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@lonemountain wrote:

Speaking of subs and rooms, I have to add the general trend toward smaller subs in higher quantity is proving to be a better solution for most rooms and studios.  The desire for one big sub creates dominant rooms modes that are a bear to remove with giant nulls and huge peaks. 

One doesn't exclude the other. Certainly in the context of my bringing up large subs it's with the outset of using two of them and no less, and more where permits and/or is willed/decided. What's most important is having the larger pair of subs placed along the front wall (preferably symmetrical to the mains); any addition of subs no. 3, 4 or more for a DBA can be significantly smaller and needn't be as extension capable/covering the same range as the larger ones; they'll still fulfill their "job" as extra bass sources to make for an acoustically smoother response. 

Although counter intuitive, adding more does indeed create more modes, but fewer are dominant.  We lose the lack of bass in one part of the room and the over abundance in another.  Locating 4 subs on 4 different walls at varying distances from corners can be a revelation.  Forget the stereo thing below 100Hz, sum it to mono and it can be very surprising.    

I find crossing subs even lower than 80Hz to necessitate symmetry-to-the-mains placement and stereo coupling. Most subs aren't low-passed with brick wall-steep slopes, and so the sloping response "bleeds" into the upper range to make for directional awareness. Moreover it can be argued whether the 80Hz barrier of "loss of directionality"-claim holds general credence. To me it's not a hard numerical value but rather a frequency range within which directionality gradually lets go, and extends further down than the oft claimed 80Hz.

Crossing higher than 60-70Hz at least while high-passing the mains I find symmetry-to-the-mains placement of subs to be paramount, and just has the whole sphere of sound snap more effectively into place. An asymmetrically placed DBA to me sounds more like headphone/inside the head bass, which isn't natural to me. I know many disagree, so be it; I'm keenly sensitive to symmetry placement and stereo coupling of subs, and so act accordingly when implementing subs.  

Good arguments all Phusis. I can think of locations we’ve been involved in where symmetry worked; other places it did not. Visually we are always drawn to symmetry. My clients want the subs right under the mains and this "looks right". But most of the acousticians I know would argue against it, even if the physical offset is smaller than they are asking for. Their argument is that both subs at 12 feet from a corner sets up a mode relating to 12 feet in length. One at 12.5 and one at 11 is better. 4 subs should be at 4 different lengths from corners. An alternative plan is an array of all 4 subs next to each other on the front wall but we can leave that for another time.

One difference may be that in my applications, the mains are NOT high passed. The argument is that all crossovers create a hole (a dip at the crossover point itself) which is increased with increasing slope of the crossover. In studios, a 48dB slope is a big NO. Most of our applications have a 12dB slope, minimizing that dip. Introducing a dip right at 100 or 80 or even 60 is very noticeable and counter intuitve to the goal of "more bass". The other issue is phase and the introduction of another phase shift that is not wanted. Subs are low passed, usually with gentle slopes.  

In all types of music now, we see extraordinary low end being inserted at the artist behest. London Grammar’s "Hey Now" is adjust such an example of unexpected but likable low end.

In our business, a filter to make sure a speaker rolls off at a new higher place is not desired, as now we have added something that makes a sound across the mains and changes them.  Even in the case of a simple and well executed LF filter, it is audible. In this application, low passing subs and not filtering anything on the mains is the basic idea.  Subs are usually sealed, have no EQ and no DSP of any kind. Blending them can be a relatively easy process and sometimes requires inverted polarity (180) to make work.  Depending on arotating phase control, which only works over a portion of the sub band, is not the fix but a fine tune. 

In large rooms one wishes for DSP to create a delay of the mains to match up to the subs, but this is often not accepted due to the audible change the DSP introduces plus the barely noticeable delay created by DSP. Any offset in time makes tracking odd, sometimes difficult where one artist is in the live room and one is the control room- both being recorded at the same time.  If the entire system is DSP driven that may be a different scenario, but with ATC we prefer 100% analog output to speaker.

Brad

Sorry @lonemountain but high passing mains,. especially residential is often the right thing to do, and done right, with quality subs and filtering on both is inaudible. There will be no shift in tone and no localization is possible.  You have to be cutting off below the Schrodinger frequency. Your subs have to be low distortion, especially anything third order and higher. That may be as much a consideration for where you're cut off frequency is as anything.   If you've got large means that can play low distortion at high volumes at base frequencies, then I would consider it beneficial to run them full range. But most mains these days don't fit that criteria. For most means I would far prefer a cut off that's not full range especially if the customer likes high volume levels. 

I don't understand your comment with respect to DSP. With any modern half decent quality ADC, you're not going to hear any sound of using an ADC and then DSP. And of course if it's an all digital system, it's a nonstarter. Talking about DSP delay is also not relevant when you bring up in the same paragraph 180° out of phase operation which is a delay. There are no absolutes speakers like a line array can be difficult to integrate with subs and an evaluation needs to be done based on mains speakers, room size, listening levels etc

@kota1 phasing sub and full range speakers is not difficult, just put you head exactly between the sub and the speakers, play and 80hz tone with all your equipment on and slowly turn the phase knob until you hear the null point and the strongest point. Go back and forth to be sure you are not 180 degrees off, stop at the strongest tone. 

thanks