Multiple heads on single cabinet?

Unless the cab says on it use this for stereo (left 8 ohm right 8 ohm as an example) DO NOT DO IT. If the cab has two jacks in parallel and you hook up two amps, one or both amps will need repair

 

^^^^!!!!! Unless the amp manual specifically states that the two inputs drive separate (eg 4x8) speaker sections, you are risking damaging the whole rig.

 

As long as the cab has a higher wattage than the amp you'll be fine. Speakers need the extra headroom in case you have an output spike from the amp (cable pulled out of your bass for example). But definitely not too heads for one cab. It's a bit like having two bowels for one... ummm, yeah. And the result is kinda similar...

 

Like the guys above say, this would likely fry the hell out of your amp (be exactly like plugging a speaker from one output jack to another output jack on your amp).

On the flipside, however, rewiring your cab for stereo would be a snap. any qualified tech could do it in short order, and you could figure it out if you really wanted to. However, given that you were thinking of cooking your amp up you might want to let a qualified guy do it just to be safe.

 

Two amps into one speaker cab that is not a stereo cab is very bad. Running a second speaker cab from a combo amp is fine if you don't exceed the min. ohm rating from the combo.
Cabs and "Amps" are two different things, a combo is a speaker "cab" with a built in "amp" as one unit.

I have the idea you have a "combo" and are hooking up a second speaker cab? This is usually fine (as long as the load doesn't go below the min. load rating).

 

Not bad in any way, your amp supplies the power. The cab uses that power to make sound, the cab won't care if you play at practice volume (20-50 watts) from your amp head.

 

Right that's fine. The problem is if you tried to run two amps into one cab. But the wattage ratings of the amp and the cab do not have to match, or be one double the other, or any of that kind of one-size-fits-all answer. The only "truth" is in how you use them.

 

No it's not bad at all cabinets have a wattage that is meant to be considerably high so that u don't **** up your speakers. Thats one major flaw with some guitar amps the matching 120 watt head and cab deal means over time ur speakers go if u continuously pull out the jack without shutting the amp off or putting it into standby. 400 watt amp is plenty of power tho to run a 800 watt cabinet

 

play loud by all means its only bad if ur amp is pumping out more watts then ur cab can handle.