I'd like to pull this next remark out of context and use it to address some others in the thread:
Originally Posted by BufordTJustice
...if somebody has the ability to match phase in the bass region between the sub and the A5's...
Any ripple-free mesh between mains and bass system takes phase agreement. Understanding this can add options to your setup, as we've been covering in this thread a bit.
Originally Posted by SmokenAshes
I see you guys talking about setting your A5 to 60hz. Looking at my AVR my bass cross over is at 80hz. For the A3 should I set my cross over to 60hz as well?
Your ideal setup takes some experimentation. There are ways to make everything more or less agree in terms of levels - getting that flat frequency response you room-correct and speaker-correct to get - but getting the phase
right in the transfer function between mains and bass system should start with a goal. That goal is the common 80Hz 4th order/24dB per octave LR response function, which is ripple free through the crossover region and has constant power.
How we get it is where the options come in and this is where your electronics and therefore your choices will vary.
The easiest way to approximate it with a speaker that hopefully has another octave of natural output below 80Hz is to just set everything electronically fo 4th order, 80Hz. Not perfect but close enough. We'll ignore the natural rolloff function of the speakers lower down and have the electronics do this work. This is a common, virtually plug and play option.
The other way to get it - which goes back to your question, SmokenAshes - is to greatly reduce the rolloff rate of the main speakers from the bass reflex rate of approximately 24dB/Octave to half that rate in a new sealed system, one we get by stopping the bass reflex ports. We raise the rolloff frequency substantially, but we get only half the rate of attenuation, which now will be 12dB/Octave.
Now we just need to add another 12dB/Octave of electronic attenuation to get to our ideal. Once that's done, we set the sub to the common 24dB/Octave and now we have approximated a flat summation. To do so you'd need a setting related to the "small speaker" switch that grants only 12dB/Octave of rolloff rate, and since we've raised the main speaker's rolloff frequency by stopping the ports, we'll probably still want to be up around 80Hz. Although, as BufordTJustice notes,
Originally Posted by BufordTJustice
I would recommend experimenting with 60hz for the A3's as well.
You'll want to experiment and if you also have the freedom to adjust your electronic crossover's frequency, start around 80Hz and then start moving down until you hear a discontinuity between the mains and the sub. If you do, raise that frequency until the sound warms excessively in the upper bass and dial back down again. You can also use your room EQ to find this relationship visually on a measurement scale. Measuring can be crucial and very informative, but how things sound is always king. Further, rooms are notorious for fouling up your best plans, especially in the bass.
If you go through this ritual, you may find that your plugged-port setup sounds cleaner than leaving the ports open, getting a sharp speaker cutoff lower down but risking added ripple in the response. Ripple is ringing, which means that the overall system is storing energy and muddying your sound.
(There are also all sorts of setup routines, features, and options in modern electronics so please realize that all of the above relates to a theoretical best case, simple method. Experts are solicited for added information on alternative setups.)
The desired combined function mentioned is how a purist sees the phase and level relationship between any two drivers in a multi-driver system. We've written about this in the Arx User Guide.