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Author Topic: Push pull configuration for LAB Horn?  (Read 17499 times)

Mark Steven Lewis

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Push pull configuration for LAB Horn?
« on: July 26, 2007, 08:54:50 pm »

In earlier discussion, it was generally agreed that the push pull driver configuration minimizes the 2nd order distortion, correct?

If so, it doesn't seem very hard to apply this to the LAB horn. Does this make sense? If so, what would be the best way to achieve the push pull arrangement? Change the horn and/or reverse the phase of the driver?

If this works, is it worth the effort? Thanks for consultation.

... Mark
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Vince Byrne

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Re: Push pull configuration for LAB Horn?
« Reply #1 on: July 27, 2007, 01:32:29 pm »

Mark Steven Lewis wrote on Thu, 26 July 2007 19:54

In earlier discussion, it was generally agreed that the push pull driver configuration minimizes the 2nd order distortion, correct?

If so, it doesn't seem very hard to apply this to the LAB horn. Does this make sense?


What problem are you trying to solve? Do you hear objectionable distortion in the output from LABs?

Distortion in the LABs is already typically single digit, and lower than the vast majority of sub designs. Of the low distortion that remains, 2nd order is the least objectionable and is musically relevant.

The LAB design is pretty optimized, and it is doubtful you could make this type of modification without negatively affecting output SPL, frequency response, extension, etc.

Quote:

If this works, is it worth the effort? Thanks for consultation.


It wouldn't be for me, only you can judge if it would be for you. A more important question might be if it doesn't work. You could end up with a very expensive pile of firewood.
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Josh Billings

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Re: Push pull configuration for LAB Horn?
« Reply #2 on: July 28, 2007, 04:07:31 am »

It's already been done. I have a pair of them

pispeakers.com

12pi

There is very little change and the added size isn't worth the difference. They are pretty much the same speakers just the push pull is quite a bit wider and more expensive Machined Aluminum parts.

I'd say stick with the labs and get a bunch of em

-Josh Billings
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Grant Rider

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Re: Push pull configuration for LAB Horn?
« Reply #3 on: July 29, 2007, 03:41:01 pm »

The machined aluminum parts are for cooling not push/pull. I built some after lots of emails with Wayne Parham and I can tell you for sure they work great. Flat pack kits make them easy to build. I was impressed.

The cooling plugs work great for sure. You should put them in labs. No reason to leave them out because its cheap insurance from blown woofers.  I blew woofers easy without plugs and don't blow them with plugs. I also tried a blower motor to cool down the woofers and it didn't work as well. The cooling plugs made my speakers work at mondo power levels.

The push/pull part makes sense to me too but I haven't got any way to check it. Maybe a side by side measurement will be made to know for sure how much distortion goes down in 12Pi basshorns compared to labs. Hopefully someone will take labs to Tulsa in October.
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Josh Billings

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Re: Push pull configuration for LAB Horn?
« Reply #4 on: July 29, 2007, 08:04:38 pm »

I've owned both and i would take the LABs any day. They are smaller, put out the same SPL (Honestly can't notice a difference) and they are cheaper to make.

You can buy the 12pis alrady assembled though for a reasonable price ($2,200). However i wish i went smaller, like the danley TH-115s in the beginning. These giant horns are just way too big.

4 TH-115s would take up a lot less space than 4 LABs/12pis and make things a lot easier on the back

-Josh Billings
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Wayne Parham

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Re: Push pull configuration for LAB Horn?
« Reply #5 on: July 29, 2007, 11:11:10 pm »


I'm sorry you feel that way, Josh. Honestly, I'm a bit surprised since you wrote to me last month asking prices for flat pack kits.  I know you wanted drivers, CNC cut wood and machined aluminum all for $750.00, but that's way below cost.  The raw materials, baltic birch, aluminum, hardware and drivers for either a 12Pi or a LABhorn cost at least that much, without precision CNC machining.

The LABhorn is a great subwoofer, so you could definitely do worse than building a set of them.  Your preference is entirely your affair.  That said, I must clarify a couple of things about the 12Pi basshorn sub.

The 12Pi basshorn uses the same drivers as the LABhorn, but the similarities end there.  The 12Pi basshorn subwoofer has a few tricks up its sleeve that set it ahead.  It uses push-pull drive to reduce distortion and it uses a patent-pending cooling system that increases its thermal limit and power handling capacity.  It is also different than the LABhorn in flare shape, throat area, mouth area and front and rear chamber sizes.

