Probably a daft question (watts, ohms, etc)

[Newfoundfreedom]

Sorry, this probably seems like a really daft question to those in the know, but here goes 

My amp is rated 300w @ 4 ohms and has 2 separate outputs.

I've just bought 2 cabs rated at 200w and 300w both at 8 ohms.

Now, as I understand it, 2 X 8 ohms cabs would give a combined resistance of 4 ohms. So no problem for the amp. 

The part that I'm slightly confused about is the watts. The total combined wattage the two cabs can handle is 500w RMS (leaving aside peaking and the fact that I wouldn't be running them flat out anyway) but as the amp is rated at 300w does that mean that there would be a 2 way split with 150w going to each cab, or does the wattage remain at 300w to both, potentially overpowering the 200w cab? 

[BassTractor]

Roughly speaking, indeed both cabs maximally "get" half of the amp's rating because the outputs on the amp are in parallel and connected to one single output stage. 

Normally you should be in the clear provided that you don't turn up the amp so much it starts clipping - depending on amp design. It has been said that more cabs have been ruined by "too small" amps than by "too big" amps.

What complicates this slightly is that the rough impedance does not state anything about the different resistance measurements at different frequencies. Since the cabs are different, they will also have different resistance curves, and their being connected in parallel means that one cab's response to the signal does have an effect on the other one.

This is one of the rare instances in playing music where listening is your friend. 😉

 

There's another aspect I know is important, but whilst writing the above I forgot what it was. Will edit if my brain starts working again.

[Newfoundfreedom]

Thanks BT. 

I figured (it at least hoped) that would be the case. I'm unlikely to ever need to crank the amp up high enough for it to make a difference anyway. I currently only have the volume on around 3 or 4 at the most, and that's through a single 2x10, which is ample to keep up with 2 guitars and drums in practice and any venue were likely to play. 

[Telebass]

No problem at all unless you cane it, clipping, as stated. But electrically no issue.

[Lfalex v1.1]

4 hours ago, BassTractor said:

Roughly speaking, indeed both cabs maximally "get" half of the amp's rating because the outputs on the amp are in parallel and connected to one single output stage. 

Normally you should be in the clear provided that you don't turn up the amp so much it starts clipping - depending on amp design. It has been said that more cabs have been ruined by "too small" amps than by "too big" amps.

What complicates this slightly is that the rough impedance does not state anything about the different resistance measurements at different frequencies. Since the cabs are different, they will also have different resistance curves, and their being connected in parallel means that one cab's response to the signal does have an effect on the other one.

This is one of the rare instances in playing music where listening is your friend. 😉

 

There's another aspect I know is important, but whilst writing the above I forgot what it was. Will edit if my brain starts working again.

To reinforce the point about big amps...

I used to use a QSC power amp capable of 400W rms into 8ohms with a Trace 2x10  whose drivers were rated at 80 watts each (160 in total) and which presented an nominal 8ohm load.

Went much louder than my Trace head could manage, with the benefit of a low end roll-off filter and much better driver control.

Never blew or melted anything.

A little amp being run into clipping does far more damage than a big one just coasting along.

 

 

[taunton-hobbit]

Where's Alex Claber when you need him?

Seriously, if you aren't playing silly loud, the speakers will, simply, work fine -

try using them spaced a fair way apart rather than just as a stack - you might be surprised............

😎