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Author Topic: Am I giving my LABs too much Juice???  (Read 5274 times)

Josh Billings

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Am I giving my LABs too much Juice???
« on: August 19, 2004, 05:40:30 am »

I have a QSC RMX 2450 running bridged mono to EACH cabinet (Basically 3 ohms each). They should run about 2400 @ 4 ohms, but i emailed the guys @ qsc and they said they would push out about 2,000 before clipping @ 3 ohms and it should be FAIRLY safe.

I push em borderline into clip like ALL the time ( i run a deep house club and they LOVE their bass). I do have the clip limiter on though so it never is really sending a CLIPPED signal to the speakers.

Anybody blown LABs yet? if so how much power were you pushing them.

-Josh
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Too Tall (Curtis H. List)

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Re: Am I giving my LABs too much Juice???
« Reply #1 on: August 19, 2004, 10:00:50 am »

Josh wrote on Thu, 19 August 2004 05:40

I have a QSC RMX 2450 running bridged mono to EACH cabinet (Basically 3 ohms each). They should run about 2400 @ 4 ohms, but i emailed the guys @ qsc and they said they would push out about 2,000 before clipping @ 3 ohms and it should be FAIRLY safe.

I push em borderline into clip like ALL the time ( i run a deep house club and they LOVE their bass). I do have the clip limiter on though so it never is really sending a CLIPPED signal to the speakers.

Anybody blown LABs yet? if so how much power were you pushing them.

-Josh




Hi Josh,


Go back through the posts on this forum. We have gone through this a few times.

There have been some failures, but I believe not one has been from thermal overload where someone melted the voice coil. The surround / cone has failed. Eminence has made a change (where it puts glue I believe or something like that). Drivers made during a certain period of time that fail from this are being re-coned gratis by Eminence even thought it is not clear that it was a factory defect. You might call it an "upgrade".


   So what you need to worry about is exceeding Xmax or excess cone movement below where the horn is working. Are you using a high pass filter on the sub, at what frequency on what slope? The number of LAB subs you stack together and if they are on a wall or in a corner are all variables here. For instance if you are using a single sub by itself away from a wall or corner you need to set the high pass filter at a higher frequency then if you have four together or place it in a corner.

Too Tall

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Too Tall
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Josh Billings

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Re: Am I giving my LABs too much Juice???
« Reply #2 on: August 24, 2004, 05:38:05 am »

I think i have my HPF @ like 30-32 or something. Maybe i should go to 35?? or higher.

I have em crossed over @ 90 right now.

And i have them over easy limited @ like the 4 setting. I have it on a DJ setup and i need to prevent the DJs from blowing my drivers when i'm not arround.

I have 2 side by side.

RMX 2450 brided pushing each one.

I really want to try out a 5,000 in stereo and see if i hear a big difference in sound quality.

-Josh
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David Trotter

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Re: Am I giving my LABs too much Juice???
« Reply #3 on: September 10, 2004, 03:58:16 am »

Are you sure the QSC isn't thermal cutting? I've used them at 2ohm a side in stereo and they have often overheated.

got the wood finally for our 4,  
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Jeff Woodford

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Re: Am I giving my LABs too much Juice???
« Reply #4 on: September 10, 2004, 06:35:39 am »

with the crown, you would be loading the amp at 1.5ohm per side stereo and the bins would get about 1k a box which aint really enough to run em to full potential.

i've got mine set at 30 to 85 hz with a 24LW high and low pass filter. running them stereo on a crown 5k, have cranked the amp to the max on my mixer and still not clipped the amp
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Jeff Woodford
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Too Tall (Curtis H. List)

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Re: Am I giving my LABs too much Juice???
« Reply #5 on: September 10, 2004, 10:36:22 am »

Jeff NB wrote on Fri, 10 September 2004 06:35

with the crown, you would be loading the amp at 1.5ohm per side stereo and the bins would get about 1k a box which aint really enough to run em to full potential.


i've got mine set at 30 to 85 hz with a 24LW high and low pass filter.




A point of interest here regarding the high pass of 30Hz would be how many stacked together, are they on the ground and up against the wall, etc. IOW how big is the horn mouth?

Jeff NB wrote on Fri, 10 September 2004 06:35


running them stereo on a crown 5k, have cranked the amp to the max on my mixer and still not clipped the amp



What are you trying to say here?
The reason I ask is the above doesn
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Too Tall
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Jeff Woodford

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Re: Am I giving my LABs too much Juice???
« Reply #6 on: September 15, 2004, 05:30:17 am »

this is a pick of the rig, 2 labs of the bottom, with 4 single 18" folded horns doing the same frequencies 30 to 85. the 18's work realy well with the labs giving a bigger horn mouth
http://gallery.squatjuice.com/albums/Laughing-Fish-Pics-of-Sand-Quarry-Technival-28-8-04/Unsorted_kodak_pics_0687.thumb.jpg

i have the gains set so the dj mixer is pushing the yellow into the x over and running the bass with no + db and the amp up full the crown has never clipped, and i still have trouble standing infront of the stack for very long without felling sick.
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Jeff Woodford
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LMC Audio Systems.
London, UK.

