BillFitzmaurice.info

Hi guys!

As you might remember, I started building som BFM speakers this summer, and the plan was to build 4 T48s with 3015LF´s and 2 DR280 with melded arrays and the 3012HO woofer, and run it with one XTi 4000 to start with. I got as far as building two T48s, 800mm wide. But then my XTi 4000 got stolen togehter with a bunch of lights and stuff.. So we kinda lost momentum during the autumn.
But time to come back to the PA and get it done!

I have gotten myself an offer on a couple of used Lab Gruppen amps, a rack and a Behringer DCX 2496 DSP, for a very good price, around 1000 euros plus VAT, the amps are: one Lab 300, one Lab 1300 and one Lab 1600, and I´m thinking of course then to run a active threeway system.
Admittedly it would feel a bit "strange" running real high end amps with a "lowly" Behringer dsp, but since you guys told me so much good about the DCX 2496, and the fact that we get that dsp for next to nothing, and we simply cant afford my first hand choice, the DBX Driverack 260 at the moment, I think were gonna go with the Behringer

The only thing I´m a bit concerned about is if I´m really gonna get a the power/voltage swing that I need from these amps. For the Piezos, the Lab 300 must surely be far enough, even when we build more tops later on, it is rated at 2x130W in 4ohms @ 0.1% THD, and I seem to remember Bill stating that 2x50 or 2x100W would be far enough for 4 arrays?

The Lab 1600 is rated at 2x780W, 4ohms @ 0.1% THD, which should deliver 60V to the T48s without problem?
But, the Lab 1300 is "only" rated at 2x350W, 8 ohm @ 0.1% THD, and that feels like it could be a bit on the low side for my DR 280s with 3012HO´s? I guess it would still be plenty loud and all that, but not really able to take the 3012HO to its max? or am I mistaken?

When the time comes to build more tops and we feel that we really need to press those last 200W out of the DRs, I could always relegate the 1300 to monitors or the future B-rig or something:P

What do you say guys, should I go for this? Anyone use any of these amps? Something special I should look for when checking them out?

It feels like a couple of used Lab amps are a better investment for the future than a bunch of Behringers or such for the same money?

//Robin
The fact that Lab Gruppen´s headquarter is located like 40km away from me, and offer service at a very good price, doesnt make it any worse

Robin_Larsson wrote:The Lab 1600 is rated at 2x780W, 4ohms @ 0.1% THD, which should deliver 60V to the T48s without problem?

60 volts requires 450 watts at 8 ohms, so you will be starving the subs somewhat. If you are just running two right now - you can bridge that amp (with proper limiting of course) and have plenty of power.

If you have all 4 running, then running two a side will be really loud - just not as loud as it could be.

But, the Lab 1300 is "only" rated at 2x350W, 8 ohm @ 0.1% THD, and that feels like it could be a bit on the low side for my DR 280s with 3012HO´s?

With the usual response being, "run the tops at about half of the max voltage" - you should have plenty to run 2 - 280s. But, I'd prefer more if you can get it.


Ultimately, the best option may be to sell the 1300, move the 1600 to the tops, and buy an amp to run the subs at full power.

I wouldn't worry, if the 280's aren't loud enough with 350watts you need more boxes anyway. The extra 100watts would only get you approximately 1db more. That seems to be a very good deal on those amps...I would not hesitate.

Thanks guys:)

Wallywally, yeah, that kinda my reasoning also, but then I might need more boxes and a bigger amp
What is really the voltage-limit for the DR´s? Is it just the drivers RMS rating? that would be 400W for the 3012HOs,(atleast according to the box) but Bill states 450W powerhandling in the plans? I´ve read that you will hear the tops complain well before they break, but if I want to use a limiter, what would then be a good setting?

Bill usually say things like, forget about watts, or watts doesnt matter, and I think I kind of understand what he means, its the voltageswing that the amp i capable of that really matters, but if one doesnt have the amp to measure it, then the only way to get the voltage is to calculate it from the wattage specs? Sadly Lab Gruppen doesnt specify the voltage, only the wattage and slew rate, the former being 60V/microsecond on the Lab 1600 for example.
If the specs are realiable, then the calculation must be correct, yes? I could of course call/email Lab Gruppen and ask;) And measure on the amps before I buy them.

