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Drivers blown but no noticeable burnt smell?
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    Posted: 19 June 2011 at 12:18pm
Hi Guys,

Any idea's what might be going on here,

We use a pair of 600 watt @ 8ohm  RMS speakers (15" + 1") and drive them with a QSC GX5 (500 watt @ 8 ohm)

I lent them to a mate this weekend for a party of about 70 people.

They have come back and the HF is fine but both the LF drivers are blown?

They told me the both just stopped working at the same time?

It cant be the amp as that's literally 2 separate circuit boards Left/Right. (Correct?)

Now from past experience drivers definitely dont stop working at the same time! but its niggling me that there is no distinct burnt smell

(ive yet to open them up)

Can a speaker blow pretty much instantly without the coil burning out? if so how did they make this happen!!??

I want to charge them for new drivers but need an argument to back it up

Cheers

Alec
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Causes could be multiple.
Leonic wires could be intrerrupt, from exceeding bass and overexcursion (no low cut used), poor speaker quality, mechanical shock, and wire desoldered, etc.
 
Best is to open that speakers (boxes), and chech speakers continuity (wires desoldered), with a 1,5 volts battery.
 
Booth speakers must click/pop.
 
If yes, is possible that the bass coil from filter, is opened circuit (durring exceeded vibration), check solderings on filter PCB.
 
If bass speaker no pops, click, etc, the coil of speaker is opened or leonic wire intrerrupted.


Edited by DjLeco - 19 June 2011 at 12:31pm
I'm A Stupid SMART Romanian...
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Points: 56 		Post Options Post Options   Thanks (0) Thanks(0)   Quote AC1 Quote  Post ReplyReply Direct Link To This Post Posted: 19 June 2011 at 12:47pm
Thanks for your reply

I understand all of that,

My issue is that the speakers are used every weekend, they are reasonable quality. But I wasn't there so don't know what happened. Both drivers on two seperate speakers went at exactly he same time.

Which excldes 70% of the other reasons you state which leaves us with over excursion etc..

But never seen this without a burning smell??

But without a distinct burning smell it's hard to point out that someone has overdriven the driver?

Most likely caus
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The bass drivers could have a momentry over-excursion of the cone,causing the lead in wires to come adrift from the voice coil.

Or they cabinets could have been dropped down on the floor,shifting the magnet,and locking the voicecoils solid.

You wouldnt get any burning smell in either of the above senarios.

Remove the bass drivers and check them with a meter or small 1.5v battery.
Be seeing you.
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Points: 56 		Post Options Post Options   Thanks (0) Thanks(0)   Quote AC1 Quote  Post ReplyReply Direct Link To This Post Posted: 19 June 2011 at 1:10pm
Cheers for the reply, the second scenario would mean that the drivers would not have worked or would have distorted early on when the event was at a lower volume.

I have to assume the drivers were blown with your first scenario.

What would be the route cause of this? They just had an iPod and a small band mixer.

Could it be that the mp3 was distorted on the file? They had 3 hours of non stop use before they blew?

Cheers guys finding this very helpful
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Points: 3864 		Post Options Post Options   Thanks (0) Thanks(0)   Quote studio45 Quote  Post ReplyReply Direct Link To This Post Posted: 19 June 2011 at 1:57pm
This is certainly an unusual problem. However if the drivers are both open circuit without having burned, then the mode of failure is, as JBL and DJLeco have said, most probably, that the connection between the terminals and the voicecoil has broken. 
I have seen this several times and it was always down to the glue joint between the voice coil former and the cone becoming weak, meaning the wires themselves take a lot more force than they should , leading quickly to metal fatigue and breakage. This did not necessarily happen due to a single over excursion event but in one case was a problem that developed over time, causing the driver to go increasingly "intermittent" and make upsetting noises despite not having been burned out. 
This is a manufacturing fault, because that glue joint should never break in normal use or even under quite serious abuse (the VC should burn first). If they're from a reputable manufacturer, you may have recourse to them under warranty....if they are not, well, replacements will be cheap LOL
Studio45 - Repairs & Building Commotion Soundsystem -Mobile PA
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Quote But I wasn't there


Sounds par for the course. They caned the system till one speaker blew and then turned everything up to 11 to compensate till the other blew.

An oft-heard story that is very common.
Kevin

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I would say I would have to agree with you on the connection breaking, but I stock rotate the speakers so pairs are different every time

is it bad luck that both speakers developed the same fault at the same time?

I've reconed speakers that have been burnt ot and replaced speakers with half their magnet cracked in 2.

But I have never seen this, it's very strange, I'll see if they are loaded with the same driver model number

but most ppl on here seem to be pointing to the fact that it could be over exurtion. Strange I've never encountered this on a pair or a single speaker before?
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Also just to add, it's a decent brand here.

My mate just said it was all fine for 5 hours it distorted for 10 seconds, and the bass had gone!

Once again no burnt smell though?

Drivers are 3 years old possibly been reconed at some point in the last 12 months but I can't remember, got alot of em! ;)

sorry lads just a tad confused here! Just need to understand it all :)
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Points: 5897 		Post Options Post Options   Thanks (0) Thanks(0)   Quote burningbush Quote  Post ReplyReply Direct Link To This Post Posted: 20 June 2011 at 12:31pm
If there is a passive cross over, I would check this over, check continuity and check the cone moves freely.  This will at least point you in the right direction.
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once again thanks for the replies.

Just seems strange both blowing in exactly the same way :)

They are both different ages etc so can only put it down to user error.. But no burnt smell... 

Ill open them up this week
Horns or reflex?
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Why would there be a burnt smell (now) ?

They smell (usually - not always!) at the time they blow. After they have been sitting there for a few hours and have cooled down the smell usually disappears.

This is what happened:
I have £50 bet here. It's yours if I'm wrong.

Originally posted by kedwardsleisure kedwardsleisure wrote:

Quote But I wasn't there


Sounds par for the course. They caned the system till one speaker blew and then turned everything up to 11 to compensate till the other blew.

An oft-heard story that is very common.
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