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Author Topic: Is the 12pi Subwoofer an upgrade to the LAB?  (Read 24606 times)

Josh Billings

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Is the 12pi Subwoofer an upgrade to the LAB?
« on: July 06, 2006, 10:06:37 pm »

I'm thinking about building 4 matching subs and i'm curious if this heat exchanger really help that much and if the push pull design is a better idea? Anybody A/B these speakers?

I've heard great things about the 12pi and it had AMAZING results at the shootout

Let me know your thoughts

http://www.prosoundshootout.com/

http://www.pispeakers.com/catalog/product_info.php/products_ id/262

-Josh Billings
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Josh Billings

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #1 on: July 11, 2006, 08:29:14 am »

200 Views and no responses?
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Gareth James

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #2 on: July 11, 2006, 08:55:03 am »

Hi Josh,

I think the key thing here is to realise what the 12pi sub is. It is basically a scaled up Labsub with slightly longer path length and greater mouth area to allow it to reach slightly lower frequencies. IMO the size difference (labsub being around 2/3 the size) doesn't warrant the extra few hz (but as said thats just my opinion).

The design is also "different" in that it incorporates the heat exchanger basically linking the rear of each driver to the aluminium plate for greater heat sink action. One of the drivers has been reversed as well to create a push-pull system to help cancel even harmonic distortion.

Seeing as the original Labsub was measured (correct me if im wrong) less than a few % throughout its useable range, i doubt you'd hear any kind of dramatic sound quality improvement.

As to the heat exchanger, i doubt the touted 3dB powerhandling increase would still be in effect once multiple subs were stacked on top of each other.

I would very much like to see recorded measurements for 4x/6x Labs vs 4x/6x 12pi's, i doubt there'd be much difference although i wouldn't want to be stacking the pis.

I guess to conclude, the labsub was a free design given to the community by Tom Danley. "12pi" sub RRP $2800 or so if i remember correctly.... Rolling Eyes
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Josh Billings

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #3 on: July 11, 2006, 05:36:11 pm »

The 12pi plans are free too, i just got a copy and we were gonna build. I actually only have space to run two subs so i was thinking about these instead of LABS because everywhere i hear the LABs need 4 to do what they are supposed to do

-Josh Billings
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Al Limberg

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #4 on: July 11, 2006, 08:18:37 pm »

I think it would be a much more reasonable statement to say you need four to reach their maximum performance potential.  Even running just a pair (preferably as a center cluster and from an aux) will still outperform an equal or greater truck space volume of double eighteens.  The only adjustment I typically make when running less than four is to raise my HPF to 32 or 36hz depending on how hard I expect to run them.

Al
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Josh Billings

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #5 on: July 12, 2006, 09:00:18 am »

As a pair though the 12pis should go a little lower and louder correct? I think with the large mouth for me just using 2 it makes more sense to build these

+ the added power handling is handy

-Josh Billings
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Wayne Parham

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #6 on: July 12, 2006, 11:16:07 am »


The 12Pi hornsub actually has several improvements, all of which I think are significant.  I originally intended to focus mostly on reduction of harmonic distortion using drivers with shorting rings and had Eminence build some prototype drivers.  I later decided to go with the push-pull arrangement instead, because it works better at very low frequencies.  I also wanted to make the response curve flatter, because I thought some improvement could be made there, particularly when small numbers of subs are used.  The heat exchanger designed for the 12Pi is another thing that provides significant improvements.  You can see test data at the links below.

To be very honest, I originally intended to make the 12Pi horn have an entirely different internal shape, largely to ensure there would be no comparisons between the LABhorn and the 12Pi other than performance.  But as I began to layout the final shape, I realized that I could make the 12Pi heat exchanger available to LABhorn owners as a bolt-on upgrade if I laid it out similarly.  LABhorn owners can simply buy cooling plugs or go to a machine shop and make their own and install them on their existing LABhorns.  I did this in the spirit of cooperation.  In my opinion, it doesn't make any sense to run a LABhorn or a 12Pi basshorn without cooling plugs because the price/performance ratio is extremely high.  Just bolt on a couple of plugs and the motors run much cooler.