The reduction in distortion from push-pull drive is evident in measurements, as is the reduction in motor temperatures and increased power handling that result.

Compare the response curves of the horns measured at the 2005 Prosound Shootout.  We measured distortion at this event, so you can compare the 12Pi basshorn with other horns that don't use push-pull drive.  In all of the charts, amplitude response is shown as a blue line and THD+N distortion is shown in violet.  You'll notice that at high power levels, the 12Pi basshorn sub has a lot less distortion than the other horns that didn't use push-pull drive.  You'll also notice that distortion doesn't rise rapidly under horn cutoff like the other basshorns do.  Rising distortion under cutoff is to be expected, since the horn unloads.  But the 12Pi doesn't rise nearly as much because of its push-pull drive.

There's one other thing that may be of interest to you as a DIY'er.  Some people omit front chamber fill.  Response is still good, so I guess it's optional.  But response is better when front chamber fill is installed as shown in the plans.

When the 12Pi basshorn is made with front chamber volume of 20 liters, response is perfectly flat from 30Hz up.  But this is difficult to do in practice, and makes manufacturing difficult.  The front chamber fill shown in the plans reduces front chamber volume to under 30 liters.  This makes nice response, having only a slight dip around 45Hz.  When the 12Pi basshorn is made without any fill in its front chambers, they're larger, causing a little more dip around 45Hz.  Response is still good, but not as good as when the front chambers are smaller.

See the post called "12Pi basshorn subwoofer - the best yet!" for more information on response changes with respect to different front and rear chamber sizes.
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Wayne Parham
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Grant Rider

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Re: Push pull configuration for LAB Horn?
« Reply #6 on: July 30, 2007, 06:58:35 am »

Josh Billings wrote on Mon, 30 July 2007 01:04

I've owned both and i would take the LABs any day. They are smaller, put out the same SPL (Honestly can't notice a difference) and they are cheaper to make.


I see the 12Pi as a souped up lab. It maybe isn't louder at the same power level but can take more power without blowing drivers. Look at it like insurance. Don't think the cost difference is much if any at all unless you use the expensive castor wheels.  Laughing

Josh Billings wrote on Tue, 17 July 2007 05:21

Maybe i'm doing something wrong but i've never experienced the LABs outperform a JBL Dual 18 (SRX). I know they are supposed to be able to...maybe only in groups of 4. I know that's supposed to be the magic number

-Josh Billings


I think you have a different perspective? Small size might be better for you so the big hornsubs are no good?  I've been told smaller indoors venues are better served with smaller nonhorn boxes.
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Josh Billings

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Re: Push pull configuration for LAB Horn?
« Reply #7 on: July 30, 2007, 07:41:08 am »

Wayne:

I'm not knocking the speaker, i'm just saying if i had it to do over again i'd probably go with 4 LABs vs. 3 12pis (Roughly Same size). The plates start warming up a bit and i don't feel too comfortable throwing much more than 1,800 watts at each cab which is 200 more than what i put at the LAB Horns with no failures (3 years of use).

The LAB Horns are a little lighter, a little smaller and a little cheaper to make (less aluminum / machining & less wood since it's a smaller cabinet). There may be a SLIGHT increase in SPL and yes it can probably handle a bit more power but with the plates warming up i know power compression is setting in and there isn't much left for the drivers to put out. More boxes is the only answer.

I'd say if you're going with one of these, make sure you do 4 to get it to sound good. We had 2 12pis & 2 LAB Horns Together (4 total) and the sound really impressed me. They were like new speakers. The block of 4 is what these things seem to need to work properly. They word well otherwise, but if you're going with less than 4 i'd recommend some good Dual 18s (EAW SB-850/1000).

I do indoor stuff and smaller venues so i do think that these big horns may of not been the right choice.

To clear everything up, the speakers sound great and they perform flawlessly and there is nothing wrong with them at all. They are fantastic speakers, but when posed with the choice of the 12pis or LABs (i've owned both) i think the LABs  are just a better choice if starting from scratch. They perform equally well (can't hear a difference between the two) and if i would have to learn towards one as being better as far as performance is concerned i'd lean towards the 12pi. It's just the added cost & size vs. minor performance increase that i would give it to the lab.

