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Author Topic: Labhorn access panels removed  (Read 12620 times)

Raj Sookraj

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Labhorn access panels removed
« 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?
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Wayne Parham

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Thermal performance
« Reply #1 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.


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Wayne Parham
π Speakers
PiSpeakers.com

David L Corns

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Re: Thermal performance
« Reply #2 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.

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Raj Sookraj

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Re: Labhorn access panels removed
« Reply #3 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.
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The Guy

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Re: Labhorn access panels removed
« Reply #4 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
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Raj Sookraj

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Re: Labhorn access panels removed
« Reply #5 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.
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Elliot Thompson

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Re: Labhorn access panels removed
« Reply #6 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,
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Elliot

Peter Morris

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Re: Labhorn access panels removed
« Reply #7 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
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Elliot Thompson

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Re: Labhorn access panels removed
« Reply #8 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,
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Elliot

Wayne Parham

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Re: Thermal performance
« Reply #9 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.

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Wayne Parham
π Speakers
PiSpeakers.com

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