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Author Topic: Lab sub questions (impedance & using 1 per side)  (Read 11902 times)

Matt F Castle

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Lab sub questions (impedance & using 1 per side)
« on: May 04, 2008, 04:02:02 pm »

Hi,

I’m looking on embarking on building a pair of Labsub’s and have a few questions before I start:

How will 2 Labsub’s (1 per side) perform, as I read there designed to work in groups of 3 or 4? Will running them singly have and detrimental effects on there performance or sound?  
The idea will be to build another pair in the future for 2 a side or a single block of 4 but until that point it will be just the one each side in most cases, so I’m after opinions if it’s worth it or for that number if I would be better off looking at other options?

What impedance will an amp see from one box?  Current power option is a QSC PLX3402 (which I’m hoping should be plenty??), looking at one of the poll’s this is quite a popular choice.
Are there different wiring options to get the impedance of a Labsub to close to 2ohm’s (I’m assuming from what I’ve read 2 lab12’s in parallel would give 1.5ohm + the horn loading and end up been nearer 2ohm+ or will that cause problems with to low an impedance on the amp?

Also roughly what sensitivity are the Labsubs (40 - 90hz)

Cheers

m
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Al Limberg

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Re: Lab sub questions (impedance & using 1 per side)
« Reply #1 on: May 04, 2008, 05:16:16 pm »

Read again oh young one.  The Lab12 is a 6 ohm driver, which, ignoring the acoustical impedance of the cab, would result in a 3 ohm load for a pair of 12s in parallel.  I run four cabs (4 Lab12s per side) off a QSC RMX5050 with great results, certainly no heat problems or early onset of clipping.  Another poster in a previous thread is running his Labs from a Crown with the onboard computer which flickers between 5 and 6 ohms with a single LabSub per channel. AS far as running a single per side, I have been more than happy with the results.  Admittedly they are a bit large to haul in such a circumstance but the performance is fine.  I typically hi pass singles at 35-38Hz and a group of 4 at 32Hz.   I can't quote you specific sensitivity figures although the early Danley posts as the LAb was developed should include some useful info in that regard.  I find that while I run a single pair or even a single cab probably 5 times for each time I get to open up four at once, it is worth it to me for those few times.  AS a matter of fact, two more will be put in service this summer for a single large festival and to give my son his own pair.  

HTH,
Al
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If the automobile had followed the same development cycle as the computer, a Rolls-Royce would today cost $100, get one million miles to the gallon, and explode once a year killing everyone inside - Robert X. Cringely

Matt F Castle

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Re: Lab sub questions (impedance & using 1 per side)
« Reply #2 on: May 04, 2008, 06:12:29 pm »

Cheers for the reply Al,  my bad I did in fact mean 3ohm for a single cab.. (day dreaming of 2 a side at the same time and silly wiring options....).  

So are you saying a single cab (2 x drivers) in the real world is around 5 to 6 ohm's load to an amp?  In which case is a PLX3402 going to be enough gas (one box per channel) to drive them?  I came across a poll that had about 40% of people using PLX3402's, not sure if that was one box per amp channel or one amp per box (bridged)?

I'm looking at them to be replacing (or as an additional option to) 4 x single 18" sub's that are running out of gas before the tops at the moment.  I would imagine (having not got the tape measure out yet) one Labsub would be around the size of 2 of my current single 18's and I’m liking them been wide enough on there side to get two mid/hi boxes on them, but I guess a lot harder to move around.

Anyway, thanks again for the reply, just trying to convince my self it's a good idea before embarking on building..
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Al Limberg

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Re: Lab sub questions (impedance & using 1 per side)
« Reply #3 on: May 04, 2008, 10:46:08 pm »

I can't imagine bridging a 3402 into a single Lab.  Afterall. that's roughly 3400w @4 amd 2200w @8 - figuring the Lab @ 6 puts your roughly halfway between.  That's some serious headroom for a 600w noise/1200 program cab.  On the other hand, bridging into a pair puts you at 3 ohms and that is pretty close to the danger zone I'm sure.  I typically run mine upright when used singly to get better height on my top boxes but I have on occasion had them on their sides with two tops as you mentio nad it makes a very solid base.
As far as moving them, I'm and old fart with a bit of a heart condition but that's why we have hand trucks.  The 13" wheel versions from Harbor Freight move them around nicely for under $40.

Al
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If the automobile had followed the same development cycle as the computer, a Rolls-Royce would today cost $100, get one million miles to the gallon, and explode once a year killing everyone inside - Robert X. Cringely

Chris Gruber

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Re: Lab sub questions (impedance & using 1 per side)
« Reply #4 on: May 05, 2008, 12:02:38 am »

On the same topic would a Crown CE4000  with 1200w/ch at 4 be a good match for 1 LAB per side?
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-Chris
Arthur Audio

"It never ceases to amaze me how many sound guys think the measure of their work is solely defined by whether or not their subs are capable of sonically vaporizing squirrels from 20 meters."

