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Author Topic: Burning Voice coils, what the heck is going wrong???  (Read 14014 times)

Tamas Tako

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Re: Burning Voice coils, what the heck is going wrong???
« Reply #10 on: August 25, 2004, 04:16:46 am »

Hi,

Just some toughts about the drivers.
After reconing 10 LAB drivers I found that
1. the surround glued to the cone can break (sealing and the top layer of the cone as seen here on some pictures)
2. (!!!) the voice coil is very rugged, but the bottom row can come away from the former sometimes, and couses some issues. this can then couse burnings and/or open circuit of the VC.
I fixed it when reconing with a very small amount of epoxy below and around the bottom row (wound)of the VC.
Thios helped out and I haven't noticed the same problem since that.
I would recommend this small threatment for everyone who uses the LABs for professional use and also this could be a modification idea for EMINENCE!!!!

I hope this will help.
Please remember, this is a DIY project where we are the Beta testers of the driver and we should give our opinions here on this forum, to be able to require some mods when it is needed.

cheers,

tamas

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Too Tall (Curtis H. List)

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Re: Burning Voice coils, what the heck is going wrong???
« Reply #11 on: August 25, 2004, 10:03:38 am »

Hi Jeremy,

Jeremy Bridge wrote on Tue, 24 August 2004 16:45

No sir, preach away Smile

I thought I was very dilligent in sealing the chambers, I used ample ammount of west system epoxy (with filler), and I also used silicone in all corners on both the inside and joints of the module.


I would stick with west system and filler anyplace you would use silicone. The exceptions being sealing an input plate, sealing wires that have to go through walls. IOW anywhere that needs to stay flexible to seal.


To check for air tight seal you need to check the impedance curve of every box. If you don't own Smaart you can download the free version of Praxis. In demo mode it has a script to measure impedance for T/S parameters (data to model what size box and port you should use). The measurement in demo is restricted to 2kHz and below, but that is more then you need.


You can measure the impedance curve of each box. At the minimum they should all look the same. In any case you can send them to me to look at.


You can take the drivers out of the box and measure impedance in free air and compare that to published specs so you know each driver not only works, but is in perfect electrical shape (i.e. no shorts in the VC, etc)


If you decide to use Praxis feel free to email me for help.

Praxis
www.libinst.com

Jeremy Bridge wrote on Tue, 24 August 2004 16:45


2 of the subs rattle horribly and scrape allong the gap, however the rest don't seem to rub at all.

I have also never actually heard the subs ever bottom out, but that doesn't mean they haven't of course.


First I really hate where you say it got louder when you lost some boxes. Could be interference patterns, but lets look how you determined all the drivers were wired correctly.
   Did you trace every wire back to the driver terminals?
   In your position, NOT ENOUGH!

The best way to be sure the drivers are wired correctly is put a 9-volt battery directly on the speaker wire where it plugs into the back of the amplifier, remove the access panels and watch which way each cone moves. It could be the guy who mounts the terminals is color blind (or drank too much Ever Clear that weekend). Anyway with something as serious and strange as you have going on you need to go to extremes.


If the signal is split to reach various amps you need to check all that wiring for correct and solid connections. I know you say it doesn't follow amplifiers, but you have to check everything. In troubleshooting you usually check the signal chain in a couple of places and easily narrow down where the problem is. This process goes to hell when you have TWO things wrong or something that is intermittent.

None of what I have suggested may have anything to do with your problem, but it is a good idea in any case.

Too Tall


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Too Tall
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Clive D Milne

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Re: Burning Voice coils, what the heck is going wrong???
« Reply #12 on: August 26, 2004, 09:11:14 am »