I belive the recommendation for the T48s is to limit the output to a few volts under 60, so something like 55-56 maybe? which should be in the capacity of the Lab 1600´s specs, I get 55,8V from 780W 4ohms and 57,3V from 410W in 8ohms? Is the difference from 56 to 60V even almost audieble under real world conditions?

Maybe bridge the 1300 for 2 subs and running the tops in stereo on the 1600?

Links to the specs for the Labs,
http://labgruppen.com/media/downloads/p ... s+spec.pdf
http://labgruppen.com/media/downloads/p ... s+spec.pdf
http://labgruppen.com/media/downloads/p ... _SPEC3.pdf

//Robin

I recommend limiting tops to 1/2 Pe. That last 3dB isn't worth trying to achieve.

Lab Gruppen doesnt specify the voltage, only the wattage

Calculate it.

Robin_Larsson wrote:Thanks guys:)

Wallywally, yeah, that kinda my reasoning also, but then I might need more boxes and a bigger amp
What is really the voltage-limit for the DR´s? Is it just the drivers RMS rating? Yes that would be 400W for the 3012HOs,(atleast according to the box) but Bill states 450W Misprint powerhandling in the plans? I´ve read that you will hear the tops complain well before they break, but if I want to use a limiter, what would then be a good setting? 56volts maximum but I would keep them at about 50volts to be safe

Bill usually say things like, forget about watts, or watts doesnt matter, and I think I kind of understand what he means, its the voltageswing that the amp i capable of that really matters, but if one doesnt have the amp to measure it, then the only way to get the voltage is to calculate it from the wattage specs?that is correct Sadly Lab Gruppen doesnt specify the voltage, only the wattage and slew rate, the former being 60V/microsecond on the Lab 1600 for example.
If the specs are realiable, then the calculation must be correct, yes? I could of course call/email Lab Gruppen and ask;) And measure on the amps before I buy them.

I belive the recommendation for the T48s is to limit the output to a few volts under 60, so something like 55-56 maybe? which should be in the capacity of the Lab 1600´s specs, I get 55,8V from 780W 4ohms and 57,3V from 410W in 8ohms? Is the difference from 56 to 60V even almost audieble under real world conditions? You could only measure the difference, you would not hear it

Maybe bridge the 1300 for 2 subs and running the tops in stereo on the 1600? That would work also

Links to the specs for the Labs,
http://labgruppen.com/media/downloads/p ... s+spec.pdf
http://labgruppen.com/media/downloads/p ... s+spec.pdf
http://labgruppen.com/media/downloads/p ... _SPEC3.pdf

//Robin

Answers above in red

Don't worry about the volume, these designs are very loud. If you were playing places big enough to require more boxes....money would not be the issue.

Thanks Bill, but please excuse my ignorance, by Pe, do you mean Peak effect or what am I missing? so as Wallywally says, 400W or 50volts to be safe for the DR 280 with 3012HO?

Yeah, I did calculate it, got 55.8 and 57.3 volts for the Lab 1600, would 56V be a reasonable guess for 5ohms? That must be good enough, dont really think I will be pushing them that hard all the time

Wallywallym, thanks again for your answers, and I do belive you are correct, when we need more than that, we should have the money by then And then we´ll use these Labs for the B-rig or monitors.

We ran our T48s in a really small room, maybe 40sqm, and by 13V it was really loud, and we really couldnt play louder there:P
The only thing is that on our own raves, both indoor and outdoor sometimes, we really want crazy levels of bass;) Thats why we´re gonna build 4 wide T48s, and then more;)

Anyone have any bad stuff about Lab that i should be aware of? would it be close to irresponsible to push them to max rms power for 10-14 hours straight, or should they manage that fine? From my own small experience with Lab, I feel that they should handle it.

Thanks again all of you!

Now I really need to start building some DRs

Robin_Larsson wrote:Thanks Bill, but please excuse my ignorance, by Pe

Thermal power rating.

Bill Fitzmaurice wrote:

Robin_Larsson wrote:Thanks Bill, but please excuse my ignorance, by Pe

Thermal power rating.

Ah, I thought it was something like that, just couldn´t see it in the acronym Thermal Power rating, is the same as RMS rating, if I´m not completly mistaken?