Power Amp + Cabs Question

[Downunderwonder]

Was doing a little research for a potential new rig I'd like to throw together. Came across a review on the Orange OBC15 1x15 cab, since I already have one and want to get a second one, so this review was helpful. The cabs are 400 watt 8 ohm. The reviewer seems to be saying he runs the full wattage out of the power amp @ 4 ohms, I am just wondering if there is potential to damage the speakers by doing this. Looked up the specs for the QSC GX7, and it is 1200w @ 4 ohm with a single channel driven, and 1000w @ 4 ohms with both channels driven. Not sure if the reviewer was just mentioning the amp can do 1200w @ 4 ohms, or if he ran out from one channel with the cabs in series, or if he is utilizing both channels at the 1000w each @ 4 ohms to each 1x15.

"I have a SansAmp RPM into a QSC GX7 (1200w @ 4ohms) to power 2 OBC115 cabs. I'm loud enough for 2 half stacks and a heavy drummer. These cabs are rated at 400w each, but they are efficient enough that my power amp doesn't have to push them very hard to produce high volume."

This is pretty much the exact set up I was imaging, just want to avoid blowing anything up.

You need some good earplugs.

Then you stand a chance of hearing your cabs complaining before they blow up.

1 channel is oodles of power.

 

[nilorius]

I don't think that this amp and cabs are so powerfull as written, so don't be afraid of any blowing.

 

[aledeville]

I use my 2x 1800W @ 4 Ohm all the time to power a variety of cabs. No problem at all. Just don't crank the bloody thing and try what it is capable of. Use ears and eyes to determine the drivers end of the road.

 

[Deleted member 165050]

Nowhere in that other guys post does he say that he is running the power amp wide open, or implying that the cabs can handle more then their wattage ratings.

There is no reason to believe that he is running that equipment at full tilt.

True, but it’s difficult to know just how much power you are putting out until it’s too late.

Those who think they can judge the amount of power being put out by an amp are - in my opinion - over-optimistic of their ability to do so.

 

[basscapes]

"I have a SansAmp RPM into a QSC GX7 (1200w @ 4ohms) to power 2 OBC115 cabs. I'm loud enough for 2 half stacks and a heavy drummer. These cabs are rated at 400w each, but they are efficient enough that my power amp doesn't have to push them very hard to produce high volume."

Simple rule- just LISTEN to your tone! If the speakers even remotely start sounding like they are stressed or just plain wonky, turn the bass control or master down a bit.

 

[MCS4]

"I have a SansAmp RPM into a QSC GX7 (1200w @ 4ohms) to power 2 OBC115 cabs. I'm loud enough for 2 half stacks and a heavy drummer. These cabs are rated at 400w each, but they are efficient enough that my power amp doesn't have to push them very hard to produce high volume."

This is pretty much the exact set up I was imaging, just want to avoid blowing anything up.

Do you already have the GX7? If not, then just get a GX5. It will save you a few bucks, and it puts out 500 watts per side at 8 ohms (use one side per cab), which should fit those cabs well.

If for some reason you ever need more volume than that setup provides, you would probably need more cab rather than more amp wattage, and the GX5 can easily power larger cabs as well (I use mine to run two MarkBass 4x10s, each getting 700 watts at 4 ohms).

 

[agedhorse]

Simple rule- just LISTEN to your tone! If the speakers even remotely start sounding like they are stressed or just plain wonky, turn the bass control or master down a bit.

Sounds simple but for those using even a little bit of overdrive (either from the preamp or a pedal) there's no way to confidently tell when it's the speakers and when it's the intended OD. This is a common fallacy IME.

 

[DWBass]

Personally, I would find a power amp more matched to the wattage handling of the cabs. While those cabs can handle 400w they probably max out at 150-200w loudness wise. No need in pumping 600+ watts into them with the potential to damage the speakers.

 

[basscapes]

Sounds simple but for those using even a little bit of overdrive (either from the preamp or a pedal) there's no way to confidently tell when it's the speakers and when it's the intended OD. This is a common fallacy IME.

Point noted- the dirtier the original tone is, the less likely one is to hear anything going south with the drivers.

Admittedly, I'm jaded in the context that I've come from two very finicky worlds- Audiophile Hi Fi and Uber-Clean Bass Rigs! Crappy speaker stuff is usually easy to hear there!

RPM can clean up nicely, but that isn't usually how I've heard them used.

 

[DWBass]

Do you already have the GX7? If not, then just get a GX5. It will save you a few bucks, and it puts out 500 watts per side at 8 ohms (use one side per cab), which should fit those cabs well.

If for some reason you ever need more volume than that setup provides, you would probably need more cab rather than more amp wattage, and the GX5 can easily power larger cabs as well (I use mine to run two MarkBass 4x10s, each getting 700 watts at 4 ohms).

More speakers will push more air. Adding wattage will not. Big misconception. 500w into any speaker cabinet is plenty.

 

[Deleted member 165050]

More speakers will push more air. Adding wattage will not. Big misconception.

That's only true to a certain point, or we'd all be running 10 watt amps into dozens of speakers. There's a point at which adding more power becomes useless and possibly even likely to damage drivers, but there's also a point at which adding speakers gains you nothing (the 3dB per driver gain only works up to 8 to 10 drivers). There's always an optimum amplifier power/number of drivers for any given circumstance.

 

[christliche]

I appreciate all the replies! The quoted review I added really didn't give us much to go on, so glad it could be picked apart. I also agree that a different power amp more suited to the cab(s) handling is the way to go. I have been interested in this route for some good clean SS power at a lighter weight (combed with a preamp in a rack, still not too bad) as well as saving some bucks, as these poweramps used can be found for under $300, same range for the preamp.

 

[BadExample]

I was looking down this path about a year ago. I came into possession of a few Genz Benz bass amps and called off the chase. I would take a look at the XLS series Crowns. Light, inexpensive, and have a DSP HPF/LPF and good warranty.

 

[Stumbo]

....I have been interested in this route for some good clean SS power at a lighter weight (combed with a preamp in a rack, still not too bad) as well as saving some bucks, as these poweramps used can be found for under $300, same range for the preamp.

TL;DR

OR, put your $600 down on a Mesa d800+:
little, light, loud and ludicrously great tone control down to 2 ohms.