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Sound Reinforcement - Forums for Live Sound Professionals - Your Displayed Name Must Be Your Real Full Name To Post In The Live Sound Forums => SR Forum Archives => LAB Subwoofer FUD Forum Archive => Topic started by: Raj Sookraj on June 27, 2006, 01:05:19 am

Title: Labhorn access panels removed
Post by: Raj Sookraj on June 27, 2006, 01:05:19 am
What would happen if the speaker access panels were to be removed?  It would allow more cooling for the Lab12's but how would it affect the response?  Has anyone tried doing this?
Title: Thermal performance
Post by: Wayne Parham on June 27, 2006, 06:48:27 pm

A driver will overheat when driven continuously at full power, whether open to free air or installed in a sealed chamber.  This is true of any driver.  The overheating condition isn't so much because the rear chamber is sealed in a particular basshorn, although trapping hot air in a small sealed chamber slightly increases the problem.  The main thing is the heat from the voice coil radiates into the pole piece and is trapped by the ceramic magnet.  This heat then re-radiates back into the voice coil, causing the glue to melt and the voice coil to separate from the former.

This is probably the most common failure mode for any loudspeaker, causing the voice coil to rub.  Over-excursion is another failure mode, and cone tearing is yet another.  But most failures occur because the voice coil becomes unglued and begins to rub, making the speaker buzz and vibrate, and eventually as the coil wears through, it will open and fail completely.

I think there has been some confusion, perhaps misinterpretation of the fact that cooling devices added to high-performance basshorns improve their thermal performance.  This isn't because the sealed chamber traps heat.  It does, but that's not the killer.  The killer is the magnet structure trapping the heat.  Even with air cooling, and with the driver fully exposed to refrigerated air, the pole piece surrounding the voice coil will get hot enough to cook on when driven to just a few hundred watts.

If you think about it, a speaker voice coil is applied several hundred watts, so it gets hot like a large soldering iron. Even if the speaker system is very efficient, you still have hundreds of watts dissipated as heat. Take a theoretical 400 watt speaker at a very optimistic 50% efficiency level - You still have 200 watts of heat. This heat source is surrounded by steel and then covered by a large chunk of ceramic. This is a pretty good heat container, one that is almost made to hold heat. So one of the best things you can do is to get a good conductor of heat down inside the motor, in contact with the pole piece. Wick the heat out of the core and radiate it away.

The best thing you can do to improve thermal performance on a LABhorn is to mount a cooling plug on its access panels and insert them into the drivers.  That's much better than leaving them open and exposed to free air, because the plug is better at removing heat than air cooling alone.  This also allows the horn to operate as it should, with its rear chambers intact.


Title: Re: Thermal performance
Post by: David L Corns on June 27, 2006, 07:20:42 pm
Here's what Eminence has on their web site about the LAB Sub:


The LABHorn design has five points that you must consider when using them:
1. You can't hear the driver distort when you push them too hard. Therefore, most people don't know when to turn them down. They
push them until they break. It takes a while to get used to the extra clean sound of this cabinet and learn how hard you can push it.
2. They were designed to be used in groups of 4 to 6 cabinets to get the desired SPL at very low frequencies (below 45Hz). Many people
are running them as singles and trying to EQ the bottom end to get more low bass output. This pushes the drivers past their safe
operating range very quickly. If you need a lot of very low bass, use more cabinets.
3. When one driver quits working, the other driver will fail too because they both fire into a common high pressure cavity. The user needs
look upon the drivers as a single (more expensive) driver. You always need to use two, so buy two.
4. Air leaks will kill the driver. The driver has a VERY loose suspension and reqires that the small chamber behind it be absolutely air tight.
5. You must use a high pass filter set to 35 Hz and that has a slope of at least 24dB per octave to realize the real potential of the design.
Many people are using huge power on these cabinets everyday, but they are the ones who run steep high pass filters on them.
   

This is found on the last page of the Cab Design PDF File.
Dave C.

Title: Re: Labhorn access panels removed
Post by: Raj Sookraj on July 24, 2006, 06:41:20 pm
Has anyone noticed that the labs sound better without the access panels 40hz and up?  I did an A-B test, two cabs about a foot apart, one labhorn with the access panels on and one labhorn with the access panels off.
Title: Re: Labhorn access panels removed
Post by: The Guy on July 24, 2006, 06:54:31 pm
With all due respect, this is just flat out wrong.  The rear chamber acts as the suspension for the driver, and is required in order to control excursion.  Maybe in your application, you perceive that they sound better without the access covers, but hell, even a small leak in the chamber will result in driver failure.  

Try your labs at a gig with the covers off, and I guarantee you'll be boxing them up to send to the reconer before the first song is over.

-JB
Title: Re: Labhorn access panels removed
Post by: Raj Sookraj on July 24, 2006, 07:43:19 pm
I have been running them without the access panels because I never made any for my labs.  I run about 1200-1500w into each labhorn with just the 30hz filter on the qsc amp active, with no compressor/limiter for about 4+ hours of recorded music with no failures.  I can see why it would fail with more than 1600w per cab for an extended period.  I'm not by any means trying to change the design, it just an idea.  I will add more processing to the setup when i'm able to do so.
Title: Re: Labhorn access panels removed
Post by: Elliot Thompson on July 24, 2006, 09:11:32 pm
Jim Bowersox wrote on Mon, 24 July 2006 23:54

With all due respect, this is just flat out wrong.  The rear chamber acts as the suspension for the driver, and is required in order to control excursion.  Maybe in your application, you perceive that they sound better without the access covers, but hell, even a small leak in the chamber will result in driver failure.  

Try your labs at a gig with the covers off, and I guarantee you'll be boxing them up to send to the reconer before the first song is over.

