In a way, all the arguments each way don't matter. I have one sub now, but I've been debating getting another one for years, but haven't yet. If I did, I'd try both ways, and then I'd see which way would work better.

http://www.avsforum.com/avs-vb/showthread.php?t=1364666

I went from one to two and then back to one and Audyssey did a good job of compensating for the changes.

Suppose the subwoofer that you EQ'd flat is sitting right next to an open door. If I closed that door tight, will your subwoofer still have a flat response? If not, why?

The response would of course change (boundary reinforcement, or not). But I don't typically open and close doors when I'm watching a movie though. So I'm not sure what your point is.

Phase seems to me to be the most immediate potential problem. If the two locations create phase cancellation, calibrating them separately and combining them would not reveal that cancellation. Beyond that, I get into a level of detail that I don't trust myself to be sufficiently informed on, but I could see EQ adjustments being made to help one sub overcome a dip or reduce a peak that could be naturally smoothed out by interaction with the other sub (which, due to a different location within the room, might be cancelling out or lessening the magnitude of the problem spots for that first sub). In both scenarios, adjusting the two subs as a unified pair would be quicker, easier, and better sounding.

It reminds me of one SMS-1 owner who had multiple subwoofers and found that his placement of those subs had already achieved enough "flattening" that using a separate sub EQ gained him nothing. Looking at each sub individually would have led him to do a lot of EQ work, whereas looking at the whole revealed that he needed very little actual adjustment.


The pessimistic answer to that would be "because they sound cool and can be sold more easily as a result." There are other less-than-optimal product ideas that are very popular for marketing reasons, or sound popular at first but eventually fade away. (Case in point: TV manufacturers are starting to re-consider "smart TV's" with all sorts of network functions built in - leaving such functions for a Blu-ray player or standalone device or receiver, all of which are duplicating those functions these days, apparently made more sense to consumers.)


Since Audyssey already had the ability in the firmware, it sounds like they just left it there for greater flexibility. And technically it can work - it just may take more effort and may yield a result that is no better than the alternative.


Do the DD subs have the ability to slave one sub to the other, or do you have to set up each individually? Since they built the EQ hardware into the sub, you kind of have to EQ each separately unless there's a master/slave option.

This is not easy stuff...


This is only likely to be true if the 2 subs are physically colocated, a situation where they are in phase at all frequencies and both elicit the same set of reverberations in the room. If they are equidistant from the listener but not colocated, they will still be in phase at all frequencies but I suspect their reverberant soundfields will interact in a way which cannot be predicted from their individually measured responses (unless they are outdoors away from any barriers or in an anechoic chamber, not typical HT environments). If they are physically separated and not equidistant from the listener, their phase relationships will vary with frequency and again their reverberant soundfields will be different. The experiment which Sanjay suggested (and which I have to assume he has performed) will prove this one way or another.

Btw, which EQ solution do you know of which equalizes phase for non-colocated, non-equidistant subwoofers? The only one I know of is Sub EQ HT.


See above.

Bottom line... I will be quite happy, and confident that I am optimizing my overall bass performance, by allowing Sub EQ HT and MultEq XT32 to handle the combined output of my 2 subs (when I get them) without any preliminary hanky-panky. If you want to go through the additional steps which you propose, are willing to spend the additional money and time to do so, and are comfortable with the added complexity, go for it. I still think it's a "bad idea", but it's your decision to make.

OK, so you would be pressurizing the room differently with the door open vs the door closed. What if you added a second pressure device, like a subwoofer, would the response change? Doesn't matter how the subs are EQ'd, I'm just asking whether the response would change.

Kevin, on further reflection I am willing to admit that if you were to use a device such as the SVS AS-EQ1 (which performs EQ in both the frequency and time domains) to individually equalize 2 subs, it is quite possible that their actual summed output in a typical room will come close to their mathematically summed individual responses. Again, it remains to be seen whether doing this prior to equalizing the subs' combined output will confer any advantage (and I won't be doing it for all the reasons mentioned) but if this is indeed your intention, it's quite possible you will come close to accomplishing your goal.

Keep us posted.

I meant to jump in sooner but I had to crack some books on this one.
Two things going in:
1. Superposition holds.
2. Standing wave room modes are independent of sub location.

Superposition is important because it basically means that the response of the sum is simply the sum of the individual responses. Where it get complicated is that the output of the sub has elements of Amplitude, Frequecy and Phase and most EQ programs only show frequency and amplitude and maybe a phase shift and give you no idea what the absolute phase is (Never played with Sub EQ HT).

The room modes are important because adding extra subs will not change the room modes. What it will do is move the peaks and valleys of the standing waves around. Note the same effect is achieved moving a single sub around in the room: The modes are the same, peaks and valley move. (Opening door, moving walls, etc. WILL change the room modes)

So what I would do if I were designing the system would be to measure the individual sub responses AND the combined response then apply individual corrections to each sub to equalize the combined response.

Yes. But you'd still be EQ'ing the 2 subs' interaction too, in addition to individually.


Ok, I see what you're getting at. Only EQ individually, but EQ individually so that the combined response is what you want it. That's another further step forward from what I'm suggesting.


You get it !! Yes, in the end, I don't know if you could get better performance or not from EQ'ing individually plus the total, vs just EQ'ing the sum total of the response. But theoretically, I like the idea of EQ'ing individually 1st, to give Audyssey smoother profiles to work with when EQ'ing the sum total of their interaction. In effect, it's an attempt to minimize the two subs' interaction before EQ'ing the sum total.