Quote:
Originally Posted by
Anthony A. 
and to add to that comment, if one uses audyssey sub eq (svs as-eq1) to help out with multiple subs, should this be run before ARC?
also, how does ARC do natively when using 2 or more separate subs within a system?
My advice is to see first if ARC gives you a satisfactory solution on its own, without any EQ from the sub system. Generally speaking it is better to do less processing if you can. You'll be able to tell from the ARC charts if things are looking good.
If you decide you want to run a sub EQ system as well, then be sure to set that up first (with ARC turned off), then run your ARC Measurement so that ARC can hear the modified output of the sub due to its EQ system. It has to be done in that order because only ARC can blend the output of the main speakers with the sub, and to do that effectively ARC has to hear what the sub will produce during normal listening -- i.e., its output as modified by the sub EQ you decided to use.
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ARC works just fine with multiple subs. It hears them playing as a set. You must manually set up the distance for the subs (use the average distance if they are different), the volume for the subs, and the Polarity/Phase for the subs.
The trick to setting up volume, polarity and phase is to power only one sub at a time and set each in turn. Keep in mind that volume adds. So for example with 2 subs the rule of thumb is to set each to 72dB SPL (using the volume knob on each sub) which will result in roughly 75dB SPL when they are played together. ARC will do any fine adjustment necessary on the volume trim for the combo of subs.
Similarly when setting Phase, you power one sub at a time and adjust its Phase to work best with the main speakers -- typically using the Left Front speaker as the surrogate for all the speakers. Set distance and do your rough volume balancing first (so that you can better hear the subtle difference between correct and incorrect Phase).
Phase operates near the crossover frequencies whereas toggling Polarity is like reversing the wires to the sub -- i.e., it affects all frequencies. That means that inverting Polarity is not the same as swinging Phase around 180 degrees. Thus you should find the best Phase for each Polarity setting and then decide which combo of Polarity/Phase is working better.
Now with more than one sub you can have cancellation not only between the sub and the main speakers (through the crossover frequencies) but also between the subs themselves (across ALL bass frequencies). And that's where Polarity comes in. The rule of thumb is to use "normal" Polarity for a sub in the front of the room and "inverted" Polarity for a sub at the rear of the room -- because the cone of the sub is facing the other direction.
You can use the Quick Measure feature to see the raw output of each sub and the combo of subs. Use Quick Measure with one sub powered at a time to refine your choice of location for each sub. Keep in mind that if you MOVE a sub you also need to recheck your choice of best Phase setting for it. If you get a good Measured curve in Quick Measure for each sub, but see problems when all the subs are powered, then that indicates you are having cancellation between the subs. Try inverting Polarity in one sub -- being sure to also switch to the matching, alternate Phase setting you determined for that Polarity when the sub was tested against Left Front.
If your subs have Phase controls but not Polarity controls, then problems of cancellation between the subs may be something you can only fix by repositioning a sub. At bass frequencies, even inches can make a difference. And again, if you move a sub, you must redetermine the best Phase setting for it (against Left Front).
Now ARC hears all of your subs playing at the same time, so it will Measure any bass response problems due to cancellation between the subs and attempt to correct such problems. Which means you must wait to Measure for ARC until AFTER you have done the best you can setting location, Polarity and Phase for each sub. If despite your Polarity/Phase settings the Measured curve for the combo of the subs still looks too poor (something you should be able to see more quickly using Quick Measure with all subs powered) even though the output of the individual subs looks good, then you will need to investigate alternate positioning for at least one of the subs.
ARC does *NOT* hear Phase problems between the subs and the mains because the test tones for the subs and any given main speaker are never playing at the same time. So again, setting up Phase (after choosing distance, volume, and Polarity) for each sub in turn is something that you need to do yourself using a sub phase test track from a calibration disc. And again, you need to do this before doing your ARC Measurement as Phase adjustments for any sub will alter how that sub cancels against any other sub.
After you've set all that, and run ARC, and gotten good looking chart results, you can verify that everything is working correctly by running a crossover sweep test (e.g, from the AIX audio calibration Blu-Ray) using that Uploaded ARC solution. This runs a test tone up and down through the crossover frequencies. If the volume sounds constant to your ear as the frequency sweeps up and down past the crossover, *AND* if the green Calculated curve for the sub combo looks clean in your ARC solution, then you can feel confident that you have eliminated cancellation problems both between the subs and the mains and also between the subs themselves.
--Bob