    I would assume that with having 11 labs in one row
you would get nulls by virtue of phase differences.  I would
also hazard a guess that this would have the unfortunate
consequence of dropping the effective impedance on the drivers.
The fact that the sound improved as cabinets dropped out seems
to lend credence to to this speculation.
  An interesting experiment you could try would be to place
four labs in a row with a defined amount of space between each
cabinet, and then feed them a pure tone.  For arguments sake,
lets say we use 60Hz, then space the cabinets (center to center)
2.87m apart.  Effectively, the cabinets will be 180 degrees out
of phase with their immediate neighbors, and in phase (but
lagging a full 360 degrees) with any cabinet 5.73m away from it.
ie) cabinet A <--2.87m--> B <--2.87m--> C <--2.87m--> D
Apply the tone to cabinets A & C only, and measure the current
flowing to the speaker coils.  Now switch on the power to B & D
and measure again.  I expect that there will be an obvious
difference to the sound as well as a change in the effective
impedance of the speakers.
 fwiw) I suggested 60Hz, so you can just use mains voltage
(120 Volts), and it goes without saying to wire them up
in series.  
   While this experiment may seem a little silly, it may
save you time chasing non-existant problems elsewhere.
   Hope this helps,
        Regards,
             Clive.
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Too Tall (Curtis H. List)

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Re: Burning Voice coils, what the heck is going wrong???
« Reply #13 on: August 26, 2004, 11:33:42 am »

Clive wrote on Thu, 26 August 2004 09:11

    I would assume that with having 11 labs in one row
you would get nulls by virtue of phase differences.



If you place the boxes in a continuous line (i.e. a "line array") other boxes in the array fill in these holes. The interference patterns that create nulls added to places where two or more sources combine to sum positive and averaged together is why a line array is as even as it is and why it drops off on the edges so drastically. (i.e. toward the center of a line array you have more summation and toward the ends more cancellation)


Clive wrote on Thu, 26 August 2004 09:11


I would
also hazard a guess that this would have the unfortunate
consequence of dropping the effective impedance on the drivers.




Hmm, I see your point, but I can't quite get my mind all the way around this. When you stack the boxes next to each other you get an impedance change. Just how far apart does this hold? Do you get further significant impedance change after the sources are more then1/3 wavelength apart?


Clive wrote on Thu, 26 August 2004 09:11


The fact that the sound improved as cabinets dropped out seems
to lend credence to to this speculation.




Well I figured one of two things. Either some drivers had their polarity flipped or it was an interference pattern. I wanted him to check polarity on everything because the root of the problem is not obvious. It may have nothing to do with his driver failures.


Clive wrote on Thu, 26 August 2004 09:11


  An interesting experiment you could try would be to place
four labs in a row with a defined amount of space between each
cabinet, and then feed them a pure tone.  For arguments sake,
lets say we use 60Hz, then space the cabinets (center to center)
2.87m apart.  Effectively, the cabinets will be 180 degrees out
of phase with their immediate neighbors, and in phase (but
lagging a full 360 degrees) with any cabinet 5.73m away from it.
ie) cabinet A <--2.87m--> B <--2.87m--> C <--2.87m--> D
Apply the tone to cabinets A & C only, and measure the current
flowing to the speaker coils.  Now switch on the power to B & D
and measure again.  I expect that there will be an obvious
difference to the sound as well as a change in the effective
impedance of the speakers.




This does look worth doing on its own, but considering he had a line array with no gaps I don't believe this will he help him find his problem.


Clive wrote on Thu, 26 August 2004 09:11


 fwiw) I suggested 60Hz, so you can just use mains voltage
(120 Volts), and it goes without saying to wire them up
in series.  
   While this experiment may seem a little silly, it may
save you time chasing non-existant problems elsewhere.
Hope this helps,
        Regards,
             Clive.



Your experiment is worthy, but not something I would try to find his problem.
Checking polarity on every line and driver is accepted trouble shooting tech, while your experiment is something you might look at after eliminating many more simple issues. Note I do not claim my guess that somewhere he may have something with the polarity flipped  is the cause of his driver failure. It's just one of the first obvious things to check. You can not assume anything is correct till you check it no matter how slim the chance when the cause is not obvious. An Eminence employee swapping the red and black terminal on some drivers is a real long shot, but after what happened I would not leave it to chance.



Here is one of my FAVORITES!
I have a large industrial tablesaw. Years ago I bought a Biesemeyer T-Square fence system for it. Cost about $550.00 or so more then twenty years ago. It has a measuring tape pasted to the square tubing the fence rides on. I would cut a test piece, adjust the gauge till it was correct and run some stock to recheck. Usually I would do it with a piece 3" to 6" wide. The trouble was that when I would cut longer pieces the cut would be a just a little longer then it should be. It wasn't much. Perhaps 1/32" to 1/16" or so. I figured the fence gave a little when I cut bigger pieces.


