Yes, you can use both at once. Your transistor amp's output stage is much less finicky about impedance matching than a tube amp would be. The net impedance will be 2.6 Ohms. That's pretty close to the 2 Ohm lower limit specified for your amp, but if it's healthy, and you don't turn everything up to 11 all the time, you should be OK.Originally posted by Raskolnikov...So I can't use both at once? Or can I?

What will happen is the amp will provide a certain amount of voltage to the speaker terminals. The speakers will each draw as much current as the voltage drives to them.

It may make more sense to you if you think in terms of water pressure (Voltage) and pipe size (Impedance). If you hook up two different diameter pipes to the same source, the larger pipe (lower impedance) will flow more (higher Current) than the smaller diameter pipe. This means more volume (Power) through the larger diameter pipe.

So, the lower impedance speaker cabinet will draw more current than the higher impedance cabinet. Since

**Power = Voltage X Current**, and the voltage is the same for both cabinets, most of the power will go to the lower impedance cabinet. In the case of a 4 Ohm cab and an 8 Ohm cab, the 4 Ohm cab will get twice as much power as the 8 Ohm cab (same Voltage; twice as much Current). If your amp is putting out 300 Watts, the 4 Ohm cab gets 200 Watts, and the 8 Ohm cab gets 100 Watts. [u]Keep this in mind if your amp is capable of providing more than 1 1/2 times the rating of your 4 Ohm cab[/u]!

Look in on the Ampeg forum to see if anybody with the same amp has any suggestons for you. That forum doesn't have anywhere near as much traffic on it as this one, but it does offer a narrower focus on Ampeg products.

Happy thumping! :)