amp choice for 2x lab15 T60s

[monekh]

thats a great idea splitting the cables bruce, hadn't thought of that - I guess equally I could switch the poles at one end of the daisy chaining cable, such that +2/-2 at one end becomes +1/-1 at the other, and then could still wire all drivers to +1/-1 in the chassis connectors. Though again your way is less complicated and uses fewer connectors and less cable.

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.

this is good to know. I think what I'm struggling to come to terms with is kind of the opposite of this - not that the amp isn't capable of maintaining absolutely full voltage with half the impedance, but that it is - as if the amp's response to doubling the load, rather than struggle twice as much, is to suddenly be able to almost double its power output... I understand it's a result of the change in impedance, and I'm sure I'll manage to accept that it's just the way it is in time! just feels like there should be some kind of trade off for almost doubling the output by doubling the load... feels like cheating!

[CoronaOperator]

as if the amp's response to doubling the load, rather than struggle twice as much, is to suddenly be able to almost double its power output

Consider this magical device:

You plug in a 100w light bulb into it and it produces 100w output. You then plug in another 100w bulb into another outlet and presto - it now outputs 200w! Almost like magic! You can continue doing this by plugging in more light bulbs but eventually the lower impedance of multiple lightbulbs in parallel increases the current flow so much that it trips that red circuit breaker thingy and all the lights go out! Same thing with your amp.

just feels like there should be some kind of trade off for almost doubling the output by doubling the load...

There is a trade off - Reliability. The more power your amp puts out the more heat it produces. That can cause your amplifier to shut down and in that case it takes out ALL the speakers you have connected to it. Your reliability of your system goes down. If you lose an amp channel, then all those speakers go down with it. Reliability is very important when doing gigs.

[NukePooch]

Consider this magical device:

You plug in a 100w light bulb into it and it produces 100w output. You then plug in another 100w bulb into another outlet and presto - it now outputs 200w! Almost like magic!

Oh? You've been to my church when we have potluck dinners then?

Wow, what's that smell? Is some food burning?
Nope, it's that you're running a dozen crock-pots and warmers off of three daisy-chained powerstrips on the end of a 50' 16g extension cord...and don't get me started about wiring Christmas lights...

[monekh]

great, thanks for the explaining people.
Think my problem was thinking of the amp as the source of power, which it obviously isn't (multitap analogy pretty helpful there!), and it can draw more power (up to a point) from the grid when required.

One more question before hopefully leaving this thread alone - would I be correct in thinking that as macrotechs are rated 2-8 ohms, it would be a bad idea to chain more than 3 cabs together off a single channel? As a fourth would bring the impedance down to 1 ohm?

[sine143]

a crown macrotech is one of the few amps I trust under 4 ohms for sub duty. its an arc welding boat anchor :p

[Bruce Weldy]

great, thanks for the explaining people.
Think my problem was thinking of the amp as the source of power, which it obviously isn't (multitap analogy pretty helpful there!), and it can draw more power (up to a point) from the grid when required.

One more question before hopefully leaving this thread alone - would I be correct in thinking that as macrotechs are rated 2-8 ohms, it would be a bad idea to chain more than 3 cabs together off a single channel? As a fourth would bring the impedance down to 1 ohm?

2-8s is 4

2-4s is 2

So, 4-8ohm speakers is 2 ohms. That amp can handle it.....

[sine143]

disclaimer, dont try this on a 15 amp breaker lol...

[Bruce Weldy]

disclaimer, dont try this on a 15 amp breaker lol...

Certainly could be the case, but it really depends on the content you are playing.

I run live sound shows with 7 Crown amps (three of 'em bridged for subs), 3 drive racks, my board, and my trusty 20 yr old fan from a single 15amp GFI. It's the GFI getting weak and tripping that I'm most worried about.

Granted the MacroTechs are old, heavy iron amps and draw a lot of juice - especially if you are playing EDM or some of those other strange genres that just go thump, thump, thump.....or, is it woof, woof, woof?

[CoronaOperator]

Granted the MacroTechs are old, heavy iron amps and draw a lot of juice - especially if you are playing EDM or some of those other strange genres that just go thump, thump, thump.....or, is it woof, woof, woof?

I've tripped 15amp (120v) breakers using a single MacroTech2400 playing EDM @ 4ohms. They sure do draw the juice. We've since installed 20amp service and all is well.

[sine143]

my post was SPECIFICALLY aimed towards macrotechs at 4 ohms or lower

dont try it on 15 amp breakers unless you are just trying to time how long it takes to trip (stopwatch ready?)