amp choice for 2x lab15 T60s

Is this amp OK?
Message
Author
monekh
Posts: 90
Joined: Mon Mar 31, 2014 5:56 pm
Location: London, UK

amp choice for 2x lab15 T60s

#1 Post by monekh »

Hello all, apologies in advance for the infuriating rookie questions… you guys must get them a lot. But here goes.

I am hoping to build a system consisting of the following.

2x Lab15 T60s
4x DR250s

I am not sure if this is a common or particularly advisable combination, any thoughts on that welcome. I am inclined towards the T60s to have the best possible low extension. Also, as not likely to be using with huge rooms/audiences, would prefer to run in stereo if possible, again, not sure if that is advisable...

From what I have read, and I hope understood, the best option would be to use an active crossover and bi-amp the system horizontally, running the two T60s off a separate amp to the DR250s. From reading the plans and driver specs, and assuming that each Lab 15 driver has 8ohm impedance and a continuous power rating of 600W, would I be correct in thinking that I should choose an amp that can supply at least 1.6 x the driver rating per channel @ 8ohms, so in this case, 960W per channel?

Looking at Bruce Weldy’s amp comparison charts, it would then seem that only a couple of the larger amps could provide enough power per channel at 8ohms, namely the XLS 5000 or Xti6000. I’ve also been looking at Macrotechs, where the 3600VZ seems to provide a similar output. So would using a 3600VZ or similar to run the two T60s, one per channel, be a sensible idea, or are there better and more efficient ways to do this?

Thanks in advance for any advice!

sine143
Posts: 3066
Joined: Sat Feb 06, 2010 3:27 pm
Location: Raleigh NC

Re: amp choice for 2x lab15 T60s

#2 Post by sine143 »

3600 vz would be a good choice (just heavy). An xti 4k will do 1 per side. The new crest pro light 5 dsp would likely do fine too
Built:
2x Tuba 30s delta12lf loaded (gone)
4x Otop12 d2512 loaded
8x t48s (18, 18, 24, 24, 30, 30) 3015lf loaded
2x AT (1 mcm, 1 gto 804)
2x SLA Pro (dayton pa6, 6 goldwood piezo loaded)
1x bastard XF208

2x OT212 (delta pro 450a loaded, eminence psd)

Grant Bunter
Posts: 6915
Joined: Mon Nov 28, 2011 11:12 am
Location: Ilfracombe Queensland Australia
Contact:

Re: amp choice for 2x lab15 T60s

#3 Post by Grant Bunter »

hi monekh
Welcome to the forum :)

It's a bit of an aside from your actual question, but there's no time better than early days to get some things sorted for you lol.

The lab 15's nominal impedance is 6 ohms. Having said that, the T60 as a cab presents an impedance of 8 ohms to the amp as the horn design adds 2 ohms in acoustic impedance. That can be confusing, I know, but it is the case.

Horn loaded cabs place different requirements on drivers compared to direct radiator cabs.
So, while the Lab 15 may have a continuous power rating of 600W, in a horn loaded design, you can't feed it that much power or it will blow.
In the plans, the displacement limit in volts for the Lab 15 in a T60 is 60V.
It can also be confusing that the limit is quoted in volts, as many people always think about output in watts. Suffice to say that watts are a calculation, or the product of voltage and impedance (using Ohms law), and as such cannot be calculated on the fly. Voltage can be read directly off the amp with a DMM at any time.
FTR 60V in an 8 ohm load is 450W.

While 2 x DR 250's per side will smooth response somewhat, I would question the need to build 4 initially. For indoors at least, the usual sub to top ratio is recommended as 1:1 (outdoors 2:1) for these designs. 4 x DR 250's per side will overun 2 x T60's. The DR250 is an astounding cab in terms of output.

Other than that, put your location in your profile (via user control panel up the top). You never know, there might be someone nearby who already has what you are looking to build, and may be able to demo for you. At the least, people nearby you will have already done the hard yards locating the required supplies to build.
Speakerhardware.com is your friend, and has exactly what you need for your builds apart from ply. The owner, Leland Crooks, is a forum member, authorised builder for BFM, and his family runs that business...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" KL3010LF , 2 x 28" 3012LF.
WH8: x 6 with melded array wired series/parallel.
Bunter's Audio and Lighting "like"s would be most appreciated...

monekh
Posts: 90
Joined: Mon Mar 31, 2014 5:56 pm
Location: London, UK

Re: amp choice for 2x lab15 T60s

#4 Post by monekh »

thanks sine143 and Grant, very helpful. especially the explantion regarding volts, I had seen posts by Bill saying watts mean nothing (or something along those lines!) but think I understand it a bit better now.

