone before - that of course would mean that the reconer would have access to all the original materials and make a lot of my babble moot.

jimrockford

Yep, fuse to the amp. For now I've turned the sub amp gain down and I'm keeping the volume low.

I'll be looking into a replacement sub soon I think. I'm headed to Hawaii next week though and that has me watching my spending for now. I really want to get the Image Dynamics iDMAX-12. I think it would be a better fit with my amp and have a lot more output. I'm pushing the limits of the IDQ-12 at 500 watts. The iDMAX wouldn't even break a sweat with that much power.

http://www.imagedynamicsusa.com/prod...idmax&type=sub

deserttoy84

this sounds like when we put a 12 polk momo with a legacy 1200w x2 i think(not tru wattage at all haha)but we push it so harsd it popped and burned coils so bad it was a brand new sub too so we hook it up to my quad and dragged it arouidn my property lol. might not of hurt the sub but more the amp. it could of got hot and shut off