One day I happened to have my scale (markings down to 1/64") laying on the tube and I lined things up to see how well it agreed with the tape. The first 12" of the measuring tape has 1/32" markings and the rest of the tape (to 101") has 1/16" markings.


The first 12" of the tape was WRONG! It slowly changed from the beginning to by the time you were at 12" it was almost 1/16" long. The tape after 12" agreed exactly with the scale. Now that was something I had assumed must be correct for YEARS and it was literally the LAST place I would check for the problem, but there it was.


Too "You can assume all you want till something goes wrong!" Tall




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Too Tall
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Phil Pope

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Re: Burning Voice coils, what the heck is going wrong???
« Reply #14 on: August 30, 2004, 04:20:03 pm »

if you are stacking all these labs together you are leaving air gaps in between for the heatsinks to work?  this wouldn't matter so much if you covered the heatsink on one side of a lab or if you were running a cluster off the same amp as the power will be redistributed to the drivers that are losing heat effectively.  However if you are running a lab off its own dedicated amp and you have it in the middle of a stack with both sinks covered you are going to make them pretty hot.

BTW my calculations are that the thermal limit is about 1200W RMS

Also I have had reconed drivers returned with the polarity the wrong way round before and it took me ages before I thought I may as well test with a battery.

Phil
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Steve Shafer

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Given the range and frequency of problems
« Reply #15 on: September 01, 2004, 08:52:05 pm »

I have been contimplating building a pair of Lab Subs for quite some time now.  I am concerned about all the stories of driver failures.  

Granted the driver has to be in properly built and sealed box.  However, i think it is safe to say that while the eminence driver provides amazing bang for the buck, i think there are better options out there.

I realise that there are some real big league heavy hitters on this board, and that I am just a beginner.  However, I have approached the company that builds the NEOMAXX driver for bassmaxx.

http://www.tcsounds.com/TC9_12_2568.htm

Granted this driver is not exactly what Tom D spec'd, but i bet one of these base models could be modified to make one heck of a driver for the Lab Subs.

Steve S
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Al Limberg

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Re: Given the range and frequency of problems
« Reply #16 on: September 02, 2004, 12:14:00 am »

If TC is willing to produce a matching driver, I'm sure there is someone out there who would be happy to put it thru its paces and compare it to the LAB12. Simply putting another off the shelf driver with different T-S parameters in to a Lab cab is a recipe for disaster. regardless of how well built the driver is. I think thought you should realize that subwoofers often end up painted with the same brush that created the old 'No Peavey' clause in riders.  Its there not necessarily bacause the gear wasn't up to snuff, but because the limited skills of the typical operator gave it a reputation that has been an albatross for years.  Subwoofers are certainly the most abused component in any system and in most cases the abuse would (and does) destroy ANY sub, regardless of brand or model or manufacturer or cabinet design/style/construction.   With the inclusiuon of such marvelous features as 'subharmonic synthesizer', even units like the DriveRack PA should receive a royalty from every speaker reconing shop in America.  Of course you will see reports of failures and questions about the LAB12 here - that's why the forum exists.  I guarantee, I have saved enough in reconing costs by replacing my EV 18s with LabSubs 2 years ago to pay for my four Labs!!  That was one of those wonderful catch 22 situations where the reconing costs would have been much better spent on new subs - and the LabSub made that possible.    

Al
p.s.  I have had more failures of JBL2226H 15s in my monitors than Lab12s
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Too Tall (Curtis H. List)

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Re: Given the range and frequency of problems
« Reply #17 on: September 02, 2004, 09:41:17 am »

Stevesb65 wrote on Wed, 01 September 2004 20:52

 I have been contimplating building a pair of Lab Subs for quite some time now.  I am concerned about all the stories of driver failures.  

Granted the driver has to be in properly built and sealed box.  However, i think it is safe to say that while the eminence driver provides amazing bang for the buck, i think there are better options out there.



