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Author Topic: Lab12’s Autopsy?  (Read 9558 times)

Silas Pradetto

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Re: Lab12’s Autopsy?
« Reply #10 on: October 19, 2009, 10:37:15 am »

John Halliburton wrote on Mon, 19 October 2009 09:43

Matt F Castle wrote on Mon, 19 October 2009 06:25

Hi Silas,

Amps are QSC PL4.0’s, clip limiters turned on, with the LMS limiters set so they can just briefly light the clip lights on peeks.   Processor is a BSS Omnidrive (sub out mono summed, L-R 24dB high pass @ 38hz), one box per channel and were being used with 2 boxes per side when they failed.  

If it was purely a bad signal or clipping issue I would have expected to see similar damage in all the cab’s (identical drive signal to all channels & amp configuration).

I’m also still miffed by the driver that has failed open circuit with no other visible damage, that still suggests to me that it failed first (while operating within it’s spec’s) and thus causing its partner to over exert it’s self with the increased power (becoming a 6ohm/8ohm load) and reduced front loading.  Which to me would make sense that it’s then moved so far as to rip the voice coil from the cone, without any visible over heating effects on the voicecoil.  I also find it hard to believe that that sort of failure would be caused by an air leak as I would have thought there would be physical damage due to over excursion.

And my thinking would also be that if it was the 2nd to fail it would have ripped it’s self to bits or at least had visible over excursion damage.  

Can anyone suggest if that is a likely failure scenario or shoot down my thinking?


They do get used in singles quite often and this is the first failure I’ve had in about 18 months of use.

Will certainly be double checking all the joins and running some silicon sealer around everywhere inside before replacing the drivers in them.  Certainly don’t want to suffer any more issues with them for a long while……

M



The joy of electronics failures-sometimes you get to see the "magic smoke" escape, many times the death is the invisible hand of physics.

If you're working the LABs out regularly, 18 months is not a bad track record.  What type of gigs are you doing with them?

And yes, I tend to agree that the first one went open, then caused a boatload of extra power to feed into driver #2, and hastened it's demise.

No burnt voice coils would tell me to look for separation in the voice windings or some other break.  The failure may not present itself even after surgery.

Best regards,

John


I don't personally think that losing one driver would cause a boatload of extra power to hit the other driver. Remember, an amplifier is a voltage amplifier, and the power per driver is constant unless the amplifier is current limiting. I find it highly unlikely that there was any extra power applied to the second driver after the first went.

Eminence has had a few defects with the LAB12s that work themselves out after time. Check with them they might send you new ones under warranty.

And remember, the remaining woofer in my blown LAB survived fine, after it ran an entire gig with it's partner blown.
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Marjan Milosevic

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Re: Lab12’s Autopsy?
« Reply #11 on: October 19, 2009, 10:48:08 am »

Hello, i had a failure that can be just as yours at 4 drivers. Problem is that the wire has burned out at the place you can not see. You will have to remove the dust cap and scrub the place where the lead from the connectors enters in the voice coil former. There is the place to look at for burns. I have just re-solder the wires and drivers works. You case is a classical Lab failure scenario. You have noticed that LAB12 has a very loose suspension. The chamber infront of the drivers acts as a compression chamber, so when one driver stops working, the other commits suicide. It looses the compression that is stoping it from over excursion. That explains the physical damage on the other driver.

Art Welter

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Re: Lab12’s Autopsy?
« Reply #12 on: October 19, 2009, 04:25:15 pm »

Marjan Milosevic(MarjanM) wrote on Mon, 19 October 2009 08:48

Hello, i had a failure that can be just as yours at 4 drivers. Problem is that the wire has burned out at the place you can not see. You will have to remove the dust cap and scrub the place where the lead from the connectors enters in the voice coil former. There is the place to look at for burns. I have just re-solder the wires and drivers works. You case is a classical Lab failure scenario. You have noticed that LAB12 has a very loose suspension. The chamber infront of the drivers acts as a compression chamber, so when one driver stops working, the other commits suicide. It looses the compression that is stoping it from over excursion. That explains the physical damage on the other driver.


I agree with you, Marjan.

I had a problem with several drivers similar to what you describe, Eminence said "problem with the crimp" and repaired them under warranty.

They all failed at different gigs, over a fairly extended time period.

I think the last of that batch of four finally failed also.
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Matt F Castle

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Re: Lab12’s Autopsy?
« Reply #13 on: October 19, 2009, 08:13:04 pm »

Hi Silas,

With the PL4’s I’m using there is a difference of ~200w between 4ohm and 8ohm power spec’s. So I would assume there is a fair (at least around 20% increase) in delivered power (regardless of actual impedance), which I would expect would only exacerbate the situation with a failed driver as the impedance rises.  I would expect most other amps have similar variations between 4 & 8 ohms power?