Matt F Castle

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Re: Lab sub questions (impedance & using 1 per side)
« Reply #5 on: May 05, 2008, 06:01:17 am »

Hi Al, Thanks again for the reply.

Things are coming a little more clear, (is there a sticky with the basic spec's/info/performance info im missing?) based on the drivers been listed as 400w each I was assuming 800rms/1600program per box (and a health margin).  And with talk of people using PL9's etc.. I was wondering how people use PLX3402's based on 800/1600 thinking with that only been 1100w @ 4ohm / Ch.

So the thinking would be one box per amp channel on a PLX3402 and that been enough gas to driver a Labsub?

I guess i'm still trying to convinvince myself if it's really worth embarking on and spending the money on the project..


Cheers

m
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Al Limberg

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Re: Lab sub questions (impedance & using 1 per side)
« Reply #6 on: May 05, 2008, 10:13:10 am »

Yikes! Its been so long since I really even considered the power specs,etc. that I may be off with my 300 per driver.  The 5050 is like having a big 60's V-8 under your foot.  You just press the pedal and it goes (we'll ignore the fuel economy ramifications in this story!)  Prior to adding the 5050 to my racks I used a pair of Yamaha H7000s rated at 750 @8 snd 950 @4.  On the single pair days I could go with 1 amp for the pair or my Labs are wired for the option of using one driver per amp channel.  In either case, tickling the clip LEDs was a rarity.
In regards to Chris's question, I would think the CE4000 would do fine on Labs.  You might do a search though as it seems to me, and this is a hazy memory, that the specs on the 4000 are quite different depending on the supply voltage, 110 vs. 220.

HTH,
Al
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If the automobile had followed the same development cycle as the computer, a Rolls-Royce would today cost $100, get one million miles to the gallon, and explode once a year killing everyone inside - Robert X. Cringely

Silas Pradetto

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Re: Lab sub questions (impedance & using 1 per side)
« Reply #7 on: May 07, 2008, 08:02:43 pm »

One per side is almost not worth bothering with. I have corner-loaded a single unit inside and with EQ it is OK. Even 2 coupled is not recommended.

A single LAB sub enclosure is about 6 to 7 ohms according to my Itech 8000.

I run the I-tech 8000 stereo with 2 LABS per side, which is 2000 watts per LAB. I can hit clip limit with no issues and no blown drivers yet.

A LAB12 woofer is 400RMS, 800 "music program". That is in free-air. Once it's horn loaded it can handle significantly more without any issue, since there is much more cone control behind a horn.

Most LAB failures are heat related from too much power over a long time. Mine never even get warm.

My LAB subs can keep up nicely with my TFR mains with about the same power, my mains having a LF sensitivity of 108. LAB subs in a stack of 2 are probably around that.

Synopsis: 1 LAB sub is about 6 ohms, 2000 watts, can't be used single except in special circumstances with EQ, and not at full power. A PLX3402 won't be enough to fully realize the power except bridged into a pair.
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Matt F Castle

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Re: Lab sub questions (impedance & using 1 per side)
« Reply #8 on: May 11, 2008, 04:58:19 am »

Thanks for the reply Silas,

Could you expand a little on what you've said and qualify why one per side is not worth bothering with and why 2 per side is not recommended?  What are the "special circumstances" 1 pair (L/R) would be ok?  

Al's posts above seem to indicate that they would perform ok in my application.


My back ground to my asking these questions:  I'm looking at 1 pair initially (2 boxes, mainly for use, one left one right, the regular gig the PA is on the front of the stage so a centre cluster wouldn't work) as that’s as far as I can make the money stretch at the moment and then be looking at a second pair in the future for 2 per side (or one block of 4).  

What I am trying to find out is will one per side work or not until I've got more. Also interested in info about 2 boxes per side if you don't think they will work ether?

The application is mainly live bands and some "disco" music in-between sort of thing so a lack of ultra low sub isn't initially a problem provided they have reasonable performance (with a bit of EQ) in ~3 or 400 capacity room.  Also my mid/hi boxes aren’t top of the range so not ultra loud, but the current 4 x single 18" subs can't keep up with them...

How low does the horn load the drivers when used singly?

On the amp front, I've ether got a PLX3402 or a Camco that can do 1600@4ohm/ch.  Al's also indicated there should be a fair performance with this amount of power, based on my application so long as they will do the job, also added with been used individually and needing some EQ to get the performance is that not a good thing not throwing bucket loads of power at them?  Bigger amps would be a upgrade further down the line when there’s more boxes to power...


Any input is appreciated, been a self build and not been able to hear them first before outlaying the money on them.

Cheers

m


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Walt de Jong

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Re: Lab sub questions (impedance & using 1 per side)
« Reply #9 on: May 12, 2008, 04:14:20 am »

If you are using one LAB on each side this probably means the venue is not very big.

In smaller values 2x18" reflex bins ussualy give better results, they are easier to set up, have less interaction with the room and so on. They seem to have more bass up close.

In larger venues, or outdoors, where you really needs lots of acoustic power, the LAB-horns will have the advantage.

Best regards,

Walt
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