When relating this displacement limit, i.e. 60v / 450W @ 8 ohms, back to the choice of amp, would I be correct in assuming there's no need to factor in headroom as this is a limit, not a continuous rating, and that therefore, a smaller amp, one capable of just 450w per channel, would suffice?

(think I will heed you and go for 2x DR250s for now!)

sine143
Posts: 3066
Joined: Sat Feb 06, 2010 3:27 pm
Location: Raleigh NC

Re: amp choice for 2x lab15 T60s

#5 Post by sine143 »

Personally im a bit more comfortable with an amp capable of around 600 watts @ 8ohms p ch limited down to 60v. This at least means you wont be running the amp "flat out"

The crest prolight dsp 3.0 even has enough juice theoretically
Built:
2x Tuba 30s delta12lf loaded (gone)
4x Otop12 d2512 loaded
8x t48s (18, 18, 24, 24, 30, 30) 3015lf loaded
2x AT (1 mcm, 1 gto 804)
2x SLA Pro (dayton pa6, 6 goldwood piezo loaded)
1x bastard XF208

2x OT212 (delta pro 450a loaded, eminence psd)

Grant Bunter
Posts: 6915
Joined: Mon Nov 28, 2011 11:12 am
Location: Ilfracombe Queensland Australia
Contact:

Re: amp choice for 2x lab15 T60s

#6 Post by Grant Bunter »

No worries, glad to be able to help!

+1 to the sine143 post.

With limiting, you don't have headroom as such, but you don't want to run your amp right up to it's capability all the time.

There is a bit of balancing act selecting an amp with "enough" output when you limit, but still allowing room to not run the amp to hard.
This comes back to the maximum amount of limiting you can obtain with DSP (which can vary brand to brand). For example, no point in buying an amp with 1500W/channel output when you need to limit to 450W/channel, as that may be beyond the capability of the limiter to achieve.

Sine143's suggestion of 600W/channel is only 9 volts over the required 60V, which most limiters would handle with ease. It would probably equate to about a -6dB setting on the limiter...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" KL3010LF , 2 x 28" 3012LF.
WH8: x 6 with melded array wired series/parallel.
Bunter's Audio and Lighting "like"s would be most appreciated...

Grant Bunter
Posts: 6915
Joined: Mon Nov 28, 2011 11:12 am
Location: Ilfracombe Queensland Australia
Contact:

Re: amp choice for 2x lab15 T60s

#7 Post by Grant Bunter »

Oh, BTW, I've just seen you're in the UK.
Here's a thread for Suppliers in the UK:
http://billfitzmaurice.info/forum/viewt ... =14&t=4140

Lean Business (http://www.lean-business.co.uk/eshop/) and Blue Aran (www.bluearan.co.uk/) seem to the businesses most often mentioned for getting drivers on the forum. I think they have deals/sales reasonably regualrly as well, but also keep your eyes open on local e-bay etc.

Speakerhardware.com might still be an option for piezo's and crossover requirements for your DR250's though, you'll need to do your sums...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" KL3010LF , 2 x 28" 3012LF.
WH8: x 6 with melded array wired series/parallel.
Bunter's Audio and Lighting "like"s would be most appreciated...

monekh
Posts: 90
Joined: Mon Mar 31, 2014 5:56 pm
Location: London, UK

Re: amp choice for 2x lab15 T60s

#8 Post by monekh »

Thanks both again. Yes Grant that thread has helped me out a lot already! Hope to be able to make some recommendations there myself once I get going.