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Wayne Parham
π Speakers
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Wayne Parham

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #7 on: July 12, 2006, 11:25:57 am »


The 12Pi is only 5.5" wider than the LABhorn.  The 12Pi basshorn fits nicely in semis, having truck pack dimensions.  And stacking is no problem, just space them apart with a 2x4 to allow airflow between boxes.  If you already haved LABhorns, you can easily add cooling plugs, as many people already have.  The difference in motor temperature is significant, as is the reduction in the number of burned voice coils after heavy use.
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Wayne Parham
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Tom Danley

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #8 on: July 12, 2006, 06:00:40 pm »

Hi

Is the pi an upgrade to a lab?
Better it is to ask what is a labsub first?
Some time ago, in a live audio forum far away, a bunch of people were talking about building some traditional bass horns, “W” bins.
I like DIY, was disgusted with several “big name” horn subwoofers on the market and had some casual rules at my job at the time (Servodrive) so I offered to take a whack at a “modern” horn alignment and a rough layout,  based on the cumulative inputs from the participants here on LAB.
The group decided on the standard truck pack dimension of 45 by 45 by 22 ½ inches this was as large and heavy as anyone wanted to move around.  A group of 6 should be good to about 30 Hz, it should be as powerful as possible.

Using the modern horn math was where Wayne first popped into the lab sub picture, over on the Audio Asylum forum.   He was first criticizing the use a horn for this project (low  frequency) and then of the Marshal Leach’s math (which I used as a starting point) vs the older hifi lore approach (of a low mass driver etc).  
A search of the archives there would be humorous if your bored.
Anyway, I derived a set of driver parameters for what would be a “modern” driver alignment and laid out the horn similar to another one I had designed, the Servodrive BT-7 which worked well.
The driver was not a stock part or close to any stock driver at the time, this was a problem.  I posted the needed parameters so any speaker company could make a driver for the project.
As this was not a company asking for a new driver but rather an internet forum, only one company ended up actually being both willing and able to make a driver.    
I have to hand it to Jerry at Eminence for stepping up to the plate on a speculative driver for the project.

Wayne, somewhere along the line “converted” to the view that maybe the heavy lab sub alignment /driver might work, he has made a somewhat larger version, the pi 12.

However, his measured curve for one pi 12 and 1 measured lab sub are only about 1 dB different at most, the measured lab sub is nicer than his model of it fwiw.

The push pull driver arrangement has the same advantage that a push pull transformer does, it reduces the (drivers electromechanical portion) of the 2 nd  harmonic (which is also the least audible of all of them) but does not improve the others or any of the odd (most objectionable) ones, hence it is rarely considered worth the bother.

Part of the reason for the odd front volume shape /size on the lab sub is that by lowering the upper passband limit with the un obvious acoustic low pass filter, one can reduce all the higher distortion components (at a given output level) at the same time.

Under some duty cycle conditions the cooling plugs probably increase the long term power capacity.
Under other more musical, dynamic conditions (pink noise has a Peak to Average ratio of only 6 dB, even compressed FM rock is more like 10dB P/A) with larger dynamic ranges it would be unlikely to have a significant effect.   It only takes seconds to smoke a voice coil and bass signals are more like large amplitude, low frequency tone bursts.

This is a DIY project, one can layout a different horn of course if you have a different space, one fellow (Brad I think his name was) did that with 4 or 6 at a Church or something I think.     If you search the archives here, one finds the acoustic dimensions and such are given if you want to roll your own horn and this is / was a DIY project.
As long as you keep the throat area and front / rear volumes in the neighborhood, the lab sub driver / horn alignment works.
Heck, Wayne went from being a vocal critic of the premise, the basic design philosophy and driver on the A.A.,  to now occasionally promoting a close copy of it and his website here so I guess that says something.

Lastly, keep in mind the idea behind this was using a modern design approach, to make a VERY powerful subwoofer for “live sound” that keeps up with / beats 95% of the other subs available at any price, that you can build yourself.  
Many have found the lab to be more than they expected so far as acoustic power.
Wayne’s box would be very powerful too.
Hope that helps,

Tom Danley

Danley Sound Labs

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Josh Billings

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Re: Is the 12pi Subwoofer an upgrade to the LAB?
« Reply #9 on: July 12, 2006, 08:43:57 pm »

The one restraint i have is that i ONLY have room for 2. I have a tiny 5x8 trailer and i do shows of about 300-500 people or so. I like the labs, but orginally these were build wrong and i'm starting to get air leaks and the cabinets are making a creaking noise and the guy who build them never put t-nuts in for the access panel and a whole bunch of crap was done wrong.

So i was going to get a new pair built but when i saw the 12pi the specs looked great. The 30" wide however is a little much. I know barely get the LABs through the doors (my casters suck). I guess i can get there through but it would be a snug fit.

How much extra do these things weigh?? ANy idea?

I also have to do 1 per side, so i figured the 30" wide mouth would be huge for that extra mouth area and lower hz.

I was going to do 4 dual 18s because they would take up the same (if not less space) but i woudl need 4x the amplifier power to do it right ( i figured 4 PLX3402s bridged when i really only need 1 right now) That also requires extra circuits and stuff that gets complicated for a mobile rig.

I love bass, but i love my back too, if the 12pis are going to be signifigantly heavier i'll probably just build the LABs with the cooling plugs.

-Josh Billings
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