-JB



I agree.

Dude, you are really doing all the wrong things to these woofers.

First, you feed the woofers a beat loop, from your QSC 4050,
at full power, in "Free Air", now this.

Why are you on a quest to destroy your woofers?

Best Regards,
Title: Re: Labhorn access panels removed
Post by: Peter Morris on July 24, 2006, 09:33:02 pm
Hi Raj

You can make a model in Hornresp and compare the two, with and without a rear chamber.

From memory what happens is you loose output below 40 hz, but get a bit more above it when you remove the cover.

Effectively you have made the LAB into a scoop.  The extra efficiency is probably due to some additional resonance, which may sound quite nice (but not accurate) around 40hz where it will occur.

In respect to the cone displacement, it more or less remains the same down to about 30 - 35 hz, at which point the sealed chamber limits the cone displacement.


Peter
Title: Re: Labhorn access panels removed
Post by: Elliot Thompson on July 24, 2006, 09:48:04 pm
Peter James wrote on Tue, 25 July 2006 02:33



Effectively you have made the LAB into a scoop.




Those two words should never be used in the same context.  Rolling Eyes


Best Regards,
Title: Re: Thermal performance
Post by: Wayne Parham on July 25, 2006, 05:39:34 pm

Looks like there was a server blip or something this weekend, because two whole threads about the LAB12 driver are missing.  So I'll re-link a previous thread here that I think may be of interest to some.  It has excursion and thermal measurement data of the LAB12, showing its most common failure mode.  Thankfully, this thread wasn't lost.

Title: Re: Thermal performance
Post by: John Roberts {JR} on July 25, 2006, 06:26:15 pm
Wayne Parham wrote on Tue, 25 July 2006 16:39


Looks like there was a server blip or something this weekend, because two whole threads about the LAB12 driver are missing.  So I'll re-link a previous thread here that I think may be of interest to some.  It has excursion and thermal measurement data of the LAB12, showing its most common failure mode.  Thankfully, this thread wasn't lost.



Maybe the server overheated....

JR
Title: Re: Labhorn access panels removed
Post by: Duane Massey on July 25, 2006, 07:08:15 pm
I've got a design for a server cooler....oh, wait, that was a water cooler...
Title: Re: Thermal performance
Post by: Evan Kirkendall on July 26, 2006, 12:20:21 am
John Roberts  {JR} wrote on Tue, 25 July 2006 18:26

Wayne Parham wrote on Tue, 25 July 2006 16:39


Looks like there was a server blip or something this weekend, because two whole threads about the LAB12 driver are missing.  So I'll re-link a previous thread here that I think may be of interest to some.  It has excursion and thermal measurement data of the LAB12, showing its most common failure mode.  Thankfully, this thread wasn't lost.



Maybe the server overheated....

JR



Looks like it could benefit from my ultra cool 8000xl pro2. It's designed to chill air to absolute zero and throw it onto the server to keep it from overheating. The design is proved to increase server speed and add extra oomph to it.

http://www.aoc.gov/cvc/photos/images/10-17-05BigFan_lg.jpg




Very Happy
Evan
Title: Re: Thermal performance
Post by: Wayne Parham on July 26, 2006, 11:42:27 am

Cool   How 'bout this one:

http://irsa.ipac.caltech.edu/IRASdocs/exp.sup/ch2/figs/figC2-1.gif
Title: Re: Thermal performance
Post by: Tom Danley on July 26, 2006, 03:15:54 pm
Hi Evan

Now that fan is cool, is that you in the photo?
I have casually been looking for a large fan like that to attach to a big old engine I have.
Have any idea where an old one could be found?
Having a big fan off in the distance during a  summer BBQ is nice both for the breeze and mosquitoes don’t like it.
The engine is a 1915 Fairbanks Morse “Y” 15hp oil engine. It has an 8 by 12 inch bore and stroke, has 4 foot diameter flywheels with a 7 inch wide rim, it weighs 6600 lb without the trailer and on a good day, takes 45 min to start by hand.  This engine runs at Full speed, slower than most car engines idle (@350RPM) and can be set down to idle at about 70 RPM where it makes a very nice Thump…. Thump…. sound from the 5 inch exhaust pipe.
Best,

Tom

Raj

The system will not have its proper response, proper excursion control or ultimate efficiency with the covers removed.  Make the covers.
Best,

Tom
Title: Re: Thermal performance
Post by: Wayne Parham on July 26, 2006, 03:56:11 pm

Arrow Engines is in Tulsa, and the mechanical engineer I consult with most often works for them.  You would probably love their engines;  Check them out.

Title: Re: Thermal performance
Post by: Evan Kirkendall on July 27, 2006, 09:28:27 pm
Hi Tom,
No, thats not me. I just pulled the pic off some random site thanks to google. Im sure if you want, you could do a search and find more about it.



Evan
Title: Re: Thermal performance
Post by: Tom Danley on July 28, 2006, 02:42:21 pm
Hi Wayne

Hey, thanks for the link, they say they carry parts for Fairbanks engines.
The narrower flywheel brothers of the one I posted were also used in oil well service.
If they had enough of a load (to make them hot enough), they could run on raw crude although I would imagine you would need to start it on kero or diesel.
Mine starts easiest by hand (if a typical 45 min is easy) on Kero and runs on diesel once warm (it has no load, my interest in a fan as a load).
So far, I have been able to make the minor parts it took to get it going although a place to get a real head gasket next time would be cool.
Thanks.

Tom Danley
Title: Re: Thermal performance
Post by: Wayne Parham on July 31, 2006, 11:14:50 am

If you ever need anything from Arrow, call Monte Vogt.  He's a mechanical engineer there, tell him I sent you.  He and I have been friends for years, one of the best motor heads I know.