I disagree with your premise. First, the Eminence built LAB 12" driver is as tough as a tank. I marvel that it doesn't cost twice as much.


Is it "exotic"?

No.
And that is also a great strength for the people using it. There are a bunch of very high priced drivers you can use to build speakers. If you're in this to make money or at least break even finding value is the name of the game, not the most expensive components you can buy. Save the exotic drivers for your home stereo. The only exception to this is if you are in the industrial sound or high-end theater where you need to be able to point to a sticker that says "Meyer" or something equally expensive


Stevesb65 wrote on Wed, 01 September 2004 20:52


I realise that there are some real big league heavy hitters on this board, and that I am just a beginner.  However, I have approached the company that builds the NEOMAXX driver for bassmaxx.

http://www.tcsounds.com/TC9_12_2568.htm

Granted this driver is not exactly what Tom D spec'd, but i bet one of these base models could be modified to make one heck of a driver for the Lab Subs.
Steve S


If you want to make a sub similar to the LAB with an 18" driver you need to design from scratch. You can copy things like the "snail" spiral design in general, but otherwise you are looking at a new design.
Good luck.

Too Tall



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Mark Seaton

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Re: Given the range and frequency of problems
« Reply #18 on: September 02, 2004, 09:59:03 am »

Stevesb65 wrote on Wed, 01 September 2004 19:52

I have been contimplating building a pair of Lab Subs for quite some time now.  I am concerned about all the stories of driver failures.  

Granted the driver has to be in properly built and sealed box.  However, i think it is safe to say that while the eminence driver provides amazing bang for the buck, i think there are better options out there.



I get a chuckle every time I hear people question failures.  What most don't realize is that YOU, the board and users are the beta testers for this design.  The driver built by Eminence was a derivation of drivers already being built for other applications.  As such, it was somewhat inevitable that a few failures would be seen.  From what I understand, tolerances in critical areas are now more controlled.  From what I have heard, Eminence has been very good about warrantying failures which bear any resemblance to manufacturing issues.

Now for the real matter at hand.  I offer that if you have a product you can't break, you also have a product with compromised performance, and excess cost.  It wouldn't be all that hard to make a driver with 1/2 the Xmax which had almost zero chance of overdriving.  I look back and figure that we should have just been guarded and said the power rating of the LAB sub was 800W (400x2), which is the alleged rating of the drivers.  The fact is that power ratings are really only one snapshot of some specific condition under which the driver survived.  We have yet for any forum member to step up and conduct power testing on their boxes in a given configuration (4 together would be preferred).  Even if that happened, that rating would be thrown out the window if you filter your subs differently.

I know the guys at TC Sounds, and they indeed build some great drivers.  I also know of at least 2 other companies who could likely build a suitable driver with potential for some refinement.  It's tough to say what the subjective differences would be relative to the increased costs.  I would pose that another driver would likely have to jump past 18-24mm in excursion to really offer some benefit.  One major problem though...  It has to still fit in the box.  I question if the driver linked would even fit in the box with the access hatch on.  I know a manufacturer who could deliver a 12" with 28-34mm of excursion each way, but I'm almost certain we would have to alter the design, and the cost would be more than 2x the cost of the LAB12.  At best, TC Sounds may indeed be able to build a driver which might fit which would be a little more linear, a little higher thermal capacity.  In the end you may be able to clack it against the back plate a few more times than the current LAB12 before you kill it, but kill it you will.

So the other question to ask is, if the drivers cost 2x as much, would as many people be building these?

Regards,
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Mark Seaton
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Re: Given the range and frequency of problems
« Reply #19 on: September 02, 2004, 01:00:10 pm »

I re-read my post, and want to clarify that I hope that some others do produce a driver for the LAB sub, and I think TC Sounds could make a very nice driver for this.  I still have a few 15", rediculously high excursion drivers they made for a DIY company, and they are pretty impressive drivers although not inexpensive.  The design guidelines are back in the archived forum and of course some modeling with something like hornres should give a general indication if the driver would be suitable.

Remember that of course I am biased and would tell most to build up some LABs and save the rest of their pennies for our SPL-td2 rather than new drivers.  Rolling Eyes

Cheers,
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Mark Seaton
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