Running Mesa Boogie Bass 400+ into 4 ohm and 8 ohm cabs

No, you have to use two matching impedence cabs: two 4ohm or two 8ohm. Tube amps don't like mixed impedences.

 

Now I'm certainly not an expert, but I thought if you were to plug one cabinet into the head, and then the other cabinet into that one, then you would end up with a total impedance around 2.6 or so?

 

I know this is possible on SS or hybrid amps, but I haven't been a tube owner myself long enough (400+ also!) to know this for sure.

 

Again, I'm not an expert so someone else please confirm or correct, but I would think that by linking the two cabs together, you're going to end up with one total impedance in the same way that you can buy a cabinet with multiple speakers that when linked together add up to one impedance.

 

The impedance of a cabinet is fully dependant on the drivers. You put a 4Ω driver into the 1x15 it will become 4Ω. Sadly it isn't as simple as that. To function at its best a driver(s) and its cabinet have to work together. You already have a driver in there that was not designed for the cabinet. If it's working for you no foul. Finding a 4Ω 15 might be a little difficult and if you do it might just fail in your cabinet.

Running both of your cabinets in parallel will result in 2.67Ω which is less than ideal for a tube amp and is something I can't recommend for bass.

 

Sounds like you need another 8ohm cab. Run both 8 ohm cabs to one 2ohm input and the 4ohm cab to the other 2ohm input. Thats what I would do.

Congrats on the twins!!

 

Asking technical advise from musicians is risky at best. You will get lots of "opinions", some better than others. Here is the bottom line: Match impedance (measured in ohms) to protect your amp, match power (measured in watts) to protect yuor speakers.

One gentle mans says your amp does not like mismatched cabinets. Thats BS. Your amp has no clue what is attached to it. The amp only see's an impedance connected and a matched impedance means 1. Maximum power transfer (ohms law) and 2. Amp does not work as hard getting those watts into your speaker.

Running an 8 ohm cabinet with a 4 ohm cabinet is totally fine. Here is the results.
1. Your amp will see a 2.6 ohm load. Is your amp rated to handle a 2 ohm load (most do not)?
2. The 4 ohm cabinet will used 2/3's the power making the 8 ohm cabinet seem like its turned way down.

Ohms law is fairly easy subject but usually misunderstood by musicians. There is a reason electronics schools spend a long time on the subject and many graduates still don't understand it. I recommend going to electronics school if you want to really understand resistance, impedance, impedance matching, watts, inductive reactance and ohms law. All these things apply to your amps and cabinets. Short of the schooling your user manuals usually spell out your parameters for hooking up stuff to other stuff. Look on the internet for user manuals in the case yours are misplaced.

Hope some of this helps.

 

From the manual:

I ran my 8 ohm 4x10 and my 4 ohm 2x15 from the 2 ohm jacks and never once had a problem. The volume difference between the 4x10 and 2x15 was acceptable to me back then.

 

A wise decision in my book. BTW congrats on the twins and I assure you, you WILL be able to sleep again.....eventually!