M
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Silas Pradetto

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Re: Lab12’s Autopsy?
« Reply #14 on: October 19, 2009, 11:03:27 pm »

Matt F Castle wrote on Mon, 19 October 2009 20:13

Hi Silas,

With the PL4’s I’m using there is a difference of ~200w between 4ohm and 8ohm power spec’s. So I would assume there is a fair (at least around 20% increase) in delivered power (regardless of actual impedance), which I would expect would only exacerbate the situation with a failed driver as the impedance rises.  I would expect most other amps have similar variations between 4 & 8 ohms power?

M



Remember that power increase is only apparent if you are running at current limit. The voltage is the same otherwise.
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Matt F Castle

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Re: Lab12’s Autopsy?
« Reply #15 on: November 15, 2009, 07:42:55 am »

Hi,

Thanks to everyone who’s posted info in this tread.  My first Lab12 failures so interesting to find out how and why they fail (with the dual driver compression chamber loading etc..).

After talking to Eminence USA, they have been really good helping with the issue I’ve had and have had the UK distributor ship out a new pair of drivers.  I think the consensus been that it’s likely a lead in wire failure and then the 2nd driver in the cab then failing from not having the correct front loading.  Thumbs up and top marks for Eminence USA’s customer support and speed with!
And especially with the Lab12 been somewhat of a special case with it’s critical loading etc.. in the Labhorn.

Also I’ve not had a chance to open the failed driver up yet (thankfully works picking up running up to Christmas and I’ve not had a chance to examine them properly, since speaking to Eminence).

Cheers

Matt
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Matt F Castle

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Re: Lab12’s Autopsy?
« Reply #16 on: February 07, 2010, 07:56:20 pm »

Just to quickly follow up on my original post now I've found 10 minutes to rip one of my dead Lab12's apart.

Having removed the cone, the voice coil looks immaculate! No blackening anywhere and no over excursion damage at the bottom (end of the former slightly protruding shows no impact damage).

Removing the blobs of glue holding the lead in wires and crimps to the cone the top of the voice coils meters with continuity and @ 4.6 ohm (from memory that is consistent with a new driver).

The removed tinsel wires meter ok from terminal to the end.

So my conclusion is the failure has happened in the area of the crimp/lead in wires where they are joined and held in place with glue.


So further questions:  

- Is this a normal point of failure for a speaker?
(I am assuming the glue and double dust cap is providing some heat retention, where as the rest of the voice coil is moving and open to the air).
- Have Eminence done anything to improve this area of the LAB12?


Cheers

Matt


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Marjan Milosevic

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Re: Lab12’s Autopsy?
« Reply #17 on: February 08, 2010, 06:47:21 am »

Marjan Milosevic wrote on Mon, 19 October 2009 16:48

Hello, i had a failure that can be just as yours at 4 drivers. Problem is that the wire has burned out at the place you can not see. You will have to remove the dust cap and scrub the place where the lead from the connectors enters in the voice coil former. There is the place to look at for burns. I have just re-solder the wires and drivers works. You case is a classical Lab failure scenario. You have noticed that LAB12 has a very loose suspension. The chamber infront of the drivers acts as a compression chamber, so when one driver stops working, the other commits suicide. It looses the compression that is stoping it from over excursion. That explains the physical damage on the other driver.


Smile

Didn't i told you that already?

Smile

Art Welter

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Re: Lab12’s Autopsy?
« Reply #18 on: February 08, 2010, 01:31:55 pm »

Matt F Castle wrote on Sun, 07 February 2010 17:56


So my conclusion is the failure has happened in the area of the crimp/lead in wires where they are joined and held in place with glue.
So further questions:  
- Is this a normal point of failure for a speaker?
(I am assuming the glue and double dust cap is providing some heat retention, where as the rest of the voice coil is moving and open to the air).
- Have Eminence done anything to improve this area of the LAB12?

Cheers

Matt



That point should not normally be a point of failure.
Eminence has identified the problem and corrected it after the failures occurred.
Looks like you, me and Marjan all had the same problem.
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Matt F Castle

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Re: Lab12’s Autopsy?
« Reply #19 on: February 10, 2010, 01:55:43 pm »

Hi Art,

Any idea as to why they are failing at this point, is it a thermal problem or a mechanical one?  

I've also has another one that has done what I think is exactly the same things (I've not opened that driver up to investigate but exactly the same failure symptoms on the surface).

This is just leaving me wondering if the other pair of cab's (drivers were all received at the same time) are going to suffer this failure at some point in there life or if there likely going to carry going and going?

btw Marjan, yes you did, I'm just repeating you and typing my train of though...  (not to mention was typing under the influence of too much coffee!) and hoping the people from Eminence would post a reply on the subject with a more definitive answer.

Cheers

Matt
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