David Trotter

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Re: Am I giving my LABs too much Juice???
« Reply #7 on: September 15, 2004, 07:36:25 am »

Have you checked the input sensitivity on the back of the crown?
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Graeme Goodacre [Centauri

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Re: Am I giving my LABs too much Juice???
« Reply #8 on: September 15, 2004, 09:39:15 am »

Jeff NB wrote on Wed, 15 September 2004 19:30

this is a pick of the rig, 2 labs of the bottom, with 4 single 18" folded horns doing the same frequencies 30 to 85. the 18's work realy well with the labs giving a bigger horn mouth


This is not good at all!!  The labs have a much longer path length than the 18s, resulting in all sorts of cancellations at different frequencies.  If you had two stacks, you could run the labs in one stack and the 18s in the other, but not together like this, unless you run the labs to say 80Hz and the 18s above that (where they would work better anyway with the short horn path).

Recommend ditch the 18s, add more Labs....
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Elliot Thompson

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Re: Am I giving my LABs too much Juice???
« Reply #9 on: September 15, 2004, 09:48:30 am »

Some Clarification With The Crown 5000

On the back of the amp, it will have a Loudspeaker
Offset Intergration Switch (One on each channel)
This is basically a cutoff filter that starts rolling
off the sub frequencies at 35Hz.

It comes factory default in the "on" position.
Are using this filter in conjunction to rolling
off your subs at 30hz?


Also, Crown Macrotechs offer no clip lights.
The 5000, offers a Load/Limit in which will
tell you when you've reached the maximium current
by turning red. You could consider this as a clip
light.

However, it won't tell you if the amp is clipping,
say, you are driving two 8 ohms cabinets. This is
due to, two 8 ohm cabinets can't meet the amplifiers
maximum current capacity. Furthermore, you might not
even see the Load/Limit lights flicker green, because
the load is too small. Are the Load/Limit lights blinking
in proportion to the IOC lights when you are using those
labs?

Are they blinking red, or are they blinking green?

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Elliot

Jeff Woodford

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Re: Am I giving my LABs too much Juice???
« Reply #10 on: September 17, 2004, 09:29:47 am »

Centauri wrote on Wed, 15 September 2004 14:39

Jeff NB wrote on Wed, 15 September 2004 19:30

this is a pick of the rig, 2 labs of the bottom, with 4 single 18" folded horns doing the same frequencies 30 to 85. the 18's work realy well with the labs giving a bigger horn mouth


This is not good at all!!  The labs have a much longer path length than the 18s, resulting in all sorts of cancellations at different frequencies.  If you had two stacks, you could run the labs in one stack and the 18s in the other, but not together like this, unless you run the labs to say 80Hz and the 18s above that (where they would work better anyway with the short horn path).

Recommend ditch the 18s, add more Labs....


in an idea world i would have 24LABs per side, but as i havwn't built them yet, well thats another story....

the 18's work really well with the labs, the horn length on the 18s is quite long and the way i have the system set up it all works well. there are nodoubt a few frequency problems but i asure you there is plenty of bass.
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Jeff Woodford
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LMC Audio Systems.
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Mark Seaton

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Re: Am I giving my LABs too much Juice???
« Reply #11 on: September 17, 2004, 11:41:15 am »

Jeff NB wrote on Fri, 17 September 2004 08:29

Centauri wrote on Wed, 15 September 2004 14:39

Jeff NB wrote on Wed, 15 September 2004 19:30

this is a pick of the rig, 2 labs of the bottom, with 4 single 18" folded horns doing the same frequencies 30 to 85. the 18's work realy well with the labs giving a bigger horn mouth


This is not good at all!!  The labs have a much longer path length than the 18s, resulting in all sorts of cancellations at different frequencies.  If you had two stacks, you could run the labs in one stack and the 18s in the other, but not together like this, unless you run the labs to say 80Hz and the 18s above that (where they would work better anyway with the short horn path).

Recommend ditch the 18s, add more Labs....


in an idea world i would have 24LABs per side, but as i havwn't built them yet, well thats another story....

the 18's work really well with the labs, the horn length on the 18s is quite long and the way i have the system set up it all works well. there are nodoubt a few frequency problems but i asure you there is plenty of bass.


Those few frequency problems could be what is killing your drivers.  Imagine this...  If you had a pair of LABs together and somehow observed the excursion of the driver when driven as a single unit, vs. a pair together, you would see decreased excursion for more output with a pair vs. the single.  This comes from changing the exit condition of the horn, where adding more, identical boxes effectively devide up the fee space load seen by each.  Now if you were to place the two LABs together, and flip the polarity of one, with the same drive level as before you would see much less output (obvious), but you would also see much greater excursion (possibly not so obvious).  

Unlike in a front loaded box where the box provides the largely dominant air spring and loading on the driver, the horn and its environment are the dominant factors in the LAB.  If you cancel out the front acoustic load, you are reduced to the sealed box loading of the rear chamber (worst/ideal case).  This is almost akin to taking a sealed driver and making a big hole in the box and still driving it with the same signal.  In short, you are killing the designed in excursion limiting.

As others have said, if anything, try running your pictured system as a two way sub section, with a very steep crossover.  If you can measure the response, you want to measure each separately, and see if there are any dips in the response when you add the others.  If there are, do whatever you have to in order to keep them from fighting.
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Mark Seaton
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