Distributed Bass Array configuration

My name has come up a few times in this thread.  I don't really see how to participate without either taking a side in an emotionally-charged "us versus them" thing that I want no part of, or turning into a self-appointed thread nanny.  Until I figure that out, I'll just tip my virtual hat to @mike_in_nc for taking the high road.  

Duke  
distributed multisub system manufacturer since 2006

There are circumstances under which a pure 80 Hz tone can be localized and circumstances under which it cannot. Outdoors or under anechoic conditions, yes. In a home-audio-sized listening room, very unlikely. This is because the reflections start arriving before the ear has time to distinguish the first-arrival sound. But notice that I specified a "pure" tone - no additional energy north of 80 Hz.

There are conditions under which a subwoofer crossing over at 80 Hz can readily be localized. Crossover filters are not brick walls, nor do they attenuate the driver’s inherent harmonic distortion (because it occurs after the crossover), and both of these can result in audible and localizable energy north of the crossover frequency. Also if the output from the subwoofer arrives before the output from the main speakers, the subs are more likely to be heard as separate sound sources. And of course if the main speakers are turned off, the subs are far more likely to become localizable at some volume level because any (virtually inevitable) energy they pass north of 80 Hz will not be masked.

If the subs must be crossed over up high, and/or if they have a gentle lowpass filter slope (1st or 2nd order), probably best to keep them near the mains or at least make sure the output from the mains arrives first.

Imo, ime, ymmv, etc.

Duke

@mapman wrote:  "I think its a fallacy if some are asserting setting up multiple subs properly is easier than one."  

@golfnutz wrote:   "I agree, using the 'throwing darts' method isn't the way I'd install a $3200 subwoofer system." 

I realize that it seems counter-intuitive to think positioning four subs in a room is easier than positioning one, but consider this:  When you change the location of a single sub, you have changed the way ALL of the bass energy is introduced into the room.  With four subs, when you change the position of any one of them, you have changed the way ONE-FOURTH of the bass energy is introduced into the room.  By following a few guidelines you can probably end up with excellent results after one or two adjustments, if not from the get-go (which seems to be the case about half the time).  I include six different setup strategies in my guidelines, most of which are very forgiving, and all of which have been used successfully.   

Regarding setting the levels, either ears or measurements can give excellent results, but in either case (and regardless of the number of subs involved) finding the exact setting IS critical.  The reason is, the ear's heightened sensitivity to changes in SPL at low frequencies.  A little bit of change in gain on the subwoofer amp translates to a disproportionate change in PERCEIVED loudness.   So it may take a while to find that magic setting on the amp's gain knob.  Note that measurements alone may not be enough - Geddes and Toole and others have observed that most listeners prefer slightly elevated bass compared to the rest of the spectrum, but the amount of elevation preferred varies.  I got excellent results fairly quickly in a challenging situation by using measurements as a starting point and then having an experienced bass player guide me as I fine-tuned the settings.  

Note that the improved in-room smoothness of a distributed multisub system allows more flexibility in setting the level.  It is the peaks which stick out like sore thumbs and are the limiting factor in how loud we can set the bass before it starts to sound unnatural.  Smaller peaks means that we can set the level a bit higher for more satisfying bass because we don't have to sacrifice a truly satisfying level across the rest of the bass spectrum to avoid over-energizing the peaks.  

Duke

@cleeds wrote: " That is completely false, notwithstanding your use of ALLCAPS for emphasis. See any basic audiology text for proof, which will show the range of increased sensitivity is typically in the midrange, 2000 - 5000 kHz. "

My bad for not explaining where I was coming from.

I do understand what you are saying, but what you are looking at is where the ears are the most sensitive; that is, where sounds of a given SPL are perceived to be the loudest. And indeed that peaks exactly where you say it does (with the peak centered around 3.5-4 kHz).

What I’m talking about is different, and is not nearly so obvious.  I’m talking about the ear’s sensitivity to CHANGES in SPL (and I would use italics instead of allcaps if that was available here). A change in SPL does not produce the exact same change in perceived loudness across the frequency spectrum; it produces more of a change at low frequencies. Go from a low volume level to a high one and the deep bass goes from being inaudible to being thunderous. The unit of measure of perceived loudness is the "phon", and by definition at 1 kHz the loudness in phons is the same as the SPL in decibels, so the two curves share that data point:

http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/eqloud.html

Now take a close look at how the equal-loudness curves bunch up below 100 Hz. A 5 dB change in SPL at 20 or 30 Hz results in a change in perceived LOUDNESS of about 10 phons, comparable to a 10 dB change in SPL at 1 kHz.

This is what I was talking about, and once you understand that, it will be clear why a small change in gain on the subwoofer amp typically results in a larger than expected change in perceived loudness. Or, to put it another way, why it takes a while to dial in the gain setting on a subwoofer amp.

Duke

@scm asked, " When using the crawl method and picking the best spot for Sub #1 are you supposed to then power up Sub #1 while crawling for Sub #2`s best spot and so on with each sub thereafter....??"

Yes.

When doing the Crawl to set up a Swarm or DEBRA system, which uses a separate amplifier, connect the additional subs in series, such that the overall subwoofer volume level stays the same. If doing your own distributed multisub system with conventional self-powered subs, I think you’d want to adjust the volume of the pre-existing subs before adding yet another, and measurements would probably help a lot with this.

Duke