Looks like it might be easier to pick up an old crown or qsc in the UK than a crest...
just been looking at the macrotech 2400, it's saying 520W / channel @ 8 ohms, do you think this would still be pushing the amp a bit hard? Safer to go for something bigger? Certainly intending to limit - just to double check, is it best to limit after crossover, with a separate limiter for each frequency band / amp?

sine143
Posts: 3066
Joined: Sat Feb 06, 2010 3:27 pm
Location: Raleigh NC

Re: amp choice for 2x lab15 T60s

#9 Post by sine143 »

I probably wouldnt feel to bad about using the 2400. Ive seen the old macrotechs bouncing off the cliplights for like 6 straight hours wired into 1 ohm multiple times.... 8 ohms is cake compared to that.
Built:
2x Tuba 30s delta12lf loaded (gone)
4x Otop12 d2512 loaded
8x t48s (18, 18, 24, 24, 30, 30) 3015lf loaded
2x AT (1 mcm, 1 gto 804)
2x SLA Pro (dayton pa6, 6 goldwood piezo loaded)
1x bastard XF208

2x OT212 (delta pro 450a loaded, eminence psd)

Grant Bunter
Posts: 6915
Joined: Mon Nov 28, 2011 11:12 am
Location: Ilfracombe Queensland Australia
Contact:

Re: amp choice for 2x lab15 T60s

#10 Post by Grant Bunter »

While it's only 5V, that's better than 1V lol.

You should also keep it in the back of your head that if you're constantly hitting the limiter at 60V, then you should have more subs.

FTR, 60V in a T60 will be very very loud...
Built:
DR 250: x 2 melded array, 2x CD horn, March 2012 plans.
T39's: 4 x 20" KL3010LF , 2 x 28" 3012LF.
WH8: x 6 with melded array wired series/parallel.
Bunter's Audio and Lighting "like"s would be most appreciated...

monekh
Posts: 90
Joined: Mon Mar 31, 2014 5:56 pm
Location: London, UK

Re: amp choice for 2x lab15 T60s

#11 Post by monekh »

so having got everything up and running, with T60s limited to 50v to be safe, it is clear (as you predicted Grant) that the mains outpower the subs. though the whole thing sounds great (and we can obviously just turn the mains down!) it seems like the next logical step to expand the system would be building more subs to balance the power of the mains.

we've been running the two T60s off one macrotech 2400, which handles 50v per channel comfortably.
now if I've understood correctly, if we were to daisy chain another sub per channel that would halve the impedance per channel to 4ohms, at which the rated output would be 750W... so I wanted to check is this power shared between the cabinets, i.e. 375 watts / 39 volts per sub? in which case the amplifier would clip way before the 50v the cabinets can handle and therefore be too weak?

we have another macrotech 2400 at our disposal, so if the above was correct, I was wondering, despite seeing Bill's warnings not to bridge and not really understanding about voltage swing, whether running bridge-mono might be appropriate in this instance... sending the left sub output from dsp to one bridged 2400, and the right sub output from dsp to the other bridged 2400. In the amp spec, it suggests 1670W 4 ohm bridge-mono - again, assuming that this power would be shared between 2 cabinets, that would be 835W / 58v per cabinet... which would seem good.

we are obviously running the subs in mono anyway so I had entertained the idea of running channel 1 via +1/-1 to the first sub and channel 2 via +2/-2 to the 2nd daisy-chained sub... but obviously this would mean making sure the driver in the 2nd sub was wired to +2/-2, so maybe bridging would achieve the same thing while wiring all cabinets the same (which I guess would be simpler/safer/preferable).

if all the above is silly nonsense, and we should just look at getting a more powerful amp to run multiple subs off each channel without bridging, please let me know!

cheers

Bruce Weldy
Posts: 8301
Joined: Fri Nov 27, 2009 11:37 am
Location: New Braunfels, TX

Re: amp choice for 2x lab15 T60s

#12 Post by Bruce Weldy »

monekh wrote: it suggests 1670W 4 ohm bridge-mono - again, assuming that this power would be shared between 2 cabinets, that would be 835W / 58v per cabinet... which would seem good.
1670 watts a 4 ohms is 82 volts.

we are obviously running the subs in mono anyway so I had entertained the idea of running channel 1 via +1/-1 to the first sub and channel 2 via +2/-2 to the 2nd daisy-chained sub... but obviously this would mean making sure the driver in the 2nd sub was wired to +2/-2, so maybe bridging would achieve the same thing while wiring all cabinets the same (which I guess would be simpler/safer/preferable).

if all the above is silly nonsense, and we should just look at getting a more powerful amp to run multiple subs off each channel without bridging, please let me know!

cheers
You are making this way too hard. If two subs are running fine off one amp....and you have another one just like it, then run the two new subs off the other amp - one sub per channel.

