Amps 101

[Michael Murphy]

Guys as you know Ive got the T39, 30" wide with the lab 12 installed. Recommende max voltage 55volts and you may also know I have the QSC 1400 amps (6) http://media.qscaudio.com/pdfs/disconti ... s/1400.pdf

I confused, questioning what I thought I knew. Ok here it comes
According to the amp specs running 2 channel it outputs
8ohms - 200W
4ohms - 300W

and if just running 1 channel nets
8ohms - 270W
4ohms - 450W
2ohms - 550W

and then bridged
8ohms -600W

So im using the voltage calculator http://www.sengpielaudio.com/calculator-ohm.htm
and this is what the above relates to in voltage
8ohms - 200W (40v)
4ohms - 300W (34V)

and if just running 1 channel nets
8ohms - 270W (46.47v)
4ohms - 450W (42.46v)
2ohms - 550W (33.16v)

and then bridged
8ohms -600W (69v)

looking at the specs I would have opted to run 1 amp to 2 parelled cabs neting a 4ohm load and 450W but when looking at the voltage, excluding the bridged value, 1channel 8ohms is 270W and 46.47v is the highest value so is it safe to say because voltage is what we can read and record that when looking for wiring options look for the one that nets the most volts and not watts?

[Bill Fitzmaurice]

Volts are what we can measure, volts are what we can limit, so volts are what matters, not watts.

[Michael Murphy]

Thanks Bill and I think Ive just wraped up another misconception in my head. Ive been looking at the individual figures not the net output
e.g 1, If I run 4 box's in 2 channel mode off of 2 amps I will net 4x40v = 160v (4 cabs)
e.g 2, If I run 2 boxes paralled per amp it would be 2 x 42.46 = 84.92v (4 cabs)
but looking at it from a watts point of view
e.g 1 nets 4 x 200W = 800W
e.g 2 nets 2 x 450W = 900W
option 2 falsely looks better!

man Ive been short changing my self for freekin years now lol

[Bill Fitzmaurice]

Thanks Bill and I think Ive just wraped up another misconception in my head. Ive been looking at the individual figures not the net output
e.g 1, If I run 4 box's in 2 channel mode off of 2 amps I will net 4x40v = 160v (4 cabs)

4x40v = 40v. What you compare using multiple boxes is decibels. For each doubling of the cab count you pick up 6dB additional output.

[Michael Murphy]

Ok. So infant eg 2 is infant the way to hook it up? Because it has the highest individual output voltage?

[Bill Fitzmaurice]

Hook it up however you have to which delivers the voltage for full output with the least amount of excess voltage swing.
The problem with bridging is that all you're looking at is the watts. There's nothing magical about bridging, an amp can only take so much juice out of the wall and that's what limits what it can put into the speakers. You can juggle the load impedances and voltage swings all about but the bottom line is you can't get ten gallons of water out of a five gallon pail.

[Ryan A]

and if just running 1 channel nets
8ohms - 270W (46.47v)
4ohms - 450W (42.46v)
2ohms - 550W (33.16v)

looking at the specs I would have opted to run 1 amp to 2 parelled cabs neting a 4ohm load and 450W but when looking at the voltage, excluding the bridged value, 1channel 8ohms is 270W and 46.47v is the highest value so is it safe to say because voltage is what we can read and record that when looking for wiring options look for the one that nets the most volts and not watts?

4 ohms is 4 less volts than 8 ohms, but it's also twice the current thus almost twice the power, or about 2db more output. So it's not just about maximum voltage but voltage combined with matched loads. Running a 10 ohm horn to a 2 ohm capable amp is going to give you max voltage but at the same time leave a lot of amplifier power on the table. There is a happy medium though. You don't want to run the minimum amplifier impedance either.

[Michael Murphy]

ok, from what I can gather lowering the ohms increases the voltage swings so its best to wire up to get max impedance. So because the lab 12 in a T39 nets 8ohms if I parallel wire them it be a 4ohm load and I could run 2 per channel off 1amp (4 cabs) giving me 34v or using 2 amps again parallel wired single channel (4 cabs) it would be 42.46v or 4 amps single channel (4 cabs) its 46.47v. Well Ill go with the 4amps simply because Iv got em and check spl. The switch over to the QSC 2450, check limiter settings, and check again however the 2450 seems to be a lil low too 650 @ 4ohms both channels driven 50.99v, the QSC GX 7 1000 @ 4ohms both channels driven 63.24v.
Ok question when choosing an amp lets say I dont have any, to drive the 4 T39's what would be reccomended and why?
Thanks again

[Michael Murphy]

What happened guys? No advice. Grant you busy or what. Bruce ya forgot to mention the PA+ only goes to 24db LR, maybe thats why you still go low HP@50hz. Any who still waiting on gear, built me self a new work bench, next a nifty squaring jig to hopefully get the next 2 T39's right and square, Leyand is just about done on the OT 12's and I have another question. When running the PA+ are the passive crossovers still needed, or only the piezo high pass filter, lets say HP@100 for the OT12, can this kill the piezos?
ps my T39 plans say 55v limit for the lab 12

[Grant Bunter]

Mate, I've answered in your other thread...

[Bruce Weldy]

Bruce ya forgot to mention the PA+ only goes to 24db LR, maybe thats why you still go low HP@50hz. When running the PA+ are the passive crossovers still needed, or only the piezo high pass filter, lets say HP@100 for the OT12, can this kill the piezos?

The 24 db isn't really an issue....actually, I high pass at 50hz because I want to protect the speakers as much as possible, and since they sound great there with a 4 string bass - no real reason to try and get more out of 'em.

You still need the passive crossovers in the OT12. Just run the PA+ as Tops and subs....no need to go three way at all. I cross the OT12 at around 118 just to give them a little more protection at higher volumes.

[Michael Murphy]

ok guys last chance to make your vote, 4T39's lab 12 loaded. As Grant has pointed out multiple QSC 1400 ent cuttin it, and stated I needed 650 watts at 4 ohms, or 50.9 v.
So heres the money que
QSC 2450 vs Peavey IPR3000 vs Crown XLS 2000
Ebay has them similarly priced new and used
QSC is heavy, Peavey the lightest
Even read on another thread that the IPR 1600 seemed to outperform the 2450 (looking at the specs its hard to believe)
So im looking for feed back from amp owners who may have used or compared these. Im leaning to the Peavey b/c (thanks miked) of the DDT, oh upstream the amp is the DR DBA PA+. And because of this I dont really need all the limiter/crossover features the IPR or XLS offers, but I like the light weight of the class D amps

Thanks a mill again guys
Mike aka pumpsfast

[Bas Gooiker]

I'd go with the RMX, generally the better amp of the 3 in my honest opinion. Reliable and proven workhorse. Max output non bridged is 54-56V.

I have to say the IPR's specs seem better on paper. But i have no experience with those, could be real or maybe Behringer watts.

[BrentEvans]

I have to say the IPR's specs seem better on paper. But i have no experience with those, could be real or maybe Behringer watts.

IPR is the real deal. I have eight of them.