-Josh Billings
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Wayne Parham

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Re: Push pull configuration for LAB Horn?
« Reply #8 on: July 30, 2007, 11:25:02 am »


Thanks for the clarification, Josh.  I agree with you about using direct radiators in small environments rather than using a small number of basshorns.  That makes sense.  I also agree with you that the 12Pi is what a person would pick if they wanted quality and could spend a little more;  It's a no-compromise basshorn.  However, I do want to point out that the cost difference between DIY building a 12Pi and a LABhorn is marginal.  It's only about $100 if buying pre-made aluminum parts, even less if you machine them yourself.  Plans for both the 12Pi and the LABhorn are available at no cost, and no purchase is necessary.

The thermal benefits of the cooling plug have been quantified.  Tests show that a LAB12 driver with a cooling plug can be run continuously with power levels that are 225% higher than one without a cooling plug.  That's significant.  I'd suggest that all 12Pi and LABhorn owners should install them.  As has been said many times before - It's cheap insurance.

You said the cooling plates on your 12Pi basshorns start to warm at 1800 watts.  That's good because it means heat is being conducted away from the motors and dissipated by the plate.  Now just imagine how hot the motors are in your LABhorns, since they have no heat condution path to the access panels.  At that power level, the voice coil glue in your LABhorns is being weakened and will eventually fail.  You told me this had already happened when we first spoke.  You were looking for driver recone kits, as I recall.

Performance improvements using the push-pull arrangement has also been quantified.  Measurements have shown this configuration to be very effective at reducing distortion.  It is employed by many manufacturers, including JBL and EAW.  The JBL 728S we measured at the 2006 Prosound Shootout uses push-pull drive, for example.

There are two woofers in both the LABhorn and the 12Pi basshorns.  Since there are two woofers in use, it makes sense to orient them so they cancel distortion.  One could argue that the distortion is euphonic or they could argue that it is not all that audible.  We've all heard those arguments about distortion in subwoofers over the years.  But if we're willing to compromise ourselves with those kinds of arguments, why bother making improvements at all?  We could all have just settled with 1970's gear and called it good.

I don't mean to be argumentative, and I appreciate your candor.  But I have worked very hard to make the 12Pi basshorn be the best I could make it.  It has undergone a lot of development and testing, and has proven itself.  So I think it is important to let people see the test data in addition to our comments here.  Some of this data is specific to the 12Pi, but a lot of it is general purpose information that is useful to anyone studying subwoofers and loudspeakers in general.


12Pi development and construction

Test results and related information
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Wayne Parham
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peter.golde

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Re: Push pull configuration for LAB Horn?
« Reply #9 on: July 30, 2007, 06:42:31 pm »

Josh Billings wrote on Tue, 17 July 2007 05:21

Maybe i'm doing something wrong but i've never experienced the LABs outperform a JBL Dual 18 (SRX). I know they are supposed to be able to...maybe only in groups of 4. I know that's supposed to be the magic number
-Josh Billings


One Lab by itself is not very impressive unless corner loaded, 4 together are a very different story. It seems maybe you went too big out of the gate without better quantifying your needs. I use 4 24" wide Tuba 30's each loaded with a single Eminence 4012 and have been beating on them regularly for over a year now (EDM). They have the same number of drivers and roughly the same size as 2 JBL SRX dual 18's, but they easily spank the JBL's for output, throw, sound quality, low freq response, efficiency, indoors or out, small room or large.
I would not recommend any front loaded boxes for bass after owning, listening to several different bass horn designs. I still say the biggest problem with huge amounts of good clean low bass, is not enough midbass. To put any front loaded box on top of Labs, you will not be getting the full potential. The Lab and other horn subs (when used properly) move serious amounts of air. In order to get the full effect of how much air is being moved, you need to do the same with a midbass horn, which will add the hard hitting impact or kick, clean and powerful. Care also has to be taken with placement within a room to reach the full potential.

Josh, you should have been happy to feel heat being sinked away from the drivers to the outside air, it can only help prolong driver life under abusive conditions. Power compression does set in, but grouping horns together, corner or wall loading, thereby increasing efficiency, helps the drivers to not have to work as hard, moving more air with the same amount of power rather than creating more heat.



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