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

monekh
Posts: 90
Joined: Mon Mar 31, 2014 5:56 pm
Location: London, UK

Re: amp choice for 2x lab15 T60s

#13 Post by monekh »

thanks Bruce - I guess I was hoping to daisy chain to avoid running extra cable, and that by bridging I could achieve pretty much the same outcome as you suggest, sending two channels to each side, but using only one length of cable.

ignoring bridging, I now understand that each driver receives the same voltage when connecting multiple drivers in parallel. but I'm really struggling to understand how this affects amp performance - why, in theory, when connecting a single driver in this case, the amp channel can deliver just enough voltage (63v) to power the driver to its xmax, but by connecting another driver and halving the impedance, the same channel is capable of delivering only slightly less voltage (54v) to two drivers? Which is almost doubling the output (in sound, if limiting to 50v anyway) of the channel?

sorry, these must be infuriating questions!
it's sometimes hard to know where to go to learn this stuff correctly - this forum is amazing, you guys have got me over so many stumbling blocks.

Bruce Weldy
Posts: 8301
Joined: Fri Nov 27, 2009 11:37 am
Location: New Braunfels, TX

Re: amp choice for 2x lab15 T60s

#14 Post by Bruce Weldy »

monekh wrote:thanks Bruce - I guess I was hoping to daisy chain to avoid running extra cable, and that by bridging I could achieve pretty much the same outcome as you suggest, sending two channels to each side, but using only one length of cable.

ignoring bridging, I now understand that each driver receives the same voltage when connecting multiple drivers in parallel. but I'm really struggling to understand how this affects amp performance - why, in theory, when connecting a single driver in this case, the amp channel can deliver just enough voltage (63v) to power the driver to its xmax, but by connecting another driver and halving the impedance, the same channel is capable of delivering only slightly less voltage (54v) to two drivers? Which is almost doubling the output (in sound, if limiting to 50v anyway) of the channel?

sorry, these must be infuriating questions!
it's sometimes hard to know where to go to learn this stuff correctly - this forum is amazing, you guys have got me over so many stumbling blocks.

Voltage is voltage. When you plug a lamp into and two way outlet, it gets 110 volts, right? If you plug another lamp in the same outlet, does it not get 110 volts also? The lights don't dim - they are all happy, but it's still just 110 volts.

We've all been taught about the almighty watt. It's a facade. There is no such thing as a watt until there is resistance to voltage. So wattage is determined after the speaker is plugged in and there is resistance. The voltage is the same.

And don't feel bad - we've all struggled with this in the beginning. I've been doing sound off and on for 40 years.....and I've only learned how this works in the last 5 thanks to this forum.

As far as the cabling - nothing says you have to use only one connector on the end of a 4 wire cable. make two pigtails with a speakon on each one and now you have two speaker cables in one.

I built these for my subs. Just takes a little heat shrink and you can make 'em look like they came from the big store in the city.
IMG_1214.JPG
IMG_1215.JPG

6 - T39 3012LF
4 - OT12 2512
1 - T24
1 - SLA Pro
2 - XF210


"A system with a few knobs set up by someone who knows what they are doing is always better than one with a lot of knobs set up by someone who doesn't."

CoronaOperator
Posts: 1648
Joined: Wed Mar 25, 2009 7:07 pm
Location: Medicine Hat, Alberta, Canada

Re: amp choice for 2x lab15 T60s

#15 Post by CoronaOperator »

monekh wrote:why, in theory, when connecting a single driver in this case, the amp channel can deliver just enough voltage (63v) to power the driver to its xmax, but by connecting another driver and halving the impedance, the same channel is capable of delivering only slightly less voltage (54v) to two drivers? Which is almost doubling the output (in sound, if limiting to 50v anyway) of the channel?
When you half the impedance by paralleling cabs, although the voltage to each cab stays the same, the current (amps) flowing through the amp output doubles. Power = volts x amps. Ideally, halving the impedance should double the output of the amp but eventually you hit the current limits of the power supply and output transistors of the amplifier design. The reason your amp will only go to 54v instead of 63v with half the impedance is because it runs out of current capability. If the amp was built more robustly with more current capability then you would get the full 63v at a lower impedance.
Built:
17" width 10" driver Autotuba
2 x 29" width dual Lab12 Tuba60
6 x DR250 2510/asd1001
In progress:
2 x DR250 2510/asd1001
For best results, point the loud end of the array towards the audience

Post Reply